Design and fabrication of liquid crystal optical phased arrays with wide deflection angle

Liquid crystal optical phased array (LCOPA) is a beam deflection technology based on devices such as liquid crystal spatial light modulators and liquid crystal polarization gratings to achieve precise angular control. Compared with mechanical beam deflection techniques, LCOPA offer distinct advantages, including the elimination of mechanical inertia, full electronic control, reduced power consumption, compact size, and simplified maintenance. We designed and fabricated the liquid crystal polarization gratings and liquid crystal tunable wave-plates, which work at 1064nm. Liquid crystal polarization gratings were fabricated by means of ultraviolet interference exposure technology with periods ranging from 1.5 μm to 60 μm. It exhibited a diffraction efficiency larger than 98% under normal incidence. We fabricated liquid crystal polarization gratings with four different periods, generating corresponding beam deflection angles of 1°, 2°, 4°, and 8° in the LCOPA system. Subsequently, we implemented the LCOPA system using a 1064 nm continuous-wave laser, enabling real-time measurement and correction of beam deflection angles. For the coarse adjustment section of beam deflection, cascaded liquid crystal tunable wave-plates and liquid crystal polarization gratings were employed to control the polarization state and diffraction direction of the beam. For the fine-tuning of beam deflection, a liquid crystal spatial light modulator was employed to load distinct phase gradients, which enabled the precise beam adjustment below 1°. We have developed software for generating corresponding driving parameters based on the deflection angles input by users, thereby facilitating the integrated control of the LCOPA. During the testing, the beam emitted by the system is focused onto the target surface of a CMOS camera via a lens. Subsequently, the acquired image is processed to determine the centroid position of the spot, and the deflection angle of the beam is calculated accordingly. The beam deflection angle of the system was measured to be ±15° × ±15°. The spot quality was analyzed by means of a beam quality analyzer, and the far-field divergence angle of the beam was 0.462 mrad. These results offer practical insights for the development of LiDAR scanning units, free-space optical communication terminals, virtual reality displays and etc.