text:
|Publication number
|Publication type
|Application number
|Publication date
|Mar 7, 1989
|Filing date
|Apr 7, 1988
|Priority date
|May 14, 1987
|Fee status
|Publication number
|Lawrence J. Bregoli, Francis J. Luczak
|Original Assignee
|International Fuel Cells Corporation
|Export Citation
|BiBTeX, EndNote, RefMan
|Patent Citations (24), Non-Patent Citations (2), Referenced by (20), Classifications (15), Legal Events (4)
|External Links: USPTO, USPTO Assignment, Espacenet
This application is a continuation of Ser. No. 049,354, filed May 14, 1987, now abandoned.
1. Technical Field
The field of art to which this invention pertains is fuel cell electrodes.
2. Background Art
A fuel cell is a device for directly converting the chemical energy of a fuel into electrical power.
A fuel cell comprises two gas diffusion electrodes, an anode and a cathode, and an electrolyte impregnated matrix. The matrix is disposed between the two electrodes. A catalyst layer is disposed on electrolyte-facing surface of each electrode.
In the operation of a typical fuel cell, a hydrogen-containing gas is fed to the back surface of the anode and an oxygen-containing gas is fed to the back surface of the cathode. The gases diffuse through the electrodes to react at catalyst sites to yield water, heat, and electrical energy.
On the anode side of the cell, hydrogen is electrochemically oxidized to give up electrons. The electrical current so generated is conducted from the anode through an external circuit to the cathode. 0n the cathode side of the cell, the electrons are electrochemically combined with the oxidant. A flow of ions through the electrolyte completes the circuit.
Several types of fuel cells have been developed and may be broadly categorized according to the type of electrolyte used, for example, acid cells, alkaline cells and molten carbonate cells. Acid cells using concentrated phosphoric acid as the electrolyte are the most commercially advanced of the various fuel cells.
There is a constant search in the art for ways in which to improve fuel cell performance. A particular problem is presented in the case of phosphoric acid cells. Phosphoric acid cells typically operate at temperatures in the range of 325� F.-425� F. The electrolyte is liquid at the operating temperature of the cell. Under some circumstances, the cell must be shut down and cooled to room temperature. The concentrated phosphoric acid electrolyte can solidify upon cooling. The solidification of the electrolyte during shutdown of the cell has a detrimental effect on the cell electrodes that results in lowered cell performance in subsequent operating cycles. In the case of a planned shutdown, the concentrated phosphoric acid electrolyte is typically diluted prior to shutdown to avoid electrolyte solidification and the associated problems. However, such dilution is not always possible as, for example, in the case of an emergency shutdown. Since unplanned shutdowns are possible, it is desirable that the electrodes be tolerant of electrolyte solidification.
A conventional approach toward improving the tolerance of electrodes to electrolyte solidification is to increase the hydrophobicity of the catalyst layer as, for example, by increasing the relative amount of hydrophobic polymer in the layer. However, this approach also reduces the peak performance of the electrode.
What is needed in this art is a fuel cell electrode that overcomes these difficulties to give improved peak performance and, in the case of phosphoric acid cells, improved tolerance of electrolyte solidification.
A method for making a fuel cell electrode is disclosed. The method comprises applying a catalyst layer comprising a hydrophobic polymer and an electrocatalyst to one surface of a porous substrate, heating the layer at a temperature between the sintering temperature and the decomposition temperature of the polymer while simultaneously compressing the layer at a pressure between 20 pounds per square inch and 100 pounds per square inch and continuing the heating and compressing for a time period of between 10 minutes and 20 minutes. A fuel cell electrode made by the process of the present invention provides increased peak performance as well as improved performance stability.
Another aspect of the invention is a fuel cell electrode made by the above process.
A further aspect of the invention is a method for generating electric current. The method comprises feeding streams of a fuel and an oxidant to a fuel cell, said fuel cell having two electrodes and an electrolyte containing matrix between the electrodes, wherein each electrode has a catalyst layer coating one surface of a porous substrate, oxidizing the fuel at the catalyst layer of one electrode to generate a stream of electrons, conducting the electrons to a second electrode, combining the electrons with the oxidant at the catalyst layer of the second electrode, and transferring ionic species through the electrolyte to complete the circuit, wherein the improvement comprises using an electrode made according to the above process as at least one of the electrodes in the fuel cell.
The foregoing and other features and advantages of the present invention will become more apparent from the following description.
The FIGURE shows cathode potential during use versus the pressing pressure applied during the press sintering process.
While any porous substrate that is compatible with the fuel cell environment may be used with the present invention, substrates already successfully used in fabricating fuel cell electrodes are preferred substrates. Carbon paper is the particularly preferred substrate for fabricating electrodes to be used in phosphoric acid cells.
Carbon paper suitable for use as the substrate of the present invention may be purchased or prepared. Suitable carbon papers are available from a number of commercial sources, for example, Union Carbide Corp., Stackpole Carbon Company and Kureha Corporation.
Carbon paper substrates may be prepared from resin bonded carbon fibers by known paper making techniques as disclosed in commonly owned U.S. Pat. No. 3,972,735. Such carbon papers can be wetproofed by impregnation with hydrophobic polymer. The wetproofing allows gas flow through the substrate while allowing the substrate to simultaneously hold electrolyte in order to accommodate electrolyte volume changes during cell operation.
A preferred method for preparing carbon paper substrates is the process taught by commonly owned U.S. Pat. No. 4,426,340, the disclosure of which is incorporated herein by reference. Electrode substrates prepared by the preferred process do not require wetproofing, as the flow of gases and flow of electrolyte through the substrate are controlled by selection of the porosity and pore size distribution within the substrate. Briefly, the process comprises selecting a dry mixture of carbon fibers and thermosetting resin, depositing the mixture in a mold, and then heating and compacting the mixture to bond the fibers. The article so formed is then carbonized in an inert atmosphere by increasing the temperature at a rate of about 40� C. per hour to 950� C. and holding at 950� C. for about 1 hour. The substrate may then be graphitized by heating at 2800� C.
The preferred process provides considerable latitude in the design of electrode substrates and allows selection of porosity and pore sizes that are adopted to specific applications. In general, it is desirable to maximize the porosity of the substrate while preserving the physical strength of the substrate. Carbon substrates having a porosity of between 65% and 80% are preferred with porosity between 70% and 80% being most preferred for the practice of the present invention. The selection of a particular pore size distribution depends upon the design of the particular cell and may be determined by conventional fuel cell design techniques. A mean pore size of between 20 microns and 70 microns is preferred for the practice of the present invention.
The catalyst layer of the present invention comprises a mixture of hydrophobic polymer and an electro-catalyst.
The hydrophobic polymer of the present invention may be any hydrophobic polymer compatible with the electrolyte to be used in the fuel cell. Compatible fluorinated polymers, such as PTFE and fluorinated ethylene propylene (FEP), having molecular weights of about 1�106 or greater are preferred. PTFE is most preferred and most widely used in the art. Suitable PTFE polymers are TFE-6 or TFE-30, each manufactured by DuPont. TFE-6 is a dry powder having a molecular weight of about 1�106 and a particle size of greater than 100 microns. The TFE-30 is an aqueous dispersion of about 0.2 micron size PTFE particles with a surfactant.
Noble metals and alloys of noble metals are suitable catalysts for use with the present invention. Platinum is the preferred catalyst for use as the anode catalyst. The platinum may be dispersed upon support by conventional methods, for example, those disclosed in commonly owned U.S. Pat. Nos. 3,857,737 and 4,040,193. Binary alloy catalysts, such as platinum-vanadium and platinum-chromium, and ternary alloy catalysts, such as platinum-chromium-cobalt are preferred for use as cathodic catalysts. Methods of making platinum-vanadium catalysts are disclosed in commonly owned U.S. Pat. Nos. 4,202,934 and 4,513,094, a method of making platinum-chromium catalysts is disclosed in commonly owned U.S. Pat. No. 4,316,944 and a method of making platinum-chromium-cobalt catalysts is disclosed in commonly owned U.S. Pat. No. 4,447,506. The disclosures of the above cited U.S. Patents are incorporated herein by reference.
The catalyst of the present invention is preferably dispersed upon an electrically conductive support material having a specific surface area of greater than about 50 m2 /gram.
Carbon blacks, such as acetylene black, and oil blacks are preferred catalyst supports. An oil black known as Vulcan XC-72, available from Cabot Corp., is the most preferred catalyst support. While the as-received carbon black is the preferred support for the anode catalyst, it has been found that graphitized carbon black is preferable for the cathode catalyst support due to its better resistance to corrosion. Carbon black particles may be graphitized by heating at a temperature between 2500� C. and 2700� C. for about 1 hour in an inert atmosphere.
The hydrophobic polymer and catalyzed carbon particles may be blended by any convenient technique that will produce a uniform mixture. For example, an aqueous co-suspension may be formed by conventional techniques, such as agitating mixture of catalyzed carbon particles, an aqueous dispersion of PTFE particles and water in a commercial Waring blendor. The aqueous suspension is then caused to floc, for example, by heating or by adding a floccing agent.
Alternatively, the aqueous co-dispersion may be flocced, dried and pulverized to produce a dry, powdered mixture of polymer and catalyzed carbon, as described in commonly owned U.S. Pat. No. 4,287,232. A dry mixture of polymer and carbon particles may also be produced by blending and pulverizing a mixture of dry hydrophobic polymer powder and catalyzed carbon particles as disclosed in commonly owned U.S. Pat. No. 4,175,055. A process for preparing a dry mixture of hydrophobic polymer and catalyzed carbon that is preferred for continuous production is disclosed in commonly owned U.S. Pat. No. 4,233,181.
The hydrophobic polymer and catalyzed carbon may be applied to the substrate using such conventional techniques as direct filtration or filter transfer.
