High-Efficiency Beam Steering LCOS for Wavelength Selective Switch

Liquid crystal on silicon (LCoS) devices have been widely applied in optical beam steering. Increasing demands for advanced applications are driving LCoS technology toward larger deflection angles and higher diffraction efficiency, while these two performance metrics are difficult to achieve simultaneously due to the fringe-field effect. To address this issue, we have trained a neural network to achieve precise compensation for the fringe-field effect and have experimentally validated the approach using a commercial LCoS device. The results demonstrate that this method achieves an efficiency over 37.8% with a continuous diffraction angle up to 10 ∘ @ 1550 nm, representing the largest deflection angle and highest efficiency yet reported for LCoS devices. This work paves the way for the practical application of LCoS in fields such as LiDAR, holography, and optical switches.

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.

Nematic liquid crystal (LC)-based beam steering has been reported for wide applications. However, for conventional nematic LC beam steering the thickness is of several microns in order to have a wider deflection angle. The response time is relatively slow and the diffraction efficiency is low. In this work, novel beam steering based on polymer stabilized blue phase liquid crystal (PS-BPLC) has been designed and theoretically analyzed. This special mesophase of the chiral doped nematic LC has several advantageous characteristics, for example no need for alignment layers, microsecond response time and an isotropic voltage-off state. The results reveal control over phase retardation. The direction of the steered beam can be tuned by voltage. Depending on voltage configuration, either diffractive beam steering (0.5deg deviation for 1st order) or a tunable continuous phase (tunable deviation of 0.002deg) can be obtained. In the first case, the deflection angle could be tuned by stacks of samples. The second option has the same phase shift for the TE and TM modes so unpolarized light could be used. Full Text: PDF ReferencesF. Feng, I. White, T. Wilkinson, "Free Space Communications With Beam Steering a Two-Electrode Tapered Laser Diode Using Liquid-Crystal SLM", J. Lightwave Technol. 31, 2001 (2013). CrossRef E. Oton, J. Perez-Fernandez, D. Lopez-Molina, X. Quintana, J.M. Oton, M.A. Geday, "Reliability of Liquid Crystals in Space Photonics", IEEE Photonics Journal 7, 1 (2015). CrossRef J. Stockley, S. Serati, "Multi-access laser terminal using liquid crystal beam steering", IEEE in Aerospace Conference, 1972 (2005). CrossRef D. Zografopoulos and E. Kriezis, "Switchable beam steering with zenithal bistable liquid-crystal blazed gratings", Opt. Lett. 39, 5842 (2014). CrossRef Benedikt Scherger, et al., "Discrete Terahertz Beam Steering with an Electrically Controlled Liquid Crystal Device", J. Infrared. Millim. Terahertz Waves 33, 1117 (2012). CrossRef M.A. Geday, X. Quintana, E. Otón, B. Cerrolaza, D. Lopez, F. Garcia de Quiro, I. Manolis, A. Short, Proc. ICSO, Rhodes, Greece, pp. 1-4 (2010). CrossRef Y. Chen, S.-T. Wu, "The outlook for blue-phase LCDs", Proc. SPIE 9005, Advances in Display Technologies IV, 900508 (2014). CrossRef G.D. Love, A.F. Naumov, "Modal liquid crystal lenses", Liq. Cryst. Today 10, 1 (2000). CrossRef V. Urruchi, J.F. Algorri, J.M. Sánchez-Pena, M.A. Geday, X. Quintana, N. Bennis, "Lenticular Arrays Based on Liquid Crystals", Opto-Electron. Rev. 20, 38 (2012). CrossRef J.F. Algorri, G. Love, and V. Urruchi, "Modal liquid crystal array of optical elements", Opt. Express 21, 24809 (2013). CrossRef J.F. Algorri, V. Urruchi, N. Bennis, J. Sánchez-Pena, "Modal liquid crystal microaxicon array", Opt. Lett. 39, 3476 (2014). CrossRef J.F. Algorri, V. Urruchi, B. Garcia-Camara, J.M. Sánchez-Pena, "Generation of Optical Vortices by an Ideal Liquid Crystal Spiral Phase Plate", IEEE Elect. Dev. Lett. 35, 856 (2014). CrossRef D. Xu, Y. Chen, Y. Liu, S. Wu, "Refraction effect in an in-plane-switching blue phase liquid crystal cell", Opt. Express 21, 24721 (2013). CrossRef Z. Ge, S. Gauza, M. Jiao, H. Xianyu, S.T. Wu, "Electro-optics of polymer-stabilized blue phase liquid crystal displays", Appl. Phys. Lett. 94 101104 (2009). CrossRef J. Yan et al., "Extended Kerr effect of polymer-stabilized blue-phase liquid crystals", Appl. Phys. Lett. 96, 071105 (2010). CrossRef X. Wang, D. Wilson, R. Muller, P. Maker, D. Psaltis, "Liquid-crystal blazed-grating beam deflector, Appl. Opt. 39, 6545 (2000). CrossRef

