NARROW-BAND FIEND ETALON FILTERS USING EXPANDED-CORE FIBERS

Narrow-band optical filters have been made by direct deposition of thin films of TiO2 and SiO2 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 have been made. It is necessary to use fibers with mode fields larger than standard single mode fiber. Here, thermal expansion was used to diffuse the core dopant and produce tapered-core fibers with mode-field diameters of 22 mum.