Ziqiang Huang

Nonmechanical Infrared Beam Steering Using Blue Addressed Quantum Dot Doped Liquid Crystal Grating

We present a scheme of nonmechanical laser beam steering using ZnS/InP quantum dots doping nematic liquid crystal as the optical recording film. Because of its internal electric field generated by blue laser-induced charge carrier distribution, liquid crystal molecules are reoriented to form a phase grating which make the incident angle steer to the angle as we desire. Being a nonmechanical programmable laser beam steering, the anisotropy of the relative permittivity tensor and blue laser-induced electric carriers play a significant effect in determining the reorientable liquid crystal molecule and reconfigurable phase modulation of the gratings, that determines the steering angle and steering efficiency.

Stochastic scanning method to shorten acquisition time using liquid crystal optical phased array

Abstract. Agile beam steering has been previously reported to be one of the unique properties of a liquid crystal optical phased array. We propose a stochastic scanning method using the property of agile beam steering to shorten acquisition time in building a free-space laser communication link. As a specific example, Gaussian stochastic scan enables higher acquisition probability and shorter acquisition time. In addition, there are two factors to influence the results: standard deviation of stochastic scanning angle and the width of the laser beam. Theoretical analysis is presented that the stochastic scanning method is a unique method to speed up the acquisition process in free-space laser communication.

Arbitrary multiple beam forming by two cascaded liquid crystal optical phased arrays

A new method for non-mechanical laser beam splitting and steering is demonstrated. Two cascaded liquid crystal optical phased arrays (LC-OPAs) controllably modulate the amplitude and phase of an incident laser beam to realize the near-field wavefronts of multiple simultaneous beams with arbitrary directions. Diffraction between the two arrays is avoided by precise 4-f imaging from one LC-OPA to the other (array resolution 1×1920). In the method of cascaded amplitude and phase (CAP) devices, numerical simulation results show the characteristics of amplitude and phase modulation profiles, as well as the far-field intensity patterns. Both the numerical and experimental results clearly demonstrate the capabilities of fast multi-beam forming with high efficiency (>85%, 4 beams) and accuracy (deviation <90μrad).

Design and experimental demonstration on improved high order grating for wide angle beam steering of liquid crystal optical phased array

To realize a non-mechanical laser beam deflector with a wide steering range, improved high order grating method (i-HOG) was theoretically proposed on the promising optical phased array device using the material of liquid crystal. In this paper, experimental prototype and results are presented to verify the performance on the wider steering range when the method of i-HOG was applied on the corresponding device. To satisfy the requirement on much deeper phase retardation, the optical film of liquid crystal was redesigned and fabricated as well as driving hardware. Comparing with the conventional methods where the modulo of phase delay is 2π, liquid crystal optical phased array using the method of i-HOG can succeed a double steering range. Meanwhile, experimental results also show better diffraction efficiency.

Theoretical model and experimental verification on the PID tracking method using liquid crystal optical phased array

Liquid crystal optical phased array (LC-OPA) has been considered with great potential on the non-mechanical laser deflector because it is fabricated using photolithographic patterning technology which has been well advanced by the electronics and display industry. As a vital application of LC-OPA, free space laser communication has demonstrated its merits on communication bandwidth. Before data communication, ATP (acquisition, tracking and pointing) process costs relatively long time to result in a bottle-neck of free space laser communication. Meanwhile, dynamic real time accurate tracking is sensitive to keep a stable communication link. The electro-optic medium liquid crystal with low driving voltage can be used as the laser beam deflector. This paper presents a fast-track method using liquid crystal optical phased array as the beam deflector, CCD as a beacon light detector. PID (Proportion Integration Differentiation) loop algorithm is introduced as the controlling algorithm to generate the corresponding steering angle. To achieve the goal of fast and accurate tracking, theoretical analysis and experimental verification are demonstrated that PID closed-loop system can suppress the attitude random vibration. Meanwhile, theoretical analysis shows that tracking accuracy can be less than 6.5μrad, with a relative agreement with experimental results which is obtained after 10 adjustments that the tracking accuracy is less than12.6μrad.

Steering performance of oblique arriving beam backward propagating through one-dimensional liquid crystal optical phased array

Liquid crystal optical phased array (LC-OPA) has been reported to be one of the promising methods to realize nonmechanical laser beam steering in free-space laser communication. The nonmechanical beam steering mechanism of LC-OPA in a free-space laser communication process is demonstrated. To analyze the steering performance of LC-OPA for a beam arriving from arbitrary directions, a theoretical model based on two-dimensional liquid crystal orient model and backward propagation method is proposed. In addition the phase characteristics are discussed both in normal and oblique incident cases, and a linear relationship between angle-of-arrival and detected incident angle is also derived. All of the theoretical results are verified by the following experiments with a good agreement.

Improved high order grating method to realize wide angle beam steering on liquid crystal optical phased array

To achieve a wider scanning range of liquid crystal optical phased array (LC-OPA), in this paper, a novel method of improved high order grating (i-HOG) is proposed in one device without introducing any other devices. The method of i-HOG breaks through the traditional ideas of modulo 𝟐𝛑 phase and takes the fringe effect into account to have a multi order extension. Subsequently, the method is verified by numerical simulation showing that it realizes a scanning range of wider than 20 degrees and even wider.

The technique of high power laser beam combination using liquid crystal spatial light modulator

Based on the phase modulation characteristics of optically addressed liquid crystal spatial light modulator (OA-LC-SLM) which is realized by controlling the power of addressing light, a physical model of coherent beam combination fiber laser using a bunch of fibers and a device of OA-LC-SLM is established on the theory of diffraction optics and liquid crystal birefringence effect. On the basis of this model, the properties of given scheme of coherent beam combination fiber laser are investigated including main lobe distribution and ability of phase modulation. Meanwhile, the plot functions of phase modulation versus the optical power of addressing light are obtained on different given driving voltage conditions and fiber alignment parameters such as core diameter and filling factor. After the numerical simulation, it shows that, this coherent beam combination fiber laser using OA-LC-SLM demonstrates an ability of coherent beam combination on the far field. With the increase of core diameter, the combination efficiency is improved better, and the divergence angle decreases narrower.