Pixel-level Observation of Phase Profile in Liquid Crystal on Silicon Device by White Light Scanning Interferometry

An improved Michelson white light scanning interferometry is demonstrated to be used to aquire the phase modulation characterization of the LCOS device and correct the gamma curve, and the phase profile of the phase gratings on the LCOS device can be observed in the pixel level. With a compensatory glass flat attached to the reference mirror, the limitation of the tiny coherent length of the white light is overcome and the contrast of the interference fringes is improved. Using the Morlet wavelet transform method to obtain the peak point of the envelope curve of the white light interference signals to reconstruct the phase profile, the actual phase resolution is 0.01 pi, and the horizontal resolution is 0.79 mu m. Using the Logistics fuction to fit the phase profile of the binary grating which the phase modulation depth is 2 pi, the width of the flyback region is 11.49 mu m. The linear phase-slope region and the flyback region are including in the blazed grating on the LCOS device with small pixels. The width of the flyback region is 8.81 mu m and the diffraction efficiency is calculated to be 71.9 % in the blazed grating whose period is 40 mu m. Analyzing the blazed gratings with different periods, the result shows that the relative width of the flyback region is broadened and the diffraction efficiency is decreased with the smaller period of the blazed grating.