Proposal of Compact Tunable 1×2 Multimode Interference Splitter Based on Multiple Quantum Well

Abstract

We propose a compact tunable 1×2 multimode interference (MMI) splitter based on an InGaAs/InAlAs multiple quantum well for an active trimmer for Mach–Zehnder modulator with a very high extinction ratio. The light power splitting characteristics of the splitter are theoretically investigated by a beam propagation method and a three dimensional finite-difference time-domain method. It is assumed that the core layer is composed of a multiple five-layer asymmetric coupled quantum well (FACQW) that is expected to exhibit a large electrorefractive index change owing to its unique quantum confined Stark effect. By applying reverse voltages and changing slightly the refractive indices of the localized regions surrounded by trenches for electrical isolation, the power splitting ratio can be tuned over a wide range. The length and width of the proposed MMI with four refractive index modulation regions are 192 and 6 µm, respectively. The length can be reduced to 115 µm if the number of index modulation regions is reduced to two, though the tuning range of the splitting ratio is narrowed. The simulation results show that the proposed compact MMI splitter has a low insertion loss and a low power consumption, and is promising for Mach–Zehnder modulators with a very high extinction ratio.