In this paper, a method for measuring the liquid refractive index based on liquid crystal on silicon (LCoS) is presented. The liquid measuring chamber is composed of two optical lenses, an inlet, and an outlet. By filling the liquid with different refractive indices, the liquid measuring chamber has different focal lengths according to geometric optics. As a reflective micro-display device, the LCoS is another key component, in which the liquid crystal (LC) molecules are arranged in a nematic phase. The programming function of the LCoS, based on the interaction of incident light and the LC molecules in the LCoS, enables the LCoS to form as a digital lens. By using the measuring chamber in the optical system and adjusting the focal lengths of the digital lens, which is loaded on the LCoS, the refractive index of the liquid can be calculated accurately when the sensor receives the focused spot. The experimental results verify the feasibility of our proposed method.

Digital Electro-optics Platform is the main concept of Jasper Display Corp. (JDC) to develop various applications. These applications are based on our X-on-Silicon technologies, for example, X-on-Silicon technologies could be used on Liquid Crystal on Silicon (LCoS), Micro Light-Emitting Diode on Silicon (μLEDoS), Organic Light-Emitting Diode on Silicon (OLEDoS), and Cell on Silicon (CELLoS), etc. LCoS technology is applied to Micro Display, Spatial Light Modulator (SLM), Dynamic Optics, Wavelength Selective Switch (WSS), Holographic Display, Microscopy, Bio-tech, 3D Printing and Adaptive Optics, etc. In addition, μLEDoS technology is applied to Augmented Reality (AR), Head Up Display (HUD), Head-mounted Display (HMD), and Wearable Devices.

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.

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.

A novel liquid crystal on silicon (LCOS)-based wavelength selective switch (WSS) is proposed, fabricated, and demonstrated. It employs a multilayered arrayed waveguide grating (AWG) as a wavelength multiplex/demultiplexer. The LCOS deflects spectrally decomposed beams channel by channel and switches them to desired waveguide layers of the multilayered AWG. In order to obtain the multilayered AWG with high yield, phase errors of the AWG is externally compensated for by an additional phase modulation with the LCOS. This additional phase modulation is applied to the equivalent image of the facet of the AWG, which is projected by a relay lens. In our previously-reported WSS configuration, somewhat large footprint and increased cost were the drawbacks, since two LCOSs were required: one LCOS was driven for the inter-port switching operation, and the other was for the phase-error compensation. In the newly proposed configuration, on the other hand, both switching and compensation operations are performed using a single LCOS. This reduction of the component count is realized by introducing the folded configuration with a reflector. The volume of the WSS optics is 80 × 100 × 60 mm3, which is approximately 40% smaller than the previous configuration. The polarization-dependent loss and inter-channel crosstalk are less than 1.5 dB and -21.0 dB, respectively. An error-free transmission of 40-Gbit/s NRZ-OOK signal through the WSS is successfully demonstrated.

Design of large-deflection-angle high-diffraction-efficiency high-dispersion hybrid gratings

For practical holographic video display, it is important to generate holographic fringes as fast as possible. It is also important to display the full-color image with a simple display system. In our previous study, a full-color hologram was realized as a rainbow hologram, which discards the vertical parallax to reduce computation complexity. Its color reproduction, however, is not enough. Since this hologram uses the horizontal slit, proper color reproduction can be obtained only from a narrow viewing area in the vertical direction. In contrast, the image hologram provided a good contrast image, although it had only a single color. Also, the image hologram has full-parallax information. In this work, we investigate the image hologram for fast calculation and the display optics for full-color holograms with full parallax. Since image points are located close to the hologram, the required computation area of the image hologram becomes much smaller than that of the entire hologram. Therefore, vastly improved computational speed is obtained. The full-color hologram is displayed on a holographic video display system, which uses part of the original optics and liquid crystal on silicon (LCoS) panels of the conventional video projector to separate and combine color components. From the experimental results, we obtain a full-parallax reconstructed image and better color reproduction compared with the rainbow hologram.

