Study On Silicon-based Optical Phase Shifters

Silicon photonics has been a hotspot with great demand in integrated photonics for optical communication. It provides low cost and high level of integration to the ever expanding demand in optical interconnections and signal processing. Among various silicon based devices, silicon optical phase shifters which realize on-chip phase control play an important role in many devices including silicon modulators, delay lines, and variable optical attenuators etc.The commonly used operation principles of phase shifters include free carrier dispersion(FCD) and thermo-optic(TO) effects. In this thesis, the study on these two types of phase shifters focuses on their working principles, simulations, and experiments. The phase shifters are optimized by analyzing the influence of various design parameters on device performances. Finally, applications of phase shifters on variable optical attenuators(VOA) are introduced. The main research contents are summarized as follows: 1. Phase shifters based on FCD effectFirst, we introduce working principle and typical structures of phase shifters based on FCD effect. The device structure is based on a silicon waveguide integrated with a p-n or a p-i-n junction. Both of these phase shifters are designed and analyzed. With optimized design, experimental results reveal the designed phase shifter is of high performance. We also explore the influence of main geometrical and physical parameters on device performances. 2. Phase shifters based on TO effectBecause of the high TO coefficient of silicon material, thermo-optic effect can be employed for effective waveguide refractive index tuning. Thermo-optic phase shifters are widely used in a variety of integrated photonic circuits. This thesis compares phase shifters with various types of heater structures, including metal film, p-i-p junction, and doped silicon. Then, we simulate and design phase shifters made of p-i-p junction and doped silicon. Main parameters are optimized including length and width of doping region, distance of doping region to waveguide, and so on. Experimental results reveal the phase shifters have low power consumption and high integration. 3. ApplicationSilicon optical phase shifters have wide applications. As an application example, the VOA constructed by phase shifters are introduced and designed in this thesis. Experiments show that the designed VOA has low power consumption and large attenuation range. In addition, we briefly analyze the effect of phase shifter length on the performance of VOA.