Two-dimension high efficiency beam steering based on liquid crystal polarization gratings

Cascaded liquid crystal polarization grating (LCPG) structure is commonly used to realize two-dimension large angle optical beam steering. In this architecture, different LCPGs have different incident angles. As a liquid crystal half-wave plate (LC HWP) is placed in front of the LCPG to control steering direction, the different incident angles will affect the phase modulation of LC HWP and then, decrease the steering efficiency. In this paper, the steering efficiency of cascaded LCPGs under tilt incidence is considered and a compensation method is proposed to increase the steering efficiency. A simple analysis model is established to calculate the steering efficiency of cascaded LCPG structure for tilt incidence with arbitrary direction. Further, the effect of tilt incidence on the phase modulation of LC HWP is compensated and a simple formula is given to compute the compensation voltage. A validation experiment is performed to verify the proposed method. All the simulated and experimental results indicate that the steering efficiency of cascaded LCPGs can be improved for two-dimension beam scanning. This work is helpful for high efficiency beam steering based on cascaded LCPGs.