A significant kickoff in OPA's practical engineering

Laser beam agile control technology is a key generic technology in free space optical communication, infrared countermeasures, target tracking and other applications. An obvious feature of these applications is the requirement for automatic aiming, capture and tracking (PAT) of moving targets. In the case of free-space optical communication for long-distance high data rate transmission, a high-resolution beam control method must be used in order to maintain the link between the directional signal beam and the distant receiver. It is difficult for the mechanical beam control device to achieve the required deflection resolution and the programmable characteristics. The optical phased array (OPA) technology has shown its unique advantages to match these requirements. The technique of the Liquid Crystal Optical Phased Array (LC-OPA) is a real-time programmable and electronically controlled beam scanning technology, which plays a crucial role on many areas, such as space laser communications, laser radar, laser weapons and adaptive optical detection etc. LC-OPA is a low voltage driven optoelectronic device, using the material of nematic liquid crystal as the working medium of phase modulation. It has some obvious advantages such as inertial less, high precision, agile scan and low SWaP (size weight and power assumption).

    Phase Optoelectronics Team led by Dr. Wang Xiangru from the University of Electronic Science and Technology of China is dedicated to the research of liquid crystal phased arrays (LCOPA), and has achieved many results in achieving wider scanning range, faster response speed, larger aperture and optimization of beam characteristics of LCOPA. Recently, the team proposed an improved i-PAPA large-caliber implementation method based on multi-sub-array parallel drive and two-stage device cascade method (PAPA). The structure of the i-PAPA device is shown in Figure 1. The improved i-PAPA structure mainly adopts the idea of partitioning the COM electrode (reference electrode), and expands the array electrode of the partition control by a single common electrode of the PAPA structure liquid crystal phased array antenna. By driving the COM electrode in a sub-region, large-caliber phase-controlled beam control is realized on a single phased array antenna, which has the advantages of single device operation and low insertion loss. The device adopts a 7-layer sandwich structure of a conventional liquid crystal device, and the upper and lower substrates are mirror-symmetrically placed, and each includes a base glass, an ITO electrode, and a PI alignment layer, and a liquid crystal layer of an electro-optic phase shifting material in the middle. Similar to the conventional LCOPA, the PI alignment mode adopts the parallel alignment mode. Its far-field diffraction efficiency drops smoothly and monotonously as the point angle increases, the diffraction the efficiency is greater than 80%. The i-PAPA large-caliber implementation method enables the optical aperture of LCOPA to be greatly increased from the order of 10 mm to the order of 100 mm or even higher. The realization of the i-PAPA method greatly promotes the further practical application of OPA technology. Fig.2 is chosen from the article "Theoretical analysis on power stability and switch time of the non-mechanical beam steering using liquid crystal optical phased array" published by their team in Liquid Crystal magazine, which is a diagram of agile laser beam steering using LCOPA.

Fig. 1   i-PAPA device structure diagram

Fig. 2  Sketches of agile laser beam steering using LC-OPA

About team
The phase optoelectronic team led by Dr. Wang Xiangru from the University of Electronic Science and Technology of China, has more than 30 full-time researchers, doctors and masters. They are mainly engaged in the research of basic theory, device technology and application schemes of liquid crystal optical phased arrays. They have got a series of innovative research results and successfully applied to many national special projects and projects. Their achievements won the title of National Defense Technology Invention Award, Aerospace Science and Technology Invention Award. The team published nearly 100 SCI papers in international authoritative journals such as Physics Review Letters, Optics Letters, Optics Express, Opitcs Communications, and has applied for nearly 30 national invention patents. More than 10 invited/oral reports were made at representative international academic conferences such as CLEO, Photonics West, and SLCP.

Zhuo Rusheng, Wang Xiangru, He Xiaoxian, et al. The realizable method for large diameter liquid crystal optical phased array and the analysis of its far-field characteristics[J]. Opto-Electronic Engineering, 2018, 45(10): 180108.