The preferred method for applying the hydrophobic polymer and catalyzed carbon to the substrate is the cloud chamber technique disclosed in commonly owned U.S. Pat. No. 4,287,232, the disclosure of which is incorporated herein by reference.
In the cloud chamber technique a layer of dry carbon and hydrophobic polymer powder is deposited on the surface of the electrode substrate by dispersing the powder as a fluidized bed in a chamber over the substrate and pulling the powder onto the upper surface of the substrate by drawing a vacuum under the substrate.
After application to the substrate, the catalyst layer is press-sintered by heating to a temperature at or above the melting point of the hydrophobic polymer yet below the decomposition point for the hydrophobic polymer while simultaneously applying a pressure above about 20 pounds per square inch absolute (psia) and below that pressure which would crush the substrate material. For carbon paper substrates, the upper pressure limit is about 100 psia. The compression at elevated temperature is continued for a time period of about 10 minutes to about 30 minutes.
A sintering temperature in the range of about 640� F. to about 670� F. is preferred for PTFE, with a temperature of about 660� F. being most preferred.
A pressure of between about 60 psia and about 100 psia is preferred with a pressure of between about 80 psia and about 100 psia being most preferred.
The electrode is simultaneously heated and compressed at a temperature and a pressure within the above ranges for a time period preferably between about 10 minutes to about 20 minutes.
A cathode electro-catalyst was made by depositing a platinum-chromium-cobalt ternary alloy on a graphite support as described in the above cited U.S. Pat. No. 4,447,506.
The electro-catalyst was then blended with TFE-6 to obtain a mixture comprising 35 percent by weight TFE-6 and 65 percent by weight electro-catalyst.
An electrode was fabricated by first applying a layer of the electro-catalyst and TFE-6 mixture to a graphitized carbon substrate using the cloud chamber technique described in the above cited U.S. Pat. No. 4,287,232. The carbon substrate was manufactured by Union Carbide.
The layer and substrate were then placed in a Carver press which was fitted with a heater plate on each of the platens. The heater plates were thermostatically controlled to maintain a temperature of 660� F. The catalyst layer was covered with aluminum foil to prevent the layer from adhering to the platen during press-sintering. Pressure was applied to the electrode through the heated platens of the press and held at the desired pressure for the entire press-sintering time of 15 minutes. The electrode was then removed from the press and allowed to cool to room temperature.
Cathode potential values for several electrodes were obtained from a half-cell apparatus containing 99 percent by weight phosphoric acid at a cell temperature of 350� F. at a cathodic current density of 200 milliamperes/cm2. The FIGURE shows the relationship between cathode performance and the pressure applied during the press-sintering process.
A cathode electro-catalyst was made by depositing a platinum-vanadium alloy on an acetylene black support is described in the above cited U.S. Pat. No. 4,202,934.
The electro-catalyst was first dispersed in water and then an aqueous dispersion containing DuPont T-30 hydrophobic polymer was added. The mixture was stirred and the pH of the mixture was adjusted to 4.0 to induce flocculation. The floc comprised 60 percent by weight electro-catalyst and 40 percent by weight T-30 polymer.
The mixture was restirred and filtered to deposit a layer of the floc on a filter paper. The layer was then transferred to a graphitized carbon substrate. The carbon substrate was manufactured by Union Carbide. The layer and substrate were dried under a heat lamp to remove the residual water.
The layer and substrate were press-sintered according to the process described in Example 1 for 15 minutes at a temperature of 660� F. and a pressure of 75 psia.
The tolerance to electrolyte solidification cycles of the press-sintered electrode and a conventional electrode were compared. Subscale 2"�2" cells using a 99 percent by weight phosphoric acid electrolyte were continuously operated at 375� F. at 200 amperes/ft2. The oxidant comprised air and the fuel comprised a mixture of 79.6 percent by weight hydrogen, 1.7 percent by weight carbon monoxide and 18.7 percent weight carbon dioxide. Once per week the cells were shut down and placed in a freezer at -25� F. for 3 days.
After the completion of six cycles, the performance of the cells was measured. The press-sintered electrode exhibited a 16 millivolt loss in cathode potential while the conventional electrode exhibited a cathode potential loss in excess of 50 millivolts.
The fuel cell electrode of the present invention provides improved peak performance and, in the case of phosphoric acid cells, improved tolerance to electrolyte solidification.
While the present invention has been described in terms of a phosphoric acid fuel cell, it will be understood by those skilled in the art that the process of the present invention is pplicable to any gas diffusion electrode having a layer of hydrophobic polymer and catalyst supported upon a porous substrate.
Although this invention has been shown and described with respect to detailed embodiments thereof, it will be understood by those skilled in the art that various changes in form and detail thereof may be made without departing from the spirit and scope of the claimed invention.
|Cited Patent
|Filing date
|Publication date
|Jun 8, 1966
|Nov 12, 1968
|Army Usa
|Method of making sintered platinumplastic electrode
|May 1, 1967
|Apr 15, 1969
|Leesona Corp
|Electrochemical cell containing an electrode comprising a catalytic layer consisting of uniformly dispersed catalytic metal particles and a hydrophobic polymer,and (in contact with the cell electrolyte) a separate porous metal layer
|Mar 1, 1965
|Jul 22, 1969
|Monsanto Res Corp
|Laminar electrode including hydrophobic and hydrophilic layfrs; method of making; fuel cell therewith; and method of using fuel cell
|Sep 18, 1973
|Dec 31, 1974
|United Aircraft Corp
|Sequential catalyzation of fuel cell supported platinum catalyst
|Mar 25, 1974
|Feb 10, 1976
|Electrostatic Equipment Corporation
|Particle cloud coating method and apparatus
|Apr 4, 1975
|Aug 3, 1976
|United Technologies Corporation
|Method for making electrodes for electrochemical cells
|Jun 28, 1978
|Nov 20, 1979
|United Technologies Corporation
|Dry mix method for making an electrochemical cell electrode
|Jun 28, 1978
|Dec 4, 1979
|United Technologies Corporation
|Catalytic dry powder material for fuel cell electrodes comprising fluorocarbon polymer and precatalyzed carbon
|Jul 3, 1978
|May 13, 1980
|United Technologies Corporation
|Noble metal/vanadium alloy catalyst and method for making
|May 30, 1979
|Nov 11, 1980
|United Technologies Corporation
|Automated catalyst processing for cloud electrode fabrication for fuel cells
|Jun 28, 1978
|Sep 1, 1981
|United Technologies Corporation
|Dry floc method for making an electrochemical cell electrode
|Sep 27, 1979
|Oct 6, 1981
|Prototech Company
|Thin carbon-cloth-based electrocatalytic gas diffusion electrodes, and electrochemical cells comprising the same
|Nov 6, 1980
|Feb 2, 1982
|United Technologies Corporation
|Dry method for making an electrochemical cell electrode
|Jun 18, 1980
|Feb 23, 1982
|United Technologies Corporation
|Noble metal-chromium alloy catalysts and electrochemical cell
|Oct 31, 1980
|Jun 29, 1982
|Diamond Shamrock Corporation
|Strengthening of carbon black-teflon-containing electrodes
|Feb 19, 1981
|Sep 21, 1982
|Diamond Shamrock Corporation
|Oxygen cathode for alkali-halide electrolysis and method of making same
|Feb 12, 1981
|Dec 7, 1982
|Electrochemische Energieconversie, N.V.
|Porous electrode
|Sep 29, 1981
|Jan 17, 1984
|United Technologies Corporation
|Process for fabricating ribbed electrode substrates and other articles
|Jan 17, 1983
|May 8, 1984
|United Technologies Corporation
|Ternary fuel cell catalysts containing platinum, cobalt and chromium
|Jan 17, 1983
|Sep 4, 1984
|Ppg Industries, Inc.
|Permionic membrane electrolytic cell
|Dec 17, 1982
|Mar 19, 1985
|Kureha Kagaku Kogyo Kabushiki Kaisha
|Process for preparing a fuel cell electrode substrate comprising carbon fibers
|Jun 20, 1983
|Apr 23, 1985
|United Technologies Corporation
|Single-batch process to prepare noble metal vanadium alloy catalyst on a carbon based support
|Jul 6, 1984
|Sep 24, 1985
|Eltech Systems Corporation
|Method of making a catalytic lead-based oxygen evolving anode
|Jun 28, 1985
|Jul 29, 1986
|Union Carbide Corporation
|Method of producing a gas diffusion electrode
|Satoshi Motuo et al., "Gas Diffusion Electrode of High Performance", J. Electroanal. Chem 160 (1984) 351-357.
|Satoshi Motuo et al., Gas Diffusion Electrode of High Performance , J. Electroanal. Chem 160 (1984) 351 357.
|Citing Patent
|Filing date
|Publication date
|Nov 27, 1990
|Jun 30, 1992
|Universite Du Quebec A Montreal
|Ternary alloy electrocatalysts
|Sep 19, 1990
|Sep 22, 1992
|Fuji Electric Co., Ltd.
|Method of stopping the operation of phosphoric acid type fuel cell
|May 17, 1991
|Nov 17, 1992
|The Dow Chemical Company
|Ion exchange membrane having increased efficiency in proton exchange processes
|Jun 27, 1991
|Apr 12, 1994
|The Dow Chemical Company
|Ion exchange membrane/electrode assembly having increased efficiency in proton exchange processes
|May 18, 1993
|May 17, 1994
|Electric Fuel (E.F.L.) Limited
|Process for preparing a single pass gas diffusion electrode
|Jul 5, 1991
|Oct 25, 1994
|Texaco Inc.
|Membrane and separation process
|Dec 20, 1993
|Mar 7, 1995
|The Dow Chemical Company
|Electrochemical cell having an electrode containing a carbon fiber paper coated with catalytic metal particles
|Jul 1, 1994
|Aug 15, 1995
|Electric Fuel (E.F.L.) Ltd.
|Process for the preparation of gas diffusion electrodes
|Mar 29, 1994
|Jan 2, 1996
|International Fuel Cells Corporation
|High current alkaline fuel cell electrodes
|Oct 10, 1997
|Mar 9, 1999
|Minnesota Mining And Manufacturing Company
|Membrane electrode assembly
|Aug 6, 1999
|Oct 24, 2000
|3M Innovative Properties Company
|Microtextured catalyst transfer substrate
|Mar 26, 1999
|Oct 23, 2001
|Ballard Power Systems Inc.
|Method of reducing fuel cell performance degradation of an electrode comprising porous components
|Jul 1, 2002
|Aug 15, 2006
|Honda Giken Kogyo Kabushiki Kaisha
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|Bdf Ip Holdings Ltd.
