On the performance of optical phased array technology for beam steering

TL;DR

This paper analyzes how non-ideal optical pixels affect beam steering in phased arrays, quantifies secondary lobes, and proposes compensation strategies to achieve high-quality steering despite imperfections.

Contribution

It provides a general framework to assess pixel performance impacts on beam quality and introduces compensation methods to mitigate imperfections in optical phased arrays.

Findings

Secondary lobes can be suppressed to be two orders of magnitude smaller than the main lobe.

Non-ideal pixel phase and amplitude control degrade beam quality but can be compensated.

Guidelines for pixel performance requirements are established for effective beam steering.

Abstract

Optical phased arrays are of strong interest for beam steering in telecom and LIDAR applications. A phased array ideally requires that the field produced by each element in the array (a pixel) is fully controllable in phase and amplitude (ideally constant). This is needed to realize a phase gradient along a direction in the array, and thus beam steering in that direction. In practice, grating lobes appear if the pixel size is not sub-wavelength, which is an issue for many optical technologies. Furthermore, the phase performance of an optical pixel may not span the required $2\pi$ phase range, or may not produce a constant amplitude over its phase range. These limitations result in imperfections in the phase gradient, which in turn introduce undesirable secondary lobes. We discuss the effects of non-ideal pixels on beam formation, in a general and technology-agnostic manner. By examining the strength of secondary lobes with respect to the main lobe, we quantify beam steering quality, and make recommendations on the pixel performance required for beam steering within prescribed specifications. By applying appropriate compensation strategies, we show that it is possible to realize high-quality beam steering even when the pixel performance is non-ideal, with intensity of the secondary lobes be two orders of magnitude smaller than the main lobe.