The Research On Fabrication And Application Of Polarization Grating Based On Liquid Crystal

As a kind of material with unique physical and optical properties,liquid crystal plays an important role in modern science and technology.In addition to its outstanding performance in LCDs technology,which is a more traditional and common application direction,liquid crystal also has more application values in photonics,which are gradually being explored by researchers.In this paper,the fabrication and application of liquid crystal polarization grating with spatial birefringence distribution are studied theoretically and experimentally.First of all,based on the research results of liquid crystal optics,polarization optics and existing liquid crystal polarization grating,this paper discusses the b asic fabrication principle and parameter selection of polarization grating,such as size,working wavelength,diffraction angle,etc.The formation of liquid crystal polarization grating microstructure is mainly realized by optical orientation technology.In terms of parameter selection: firstly,the influence of substrate specifications and types on the fabrication and application of polarization grating is discussed;secondly,in order to achieve the maximum diffraction efficiency,how to control the thickness of liquid crystal layer near the half wave delay film thickness determined by the specific working wavelength is explored;finally,how to calculate the actual exposure position according to the desired target diffraction angle is discussed.After that,the key points in the preparation of liquid crystal polarization grating are described,and the parameters of the grating samples are measured and analyzed.In this paper,the special process steps,such as substrate preparation,optical path adjustment and interference exposure,are explained in detail.Finally,we get several grating samples with different periods,different working wavelengths and high diffraction efficiency: among them,the period of flawless grating microstructure can be as small as about 2 ? m,as large as over 100 ? m;taking 450 nm,532nm and 635 nm as typical examples,the working wavelengths of liquid crystal polarization grating cover almost the whole visible bands.The diffraction efficiency of the grating is more than 98% by controlling the film thickness accurately.After studying the preparation process and characteristics of the liquid crystal polarizing grating,the paper further discusses the application direction of the liquid crystal polarizing grating —— the adjustable resolution optical edge detection system.Combining the large period liquid crystal polarization grating with 4F optical system,using its small diffraction angle and the modulation characteristics of the beam polarization state,the analog optical edge detection can be realized.In addition,the superposition of two liquid crystal polarization gratings can further realize the realtime adjustment of detection resolution.At the same time,the method retains the widespectrum applicability.The low-cost and easy mass production characteristics of the liquid crystal polarization grating make the practical application of the edge detection mechanism possible.