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|Honda Giken Kogyo Kabushiki Kaisha
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|Knights Shanna D.
|Supported catalysts for the anode of a voltage reversal tolerant fuel cell
|Apr 20, 2007
|Jun 5, 2008
|Ronald Mah
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|Dec 1, 2014
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|Apr 22, 1999
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|U.S. Classification
|429/533, 502/101, 429/535
|International Classification
|Cooperative Classification
|European Classification
|Aug 13, 1992
|Fee payment
Year of fee payment: 4
|Oct 15, 1996
|Maintenance fee reminder mailed
|Mar 9, 1997
|Lapse for failure to pay maintenance fees
|May 20, 1997
|Expired due to failure to pay maintenance fee
Effective date: 19970312


text:
What is 'Operating Leverage'
Operating leverage is a measurement of the degree to which a firm or project incurs a combination of fixed and variable costs.
1. A business that makes few sales, with each sale providing a very high gross margin, is said to be highly leveraged. A business that makes many sales, with each sale contributing a very slight margin, is said to be less leveraged. As the volume of sales in a business increases, each new sale contributes less to fixed costs and more to profitability.
2. A business that has a higher proportion of fixed costs and a lower proportion of variable costs is said to have used more operating leverage. Those businesses with lower fixed costs and higher variable costs are said to employ less operating leverage.
BREAKING DOWN 'Operating Leverage'
The higher the degree of operating leverage, the greater the potential danger from forecasting risk. That is, if a relatively small error is made in forecasting sales, it can be magnified into large errors in cash flow projections. The opposite is true for businesses that are less leveraged. A business that sells millions of products a year, with each contributing slightly to paying for fixed costs, is not as dependent on each individual sale.
For example, convenience stores are significantly less leveraged than high-end car dealerships.
Leverage1. The use of various financial instruments or borrowed capital, ...
Degree Of Combined Leverage - DCLA leverage ratio that summarizes the combined effect the degree ...
Degree Of Operating Leverage - ...A type of leverage ratio summarizing the effect a particular ...
Operating CostExpenses associated with the maintenance and administration of ...
Leverage Build UpThe accumulation of additional debt to enter a position that ...
Maximum LeverageThe maximum size of a trading position permitted through a leveraged ...
The Operating Leverage And DOLOperating leverage tells investors about the relationship between a company's fixed and variable costs. The higher a company's fixed costs in relation to its variable costs, the greater its operating ...
Operating Leverage Captures RelationshipsFind out how fixed and variable costs interact to shed new light on old companies.
Leverage: Is It Good for Your Portfolio?Discover the concept of financial leverage. Learn multiple ways to get leverage in your portfolio, and decide if leverage is a good idea for you.
Borrowing Smart In A Debt-Filled WorldLeveraging your money can have many perks, but it's not always the smartest financial plan.
Explaining Leveraged LoansLeveraged loans are loans extended to companies or people who already have large amounts of debt.
How Much Leverage Is Right for You in Forex TradesIt isn't economics or global finance that trip up first-time forex traders. Instead, a basic lack of knowledge on how to use leverage is at the root of trading losses.
Leverage: What It Is And How It WorksLeverage is an investment strategy of using borrowed money to generate outsized investment returns. Before getting into greater detail on how leverage works in an investment context, it is useful ...
Adding Leverage To Your Forex TradingThe use of margin to trade in the foreign exchange market can magnify profit opportunities.
Forex Leverage: A Double-Edged SwordFind out how this flexible and customizable tool magnifies both gains and losses.
Leverage's "Double-Edged Sword" Need Not Cut DeepLearn to cut out losses quickly, leaving profits room to grow.
What is the difference between operating leverage and financial leverage?Discover the two equity valuation metrics, operating leverage and financial leverage, how they are similar and what differentiates ... Read Answer >>
How can a firm bring down its operating leverage?Discover how to determine a company's operating leverage and how this metric can be helpful to analysts and investors when ... Read Answer >>
What are the risks of having both high operating leverage and high financial leverage?In finance, the term leverage arises often. Both investors and companies employ leverage to generate greater returns on their ... Read Answer >>
What is the relationship between degree of operating leverage and profits?Find out why a company's degree of operating leverage is an important consideration when predicting future operating income ... Read Answer >>
How does operating leverage affect business risk?Learn how operating leverage affects business risk and how companies measure it. Review a relevant example of operating leverage ... Read Answer >>
How do I calculate the degree of operating leverage?Learn about the degree of operating leverage, what it measures and how to calculate a company's degree of operating leverage ... Read Answer >>

subset: commoncrawl


text:
MESA, Ariz. -- Arizona Diamondbacks general manager Josh Byrnes acknowledged Friday that pitcher Brandon Webb could open the season on the disabled list if he doesn't begin making more progress soon in his comeback from shoulder surgery.
Webb, the 2006 National League Cy Young Award winner, said he felt "stagnant" after a 45-pitch bullpen session Thursday. The Diamondbacks have no idea when he'll appear in his first Cactus League game, and Byrnes said the team plans to take the long-term view rather than rush Webb into action this spring before he's ready.
"It's a long season," Byrnes said. "If we get 30 starts from him, great. If we get 20, that's great. I think we just need to get it right.
"His shoulder is strong. He's done a lot of work. Now I think it's more a function of the inactivity -- 10 months between being on the mound. In many respects, he's about where we want him to be. But he needs to have four or five spring training starts to be ready for the first regular-season start. If that's going to happen, we need to know fairly soon."
Byrnes pointed out that in recent years, the Diamondbacks have taken it slowly with starters Max Scherzer and Randy Johnson when they were rehabilitating from injuries in spring training.
"If you have to concede a little bit of time at the front end of the schedule to keep them healthy for the long haul, that's what we'll do," Byrnes said. "We haven't had to make that decision yet."
The Diamondbacks need Webb to make a significant contribution this year if they're going to rebound from a 70-win season and contend in the National League West. A healthy Webb would team with Dan Haren and Edwin Jackson to give Arizona one of the most formidable top-of-the-rotation threesomes in the majors.
If Webb does begin the season on the DL, Byrnes said it's more likely the Diamondbacks will fill the void from within rather than look outside the organization for another starter. Former New York Yankees Ian Kennedy is expected to fill the fourth spot in the rotation, and Billy Buckner, Kevin Mulvey, Rodrigo Lopez and Bryan Augenstein are in contention for the fifth spot.
The Diamondbacks don't have much money to spend, and they don't expect to make a play for Braden Looper, Jarrod Washburn or any of the free-agent starters still on the market.
Barring a change of plans, the Diamondbacks expect Webb to throw live batting practice for the first time Sunday or Monday. But his scheduled April 7 start against San Diego will be in jeopardy if he doesn't pick up the pace soon.
"I'm impatient right now," Webb told reporters Thursday. "I'm ready to go and let it loose. I want to throw in a game and stuff like that. Obviously I'm not ready to do that right now. The next step is facing live hitters and that will be coming up."
From Opening Day 2004 through the end of 2008, Webb ranked second in the majors to Johan Santana with 1,135 innings pitched. He made three All-Star teams and reeled off a streak of 42 consecutive shutout innings in 2007.
Webb shut it down last year after pitching four innings against Colorado on Opening Day. He underwent a shoulder cleanup -- also known as a "debridement'' -- in August.
The Diamondbacks exercised an $8.5 million option on Webb in November, and he'll be eligible for free agency after this season.
Senior writer Jerry Crasnick covers Major League Baseball for ESPN.com.


text:
Lieutenant Michael O'Connor acknowledges that when he joined the Atlanta Police Department, he didn't know quite what he was walking into. "I was in Panama City at the time, couldn't find a job in Florida, and Atlanta was hiring for the Olympics," he recalls. "I didn't put any thought into the crime rate — I just wanted to be a cop and they were hiring."
It was 1996. Most of the city's public housing communities were still operational, the murder rate was 79 percent higher than last year's, and crack was king. O'Connor recalls people standing on street corners, wantonly holding what they called "bombs," or large amounts of crack rocks, in their pockets, jut waiting for the next customer to stroll by. When asked about the current cocaine problem in Atlanta, O'Connor — who was recently promoted to commander of the narcotics unit — reflexively compares it to the drug's heyday. "Well, when I joined, it was a huge problem," O'Connor says. "[All crime] seems to be tied to this open-air drug trade. That's not the case anymore."
"Not to say we don't have a drug problem," he continues, "but not near the problem we had when I first joined the force."
O'Connor's take is completely understandable given the city's history and his 15-plus years of experience. But the extent of Atlanta's drug problem is still alarming.
But every year, data collectors with the Office of National Drug Control Policy spend a couple weeks in detention facilities in 10 U.S. cities — Atlanta, Charlotte, Chicago, Denver, Indianapolis, Minneapolis, New York, Portland, Ore., Sacramento, and Washington, D.C. — drug testing and surveying inmates as they're booked. It's called the Arrestee Drug Abuse Monitoring program (known as ADAM II), and it's intended to "provide policymakers with critical data" about a group of potential drug users the ONDCP says are underrepresented in other studies: men at their point of entry into the criminal justice system. The supposition is that many who commit crimes do so while under the influence of drugs, or, conversely, that lots of the people who abuse drugs wind up committing crimes.
