Optimal cascade operation of optical phased-array beam deflectors

Biaxial 360-degree scanning LIDAR using a liquid crystal control

Sophisticated non-mechanical technology for LIDARs is needed to realize safe autonomous cars. We have confirmed the operating principle of a non-mechanical LIDAR by combining concentric circular-grating couplers (CGCs) with a coaxially aligned rod lens. Laser light incident vertically on the center of the inner CGC along the center axis of the lens is radiated from the outer CGC and passes through the side surface of the lens. It is converted to a parallel beam that scans in two axes by applying voltages to two area-segmented electrode layers sandwiching the CGCs and a liquid crystal layer formed on the CGCs. We have demonstrated scanning whose motion ranges were 360 degrees horizontally and 10° vertically. A beam with a spread angle of 0.3° × 0.8° at a minimum swept vertically up to a frequency of 100 Hz and ten equally spaced beams scanned rotationally with a 6-degree cycle variation of spread of between 0.8° and 3.5°.

Double wedge prism based beam deflector for precise laser beam steering

Aiming to increase laser beam pointing stability required in interferometric measurements, we designed a laser beam deflector intended for active laser beam stabilization systems. The design is based on two wedge-prisms: the deflecting wedge driven by a tilting piezo-platform and the fixed wedge to compensate initial beam deflection. Our design allows linear beam steering, independently in the horizontal or vertical direction, with resolution of less than 1 μrad in a range of more than 100 μrad, and no initial deflection of the beam. Moreover, the ratio of the output beam deflection angle and the wedge tilt angle is less than 0.1; therefore, the noise influence is significantly reduced in comparison to standard mirror-based deflectors. The theoretical analyses support the designing process and can serve as a guide to wedge-prism selection. The experimental results are in agreement with theory and confirm the advantages of the presented double wedge system.

Optical phased-array beam steering controlled by wavelength

A scheme for optical phased-array beam steering controlled by wavelength is proposed. In this scheme, the optical scanning device consists of arrayed optical waveguides with specific length differences, by which the desired phase slope that results in optical beam steering is formed at the ends of the waveguides and can be changed by varying the optical wavelength. By introducing the concept of irregularly spaced arrays, sidelobes can be dramatically suppressed regardless of large center-to-center interelement spacing. The absolute phase difference between adjacent elements plays a vital role in optical beam steering, and the relation between the nonuniform length difference and the corresponding center-to-center spacing among elements is found.