Design And Research Of Free Space Optical Input 90 Degree Hybrid

Space optical communication is the optical communication with the transmission medium based on free space.With the development of optical communication,applications of optical communication technology have been expanded.A typical optical communication medium is optical fiber.And in some scenarios,it is not or should not take fiber as the transmission medium.The traditional optical modulation is amplitude modulation.When the medium is fiber,distortion and SNR(signal noise ratio)of the amplitude modulation are all excellent.But when the medium is free space,amplitude modulation can't satisfy with the requirements of the optical communication system.In the field of space optical communicat--ion,coherent optical communication technology has applied generally.Optical hybrid is the key device of the free space communication system.The input of general hybrids is fiber.This thesis designed and completed a 90° hybrid with the signal input is free space optical.This optical hybrid can receive the laser which has transmitted a long distance,which satisfied with some special requirements in the laser communication.This thesis presents a 90° hybrid structure.On the basis of analyzing principles of this optical hybrid,we built a mathematical model.We derived a mathematical relationship between input and output with the Jones matrix algorithm.It discussed effects of every component to the device performance.It emphatically analyzes the various factors which make phase error and loss.According to the research,we completed the free space optical input 90 degrees hybrid with polarization beam splitters,wave plates,collimators and other components in optical bench.We designed some experiments to test the phase difference and insertion loss of the device.The insertion loss is less than 3.5 dB,time delay is about 5 ps.At last,we propose some ways to improve the performance of free space optical input 90 degrees hybrid.