Not surprisingly, it's a pretty astute assumption.
According to ADAM's 2010 report [PDF], released just a few months ago, 66 percent of the men booked into Atlanta's jails during the study period had drugs in their systems. That percentage was higher in several other cities; for instance, in Chicago, where more than 80 percent of arrestees were found to have drugs in their systems. (Atlanta was also beat out by Charlotte, Indianapolis, Minneapolis, New York, Portland, and Sacramento.) But the ATL stands out in terms of the use and abuse of a particular drug: cocaine. More than 33 percent of Atlanta's male arrestees — more than in any other city — were under the influence of cocaine when they were booked. In the majority of those cases, the inmates reported they'd smoked crack.
Generally, the consensus among local and national law enforcement agencies is that Atlanta's coke-crack problem pales in comparison to what it was in the '80s and '90s, as O'Connor noted. As recently as 2000, ADAM's research showed that nearly half of all Atlanta's arrestees had cocaine in their systems. Technically, then, one-in-three is an improvement. Still, O'Connor calls Atlanta one of "the last of the cocaine holdouts in the urban Southeast." And when drugs are so irrevocably linked to crime — and police link cocaine use and sales, in particular, to violent and property crime — law enforcement has a stake in figuring out why a third of the people arrested here have it coursing through their veins (and through their bladders, as it were). Compared to other cities, why does Atlanta continue to be Cocaine Town, U.S.A.?
The ADAM study certainly has its limitations. For instance, arrestees in Los Angeles weren't included in the research, nor arrestees in any cities in Texas. Still, it paints a picture of a city with a unique drug problem, one that began when Atlanta became a full-fledged trafficking hub.
In 2012, it's required by the doctrine of giving-credit-where-it's-due that any discussion about crime or other illicit activities be prefaced by the acknowledgement that, yes, crime is down. That's pretty much the case nationwide. Preliminary crime stats released by the Atlanta Police Department indicate that, citywide, overall crime decreased 1 percent in 2011 from the previous year, even though there were more rapes — a lot more, in fact — as well as more robberies, larcenies, and auto thefts.
So, all in all, it would appear fewer people are committing crimes. What the ADAM report does, though, is offer insight into the people who are still offending.
Per the study's methodology, ADAM researchers spent two weeks in Atlanta in 2010 — one week in the Atlanta City jail, the other in the Fulton County jail — performing urinalyses and asking questions of inmates who were booked no more than 48 hours earlier. Besides substance abuse data, researchers compiled sociological and economic stats about each inmate: a racial breakdown, his employment status, current living arrangement, and age. Apart from Washington, D.C., where 88.1 percent of the inmates booked during the study period were African-American versus 7 percent white, Atlanta had the starkest racial disparity among arrestees, with 82.7 percent of the inmates booked being of African-American descent, 12.8 percent white, and 7 percent Hispanic. Other interesting figures in the report include that upward of 35 percent of inmates reported having no education, nearly half — 49.6 percent — were actually gainfully employed, and their mean age is perhaps older than you'd imagine at 35.
And as far as the drug data's concerned, all the news wasn't necessarily bad news.
As of 2009, Atlanta was the only city where cocaine was the drug most often found in inmates' systems. In 2010, marijuana actually replaced cocaine as the drug-of-choice among arrestees, allowing Atlanta to join the rest of the study cities in that respect. And it wasn't because marijuana use increased in Atlanta, but because cocaine use decreased (it's steadily decreased since 2007, as it has most places). Still, Atlanta managed to hold strong as the cocaine capital among ADAM sites, proving it's still the drug of choice for those committing (or at least being arrested for committing) crimes.
Last week, one of Big Boi's Twitter followers wanted to know, "Why they gotta make niggas be drug bosses in movies like ATL?" The OutKast frontman's response: "Cause niggas in Atlanta sell Dope nigga." Not, perhaps, the most eloquent way to elucidate of the city's less-than-illustrious position as a thriving center for the sale and purchase of drugs.
But the story of cocaine in Atlanta begins well before an inmate is booked into jail. It begins well before said inmate purchases it in crack form on the street, stuffs it into a little glass tube, and then carjacks you. It begins even before the guy he bought it from bought it from someone else, mixed it with baking soda, and cooked it up on the stove.
John Horn, First Assistant U.S. Attorney for the Northern District of Georgia, explains: "There's sort of a local side to the picture, and sort of a wholesale or a more national component to the Atlanta drug trade." His office doesn't deal much with street-level sales or consumption, rather large, multistate drug trafficking operations. "[The drugs on the street] are coming from the same people, but three or four levels below," Horn says. "What we focus on is the high-level — and it's almost 99 percent Mexican [cocaine]."
Here's a condensed version of how, in recent years, Atlanta became a "hub" for the distribution of Mexican cocaine: In the '80s and '90s, most of the cocaine coming into the U.S. was coming through Miami from Colombia. The Mexican drug lords wanted in on the action, so they offered to become middlemen. The Colombians were like, "Well, yeah, obviously." Anyway, that's when it started coming through Texas on tractor-trailers, and the big Mexican cartels — the Gulf Coast Cartel and, later, the Sinaloa Cartel — formed. Around the mid-2000s, Mexican middlemen began to set up stash houses in and around Atlanta — in Gwinnett County, in particular — where cocaine is brought by truck, unloaded, packaged, and then moved to other cities like Philadelphia, Baltimore, and Detroit. Then the cash proceeds from the drug sales come back to Atlanta to be packaged before they're sent back down to Texas.
Even though the vast majority of the cocaine that comes to Atlanta will someday be shipped elsewhere, Horn points out that "some of the stuff trickles down to street-level distributors."
In its 2010 annual report, the Atlanta High Intensity Drug Trafficking program, a regional law enforcement effort to dismantle high-level trafficking organizations, says that on the retail end, street gangs continued to contribute to significant cocaine and marijuana sales, particularly in Southeast Atlanta. But, even since that report was released, street gangs like 30 Deep — like the much larger, much more organized, and much more criminally prolific Black Mafia Family before them — have largely been arrested into oblivion. The first three months of 2011 were calamitous for 30 Deep, a gang that was actually known less for its drug activity than the burglaries and murders its members committed, including the 2009 shooting of Standard bartender John Henderson. In March, purported member Jonathan Redding received a life sentence plus 70 years for the Standard shooting. That same month, U.S. Marshals executed Operation Zero Deep, serving warrants to around 40 people suspected to be connected to the gang. And a month earlier, Redding's cousin — and 30 Deep ringleader — George "Keon" Redding received two life sentences in prison.
Another factor that's changed the nature of crack and cocaine sales in recent years is the almost wholesale demolition of Atlanta's housing projects, which basically operated as open-air flea markets for drug dealers, minus the tarps and tables. Lt. O'Connor says that in the post-public-housing era, drug sales have become hyper-localized and open-air sales have declined. "The drug market moved inside," O'Connor says. "We don't have a RED DOG anymore, but they did have an impact. That [unit] and beat officers, over time, pushed those people inside. Now the neighborhood drug dealer will sell from his home or his apartment."
That would appear to hold true — except when it comes to crack. ADAM data collectors also asked inmates where they'd made their last drug purchase. Sixty-eight percent of the inmates who reported last purchasing crack said they still did so in an outdoor area, the highest outdoor sales percentage of any drug. Powder cocaine, like the rest of the narcotics, was most often purchased inside someone's house or apartment. That Atlanta's drug dealings now exist largely behind closed doors would seem to present new challenges for narcotics investigators. But, Lt. O'Connor won't discuss enforcement tactics in any detail for risk of his unit losing its "operational edge" on criminals.
"Do you watch TV?" O'Connor asks. "Well, rent 'Traffic' or something. They probably got it right."
Judge Doris L. Downs, who oversees Fulton County's drug court program, spends her days trying to give lower-level offenders the chance to get treatment rather than just rotting behind bars. "I think that drug use plays an extremely high part in our arrest records, across the board," Downs says.
"And if you want to reduce the chance crime will happen again, reduce the recidivism rate for any one person, the way you do that is treatment," she adds. "Incarceration may be a necessary evil, but treatment is a must, whether you're incarcerated or not. It should be a requirement of the sentencing for anything drug-related."
But where Atlantans excel in the doing of drugs, they falter in the getting of help. According to ADAM's report, only 8 percent of inmates in Atlanta said they'd ever utilized outpatient drug treatment — the lowest percent of all the sites. Only 12 percent ever utilized inpatient treatment, also the lowest percentage. And those figures represented a sharp drop since even the previous year. Jack Killorin, director of Atlanta's HIDTA, says he's encouraged by a trend he's noticed, one that could eventually negatively effect demand for cocaine: The price is going up, and the quality is simultaneously going down. "The drugs are approaching a level of crap and the price is going up," says Killorin. "That's a great victory, other than what we'd like them to do, which is seek treatment."
Unfortunately, rather than seeking help, many addicts just seek a new drug. Killorin says his agency is already observing a move into other substances.
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@ 1msluckie How do you know he didn't ask? How do you know she started…
He didn't ask for any of this. She took it upon herself to start this…
Not a huge fan of the ankle cuff sneakers that Serena (and KD) are wearing…
Kind of strange that some random lady started a GoFundMe for that kid. I'm curious…


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B-Sens rally from two goals down to beat Hershey
Binghamton, NY (WBNG Binghamton) The Binghamton Senators overcame a 2-0 first period deficit to comeback for a 5-3 victory over the visiting Hershey Bears.
Puempel recalled by the Sens
Binghamton, NY (WBNG Binghamton) The Ottawa Senators recalled B-Sens forward Matt Puempel on Thursday. Puempel replaces Shane Prince, who was sent back down to Binghamton on Thursday.
B-Sens to hold D.I.F.D. night
Binghamton, NY (WBNG Binghamton) The Binghamton Senators home game on Friday is the teams first in two weeks, but it has an even more special meaning for coach Luke Richardson for a different reason.
