Highly stable wavefront control using a hybrid liquid-crystal spatial light modulator

摘要

We have developed a hybrid liquid-crystal spatial light modulator (LC-SLM) in which a reflection-type optically addressed (OA) LC-SLM is combined with a liquid crystal display (LCD) via coupling optics. The LCD is controlled by 8-bit video signals. This construction allows us to eliminate diffraction artifacts due to the pixellated structure of the LCD from the modulated light of the hybrid LC-SLM and enables the hybrid device to be electrically addressed. Nematic liquid crystal molecules in the OA LC-SLM are homogeneously aligned to create pure phase modulation having a variation of one wavelength. These features make the hybrid LC-SLM suitable for wavefront control. Wavefront control with large phase stroke and high stability is desirable to realize high-quality adaptive optics, high-quality optical manipulation, and so forth. Therefore, we experimentally investigated the stroke and stability of the phase modulation of the hybrid LC-SLM. We used the wrapped-phase representation to expand the phase stroke virtually. The results show that the hybrid LC-SLM could produce a phase stroke of more than 20 wavelengths and a phase instability of less than 0.001 wavelengths. We also conducted an experiment to compensate for the nonlinearity of the phase modulation. The results suggest that nonlinearity could be suppressed to less than 1%, and that approximately 200 gray levels over one wavelength of phase variation were available, even after compensation.