Liquid Crystal Phase Modulator Research Articles

Research on reconfigurable waveguide devices based on liquid crystal on silicon

AbstractDue to the limitation of materials, PIC cannot achieve large magnitude phase modulation in a small size, and lacks the reconfigurable ability. Because of its birefringence characteristic, liquid crystal can be used in the liquid crystal on silicon (LCoS) device to achieve a large amount of phase modulation in a small size and has the capacity of reconstruction. Based on the experimental results of LCoS devices and basic liquid crystal waveguide devices, the liquid crystal waveguide device is prepared. While retaining the LCoS spatial optical phase modulation capability, the liquid crystal waveguide and phase modulation capability are realized. The beam splitter, optical switch, and Mach–Zehnder interferometer structure are constructed, which verifies the feasibility of the liquid crystal waveguide phase modulator.

Polarization‐independent liquid crystal device with microdomain twisted structure

AbstractThe polarization‐independent liquid crystal (LC) phase modulators can greatly improve the efficiency and reduce the complexity of the optical system. However, it is difficult for the LC phase modulator to achieve both good low‐loss modulation and polarization‐independent properties. A LC phase modulator of single layer microdomain twisted structure has been proposed to achieve good polarization independence and low loss in phase modulation. However, the multi‐exposure in fabrication is difficult to realize in production process. To simplify the fabrication process, an alternate LC (ALC) mask is proposed with the alternate arrangement of twist‐nematic (TN) LC and nematic LC. The fabrication process is optimized to two steps exposure with the usage of ALC and is suitable for large‐amount‐production. The measurement results showed that the single layer microdomain twisted LC phase modulator may get very low polarization dependence, about 3.52% under 2π phase modulation depth, with low loss. The device shows good potential application in optical communication, wearable device, and display.

Scaled-laboratory demonstrations of deep-turbulence conditions

This paper uses five spatially distributed reflective liquid-crystal phase modulators (LcPMs) to accurately simulate deep-turbulence conditions in a scaled-laboratory environment. In practice, we match the Fresnel numbers for long-range, horizontal-path scenarios using optical trombones and relays placed between the reflective LcPMs. Similar to computational wave-optic simulations, we also command repeatable high-resolution phase screens to the reflective LcPMs with the proper path-integrated spatial and temporal Kolmogorov statistics.

Optical Phased Array-Based Laser Beam Array Subdivide Pixel Method for Improving Three-Dimensional Imaging Resolution

The small number of pixels in the current linear mode avalanche photodiode (LM-APD) array limits its three-dimensional (3D) imaging resolution. We use an optical phased array-based beam array subdivided pixel method to improve the 3D imaging resolution, using an optical phased array to generate a beam array with the same number of pixels as the LM-APD array and matching positions and controlling each sub-beam in the beam array to scan in the field of view of the corresponding pixel. The sub-beam divergence angle in the beam array is smaller than the instantaneous field of view angle of a single pixel in the LM-APD array. The sub-beam scanning in a single pixel’s field of view realizes the multiple acquisition of the target 3D information by the LM-APD array, thus improving the resolution of the LM-APD array. The distribution of the beam array in the far field is simulated, and the main performance parameters of 3D imaging are analyzed. Finally, a liquid crystal phase modulator is used as an optical phased array device to conduct experiments on a target 20 m away, and the results prove that our method can improve the resolution from 4 × 4 to 8 × 8, which can be improved at least four times.

P‐89: Digital Holography Microscope with liquid crystal phase modulator

We proposed a DHM system with improved resolution property by using liquid crystal (LC) phase modulator. The LC phase modulator can stably control the phase modulation characteristics of the interference pattern and implements the four‐step phase shifting scheme. The proposed DHM system showed a four‐fold improvement in resolution compared to the conventional DHM with polarized camera. Finally, it was confirmed that the modulation transfer function (MTF) value was improved 2 times at the resolution target of 105 lines/mm.

40.4: Research on Reconfigurable Waveguide Devices Based on LCoS

Due to the limitation of materials, PIC cannot achieve large magnitude phase modulation in a small size, and lacks the reconfigurable ability. LCoS makes use of the birefringence characteristic of liquid crystal to achieve a large amount of phase modulation in a small size, and has the capacity of reconstruction. Based on the experimental results of LCoS devices and basic liquid crystal waveguide devices, a liquid crystal waveguide is fabricated. While retaining the LCoS spatial optical phase modulation capability, the on‐chip liquid crystal waveguide and phase modulation capability are realized. The beam splitter, optical switch and Mach‐Zehnder interferometer optical circuit structure are constructed, which verifies the feasibility of the on‐chip waveguide structure of the liquid crystal waveguide phase modulator.

Reconfigurable design of a thermo-optically addressed liquid-crystal phase modulator by a neural network.