Johnson's goal gives B-Sens an OT win
Allentown, Pa. (WBNG Binghamton) The Binghamton Senators twice overcame a one-goal third period deficit to defeat their host Lehigh Valley Phantoms in overtime 4-3.
Pageau recalled by Ottawa; Hammond likely to start for Sens
(WBNG Binghamton) After spending just two games with the Binghamton Senators, Jean-Gabriel Pageau was recalled on Tuesday evening by Ottawa.
B-Sens fail to sweep Marlies, lose in Toronto
Toronto (WBNG Binghamton) The Binghamton Senators fell 5-4 to the Toronto Marlies in their final matchup of the season and the end of a home-and-home series at their parent National Hockey League club's arena.
Shane Prince called up to Ottawa
Ottawa (WBNG BINGHAMTON) Shane Prince has been called up to play for the Ottawa Senators, the club announced Sunday. It is the first recall of Prince's career.
B-Sens score road win at Lehigh Valley, 3-2
Allentown, PA (WBNG BINGHAMTON) The Binghamton Senators held on for a 3-2 win over the Lehigh Valley Phantoms giving the B-Sens their first victory on the road over their newest division foe. Peter Mannino stopped 28 of 30 shots faced to guide Binghamton to the win.
B-Sens blasted by Penguins, 4-1
Wilkes-Barre, Pa. (WBNG Binghamton) Dominik Uher notched a pair of first period goals to help the Wilkes-Barre/Scranton Penguins defeat the visiting Binghamton Senators 4-1 Wednesday night.
Behind the Boards: Breaking down the B-Sens' breakdowns (web extra video)
Binghamton, NY (WBNG Binghamton) Entering last weekend, B-Sens coach Luke Richardson said he was hoping to get five or six points, but Binghamton only got two. In the two losses there were a few more breakdowns which lead to goals.


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by Judy and Mark
Next time you worry about how much you can take on the plane... just be glad they don't weigh YOU!
This airline weigh-in was not for our luggage... it was for us! We're always telling you to travel light, but this is taking it to the limit!
We were in the Peruvian Amazon, and before we could fly out of Manu National Park, we had an airline weigh-in.
In this case, we knew there was a luggage weight limit.
We had a custom tour set up for this adventure, and our tour operator had told us that our suitcases could only weigh 10 kilos, that's 22 pounds. With our travel light philosophy, that's about what our suitcases weigh in any case. We do, however, also carry a travel purse. That carry-on goes with us on the plane as a "personal item". It's sometimes pretty heavy in it's own right.
So about this airline weigh in. The flight from Manu to Cusco is operated by the Peruvian Air Force. The weather conditions have to be right for the flight to operate because of the altitude at Cusco. The Cusco airport is at 10, 859 ft (3,310 m)... and altitude makes a different for airplanes as well as for people.... all that lack of oxygen and all.
We got word at the Manu Wildlife Lodge that the flight was a go for our departure, so we took the two hour boat ride to get to the airport at Boca Manu.
They were assembling all kinds of cargo.... and everything got weighed. The cargo, our suitcases... and us... with everything we were carrying on! Kinda made us glad we hadn't been overeating!
That plane is a Twin Otter, and it has to fly over a 13,100 ft (3,993 m) pass. The weight and balance for the plane is crucial. With everything weighed and measured and packed into the plane, we climbed right up to 16,000 feet (4877 m)... Just enough to get through that pass... and just one more adventure on a trip that was full of them.
I guess the travel moral here is.... next time you're worried about how much you can take on an airplane... think about this and be glad that most airlines don't weigh you.
For the real information on how to pack and what is allowed, start with our Packing List page... you'll find a list that will lead you to lots of information on how to pack light... so at least your luggage will pass an airline weigh-in... even if you don't!
Happy travels, J & M
Join in and write your own page! It's easy to do. How? Simply click here to return to Recent Travels.
Happy travels... even if you don't travel the world... just remember that life is a journey... embrace and enjoy it! Judy and Mark
Curious about what else we've written about? Search our site for a destination or travel tip.
But... We'd love to have you share this page or comment on it…
Thanks, Judy and Mark
Summer Vacation
Travel is fun in the Northern summer... but don't neglect the Southern Hemisphere at this time of year.
Yes, it's winter in South Africa, but that's their dry season. It's a good time to travel there.
Sometimes you need to watch rain patterns instead of just seasons to figure the best time to travel...
And here's a suggestion if you don't want to plan it all yourself and you want great help....
DreamTrips can get you traveling sooner and cheaper that you thought possible
Whether you're taking a road trip close to home or traveling abroad...
Whether it's summer or winter in your part of the world...
the way you pack can make it all more pleasurable.
Check out all our Packing Lists and Tips.
Need travel ideas?
Things to See in Europe
Africa Calls!
Travel In America
Don't just dream about it...
Start making plans!
Custom Tour Planning List
International Travel Planning Tips
Foreign Is Fun - Not Scary!
Get Your Passports and Visas
And Expect Good Things
There Are Tourist Angels
Search MouseToursTravels
Travel questions or destination info?
Find our answers faster...
We want you to feel comfortable out in the world and on our pages - so surf away in your own language...
U.S. government Trusted Traveler Programs... designed to get some travelers through customs faster. TSA Pre-Check gets you through security faster. What they are and where to get info.
We need to take a DreamTrip before we could encourage you to be a member. This New Orleans DreamTrip was our first one… and it won't be our last. It was great!
A castle stay is always fun, but what if they give you the keys to the castle?!


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Check this section for local meets, events, and to chat with other Supra owners in your area!
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Discuss everything relating to the MKIII that isn't technical engine talk.
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This forum links to www.mkiiitech.com. This forum is very heavily techcentric, and aimed more specifically at technical information for the MKIII Supra.
For everything else that doesn't have a forum
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Coil on plug convertion with...
October 20th, 2015, 06:05 PM
Specializing in Unique Billet and High Performance Toyota parts. Click here for the website.
June 1st, 2016, 11:44 PM
New product available. Lokar...
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EMU Sale through June 15th,...
May 23rd, 2016, 10:25 AM
Looking for the discount code?
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Sethron71 Intake Manifolds,...
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This is a direct link to the Sound Performance website.
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Authorized Vendors without their own section may post here. Vendors who generate enough interest in this section may apply for their own forum.
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Welcome to our newest member, JiHoonie


text:
|Publication number
|Publication type
|Application number
|Publication date
|Apr 10, 2007
|Filing date
|Feb 14, 2005
|Priority date
|Oct 21, 2004
|Fee status
|Also published as
|Publication number
|George Edward Berkey, Xin Chen, Joohyun Koh, Ming-Jun Li, Daniel Aloysius Nolan, Donnell Thaddeus Walton, Ji Wang, Luis Alberto Zenteno
|Original Assignee
|Corning Incorporated
|Export Citation
|BiBTeX, EndNote, RefMan
|Patent Citations (16), Referenced by (16), Classifications (36), Legal Events (5)
|External Links: USPTO, USPTO Assignment, Espacenet
This Application claims the benefit and priority to U.S. Provisional Patent Application No. 60/621,389, filed Oct. 21, 2004. This Application also claims the benefit and priority to U.S. application Ser. No. 10/930,889, filed on Aug. 30, 2004.
Parts of this invention were made with Government support under Agreement No. MDA972-02-3-004 awarded by DARPA. The Government may have certain rights in some of the claims of the invention.
The present invention relates generally to optical waveguide fibers, and more particularly to a rare earth doped optical fiber exhibiting single polarization properties.
1. Field of the Invention
The present invention relates generally to double clad rare earth doped optical fibers, and particularly to all glass rare earth doped optical fibers suitable for use with high power light sources or in optical fiber lasers and optical amplifiers.
2. Technical Background
Optical fiber has become a favorite medium for telecommunications due to its high capacity and immunity to electrical noise. Single clad rare earth doped optical fiber has been widely used in the field of optical amplifiers and fiber lasers. This type of fiber has low capability of handling high power multimode optical sources due to the difficulty of efficiently coupling multimode light from a high power optical (light) source (also referred to herein as optical pump or pump) into the rare-earth doped fiber core.
To solve this problem and to increase the output power of fiber lasers, those of skill in the art utilize optical fiber with a double clad structure (referred herein as double clad optical fiber). Double clad rare-earth doped optical fiber is a fiber that has a core, an inner cladding layer surrounding the core and an outer cladding layer surrounding the inner cladding layer. Optical fibers with Yb doped cores and two cladding layers surrounding the core are disclosed, for example, in U.S. Pat. Nos. 6,477,307; 6,483,973; 5,966,491 and 5,949,941.
Double clad optical fiber has been used in applications requiring utilization of optical sources providing between 10 to 1000 Watts of optical power, because double clad optical fiber is more efficient in retaining/utilizing optical power provided by the pump than single clad optical fiber. This higher efficiency is due to fiber's utilization of clad-to-core coupling of optical pump power. More specifically, rare-earth doped double clad optical fibers accept light from the optical pump into the inner cladding and then transfer light to the rare-earth doped core through the coupling of pump light between the core and the inner cladding, along the length of the optical fiber. Thus, the optical fiber converts a significant part of the multi-mode light propagated through the inner cladding into a single-mode output at a longer wavelength, by coupling this pump light into the rare-earth doped core.
The inner cladding of the double clad optical fiber has a higher index of refraction than the outer cladding, thus the pump energy is confined inside the inner cladding and is re-directed into the core. The optical fiber is optically active due to the presence of rare-earth dopant in the core, which can be excited to higher electronic energy levels when the optical fiber is pumped by a strong optical pump. Cladding pumping can be utilized in fiber amplifiers, or employed to build high-power single mode fiber pump lasers.
The single-stripe broad-area diode laser remains the most efficient and least expensive pump source. Recent progress in semiconductor laser technology has led to creation of a single-stripe multi mode broad-area laser diodes with output powers of more than 10 Watts.
