Abstract
The ability of phase modulation enables liquid crystal spatial light modulator (LCSLM) to control wavefront. However, the disadvantage of its inherent nonlinear phase response will decrease the wavefront control accuracy. In this paper, a compensation for the nonlinear phase response is proposed based on Inverse Interpolation method. Characteristic curve of phase retardation versus gray levels for a 256×256 pixels phase-only LCSLM has been measured and calibrated by Inverse Interpolation. A mapping relationship between input gray levels and driving gray levels has been built and recorded by a linear look-up table ANTI2.LUT. The nonlinear error of the phase drops from 15.9% to 2.42% by using ANTI2.LUT. Further more, the mapping curve of ANTI2.LUT is almost consistent with 290.LUT from the manufacturer, which proved the efficiency of the compensation of phase nonlinearity. Finally, the distorted wavefront caused by a liquid crystal flake is corrected using LCSLM based on ANTI2.LUT. Experimental results show that the peak-valley value of the distorted wavefront decreases from 1.56λ to 0.26λ (λ =0.6328 μm), the root-mean-square value decreases from 0.25λ to 0.02λ and the Strehl ratio of diffractive spots increases from 0.08 to 0.97. So LCSLM can be applied to realize high-precision and high-resolution wavefront correction with linear phase response.
Highlights
Liquid crystal spatial light modulator (LCSLM) is regarded as a perfect wavefront controller because of its advantages such as low-power consumption, high-resolution, non-mechanical and programming control
In the field of adaptive optics, when LCSLM is used as a wavefront corrector, phase nonlinearity leads to the complex transform of feedback signals, which will reduce the data processing efficiency and further introduce a transform error
This paper proposes a compensation method for the phase nonlinearity based on an Inverse Interpolation method
Summary
Liquid crystal spatial light modulator (LCSLM) is regarded as a perfect wavefront controller because of its advantages such as low-power consumption, high-resolution, non-mechanical and programming control. Gamma correction needs a long time-consuming and is not suitable for phase-only LCSLM which asks a linear driving relationship between the phase retardation and the control voltage Another simple method of phase nonlinear compensation is an approximate correction method for the phase-only LCSLM [14, 15]. The process is to put the measured phase curve and the ideal linear curve into one coordinate system, and find the mapping relationship of corresponding grayscale values of two groups, at last write the mapping relationship into a LUT to obtain a linear driving to LCSLM This method increases the resolution of controllable phase, but it is hard to calibrate LCSLM rapidly due to the complex operating process and low efficiency. A high resolution wavefront correction is completed using LCSLM with the linear LUT
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