Abstract
In the fields of optics and photonics, phase-only spatial light modulators (SLMs) play an increasingly important role in wave-front engineering. However, the SLMs are subject to wavefront distortion arising from the imperfection in the birefringence effect and physical structure of modulators. This paper presents a simple self-interference phase calibration method applicable to liquid-crystal SLM. We build an interferometric imaging system based on the Pancharatnam phase-shifting to measure the phase distribution of a light beam coming from SLMs. Two types of phase modulation errors of SLMs can be characterized in the measurement process: the erroneous gamma curve and shape aberration. The former belongs to dynamic phase distortion and is measured through a four-step Pancharatnam phase-shifting interference, which allows a one-shot recording of interference pattern via a polarization camera; the latter represents static phase distortion and is extracted from the interference between light waves coming from different regions of the SLM panel by using Zernike polynomial fitting. Our method has the advantages of high-precision pixel-wise phase correction and robustness against environmental disturbance and thus can facilitate the applications of SLM in optical field manipulation.
Highlights
AS a dynamic and programmable optical element, the liquid crystal spatial light modulator (LC-SLM) has been playing a very important role in the application of wavefront shaping and beam steering
To meet the requirement of high-precision wavefront controlling in practical applications, a variety of calibration schemes for compensating the phase distortion have been developed, which are mainly based on three types of measuring principles: interferometry[11]-[14], diffraction technique [15]-[18] and polarimetry [19]-[21]
The three schemes have their pros and cons: interferometric methods are appreciated as the high-precision measurement but are susceptible to environmental vibration; diffraction methods are robust against environmental disturbance but cannot afford spatially varying phase modulation measurement, thereby lacking the ability of pixel-wise calibration; polarization measurement can characterize electro-optic birefringence property of the LC, but the phase estimation operation via birefringence-based optical modeling is a rather complicated process and is usually challenging to achieve pixel-wise phase measurement
Summary
AS a dynamic and programmable optical element, the liquid crystal spatial light modulator (LC-SLM) has been playing a very important role in the application of wavefront shaping and beam steering. The phase distortion is mainly caused by the phase modulation nonlinearity and non-uniformity of SLM’s physical structure and environmental conditions, and can be ascribed to two factors: (1) the erroneous driving electric signal exerted on the liquid crystal (LC) [9] and (2) and the backplane curvature and/or thickness variation of the LC layer in SLMs [10] The former leads to dynamic phase response errors, while the latter results in static wavefront aberrations. The proposed technique holds promise in three aspects: (1) pixel-wise voltage-phase calibration through a microscopy-based interferometric measuring arrangement; (2) high-precision static surface compensation via Zernike polynomials fitting; (3) robustness against environmental disturbance due to its self-interference character and common-path arrangement.
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