Recent progress in semiconductor laser technology has led to the creation of light sources utilizing either single stripe broad-area laser diodes or laser diode bars, directly coupled to the intermediate fiber incorporated within the light source. The maximum output power of these light sources is more than 150 Watt at a wavelength of 976 nm at the output end of the intermediate fiber. The intermediate fiber diameter and numerical aperture NA of the light source is 200 μm and 0.22, respectively.
In a double-clad laser, an outer cladding of the optical fiber confines the pump light provided by an optical pump in the optical fiber's multi-mode inner cladding. The much smaller cross-sectional area of the optical fiber's core is typically doped with at least one rare-earth element, for example, neodymium or ytterbium, to provide lasing capability in a single-mode output signal. Typically, a neodymium- or ytterbium-doped double-clad fiber is pumped with one or several high-power broad-area diode lasers (at 800 nm, 915 nm or 976 nm) to produce a single transverse mode output (at the neodymium four-level transition of 1060 nm or the ytterbium four level transition of 1030 nm–1120 nm, respectively). Thus, conventional double-clad arrangements facilitate pumping of the fiber using a multi-mode inert cladding for accepting and transferring pump energy to a core along the length of the device. Double-clad laser output can also be used to pump a cascaded Raman laser to convert the wavelength to around 1480 nm, which is suitable for pumping erbium.
How much pump light can be coupled into a double-clad fiber's inner cladding depends on the inner cladding size and its numerical aperture NA. As is known, the "etendue" (numerical aperture multiplied by the aperture dimension or spot size) of the inner cladding should be equal to or greater than the etendue of the optical pump for efficient coupling. If the numerical aperture and spot size of the optical source (optical pump are) be different in both axes, in order to have better coupling efficiency, the etendue of the inner cladding should be maintained or exceed that of the pump in both the x and y directions.
Typically, a high numerical aperture NA of the inner cladding, which is related to the difference in refractive index between the inner and outer cladding, is desired. In the well-known design, the first clad layer (inner cladding) is made of glass and the second layer (outer cladding) is made of plastic (for example, fluorinated polymer) with relatively low refractive index in order to increase the numerical aperture NA of the inner cladding. Such plastic may not have the desired thermal stability for many applications, may delaminate from the first cladding, and may be susceptible to moisture damage. In addition, this type of double clad optical fiber may be suitable only for sustained use with relatively low power (lower than 20 Watts) optical sources. When high power sources (more than 100 Watts) are utilized, this type of optical fiber heats and the polymer material of the outer cladding layer carbonizes or burns, resulting in device failure, especially when the fiber is bent. At medium powers (20 Watts to below 100 Watts), the polymer outer cladding ages relatively quickly, losing its mechanical and optical characteristics and becoming brittle, thus shortening the device life.
All-glass, Yb doped optical fibers are also known. An example of such fiber is disclosed in U.S. Pat. No. 6,411,762. The disclosed fiber, however, is not suitable for high power applications because it has a relatively low outer cladding diameter and NA, and therefore, low coupling efficiency due to light leakage outside of the optical fiber. That is, a relatively large portion of the light does not enter the optical fiber and is lost. Although this may not be an issue in applications when only a small amount of optical power needs to be coupled into the fiber, such fiber is not efficient for high power applications when the light source power is 100 Watts or more.
Single polarization optical fibers are useful for ultra-high speed transmission systems or for use as a coupler fiber for use with, and connection to, optical components (lasers, EDFAs, optical instruments, interferometric sensors, gyroscopes, etc.). The polarization characteristic (single polarization) propagates one, and only one, of two orthogonally polarized polarizations within a single polarization band while suppressing the other polarization by dramatically increasing its transmission loss.
Improvement in the polarization performance of single mode optical fibers has been achieved by elongating or distorting the fiber core geometry, as a means of decoupling the differently polarized light components. Examples of such optical fiber waveguides with elongated cores are disclosed in U.S. Pat. Nos. 4,184,859, 4,274,854 and 4,307,938. However, the noncircular geometry of the core alone is, generally, not sufficient to provide the desired single polarization properties. It is also noted that this type of optical fiber has relatively low birefringence (i.e., 10−5 or less). Furthermore, these fibers are not optically active fibers and, therefore are not suitable for use as a laser or an amplifier fiber.
It has, therefore, been an area of ongoing development to obtain an optical fiber that will single polarization performance while being suitable for use as optical amplification medium, and which is also easily manufacturable.
The following definitions and terminology are commonly used in the art.
Refractive index profile—the refractive index profile is the relationship between the refractive index (Δ%) and the optical fiber radius (as measured from the centerline of the optical fiber) over a selected portion of the fiber.
Birefringence—birefringence is the difference between the effective refractive indices of the two polarization modes.
Radii—the radii of the segments of the fiber are generally defined in terms of points where the index of refraction of the material used takes on a different composition. For example, the core has an inner radius of zero because the first point of the segment is on the centerline. The outer radius of the core is the radius drawn from the waveguide centerline to the last point of the refractive index of the core having a positive delta. For a segment having a first point away from the centerline, the radius of the waveguide centerline to the location of its first refractive index point is the inner radius of that segment. Likewise, the radius from the waveguide to centerline to the location of the last refractive index point of the segment is the outer radius of that segment. For example, an down-doped annular segment surrounding the core would have an outer radii located at the interface between the annular segment and the cladding.
Relative refractive index percent Δ%—the term Δ% represents a relative measure of refractive index defined by the equation:
Δ%=100�(n i 2 −n c 2)/2n i 2
where Δ% is the maximum refractive index of the index profile segment denoted as i, and nc, the reference refractive index, is taken to be the refractive index of the cladding layer. Every point in the segment has an associated relative index measured relative to the cladding.
In accordance with some embodiments of the present invention, an optical fiber is provided which exhibits polarization maintaining (retaining) properties while being suitable for use as an optical amplification media. In accordance with some of the embodiments of the present invention, a rare earth doped optical fiber is provided which exhibits single polarization properties within a Single Polarization Band (SPB). The fiber parameters are preferably selected such that the SPB coincides with an operating wavelength band.
According to the present invention the optical fiber includes a core with a first refractive index n1, a moat least substantially surrounding the core, the moat having the refractive index n2 such that n1>n2, a silica based inner cladding surrounding the moat, the inner cladding having a third refractive index n3, wherein n1>n3 and n3>n2 and a silica based outer cladding surrounding the inner cladding and having a fourth refractive index n4 such that n4<n3. The optical fiber exhibits single polarization at the operating (i.e., output) wavelength band.
According to some of the embodiments of the present invention, the core of the optical fiber may include a hole situated inside the core.
One advantage of the optical fiber of the present invention is its capability to produce gain, thus being capable for use in a laser or an optical amplifier while (i) performing as single polarization fiber and exhibiting a single polarization band SPB width of greater than 10 nm and even more preferably greater than 15 nm, and (ii) being capable of handling relatively large amounts of optical power. Another advantage of the optical fiber of the present invention is that because it performs both as a gain fiber and the SP fiber, it eliminates the need to for splicing together gain fiber and the single polarization fiber, thereby reducing the splicing loss, the overall fiber length, while eliminating work and cost associated with splicing the two fibers together.
More particularly it is believed that in these embodiments the effective refractive index of one of the polarizations is such that this polarization cannot propagate within the SPB, while the other orthogonal polarization associated with different effective refractive index is such that this polarization may still propagate in the SPB. Accordingly, single polarization propagation within the SPB is provided by the rare earth doped fiber with a relative simple structure. In some of the embodiments of the optical fibers according to the present invention the SPB width is 20 to 40 nm.
Additional features and advantages of the invention will be set forth in the detail description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the invention as described herein, including the detailed description which follows, the claims, as well as the appended drawings.
Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Whenever possible, the same reference numerals will be used throughout the drawings to refer to the same or like parts. One embodiment of double clad single polarization optical fiber in accordance with the present invention is shown schematically in
The optical fiber 10 illustrated in
The elongated core 12 extends radially outward from the centerline, CL, of the fiber 10 and includes up-doped silica having, preferably a step index profile shape. The exemplary refractive index profile of the optical fiber of
The optical fiber core 12 is preferably elliptical, as shown in
The lateral dimensions, a, and, b, of the elongated core 12 are preferably designed to be in the range between 1.0 to 13.0 microns. It is preferred that the dimension a be between 1 and 6 microns (more preferably a=1.0 to 4.0 microns), and that dimension b be between 3.0 to 20.0 microns (more preferably b=3.0 to 13.0 microns), respectively. Furthermore, the average diameter, Davg={a+b}/2, of the core 12 is preferably between about 2.0 and 13.0 microns; more preferably between 2.0 and 8.0 microns. Alternatively, the core 12 may have a circular cross-section and contain a center hole 11. If the core 12 is circular, the preferred radius of the core 12 is 2 to 8 microns, more preferably 3 to 7 microns.
The core 12 delta is preferably less than 0.5% Δ. The numerical aperture NA of the core 12 is between 0.05 (for high power laser application) and 0.25 (for lower power application). The numerical aperture NA of the core 12 is defined as (n1 2−n2 2)1/2, where n1 is the index of refraction of the core 12 and n2 is the index of refraction of moat 13.
As shown in
It is preferable that the moat 13 substantially enclose the core 12. The moat 13 may be larger than the core 12, thus totally surrounding the core 12, or may be the same size as the core, along one of the axis, so as to be tangent to the core 12 along that axis.
The moat 13 is generally circular in shape as illustrated by
The inventors herein discovered that the proper combination of sizes and shapes (ratios) of the core 12 and moat 13 provide the fiber's excellent single polarization properties. In particular, the combination of a/b and d/a ratios are believed to be important to optimize single polarization capability. In operation, because of the geometry and materials used in the core 12 and moat 13 it is believed that the effective refractive indices associated with each orthogonal polarization state are substantially different within the SPB. In particular, it should be recognized that the effective refractive index within the SPB 60 of the one polarization state is such that propagation occur within the SPB, while the other polarization mode is very lossy because its effective refractive index so close to cladding (preferably equal to or less than cladding) that it does not effectively propagate (is cut off) within that range of wavelengths of the SPB, i.e., it is not a waveguide.