We present a machine learning approach to program the light phase modulation function of an innovative thermo-optically addressed, liquid-crystal based, spatial light modulator (TOA-SLM). The designed neural network is trained with a little amount of experimental data and is enabled to efficiently generate prescribed low-order spatial phase distortions. These results demonstrate the potential of neural network-driven TOA-SLM technology for ultrabroadband and large aperture phase modulation, from adaptive optics to ultrafast pulse shaping.

Non-mechanical self-alignment system for free-space optical communications based on a cascaded liquid crystal optical antenna.

Free-space optical (FSO) communication has attracted extensive attention in recent years. To maintain a reliable FSO link, two main issues need to be addressed: beam drift and vibration. In this paper, we demonstrate a non-mechanical self-alignment system based on a cascaded liquid crystal optical antenna, in which a frequency decoupled hybrid integration Kalman filter (FDHI-KF) method is proposed to achieve predictive beam drift tracking and vibration mitigation. By leveraging the integrated control on our lab-made liquid crystal phase modulation devices, and implementing the adaptive algorithm on a heterogeneous field programmable gate array (FPGA), this system is capable of realizing precise self-alignment without any moving parts. Experiments are conducted to verify its performance in practical applications. We envision it to set a benchmark for future liquid crystal non-mechanical beam-steering systems in FSO communications.

Polarization-independent liquid-crystal phase modulator with multi-microdomain orthogonally twisted photoalignment

Polarization-independent liquid-crystal phase modulator with multi-microdomain orthogonally twisted photoalignment

40.2: A Polarization‐independent Liquid Crystal Device with large Phase Retardation

A polarization-independent liquid crystal (LC) device for large optical phase depth is demonstrated. Using LC layer with the twist angle of 180°, the parallel rubbing LC device shows good polarization-independence. A phase modulator with a 180° twist LC layer and cell gap of 12um was fabricated whose polarization dependence can be lowered to 0.1% for 8.7π phase retardation at 532nm. The proposed LC phase modulator shows great potential for optical communication and imaging systems.

Dynamic phase measurement of fast liquid crystal phase modulators.

We present dynamic time-resolved measurements of a multi-pixel analog liquid crystal phase modulator driven at a 1 kHz frame rate. A heterodyne interferometer is used to interrogate two pixels independently and simultaneously, to deconvolve phase modulation with a wide bandwidth. The root mean squared optical phase error within a 30 Hz to 25 kHz bandwidth is <0.5° and the crosstalk rejection is 50 dB. Measurements are shown for a custom-built device with a flexoelectro-optic chiral nematic liquid crystal. However, the technique is applicable to many different types of optical phase modulators and spatial light modulators.

Electrically tunable polarization independent liquid crystal lenses based on orthogonally anisotropic orientations on adjacent micro-domains.

Polarization dependency is an intrinsic property of liquid crystals (LC) devices but major problem is optical efficiency. We demonstrated a polarization independent liquid crystal phase modulation based on the orthogonal nematic LC (OLC) mode wherein the optics axes of nematic liquid crystal molecules are set orthogonally to adjacent sub-domains for the first time. Such an OLC mode includes sub-domain with anisotropic orientations but collectively presents a capability of a polarizer-free optical phase modulation. An OLC mode cell provides a tunable optical phase of ∼3.35π radians for unpolarized light and different linearly polarized light. Among the polarizer-free LC mode, the proposed OLC mode is single-layered with large tunable optical phase. We also demonstrated a polarizer-free LC micro-lens. We expect this novel LC mode provide alternatives technology roadmap for upcoming optical applications, such as electrically tunable ophthalmic lenses and optical systems for augmented reality.

33.3: Adaptive Modulation System of the Liquid Crystal Phase Modulators

An adaptive modulation system for a liquid crystal (LC) phase modulator is demonstrated. In order to achieve the highresolution phase distribution, the information of the transmittance distribution transformed by phase retardation is applied. By the adjustment algorithm and adaptive algorithm, the phase distribution of the LC phase modulator can perfectly match the designed phase profile in a short modulation time. The adaptive modulation system shows potential application in optical communication, wearable device and display.

Rough surface scattering using a source able to produce an incident beam with controlled polarization and coherence.

We present a comparison of the first numerical and experimental results for the scattering of light from rough surfaces using a recently developed variable coherence polarimetry source that permits obtaining information on the object without having to scan over incidence or scatter angle. We present, for the first time, we believe, the application of this source to a 1D rough surface and show how to analyze the scattered field to retrieve useful information about the surface. This source uses a liquid-crystal phase modulator to control the polarization as well as the coherence of the beam illuminating the rough surface. Changing the polarization state distribution at the source plane, by controlling the phase distribution on a spatial light modulator, gives a scan of two source spots over the rough surface. The scattered beam is analyzed with a Stokes polarimeter. The Kirchhoff approximation is used to calculate the scattered Stokes vector using the experimental incident Stokes vector and intensity distribution as a source. Good agreement is obtained between the numerical and experimental results, for a simple calculation of the number of intensity maxima obtained as the two first-order source spots are scanned across the sample.

