Directional coupler-type wavelength filters having an integrated multiple-waveguide structure

This paper proposes an optical filter consisting of GaInAsP/InP waveguides whose performance is examined analytically. This filter is composed of a vertical three- or four-waveguide directional coupler. Based on an eigenmode analytical method, a compact and demultiplexing device is realized. The propagation characteristics of such devices are calculated as being expressed in terms of the superposition of the eigenmodes. A design criterion for both a demultiplexer and bandpass filter is presented. The demultiplexing of the two wavelengths of 1.545 and 1.585 μm with a crosstalk level better than -23 dB at a coupling length 265 μm is demonstrated. Also, with a multiple quantum well waveguide, a value of 6.9 nm for the -15 dB bandwidth at a coupling length 972 μm is obtained. Furthermore, the demultiplexing of the three wavelengths of 1.51, 1.545, and 1.60 μm is found to be possible in a four-guide coupler structure (coupling length 942 μm) with MQW waveguides.