Study On Variable Optical Attenuator Based On SOI Technology

Dense wavelength division multiplexing(DWDM)technology is the main way to improve the transmission bandwidth of the optical communication system.In optical communication system,especially in the wavelength division multiplexing(WDM)system,the signal transmission energy is often required to adjust dynamically to the required level,so the variable optical attenuator becomes an important part of long-distance optical communication system.And the most common application in wavelength division multiplexing(WDM)system is balancing the power between different channels.Based on different attenuation mechanisms and different materials,different types of variable optical attenuator(VOA)arises have been proposed,such as variable optical attenuator based on MEMS,variable optical attenuator based on liquid crystal,variable optical attenuator based on polymer as well as the variable optical attenuator based on SOI,etc..Between different designs,the silicon optical waveguide has the merit of good material stability,moderate thermo-optic coefficient and power consumption,high desity integration,and good compatibility with the CMOS process.Therefore,the variable optical attenuator based on silicon waveguide has attracted enormous attention.Three types of variable optical attenuator(VOA)based on the SOI waveguides were investigated,including the VOA based on the PIN structure,the MZI structure and the microring resonator structure were studied.By introducing the trench-down recessed contact structures,the power efficiency of the device can be improved while the polarization dependent characteristics were kept unchanged.The effects of the trench-down recessed contact structures on the device's tuning efficiency,response time and polarization dependence were analyzed.And the simulation results show a much lower power of 7.5mW for 20 dB attenuation can be obtained compared with 22.67 mW of the variable optical attenuator without the trench-down recessed contact structures.Besides,the tuning speed is in tens of nano-seconds.Also,the design based on VTT's SOI platform was investigated,which needs 203.4mW to achieve 20 dB attenuation,and the tuning speed is in sub-microsecond.Besides,two VOAs based on the thermo-optic effect of the SOI waveguide were designed and fabricated.One is the microring resonator type VOA,which achieved 21.6dB attenuation with 0.15 mW power consumption.For the VOA based on the MZI structure,the electrode length was optimized then the tuning characteristics and attenuation characteristics of the VOA were measured and the results show that the extinction ratio is around 30 dB,which indicates the device can achieve about 30 dB attenuation.Besides,17 mW power consumption was needed for 20 dB attenuation,which is well-matched with the simulation results.