Design and simulation of a dynamically tunable 1× 2 power splitter using MZI configuration in telecom regime

Abstract

We propose an ultra-broadband, ultra-compact and a dynamically tunable 1×2 power splitter on silicon on Insulator (SOI) platform with 220 nm thick silicon light-guiding layer, using two multimode interference (MMI) couplers connected with graphene-based waveguides as phase-tuning section through a Mach-Zehnder Interferometer (MZI) configuration. First, we theoretically present and demonstrate a novel design for the MMI couplers by combining the plane wave expansion method (PWEM) and the mode expansion conjecture concept. To verify the proposed theory, a center-fed 1×2 MMI coupler and a 2×2 MMI coupler, respectively, as the input and output sections of our proposed device, are designed and simulated. The simulation results achieved by Lumerical FDTD show good agreement with the design theory. Then, a highly tunable graphene-embedded silicon waveguide, for highly efficient modulation of effective mod index (EMI), is duly designed using Lumerical Mode Solutions. As the two MZI arms, a pair of the proposed waveguides is introduced into the middle of the cascaded MMI couplers. Accordingly, the integration properties of the analytically designed MMI couplers and the numerically designed waveguide is demonstrated through our proposed device for the aim of achieving any wanted power splitting ratio. To this end, we consider the case that the real part of the EMI of the waveguide in the lower MZI arm is modulated by varying the graphene Fermi level values, being the same for all the layers belong to the same waveguide, while that of the upper arm is constant. The corresponding power splitting ratio can be dynamically tuned in the range of 0.5:0.5-0.85:0.15. All reported results assume TE polarization. The designed MZI-based splitter possesses a bandwidth of 400nm over the wavelength range from 1.35μm to 1.75μm for various power splitting ratios, maintaining the averaged insertion loss and the averaged power imbalance, respectively, below as low as 0.39dB and 0.48. The overall footprint of the proposed device is also highly small, i.e., about 58μm × 3.5μm.