Optimizations of Si PIN diode phase-shifter for controlling MZM quadrature bias point using SOI rib waveguide technology

Commercial high-speed silicon (Si) Mach-Zehnder modulator (MZM) required to be active around the quadrature bias point (linear transmission area) with low power consumption, small footprint, and small drive voltage. The bias controlling is done by an optical phase-shifter (PS). However, the accuracy is limited by the drive voltage, laser thermal drift, and fabrication errors. To overcome these problems, we propose in this paper the study and analysis of Si PIN diode PS under forward biasing at 1550 nm wavelength using the standard 220 nm substrate silicon-on-insulator (SOI) rib waveguide technology. Numerical investigations were carried out on the key geometrical parameters, doping concentration, doping locations, operating wavelength, biasing level. Results show that the optimal design can be operated with a lower voltage (V_π = 1.629 v), lower attenuation (α = 28.985 dB/cm), and short device length with an extremely small voltage-length product V_πL = 0.815 vmm. Thus, this PS can be used for designing an efficiency high-speed MZM and to obtain better performances in the optical commutation system.