The emission wavelength of the tunable diode laser, viz. Yttrium iron garnet (YIG) spheres can act as tunable microwave resonators. The wide bandwidth makes them particularly suitable for tunable lasers and pulsed lasers. Further extensions to VCSOA technology are the demonstration of wavelength tunable devices. The nonlinear nature of ferroelectric materials can be used to make capacitors with tunable capacitance. The range of applications of tunable lasers is extremely wide. This is implemented using a radio receiver having a tunable receiving frequency. Coumarin dyes are extensively used as gain media in blue-green tunable organic dye lasers. Inorganic polymers with tunable or responsive properties are sometimes called smart inorganic polymers. By making one of the lasers tunable, the VUV can be tuned. There are many types and categories of tunable lasers. Ironically, single component polymeric materials are some of the most easily tunable composite materials known. These are the new class of highly tunable microwave filters. For cold-atom applications requiring tunable interactions, Rb is preferable due to its rich Feshbach spectrum. It is conceptually simple, tunable and deterministic.