A Compact Full 2π Flexoelectro‐Optic Liquid Crystal Phase Modulator

AbstractWavefront shaping, which is often achieved using liquid crystal (LC) spatial light modulators, is particularly important for a wide range of applications including laser microfabrication and micromanipulation, microscopy, and quantum optics. In this work, results are presented for the first integrated LC phase modulator that combines a flexoelectro‐optic LC layer (that behaves as a switchable λ/2 waveplate) with a polymerized reactive mesogen layer (which acts as a λ/4 waveplate) and a mirrored substrate that creates a double‐pass geometry. For a flexoelectro‐optic LC layer that exhibits switching angles of ±45° at a voltage of ±85 V a full 2π phase modulation is observed when driven by a 1 kHz waveform. Experimental results are also compared with modeling using Jones calculus of the amplitude and phase variation when the LC and the polymer layer deviate from their desired waveplate conditions. The development and demonstration of an integrated device is particularly significant for applications where size and cost are critical factors such as in LiDAR for the Space and Automotive industries, respectively.

Fast-Response Liquid Crystal Phase Modulators with an Excellent Photostability

We report a new mixture, which is modified from Merck TL-216, for liquid-crystal-on-silicon spatial light modulators (SLMs). To achieve 2π phase change at λ = 633 nm with 5 V operation voltage, the measured response time is about 3 ms at 50 °C. Meanwhile, our mixture exhibits no sign of photodegradation and even the total dosage has exceeded 400 MJ/cm2 at a blue laser wavelength λ = 465 nm. In comparison, E7 died at about 30 MJ/cm2. Widespread applications of this material for high brightness SLMs, near-eye displays, and head-up displays are foreseeable.

Application problems of liquid crystal phase modulators to high power lasers

The liquid crystal phase modulators (LCPMs) have applications and prospects in fusion ignition, laser processing, optoelectronic countermeasure, laser radar, laser communication, laser protection and so on. However, owing to the limited laser damage resistance of the materials constituting the LCPMs as well as insufficient system research on the laser damage and the phase modulation performance degradation of LCPMs induced by high power lasers, the laser handling power of LCPMs cannot satisfy the requirements of high power laser developments. To provide guidance for optimizing the fabrication process of LCPMs with high laser handling power, we reviewed the laser damage and the phase modulation performance degradation characteristics of LCPMs irradiated by high-peak-power lasers and high-average-power-lasers and then summarized the methods to improve the laser handling power of LCPMs.

Polarization-independent nematic liquid crystal phase modulator based on optical compensation with sub-millisecond response.

In this paper, we propose a design utilizing two identically parallel-aligned nematic liquid crystal (LC) plates for fast-response and polarization-independent phase modulator. Driven by synchronized voltage signals, such a polarizer-free variable phase modulator shows a wide tunable range from zero to more than 3π, back and forth at 532nm. Due to the optical compensation of the two plates, the rise and fall time of the phase retardation corresponds to the switching-on time of the two plates. Several advantages are illustrated based on the optical compensation of two identical parallel-aligned plates. First, zero phase retardation is obtained, which overcomes the residual phase due to surfaced anchored liquid crystal molecules. The second advantage is sub-millisecond response of rise and fall of retardation since simultaneous relaxation of the two plates remains optically hidden during the synchronized voltages fall. This fast-response and polarization-independent phase modulator has great potential for practical use, including optical communications and light field imaging systems.

Adaptive optics scanning system with two-zone phase filters

ABSTRACTAn adaptive confocal system employing pupil filters and two light sources has been designed, providing improved transverse resolution. Coherent transfer functions are studied to show the transfer capability at different frequencies and the limitations of the filters in obtaining clear improvements in the focal plane. Then, intensity point spread functions are analysed to reveal the dependence of the resolution on the size of the pinhole and the inner radius of the filter. An experiment has been carried out using a liquid crystal phase modulator and an artificial eye to validate the simulation results. It proves that the system with two light sources can correct the aberrations, with the basic effect of the phase modulation being to decrease the low spatial frequencies and increase the high spatial frequencies. Improvement of the transverse resolution can be achieved by sacrificing light intensity and contrast.

44‐3: Large Area Multi‐Layer Liquid Crystal Phase Modulators Enabled by Two‐Photon Polymerization

We demonstrate multi‐fold speed enhancement of liquid crystal phase modulators through laser written sub‐micron scaffolds. The versatile fabrication process allows devices with arbitrary liquid crystal alignment and, therefore, polarization dependence. We lastly discuss the prospects of the technology for large area (&gt;0.5 in2) spatial light modulators.