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Low noise high power ultra-stable diode pumped Er-Yb phosphate glass laser

We are developing a low noise high power ultra-stable diode pumped Er-Yb co-doped phosphate glass laser. Erbium doped phosphate glass permits high co-doping with ytterbium ions that strongly absorb at 976 nm and efficiently transfer their energy to the active erbium material. This drastically decreases the absorption length at the 976 nm pump wavelength and thus the overall size of the laser. Aside from the advantage for packaging a short cavity length results in a large longitudinal mode-spacing (>40 GHz), which allows for single longitudinal mode operation in the 1530-1565 nm C-band for telecommunication by inserting a tunable low-finesse etalon in the laser cavity. In addition, due to the energy transfer between the co-dopant and the active material, the laser shows a strongly reduced sensitivity to fluctuations in pump power. The strong peak in the RIN spectrum at the relaxation oscillation frequency (0.1-1 MHz) due to cavity-loss perturbations can be drastically reduced with a non-linear absorbing material inside the laser cavity. Using this approach for an optimized laser cavity design we have achieved -160 dB/Hz RIN at 1 MHz for 35 mW output. Above 100 MHz the RIN becomes shot noise limited (-168 dB/Hz @ 20mA photocurrent). The laser has excellent long-term frequency stability when locked to our wavelength locker (<250 kHz). Furthermore, the laser has been shown to have a narrow intrinsic linewidth (~10 Hz) that we are working towards by means of intra-cavity phase modulation.