Broadband programmable optical frequency filter.

Programmable optical frequency filters with a lattice configuration composed of circuit units can provide a wide variety of filter characteristics. A circuit unit is composed of a tunable coupler and a thermo-optic phase shifter. We have already fabricated programmable optical frequency filters using planar lightwave circuits and have realized a variable group-delay equalizer. The filter frequency range of these programmable optical frequency filters, however, is limited to less than 1000 GHz because of the wavelength dependence of the tunable couplers and optical phase shifters. In this paper, we report the design of a novel tunable coupler with wavelength-independent amplitude and phase characteristics, and use it to propose a novel algorithm for synthesizing programmable optical frequency filters in order to broaden the filter frequency range. We show numerically that this novel filter can realize a broad filter frequency range of about 10,000 GHz, which is ten times that of our conventional programmable filters. © 1998 Scripta Technica, Electron Comm Jpn Pt 2, 81(10): 1–11, 1998 [ABSTRACT FROM AUTHOR]