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Wavelength Division Multiplexing (WDM) networks with reconfigurable optical add/drop multiplexers (ROADMs) realize automatic scheduling and restoration at the wavelength level and are therefore part of the solution to meet increasing bandwidth and routing flexibility requirements for transport networks. The wavelength selective switch (WSS) is the key component in all commercial ROADM systems. Liquid crystal on silicon (LCoS) technology dominates current WSS installations as LCoS-based WSS can support Flexgrid technology enabled networks, and high port counts with excellent performance. WSS designs are becoming increasingly specialized for a wide variety of applications. For single WSS used in broadcast and select (B&S) architecture, superior port isolation is key for the desired signal to be filtered from the whole spectrum. While for twin WSS deployed in route and select (R&S) nodes, many features are desired for various network applications. These include multiple common ports, premium ports with superior port isolation, and high port counts. Future WSS may be asked to address a number of different end user applications, and as such there is a demand for combinations of custom spectrum range, compact form factors, increased WSS port count, low cost, thermal and mechanical ruggedization. The first commercially available quad WSS is part of this increasing trend of utilization of WSS throughout network architectures.

Phase liquid crystal (LC) spatial light modulators (SLM) are widely used for optical reconstruction of diffraction optical elements, including holograms. For this purpose high stability and linearity of phase response of SLM is required. In modern high resolution SLM digital signal addressing scheme which leads to emergence of effect of phase shift fluctuations during frame time is applied. In this paper measurements of character and peculiarities of modulation of phase shift of modern high-resolution LC SLM Santec SLM-200 were performed. Optical reconstruction of images from diffraction elements of different types was carried out, the quality of reconstruction and diffraction efficiency were assessed.

Quantization-induced limit cycle oscillations (LCOs) in digitally controlled dc–dc converters are addressed in this article. The novel dyadic digital pulsewidth modulator is proposed to increase the effective pulsewidth modulator resolution, as required for LCO-free operation, at low cost, without sacrificing dc accuracy and with no detrimental effects on the ripple voltage. Experimental results on a synchronous buck validate the approach highlighting effective LCOs’ suppression and dc accuracy enhancement at 5× reduced peak output voltage ripple and up to 16-dB lower frequency harmonic component reduction compared to thermometric dithering for the same resolution increase.

This report discusses the effect of speckle size on the quality of holographic images based on a liquid-crystal-on-silicon (LCoS) spatial light modulator (SLM). Further, it proposes methods of quantifying the average speckle size and holographic image resolution. These methods enable both characteristics to be compared using the same unit (the number of pixels in the holographic image), providing an intuitive and effective comparative analysis method. In particular, by varying the LCoS resolution ratio, the change in the resolvable minimum pixels of the holographic image is interpreted in conjunction with the average speckle size; moreover, an analysis of the correlation between the latter two is presented. This approach, based on LCoS resolution division, could provide useful insights into single-SLM-based, full-color holographic displays using space division. Furthermore, it could be extended to other components, including more advanced LCoS SLMs, and used to identify the relative effects on image quality with speckles.

Iterative Fourier transform algorithm (IFTA) has been widely applied to achieve holograms in diffractive optical elements, however it is insufficient for designing holograms uploaded on liquid crystal on silicon (LCOS) to steer multi-beams in a wavelength selective switch (WSS). In this paper, a three-step hybrid algorithm including IFTA, Symmetrical IFTA with both phase and amplitude freedoms (SIFTA-2) and Genetic algorithm (GA) is developed to optimize the multi-casting hologram and experimentally demonstrated the multi-casting function of WSS. The reconstructed output field not only has max 128 fan-out patterns with flexible power ratio, but also can be adjusted to balance multi-indicators like reconstructed root mean square error (RMSE), diffraction efficiency and crosstalk power by setting flexible weightings of fitness functions in GA.

This work demonstrates that wavefront encoding technique can be used reduce the peak transient crosstalk by >10 dB in holographic optical switches based on the liquid crystal on silicon (LCOS) technology, when compared with switches based on the conventional Fourier transform optical setup. At the same time, this technique also reduces the switching time, without any modifications needed to either the LCOS device or its driving circuits.

Funder: Foundation of German Business, Driver's access to information about navigation and vehicle data through in-car displays and personal devices distract the driver from safe vehicle management. The discrepancy between road safety and infotainment must be addressed to develop safely-operated modern vehicles. Head-up Displays (HUDs) aim to introduce a seamless uptake of visual information for the driver while securely operating a vehicle. HUDs projected on the windshield provide the driver with visual navigation and vehicle data within the comfort of the driver's personal eye box through a customizable extended display space. Windshield HUDs does not require the driver to shift the gaze away from the road to attain road information. This article presents a review of technological advances and future perspectives in holographic HUDs by analyzing the optoelectronics devices and the user experience of the driver. The review elucidates holographic displays and full augmented reality (AR) in 3D with depth perception when projecting the visual information on the road within the driver's gaze. Design factors, functionality and the integration of personalized machine learning (ML) technologies into holographic HUDs are discussed. Application examples of the display technologies regarding road safety and security are presented. An outlook is provided to reflect on display trends and autonomous driving. This article is protected by copyright. All rights reserved.

The technology of five-dimensional (5D) optical data storage in transparent materials paves a promising way to unlimited lifetime data storage for future cloud use. Phase-only liquid-crystal-on-silicon spatial light modulators (LCOS SLMs) have already exhibited its potential for this application in tailoring ultrafast laser writing beams for 5D optical data storage. A phase-only LCOS SLM can generate arbitrary data patterns by using diffractive holographic imaging for data writing light beam generation. However, the polarization control of the output holographic image is still achieved by using an external polarization modulator, which leads to complications, bulkiness, and large delays in current methods. In this paper, we presented an efficient phase and polarization modulation method through a compact system based on a single phase-only LCOS SLM to simultaneously control both the holographic image and its polarization state. The proposed method utilizes two-polarization-component coding in conjunction with a polarization component rotation technique in a compact system. Using this polarization rotation technique, two light components can be independently coded by separately using two holograms on two halves of the LCOS SLM. We experimentally construct a proof-of-concept prototype of the compact system, and the effectiveness of the system has been experimentally verified.

Liquid crystal on silicon (LCOS) technology has initially been developed for imaging and display applications. This technology combines the unique light-modulating properties of liquid crystal materials and the advantages of high-performance silicon complementary metal oxide semiconductor (CMOS) technology through dedicated LCOS assembly processes. Phase-only LCOS SLM are becoming an important tool for laser processing in a range of systems. A recent breakthrough in laser-induced self-assembled nanostructure in glass has made it possible to store data in fused silica. The technology of 5D optical data storage in transparent materials paves a promising way to almost unlimited lifetime data storage for future cloud. The phase-only SLM has already shown its potential for this application in tailoring ultrafast lasers writing beam for optical data storage. In data writing process, a light filed of target data pattern (multi-beam arrays) with target linear polarization state is required to encode information onto the nanograting structure created by laser pulses. In data writing beam generation, phase-only LCOS SLM can generate arbitrary data pattern by using diffractive holographic imaging. However, the polarization control of output image is still achieved by using an external polarization modulator. This leads to the complication, bulkiness, and large delay in current methods. