2-D liquid crystal optical phased array

Beam steering devices have wide applications in both military and civil fields. The ultimate goal for such devices is to reduce their size, weight, and power consumption. However, the laser source in these devices is spatially separate from the phase shifter, resulting in large size, complex packaging, and low coupling efficiency. To solve these problems, a novel electrically controlled beam steering chip based on coherently coupled vertical cavity surface emitting laser (VCSEL) array directly integrated with liquid crystal optical phased array (LCOPA) is proposed in this paper. Implant-defined in-phase coherently coupled VCSEL arrays (CCVAs) with uniform near-field are designed and fabricated first to act as the coherent laser source for the chip. Then, taking advantage of the CCVA planar structure, the LCOPA is integrated directly on the CCVA by conventional process. The coherent light generated by the in-phase CCVA is uniformly and normally incident into the LCOPA and is electrically steered by the LCOPA. One-dimensional beam steering is achieved by two proof-of-concept integrated chips. The chips based on a 4 × 4 square CCVA and a 16-element hexagonal CCVA offer a field of view of 2.21° and 6.06°, respectively. Independent control of the CCVA and LCOPA guarantees a relatively high wavelength stability and power stability. Theoretical calculations are also performed, which are consistent with the experiments.

Non-mechanical beam steering is required for holographic displays, free-space optical communication, and chip-scale LiDAR. Optical phased arrays (OPAs), which allow for inertia-free, high-speed beam control via electronic phase control, are an important research topic. The present study investigates the primary material platform for on-chip OPAs: Liquid crystal OPAs (LC-OPAs) employ electrically tunable refractive indices for low-voltage operation; lithium niobate OPAs (LN-OPAs) utilize high electro-optic coefficients for high-speed, low-power consumption, and large-bandwidth operation; and silicon-based OPAs (Si-OPAs) apply mature photonic integration to achieve high integration density and GHz-range steering. The paper thoroughly examines OPA basics, recent material-specific advancements, performance benchmarks, outstanding issues, and future prospects.

A new, lower-cost, and 10FPS-attainable lidar scanning system has been developed. The functions of the system include steering the incident laser, correcting the alignments and aberrations, outputting the signal of the misalignment, and laser incident timing. The system incorporates low-cost parts that include a Liquid Crystal on Silicon (LCOS), a spherical mirror with a transparent layer (SMT), a spherical surface meniscus lens, and photosensors. The key component in this system is the SMT, which increases the LCOS scanning area, reduces the aberration, and creates a reference reflection for optical system correction. Beam steering by the optical phased array is accomplished by varying the refractive index of the liquid crystal in the LCOS. Scanning flash lidar is realized by the combination of the LCOS and SMT, which can emit an intensity distribution-corrected conical beam. The SMT reference reflection corrects three types of errors by adjusting the control parameters of the LCOS: misalignment upon lidar fabrication, long-term or temperature-dependent variation of the optical system, and installation error. In addition, the alignment process manhours and investments for a factory are reduced by eliminating the need for mechanical adjustments. The system can realize flash area-varying lidar, which can achieve a field of view of 1.8 rad in the horizontal direction and 0.3 rad in the vertical direction. An arbitrary irradiation area can be designed using optical phased array techniques.

Optical phased arrays (OPAs) are a key technology in solid-state beam scanning, capable of achieving beam steering and scanning without relying on any mechanical moving parts. However, their application in the field of scanning is constrained by two significant limitations: a narrow scanning field of view (FOV) and long scanning periods. To address these limitations, we propose an omnidirectional scanning model combining a liquid crystal optical phased array (LC-OPA) and a conical mirror. The experimental results demonstrate that by generating annular beams with the LC-OPA and combining them with a passive conical mirror, a scanning FOV of 360°×2.1° was achieved. The scanning error was less than 0.04°, and the scanning period was reduced to 1/4800 that of a two-dimensional grating scanning system, and no mechanical moving parts were involved.

In 3‐D display system based on opto‐electronic reconstruction of digitally recorded hologram, the field of view of such a system is limited by the spatial resolution of the liquid crystal on silicon (LCOS) spatial light modulator (SLM) used to perform the opto‐electronic reconstruction. In this article, the spatial resolution limitation of LCOS SLM associated with fringe field effect and interpixel coupling is determined by liquid crystal director simulation and Finite Difference Time Domain (FDTD) simulation. The diffraction efficiency loss associates with the imperfection in phase profile is studied with an example of opto‐electronic reconstruction of an amplitude object. A high spatial resolution LCoS SLM with wide reconstruction angle is proposed.

Surface-stabilized antiferroelectric liquid crystals (AFLCs) and V-shape smectics share the spontaneous generation of intermediate transmission states, i.e. analogue grayscale. On the other hand, liquid crystal on silicon (LCOS) appears to be a promising alternative to thin-film transistors (TFTs) in the preparation of reflective microdisplays and spatial light modulators (SLMs). The feasibility of preparing LCOS SLMs using AFLC and V-shaped LCs has been analyzed. A comparative study of a number of AFLC and V-shape materials as candidates for LCOS SLMs has been carried out. Test cells below 1 µm have been prepared using an ITO-coated transparent glass plate and an aluminized silicon back plate mimicking the actual LCOS device. AFLC waveforms compatible to low-voltage operation of the silicon backplane have been demonstrated. V-shape waveforms have been designed and demonstrated as well. The results show that both LC families may be employed in this specific application. Dynamic behavior, with frame rates over 200 Hz, is especially remarkable.

Liquid crystal on silicon (LCoS) spatial light modulators (SLMs) are versatile scientific tools relevant to an increasingly wide variety of research and technological applications including digital holography, wavefront correction, optical tweezing, and non-mechanical beam steering to name a few. Since SLMs are used in a multitude of different ways, some aspects of device performance (e.g., response time) are crucial to certain applications while being irrelevant to others. In this work we couple our standard SLMs with a thermo-electric cooler, allowing for tunability of the device operating temperature from 0° to 75 °C. We show that there is an inherent tradeoff between the liquid crystal response time and the phase stability of an SLM, and that the operating temperature offers a means of controlling this tradeoff. Furthermore, this paper aims to provide the reader with a brief but thorough explanation of SLM operating principles and device structure, defines the performance metrics of the SLM, and provides a methodology for measuring the specifications. By allowing control over the SLM operating temperature and detailing how temperature affects device functionality, SLM users are afforded greater experimental flexibility and will be better able to tailor the performance of their device for the given project or application at hand.

Beam steering characteristics of transmission liquid crystal optical phased array(LC-OPA) were measured using ultra precision electronic autocollimator. A continuous beam steering with a constant angular resolution in the order of 20 μrad is obtained experimentally from 0° to 6° based on the method of variable period grating (VPG).Meanwhile, the angular repeatability of less than 4 μrad (RMS) has been achieved.

Three multi-beam forming methods based on optical phased array technology are presented in this paper. These methods can achieve simultaneous multiple-beam pointing in the optical band. The principles of these methods are introduced, the far-field pattern calculation formulas of the subaperture method and the array division multiplexing method are derived, and the algorithm flow of the iterative Fourier transform method is described in detail. Simulations and experiments have been conducted to verify the validity of these methods.

Optical phased arrays (OPAs) with the ability of dynamic beam-steering hold great promise for LiDAR applications. In contrast to mechanical scanning, OPAs have the advantage of being capable of agile beam pointing, allowing the multifunctional operation in LiDARs. In this paper, we propose a liquid crystal (LC) tunable OPA to achieve 2D beam steering. This approach enables a LC-tunable beam control in a second axis in addition to an OPA-tuning, thereby achieving 2D beam steering at a single wavelength. The LC-tunable OPA is fabricated using a standard Si photonics process and a LC process common for commercialized LC displays and LC on Si (LCOS) devices. We have fabricated samples of LC-tunable devices and LC-tunable OPA devices for 1D and 2D steering respectively and demonstrated a LiDAR using the 1D steering device. By taking advantage of non-mechanical movement of the device, a target tracking is realized by detecting a person from a camera image and irradiating the steering beam in that direction with more than 10 frames per second. With a faster 2D steering, a 3D target tracking even for multiple targets could be realized in the future.

For laser beam steering, a pure optical-electric system without mechanical or inertial parts is used. The new device is a Liquid Crystal Optical Phased Array (LCOPA). Supplying electric field to liquid crystal cell with electrodes, the extraordinary refractive index changes, which results in phase shift that modulates the direction of incident beam. The advantages of this device are small size, less energy consuming, programmable and addressable control. A one dimensional device is designed and tested. The resolution of the steering angle is 20 μrad, the range is ±2o. The effect of flyback region and phase valley on diffraction efficiency is also discussed briefly.

A practical numerical model for a liquid crystal cell is set up based on the geometrical structure of liquid crystal optical phased arrays. Model parameters include width and space of electrodes, thickness of liquid crystal layer, alignment layers and glass substrates, pre-tilted angles, dielectric constants, elastic constants and so on. According to electrostatic field theory and Frank-Oseen elastic continuum theory, 2D electric potential distribution and 2D director distribution are calculated by means of the finite difference method on non-uniform grids. The influence of cell sizes on director distribution is analyzed. The fringe field effect between electrodes is also discussed.

In one-dimensional (1D) liquid crystal optical phased array (LCOPA) device, liquid crystal molecular is controlled by discrete strip-shaped electrodes. The size of electrodes influences directly the phase modulation characteristics and far field diffraction efficiency. The model of LCOPA device was set up and the director distribution of liquid crystal in electric field was simulated. The influence of electrode size on phase modulation and diffraction efficiency was analyzed. The results showed that diffraction efficiency increases monotonously with electrode space decreasing. However, when electrode space decreases to less that 1μm, the increment of diffraction efficiency is very small and less than 1%. This means that 1μm of electrode space is small enough for the design of LCOPA devices.

We present high-performance integrated optical phased arrays along with first-of-their-kind light detection and ranging (LiDAR) and free-space data communication demonstrators. First, record-performance optical phased array components are shown with low-power phase shifters and high-directionality waveguide grating antennas. Then, one-dimensional (1-D) 512-element optical phased arrays are demonstrated with record low-power operation ( $ 1 mW total), large steering ranges, and high-speed two-dimensional (2-D) beam steering ( $ 30 $\mu$ s phase shifter time constant). Next, by utilizing optical phased arrays, we show coherent 2-D solid-state LiDAR on diffusive targets with simultaneous velocity extraction at a range of nearly 200 m. In addition, the first demonstration of 3-D coherent LiDAR with optical phased arrays is presented with raster-scanning arrays. Finally, lens-free chip-to-chip free-space optical communication links up to 50 m are shown, including a demonstration of a steerable transmitter to multiple optical phased array receivers at a 1 Gb/s data rate. This paper shows the most advanced silicon photonics solid-state beam steering to date with relevant demonstrators in practical applications.

An autostereoscopic display system was designed and constructed. The design, which uses pupil imaging with a curved mirror, is described. It employs a monocentric configuration to enable a wide field of view and large pupils while keeping the lens diameters small to fit them within the interoccular separation. For each eye, image formation was accomplished using 1920 x 1200 liquid crystal on silicon (LCOS) spatial light modulators in a 3-panel configuration. The design employs custom curved diffusers, which were developed to optimize throughput, contrast, and pupil illumination uniformity.