| The twisted nematic liquid crystal spatial light modulator(TN-LCSLM)is a programmable optical device and it has wide applications in optical micromanipulation,automatic on-line detection,digital holography,3D imaging and so on.At the same time,the fringe projection 3D topography measuring technology is an extremely important measuring mean for profile.It is highly attractive for some advantages such as non-contact,non-destructive,high resolution,high reliability,and rapid measurement.This dissertation focuses on the technical theory of TN-LCSLM applying in fringe projection and technical parameters and the application performance of Daheng company GCI-770102 transmission TN-LCSLM.The main work completed includes the following three parts.At first,according to birefringence effect,electro-optic effect and phase modulation principle of the TN-LCSLM,LC twist angle,molecular director in front and back surface are measured experimentally,which provides the basic data for subsequent experimental test.The Mach-Zehnder interferometer structure is established to measure the maximum phase modulation depth and only-phase modulation characteristics of the TN-LCSLM.The results show that this TN-LCSLM has a twist angle of 90° and can achieve an only-phase modulation with a maximum modulation amount of 1.3?.In this case,the amplitude modulation fluctuation is about 5.2%.Then,the relationship between the output light intensity and the rotation angles of the two polarizers placed before and after the TN-LCSLM is experimentally tested when the linearly polarized light incidents to the TN-LCSLM.Combined with theoretical analysis,the polarized splitting characteristics and intensity synthesis principle for 90°-twisted TN-LCSLM are verified under a zero-gray driven image being loaded.This result provides new research ideas for analyzing the influencing factors of output light intensity and for deeply understanding the modulation characteristics of TN-LCSLM.Finally,while the output light intensity appears the maximum linear changing law,the parameter setting requirements of the auxiliary devices in the optical system are tested.Furthermore,the control function of the output intensity of liquid crystal is obtained by fitting to the optimum intensity modulation curve with least square method.Based on the intensity control function,the TN-LCSLM generates sine or rectangle fringe patterns,and performs the performance test of the actual fringe projection by changing the sine fringe parameters.The experimental results show that TN-LCSLMs can be applied to the fringe projection technology.Its application advantage will be especially obvious when it is used to generate such low-frequency and gradual-change fringes as sine function. |
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