Narrow-band FiEnd etalon filters using expanded-core fibers

Narrowband optical filters were made by direct deposition of thin films of TiO/sub 2/ and SiO/sub 2/ on the ends of optical fibers. Single-cavity etalons with bandwidths of 1.1 nm, insertion loss of 1 dB, and 2.25 nm, insertion loss of 0.5 dB, were made. It is necessary to use fibers with mode fields larger than standard single mode fiber. Thermal expansion was used to diffuse the core dopant and produce tapered-core fibers with mode-field diameters of 22 mu m.<
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