Studies On 90 Degree Optical Hybrid By PLC Technology

90 degree optical hybrid is an important optical coherent demodulation device that can obtain phase difference between two input optical beams by measuring optical intensity of its four outputs.This device has potentially extensive application in the fields of coherent optical communication,coherent optical imaging,and optical sensing as well.Therefore,design and manufacture of this device has long been concerned by researchers.Planar lightwave tenhnology(PLC)provides optical devices with compact structure,stable performance,mass production and low cost,and thus integrated optical hybrid is considered a promising solution.In this thesis,the key structures of 90-degree optical hybrid have been optimized,after which,silica-based PLC optical hybrids are designed and manufactured,and finally,performance of these devices are experimentally characterized.The main works are listed as follows:1.Integrated 90-degree optical hybrid of different structures is compared,and selected preferentially.And then performance simulation and structural design of the optical hybrid with 3dB time-delay splitting are carried out.2.Based on the high-order modulation mode of coherent optical communication,analysis is performaed on the influence of device fabrication error,including phase shift error and power imbalance,on signal reception quality.This analysis provides a theorectical basis for device performance evaluation.3.Performance of 90-degree optical hybrid key structures have been experimentally optimized.Results show that insertion loss of cross waveguide is less than 0.7dB and crosstalk loss is less than-40dB with crossing angle of 20 degrees;deviation of 90 degree phase shift delay line is less than 1.5 degrees;the coupling length of 3dB splitter is approximately 1.2 times designed value.4.Performance of 90-degree optical hybrid are characterized experimentally.Results shows that device insertion loss is about 1.0 dB;relative phase difference from four output lights of this device deviates from ideal value by less than 5 degrees;and the amplitude equalization error of upper and lower channel signals is within 4%.Key performance indicators of manufactured device are basically of the same level as optical hybrid products comercially available.