Compact 4 cm aperture transmissive liquid crystal optical phased array for free-space optical communications

Abstract

There is a critical need for high bandwidth, high availability free-space optical communication links between the battlefield and the global information grid. Compact large aperture transceivers with low size, weight and power (SWaP) are needed to initiate and maintain communication links involving airborne platforms. The transceiver optical beam director typically contains fine and coarse steering stages. Existing beam director technology is based on electromechanical gimbaled mirrors with large SWaP that hinders deployment on many airborne platforms. To address the need for compact beam directors, we designed, fabricated, and tested an optical phased array (OPA) based on electrooptic dual frequency liquid crystal technology. This OPA has a transmissive architecture that enables a lower system SWaP, as compared to conventional reflective OPA. It has an 8 µm pixel pitch and steers over a 2.5° field of regard in one dimension at 1.55 µm. Two such OPAs can be stacked to steer in two dimensions. It has four independently addressable 1 cm x 4 cm regions arranged in a linear array to produce a continuous 4 cm x 4 cm aperture. The device incorporates novel addressing schemes to reduce the number of control channels by over an order of magnitude compared to conventional OPA addressing methods. It also utilizes proprietary low-loss transparent conductive Transcon TM film for low optical absorption in the infrared. The OPA uses a custom multi-channel controller circuit operating at a 500 Hz frame rate. We present results on OPA design, fabrication, and optical performance on steering.

3871104.pdf

“…Liquid crystal (LC) OPAs have been developed more than two decades ago [1]. LC OPAs offer 2-D beamforming, large apertures and broad transmittance spectrum [2], [3]. However, the response time of LC OPAs is limited to milliseconds, too slow for many applications.…”

Liquid Crystal Wavefront Correctors

“…In recent years, Prof. Xuan's group has completed series of valuable studies [31][32][33][34][35][36][37][38][39][40][41][42]. Recently, the applications of LCWFC have been extended to other fields, such as retina imaging [43][44][45], beam control [46][47][48][49][50], optical testing [41], optical tweezers [51][52][53], dynamic optical diffraction elements [54][55][56][57], tuneable photonic crystal fibre [58,59], turbulence simulation [60,61] and free space optical communications [62,63].…”

Four-access, 80 mm aperture all phase-controlled liquid crystal laser antenna

“…LC-OPA has been implemented in FSO system to achieve beam deflection in prior publications; 13 many of the aspects of enhancing LC-OPA’s performance have been studied, including diffraction efficiency improvement, 14 steering range expansion, 15 , 16 steering error reduction, 17 and aperture scale increasing 18 , 19 . One of the most critical limitations in utilizing LC-OPA to FSO communication system is its steering range.…”

“…LC-OPA has been implemented in FSO system to achieve beam deflection in prior publications; 13 many of the aspects of enhancing LC-OPA's performance have been studied, including diffraction efficiency improvement, 14 steering range expansion, 15,16 steering error reduction, 17 and aperture scale increasing. 18,19 One of the most critical limitations in utilizing LC-OPA to FSO communication system is its steering range. This is because, due to the limitation of the flyback region 20,21 caused by fringing fields and polarization distortion 22,23 induced by phase resets, LC-OPA's steering efficiency is low in large angles.…”