Alternatively, as best shown in
It is also important to recognize that in all embodiments described herein, the ratio of the dimension, d, (along axis (Y—-Y) of the moat 13 to the minimum dimension, a, of the elongated core 12, namely the ratio d/a, is preferably in the range of between 2.0 to 7.0; more preferably 2.5 to 5.0; and in a large number of the embodiments, 2.5 to 4.0. Again, maintaining this d/a ratio was discovered to be one important factor in providing good single polarization properties along with maintaining the desired b/a ratio described above.
The inner cladding 14 surrounds the moat 13. If the inner cladding 14 does not have a circular cross section, the diameter DIN of the inner cladding 14 is defined as the smallest distance from one side of the inner cladding's cross section to the oppositely situated side of the cross section. The diameter DIN of the inner cladding 14 is preferably at least 125 μm and more preferably at least 200 μm. It is even more preferable that inner cladding diameter DIN is at least 225 μm and most preferable at least 250 μm. More specifically, it is preferable that the inner cladding diameter DIN be about 125 μm to 2000 μm and more preferably about 150 μm to 1500 μm. It is even more preferable that DIN be about 150 μm to 350 μm. Applicants discovered that the thick inner cladding 14 and all-glass construction of the optical fiber work in synergy to allow the optical fiber to be coupled to high energy source, and to couple the high power into the core 12 without damaging the optical fiber, while elongated core 12 in conjunction with the moat 13 make this fiber a single polarization fiber.
It is preferable that the inner cladding's 14 cross-sectional area be at least 200 times larger than the cross sectional area of the rare earth doped core 12. It is even more preferable that the cross sectional area of the inner cladding 14 be between 300 and 3000 times larger than the cross sectional area of the core 12. For example, the cross sectional area of the inner cladding 16 may be 500, 700, 1000, 1200, 1500, 1600, 2000 or 2500 times larger than the cross sectional area of the rare earth doped core 12.
The silica based inner cladding 14 may have a circular outer perimeter, as shown in
Surrounding the inner cladding 14 is an outer cladding 16. It is preferable that the outer cladding 16 be relatively thin, with wall thickness less than 80 μm and preferably between about 5 μm and 35 μm. It is most preferable that the wall thickness of the outer cladding 16 be between about 10 μm to 25 μm. It is preferable that the diameter of the outer cladding diameter (DOUT) be about 145 to 2100 μm, more preferably between about 145 μm to 1600 μm and even more preferable that DOUT be about 145 μm to 500 μm. It is noted that the outer cladding 16 may not be circular. If the outer cladding 16 is not circular, DOUT is defined as the smallest distance from one side of the outer cladding's cross section to the oppositely situated side of the outer cladding's cross section.
According to this embodiment, the fiber core 12 includes, in weight percent:
Rare earth
0.1 to 2.5 wt %;
0 to 5 wt %;
0.5 to 15 wt %;
0 to 15 wt %;
0 to 1 wt %.
The rare earth dopants in the fiber core 12 provide active ions to enable either a gain or a lasing action. Exemplary rare earth dopants are Yb, Er, Nd, Tm, Sm and Tb. It is preferable that the amount of rare earth dopant in the core 12 be 0.5 wt % to 1.5 wt %. Phosphorus may be added to the core materials in order to lower the softening temperature of the core glass, which may be advantageous if the core is produced by the inside vapor deposition process. Phosphorus may also be utilized as a refractive index raising agent. However too much phosphorus (10% or more) provides nonlinearity through Stimulated Raman Scattering which may inhibit the lasing action. Aluminum may be added to the core as a de-clustering agent (for example, to de-cluster Yb, preferably at the ratio of Al to Yb of 5:1 to 10:1). The core 12 may also include Germanium which is an index raising dopant, and/or fluorine which is an index lowering dopant as well as a de-clustering agent.
The preferred ranges of the core 12 composition in weight percent are:
Rare earth 0.3 to 1 wt %; P 0 to 2 wt %; Al 2 to 8 wt %; Ge 3 to 20 wt %; and F 0.1 to 0.5 wt %.
It is preferable that the amount of Ge in the core 12 be within 5 to 15 wt %. The Yb-doped core 12 will laze at 1.03–1.11 micron range.
It is preferable that the index lowering dopant of the moat 13 comprises Fluorine and/or Boron in weight percent:
F 0.5 to 5 wt %; and/or B 0.5 to 20 wt %.
It is preferable that the moat 13 has less than 5 wt % of F, and 15 wt % or less of B. It is even more preferable that the amount of B and F be 2 to 4 wt % of F and 3 to 15 wt % of B.
It is preferable that the inner cladding 14 contain 5 wt % to 20 wt % Ge in order to provide high NA. It is even more preferable that the inner cladding comprise 5 wt % to 10 wt % Ge. It is noted that 5 wt % to 10 wt % Ge works well for many applications.
It is preferable that the index lowering dopant of the outer cladding 16 comprises Fluorine and/or Boron in weight percent:
0.5 to 5 wt %;
0.5 to 20 wt %.
The amount of dopant(s) for the outer cladding 16 is chosen to preferably result in inner cladding NA of between 0.15 to 0.5. However, it is preferable that the outer cladding 16 contain at least one of B or/and F. It is preferable that the amount of B is at least 3 wt %. It is preferable to have more than 1 wt % and more preferably more than 2 wt % of F along with more than 8 wt % of B in the outer cladding 16. It is preferable that the outer cladding 16 has less than 5 wt % of F, and less than 15 wt % of B. It is even more preferable that the amount of B and F be: 2 to 4 wt % of F and 3 to 15 wt % of B.
In general, a double-clad structure that could be used in a fiber laser or in an amplifier includes two claddings. A first (inner) multi-mode cladding 14 acts as a multi-mode pumping core. The inner cladding 14 is adjacent to the moat 13 and a second (outer) cladding 16 surrounds the first or the inner cladding cladding 14. The rare earth doped core 12 may be either single mode or multi mode at the core lasing wavelength. The inner cladding 14 serves as a waveguide with a high numerical aperture NA for the input (pumping) light. That is, the inner cladding serves as a pump cavity. The larger the inner cladding diameter, the more pump light is coupled into the inner cladding from the optical source. The cross-section of the first multi-mode inner cladding (DIN is the shorter dimension of the inner cladding) may be designed to have a desired shape, e.g., matched to the near field shape of the pump source or have any other which increases coupling efficiency of the (pump) light from the light source to the inner cladding. The numerical aperture of the inner cladding must be high enough to capture the output of the light source, such as the laser diode.
Recent progress in semiconductor laser technology has led to the creation of light sources utilizing discrete or arrayed broad-area laser diodes coupled to the intermediate fiber incorporated within the light source. The output power of this light source is more than 150 Watt at 976 nm at the output end of the intermediate fiber. The diameter of the intermediate fiber and NA of light source is 200 μm and 0.22 NA, respectively.
The light from this light source is then coupled to a double clad optical fiber via high NA and large aperture lenses. With this approach one can obtain 75–90% of coupling efficiency.
The invention will be further clarified by the following examples.
The specific composition for the optical fiber of this example is:
Core 12: 0.8 wt % Yb2O3; 9.5 wt % P2O3; 5.4 wt % GeO2;
Moat 13: 1.3 wt % F;
Inner cladding 14: Pure Silica;
Outer cladding 16: 2.3 wt % F.
The optical fibers according of this example have a single polarization range (SPB) of 10 nm to 40 nm, depending on the size (along the minor axis) of the core 12. Larger SPB is possible if the core 12 contains a central, preferably elongated, air hole 11 (extending through the length of the optical fiber) with largest cross-sectional dimension of about 0.5 μm or less.
Alternatively, the moat 13 can be made of pure silica and the inner cladding can be up-doped with an index raising dopant, for example Ge, so that n1>n2, and n3>n2. The exemplary profile for this fiber is illustrated schematically in
The double clad fiber produced by the OVD process is especially suitable for use in a higher power fiber laser device.
The geometrical parameters of this fiber and two other exemplary fibers are provided in Table 1, below. The core delta (%) of these exemplary fibers ranges from 0.1% to 3%, relative to the inner cladding's index of refraction. All other parameters were adjusted to provide the desired SP Bandwidth, such that the SP wavelength range includes a 1060 nm wavelength. We have found that the higher core delta fiber (with the same size air hole) has correspondingly smaller core dimensions than the lower core delta fiber with the same SP wavelength (for example, 1060 nm). On the other hand, when the core delta was lowered, the SP Bandwidth became smaller. However, even with a core delta of 0.1%, relative to the inner cladding, the SP Bandwidth (situated around the desired wavelength) is larger than 20 nm.
TABLE 1 a′/2 b′/2 Core Moat (air (air a/2 b/2 d/2 c/2 delta delta hole) hole) (core) (core) (moat) (moat) (%) (%) Fiber 1 0.12 0.5 3.45 3.45 8 8 0.3 −0.5 Fiber 2 0.12 0.5 4.26 4.26 8 8 0.2 −0.4 Fiber 3 0.12 0.5 6.175 6.175 8 8 0.1 −0.4
All delta values in Table 1 are measured relative to the inner cladding 14. The preferred inner cladding 14 dimensions of the fibers of Table 1 are between 65 μm and 450 μm. More preferably the inner cladding diameter DIN is at least 200 μm. A larger inner cladding facilitates more pump power to enter into the optical fiber, thus more pump power is absorbed by the core 12, providing greater gain. The thickness of the outer cladding of the fibers of Table 1 is relatively small, preferably between 5 μm and 35 μm.
