Integration Of Free-space Optical Hybrid

Birefringence effect and electro-optic effect,which play an important role in the optical device integration,are the theoretical basis of crystal optical device design.As the core device of free-space coherent laser communication,the integration level of free-space optical hybrid has a direct influence on the whole communication system's miniaturization and light weighting.Therefore,this article intends to do a research on the integration of free-space optical hybrid mainly basis of birefringence effect and the electro-optical effect of crystal.Two types of stacks integrated of free-space 2×4 90°optical hybrid were designed.Details are as follows:1.Based on the electro-optic effect,birefringence effect and bireflection effect of crystal,a free-space 2×4 90°optical hybrid with crystal integrated structure was designed.The device consists of electro-optical crystals with different structures and a pair of half wave plates.The first pair of crystals was designed to split the signal laser and local oscillation laser according to the birefringence principle,and to produce corresponding phase shift based on electro-optic effect.The second pair of crystals was designed to combine and re-split the signal laser and the local oscillation laser through bireflection principle,and to control the polarization of the combined laser by use of electro-optic effect,to make sure that each beam of laser is still the combined one when being re-split.The phase shift of 90°among the four beams of output combined laser can be obtained by adjusting the voltage of the first pair of crystal.The function of free-space 2×4 90°optical hybrid is thus achieved.The crystal structure and the structure parameter were designed through analysis.2.The free-space optical hybrid designed in chapter 3 is further integrated.The idea is to simplify the two pairs of electro-optic crystals into one crystal which are respectively a birefringent crystal and an electro-optic crystal.The birefringent crystal is used to polarize the beam split of signal laser and local oscillation laser.The electro-optic crystal is used to achieve the coupling of signal light and local oscillation laser.The phase shift of 90°is produced by a ?/4 wave plate,thus a free-space 2×4 90°optical hybrid is formed.Free-space optical hybrid with such a structure requires less unit devices.It has a compact structure and low loss,which is applicable to free space coherent laser communication.