A variety of methods have been developed in the last years to generate vector beams. In this work we will present some techniques that we have developed for the efficient and compact generation of arbitrary polarized vector beams. They are based on the use of geometric-phase elements combined with liquid-crystal on silicon (LCOS) spatial-light modulators (SLM) in a common-path architecture. LCOS-SLMs were used to encode a phase-only diffractive mask that encodes complex functions with high diffraction efficiency. We demonstrate the generation of arbitrary scalar modes and vector beam modes.

One of the key technologies to evolve in the displays market in recent years is liquid crystal over silicon (LCOS) microdisplays. Traditional LCOS devices and applications such as rear projection televisions, have been based on intensity modulation electro-optical effects, however, recent developments have shown that multi-level phase modulation from these devices is extremely sought after for applications such as holographic projectors, optical correlators and adaptive optics. Here, we propose alternative device geometry based on the flexoelectric-optic effect in a chiral nematic liquid crystal. This device is capable of delivering a multilevel phase shift at response times less than 100 microsec which has been verified by phase shift interferometry using an LCOS test device. The flexoelectric on silicon device, due to its remarkable characteristics, enables the next generation of holographic devices to be realized.

According to the advent of ubiquitous world, the requirement for the mobile information devices with high display quality and compact device size is surprisingly increased. Among the diverse candidates for this mobile display system for mobile devices, Liquid Crystal on Silicon (LCoS) is the most competitive device due to the high aperture ratio and simple fabrication process. The inorganic liquid crystal (LC) alignment layers are widely used for LCoS devices because of the thermal and photochemical stability. In this work, the reactive sputtering was selected for the preparation method of inorganic LC alignment layers. The nitrogen (N2) gas had the effect on the deposition process of SiO2 and the surface morphology of SiO2 thin layers were affected by the N2 mixing ratio of sputtering gas. In addition, the LC alignment properties on SiO2 thin layer were also closely related with the N2 mixing ratio and other sputtering conditions. In the case of high RF power of reactive sputtering, the N2 mixing ratio has little effect on the LC alignment on SiO2 thin layers. However, in the case of low RF power of reactive sputtering, the LC alignment properties were enfeebled by increasing the N2 mixing ratio. This result might be attributed to the change of the surface morphology of inorganic SiO2 thin layers.

Micro-Electro-Mechanical Systems are nowadays frequently used in many fields of industry. The number of their applications increases and their functions become more responsible, therefore precise knowledge about their properties is necessary. Due to its fragility and small sizes non-contact and high sensitive measurement method is required. Two-beam laser interferometry is one of the most popular testing methods of microelements. Such method implemented in Twyman-Green interferometer allows for full-field shape determination and out-of-plane displacement measurement. However the elements under test may bring additional challenges: their surfaces may have complicated shape or large shape gradients which prohibit their testing by means of interferometer with a flat reference mirror. To overcome such problems we propose to use LCOS (Liquid Crystal On Silicon) - phase, reflective SLM as an active reference element. LCOS serves as an adaptive reference mirror and phase shifter. The use of such element allows increasing measurement range of the interferometer and simplifies out-of-plane displacement measurement through object wavefront compensation. The applicability of the modified Twyman-Green interferometer will be shown at the examples of active micromembranes testing.

The wavefront reconstruction with interaction matrix composed of high-order Zernike polynomials as basis may be unintendedly less accurate when the wavefront manipulator of huge number of elements such as Microelectromechanical systems (MEMS) mirrors and Liquid Crystal on Silicon (LCOS) is used. One of the reasons of the lack of the accuracy in reconstruction comes from the mismatch between the rectangular elements of the LCOS in the orthogonal arrangement and the projected patterns obtained by the Zernike polynomials defined in the polar coordinates. To improve the accuracy of the wavefront reconstruction by the LCOS, the use of the random phase patterns is proposed with presumption to be appropriate for the orthogonally arranged high number of elements. The residual fitting errors of reconstructed wavefront are evaluated by numerical simulation to show the potential of the use of the random phase patterns instead of the use of the Zernike polynomials. It is found by the Monte-Carlo simulation of the Kolmogorov model that the more random phase patterns one uses, the more accurate one achieves to reconstruct the wavefront compared to the use of the Zernike patterns. Additionally, the comparison of the Strehl ratio of the AO system obtained with the Zernike patterns and that of the random patterns is performed.