Pixel-level Observation Of Liquid Crystal On Silicon Device And Fringing-field Effect

Spatial light modulators used by Liquid Crystal on Silicon(LCOS)technology have many advantages such as excellent phase stability,quick response speed and small pixel feature size in a wide range of applications such as wavefront correction and beam deflection.The LC material of a phase-only LCOS device is used by electrically controlled birefringence effect.The incident light have beam deflection by the dynamic phase grating on a LCOS device.Combining with the inherent elasticity of the LC material and the anchoring of the alignment layer,the fringing-field effect makes the profile of phase gratings different.As the phase trasition region broadening into the phase flyback region,the parasitic grating appears and the diffraction efficiency reduces.Therefore,we demonstrate an improved white light scanning interferometer.In this interferometry,a compensatory glass flat is attached to the reference mirror to compensate the influence to the optical path difference of the cover glass on the LCOS device.According to the interferometer,we discover the phase modulation characterization of the LCOS device and the phase profiles of the gratings and we analyze the influence of the fringing-field effect on the phase profile.In this paper,we firstly introduce the basic physical properties of the LC material and the principle of phase modulation in the LCOS device.In the meantime,we simulate the one-dimensional distribution of the LC directors by the difference iterative algorithm and acquire the simulation curve of the phase modulation characterization.Secondly,by the comparison of different algorithms seeking for the peak of the white light interference signal,we prove the features of the Morlet wavelet transform method such as high solving accuracy and strong anti-noise ability.In addition,we introduce the structure and the related devices of this interferometer so that the horizontal resolution is 0.79?m and the actual phase resolution is about 0.01?.The result shows that the white light scanning interferometer could observate and calculate the phase modulation of the LCOS device by pixel-level.We also aqiure the actual curve of the phase modulation characterization and apply it to the phase linear correction.Thirdly,fitting the phase profile observed in this interferometer by the Logistic function,in a binary grating that the grating period is 80?m and the phase modulation amplitude is 2?,the flyback width is 11.49?m and in a blazed grating that the grating period is 64?m,the flyback region width is 8.31?m and the phase modulation amplitude is 1.60?.Futhermore,the result shows that after the increasing of the electrode width,the phase profile of the blazed grating transforms from the zigzag structure to the step structure.What's more,as the grating period reducing,the fringing-field effect is getting strong and the relative width of the flyback region is increasing which cause the decrease of the diffraction efficiency.Finally,we demonstrate a beam deflection system to confirm the diffraction efficiency of the blazed gratings with different periods.