Eight-Channel Reflection-type Transversal Filter for Compact and Easy-to-Fabricate InP-Based Optical Multiplexer

We developed an eight-channel (8ch) reflection-type transversal filter (RTF) with a 9 × 9 multimode interference coupler on an InP wafer to prove channel scalability of RTFs. Fabricated two types of 8ch RTF with different sizes (1-mm and 1.5-mm long) exhibited comparable filter performance and peak wavelength fluctuation less than 1 nm, and each excess loss from a designed transmittance was about 2-3 dB, which was also comparable to that of our previously reported 4ch RTF.