Table 2 provides the values for the cutoff wavelength and for the 5 μm bandwidth for the optical fibers of Table 1.
First cutoff
Second cuttoff
wavelength λ1
wavelength λ2
SP Bandwith
Fiber 1
30 nm
Fiber 2
26.5 nm
Fiber 3
21.5 nm
The specific core material composition for the optical fibers of Tables 1 and 2 are:
Core 12, fiber 1: 0.5 wt % Yb2O3; 4.5 wt % Al2O3; 6.6 wt % GeO2; 90.2 Wt % SiO2;
Core 12, fiber 2: 0.5 wt % Yb2O3; 4.5 wt % Al2O3; 4.8 wt % GeO2; 90.2 wt % SiO2;
Core 12, fiber 3: 0.5 wt % Yb2O3; 4.5 wt % Al2O3; 3 wt % GeO2; 92 wt % SiO2.
The specific moat material composition for the optical fibers of Tables 1 and 2 are:
Moat 13, fiber 1: pure silica;
Moat 13, fiber 2: 1.8 wt % GeO2 doped silica
Moat 13, fiber 3: 3.6 wt % GeO2 doped silica.
The inner cladding 14 material composition for the optical fibers 1–3 of Tables 1 and 2 is 9 wt % GeO2 doped silica. It is noted that the inner cladding's delta, relative to that of pure silica, is 0.5%. The outer cladding material composition for the optical fibers 1–3 of Tables 1 and 2 is 9 wt % B2O3 and 2.7 wt % F doped silica.
The fiber of
More specifically, the following steps are utilized to make the rare earth doped double clad single polarization fiber of
1. Core cane formation. The core cane is formed first. The core is manufactured, for example, by a standard OVD process. The core materials are deposited onto the bait rod during the laydown step. The exemplary vapor-precursor-materials used to make the fiber core cane are Yb(fod)3, AlCl3, SiF4, SiCl4, GeCl4 and tri-ethyl borate (or BCl3 or BBr3). Other rare-earth materials may be utilized either in addition to Yb, or instead of Yb. During the core deposition process we achieved a uniform AlCl3 gas-phase delivery. This was accomplished by utilizing heated inert Helium as carrier gas 30 (instead of Argon gas) for AlCl3 delivery illustrated schematically in
As shown in
The Yb vapor delivery is carried by Argon gas and is accomplished by heating organometallic Yb(fod)3 in the temperature range of 150� C.–180� C., which results in a soot preform core with Yb2O3 concentration from about 0.2 wt % to 3 wt %. In order to make the optical fiber 10 of this example, the Yb(fod)3 containing vessel temperature of 163� C. was used to achieve the Yb2O3 concentration of about 0.6 wt %. The delivery of other materials is carried out by conventional oxygen delivery at temperatures below 100� C.
More specifically, according to one embodiment of the present invention, the Yb(fod)3, AlCl3, SiF4, SiCl4 and GeCl4 are delivered to a gas burner 56. (See
After the core soot preform layer is layered down and the core soot preform 62 is cooled to room temperature, the bait rod 59 is removed from the center of core soot preform 62. The removal of the bait rod 59 leaves a center hole (preferably circular or elliptical in cross-section) in the center of the core soot perform 62. The core soot preform 62 is then consolidated (densified into the solid glass) to become a solid glass-preform 62A, with or without the center hole, according to the desired fiber geometry. The solid glass-preform 62A is then drawn into core cane 62B. (See
Applicants discovered that a proper choice of high temperature and fast down-feed rate during consolidation results in low crystallization formation in the resulting solid glass preform, which results in an optical fiber having very low passive (background) loss, and also eliminates the conventional double-redraw process associated with Al doped blanks.
More specifically, soot preform 62 is down fed relative to the furnace at the rate and temperature sufficient to minimize crystallization such that the background loss of the resultant fiber core is less than 8 dB/km, and preferably 3 dB or less, at a wavelength of 1280 nm. As illustrated in
With the above described high consolidation temperatures and fast down-feed rate, the resultant optical fiber 10 has the core background loss of less than 8 dB/km. More preferably, the optical fiber exhibits core background loss of less than 5 dB/km. In this example the background loss of the core is less than 3 dB/km. The core background loss was measured by making (single mode) optical fiber without the outer cladding and measuring the background loss of this fiber. (See
The core soot preform 62 has sufficient amount of Ge to produce the required core delta. After the core preform 62 has been consolidated, as described above, it is drawn into the core cane 62B. The core cane 62B is preferably 1 meter long and about 8 mm in diameter. The core cane 62B is illustrated schematically in
2. First blank formation. The core cane 62B is overclad with down doped silica soot to form a core/moat (soot) blank (referred herein as the first bank 63). The first clad blank is then consolidated to form cane 63A. The first blank 63 has a core to the moat diameter ratio of 0.4 to 0.6. Cane 63A is illustrated schematically in
Alternatively a sleeving process may be utilized to form cane 63A, by placing a down doped silica sleeve around the core cane 62A. If the center air hole is desired, the sleeving process is performed with a appropriate amount positive pressure (about 1 psi, for example) along the centerline. Application of negative pressure (vacuum) will close the center hole.
More specifically, in order to produce a down doped inner core layer or a moat, soot particles of silica with index lowering dopants may be deposited onto the core cane 62A. The index lowering dopants are, for example, B and F. The soot particles of B and F provide low refractive index (less than that of pure silica). If the moat region or the down-doped inner core region is desired, the B2O3 and SiO2 are vapor deposited to form a B2O3 and SiO2 soot layer by using tri-ethyl borate and SiCl4 and/or SiF4 delivered to the burner. The blank covered with the B2O3 doped silica soot layer is then Fluorine doped during the consolidation step by using SiF4 gas provided to the consolidation furnace. During this consolidation step, the consolidation furnace is operated at the temperature range of 1300� C.–1400� C. At these consolidation temperatures Fluorine diffuses into the boron/silica soot layer, but does not penetrate into the underlying (core) glass layer. In some of the exemplary embodiments of the present invention when the core delta was 0.3% Δ, the depressed index of the first clad layer (relative to that of pure silica) was about −0.3 to −0.5% Δ.). In some of the exemplary embodiments of the present invention when the core delta was about 1% Δ, the depressed index of the first clad layer (relative to that of pure silica) was about −3.35 to −0.7% Δ.) and the SPB was 20 nm to 25 nm wide. The clad blank 63 is then drawn into canes 63A.)
3. Grooved cane formation. The cane 63A includes sections 112, 113 which correspond to the core 12 and the moat 13 of the optical fiber 10 and which has a core/moat ratio of about 0.45. Cane 63A is preferably about 1 meter long and about 8 mm in diameter. Grooves 54 are then ground into the diametrically opposite longitudinal sides of the cane 63A to a width of about 6.4 mm and to a depth of about 8 to 10 mm, thereby forming grooved cane 63B. (See
The grooved and redrawn cane 63B is then inserted into a 1 meter long silica tube or sleeve 65 overclad with silica soot 67 (for example, about 800–1000 gms.), as shown in
The preform subassembly 70 of
This cane 78, now having an elliptically shaped core (with or without the center hole), is again inserted into a 1 meter long silica tube 65A which is overclad with about 1000 grams of silica soot 67A, as shown in
It is noted that the glass portion 114 may also be up-doped or down doped in order to either rise or lower its index of refraction relative to that of pure silica.
The consolidated blanks 70C are then machined, if needed, to desired shape. Breaking circular symmetry in the inner clad layer enhances pump light absorption efficiency. A machined core/inner cladding blank 70D is illustrated schematically in
The machined blank 70D (or blank 70C) is overclad again, for example by SiO2 with index lowering dopants (for example B and/or F, to provide lower refractive index than that of a pure silica)) and then consolidated to a consolidated blank 71. The down-doped silica layer of the consolidated blank 71 will form the second, or outer cladding 16 of the optical fiber 10.
More specifically, B2O3 and SiO2 were vapor deposited on the ground glass preform to form a B2O3 and SiO2 soot layer by using tri-ethyl borate (BCl3 or BBr3) and SiCl4 delivered to the burner. The blank (i.e. machined or ground glass preform) covered with the B2O3—doped silica soot layer was then Fluorine doped during the consolidation step by using SiF4 gas provided to the consolidation furnace. During this second consolidation step, the consolidation furnace is operated at the temperature range of 1300� C.-–1400� C. At these consolidation temperatures Fluorine diffuses into the boron/silica soot layer, but does not penetrate into the underlying glass layer. The optical fiber of this example was produced by utilizing consolidation temperature of 1350� C., so as to facilitate adequate Fluorine doping through diffusion. In this example, the fourth layer of the preform (outer cladding) has a shape similar to that of the third layer (inner cladding).
The consolidated blank 71 is then suspended from a handle 81 in a draw furnace 80 as shown in
As should be recognized, the elongation of the core (and/or control for the presence/absence and the size of the central air hole) may occur in the redraw step, the draw step, or combinations thereof to achieve the desired aspect ratio of the core and the size, shape of the central air hole.
The resulting all-glass double-clad optical fiber has the following core, inner-cladding, outer-cladding compositional format:
Core: Yb2O3:Al2O3:SiO2:GeO2:F;
Moat: B2O3:F:SiO2.
Inner cladding: SiO2, or SiO2:GeO2;
Outer cladding: B2O3:F:SiO2.
The amount of each dopant is optimized to ensure the high laser efficiency and SP bandwidth in the operating wavelength range.
It will be apparent to those skilled in the art that variations and modifications can be made to the present invention without departing from the scope of the invention. For example, although step index structures are show, other graded index structures may be employed. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.
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|U.S. Classification
|385/123, 385/126, 385/125
|International Classification
|Cooperative Classification
|European Classification
|Feb 14, 2005
Owner name: CORNING INCORPORATED, NEW YORK
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|Apr 2, 2007
Owner name: DARPA, VIRGINIA
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