Research On Liquid Crystal Optical Phased Array Devices In The Mid-infrared Band

As the mainstream of non-mechanical beam digital scanning,optical phased array has become a research hotspot nowadays.The liquid crystal optical phased array has the advantages of high control precision and programmable electronic control in the nearinfrared band.The mid-infrared band of 3-5 ?m is the main working area of laser weapons,infrared guidance and infrared detection.It is of great significance to expand the liquid crystal optical phased array technology to the mid-infrared band of 3-5 ?m.Response speed has always been an important indicator to measure the performance of liquid crystal optical phased arrays.Based on the realization of the beam scanning of liquid crystal optical phased array in the mid-infrared band,thesis aims to improve the response speed of the mid-infrared liquid crystal optical phased array.The main research contents include:(1)According to the transmittance test of mid-infrared laser,sapphire was selected as the transparent substrate of the mid-infrared liquid crystal optical phase shifter,ultrathin ITO as the conductive film and C09 mid-infrared liquid crystal as the electro-optical modulation crystal.The mid-infrared liquid crystal optical phase shifter is developed by semiconductor technology and its optical properties are tested.A liquid crystal optical phase shifter with a cell thickness of 20 ?m can achieve a phase modulation depth of2.59? for a mid-infrared laser with a wavelength of 3.9 ?m.When the effective value of the switching voltage changes from 2.65 V to 3.37 V,the response time can reach 19 ms,which meets the functional requirements of the liquid crystal optical phase shifter in the mid-infrared band.(2)Research and preparation of mid-infrared liquid crystal optical phased array devices.The mid-infrared liquid crystal optical phased array grating period is designed to be 20 ?m,the electrode width is 5 ?m,the electrode spacing is 15 ?m,and the number of grating electrodes is 720,which is controlled by a single flexible flexible strip line(FPC)and digital chip(IC).The mid-infrared liquid crystal optical phased array device is prepared by a full set of semiconductor processes,and the optoelectronic integration of the mid-infrared liquid crystal optical phased array system is realized.The mid-infrared liquid crystal optical phased array with a cell thickness of 15?m,the near-field phase modulation depth is 2.018?,and the dynamic response time is 60ms;the far-field diffraction can achieve small-angle deflection from 0° to 0.6°.When the deflection angle is 0.1°,the far-field diffraction efficiency reaches the maximum value of 57.6%.(3)The characteristic parameters for the dynamic response time were optimized using a polymer network liquid crystal(PNLC)and a Fabry-Polo(F-P)cavity.So as to improve the purpose of rapid response.The mid-infrared PNLC device prepared by using B40 mid-infrared liquid crystal,5.3% wt RM257 polymer monomer,and 0.2% wt photoinitiator has a response time of 7.6 ms,which can achieve the purpose of fast response.By reducing the cell thickness d of the mid-infrared liquid crystal optical phase shifter,improving the response speed and using the optical slab with high reflectivity in the F-P cavity structure to compensate the phase,the relationship between the response time and the phase modulation depth can be effectively balanced.