The switching characteristics of multimode interference photonic switches (MIPS) are analyzed by wide-angle finite difference beam propagation method (FD-BPM). As a result, it is found that the MIPS with a multimode interference (MMI) length of 599 µm can switch the output light polarization insensitively with a crosstalk of less than -20dB for a wavelength range of 70nm. These analyses show that the MIPS can also have a 3-dB coupler function. Experimentally,an InGaAsP/InP 1 × 2 MIPS with a thicker InP cladding layer was fabricated and exhibited switching operation with crosstalks of -8 dB and -10 dB at 0 and 20 mA current injections,respectively. For a 2 × 2 MIPS with a thinner InP cladding layer, better switching characteristics with a crosstalk of -13 dB and an extinction ratio of 17 dB were realized.
Shuichi Nagai, Goh Morishima, Hirokazu Inayoshi, and Katsuyuki Utaka, "Multimode Interference Photonic Switches (MIPS)," J. Lightwave Technol. 20, 675- (2002)