A Novel Integrated Variable Optical Attenuator Based On SOI Material

A novel integrated variable optical attenuator based on SOI materialHan Xiaofeng(micro electronics and solid-state electronics)Directed by Professor Wu YarningABSTRACTVariable optical attenuator is one of the most important optical devices in optical networks. In this thesis, a novel integrated. VOA based on SOI material is proposed. We introduced the principle and framework of the device as well as the process methods. We put forward a model to approximately analyze and optimize the device. Finally, we presented the test result of the device.The electro-optical effects in silicon and SOI material are introduced. We analyzed the methods to realized the VOA. VOA with straight waveguide structure has advantages such as simple structure, low insert loss, high tolerance, low cost and high yield. We used this structure to design our device.After analyzed the characteristics of transverse PIN junction on rib waveguide, we put forward a new type transverse PIN junction which is formed on double-rib waveguide. The new structure can enlarge the injection area and accordingly enhance the efficiency of the charge carriers utilization. We designed tapered waveguides according to the tapered waveguide mode transformer to reduce the losses derive from the mode mismatching between the input/output waveguides and the modulator. The device contains three parts which are: the input/output waveguides, the tapered waveguides and the modulator.We put forward a model to approximately analyze and optimize the device. We presented the optimized value of the parameters such as the thickness of the heavily doped regions, the doping concentration of the heavily doped regions and the half-length of the middle intrinsic region. We also analyzed the distribution of the carriers in intrinsic region , the insert loss and the response time of the device .We introduced the main fabrication processes and predict the parameters in these processes according to the special request of the fabrication of the VOA. All of the processes and the final fabrication results are presented.The test parameters and according test results are also presented and analyzed. The VOA can achieve up to 20dB attenuation with the highest power consumption of 650mW, The on-chip insert loss of the device is about 4dB. The response time of the device is less than 800 # s, and the polarization dependent loss is no more than 0.4dB. we can reduce power consumption and the insert loss by improving the design and the processes.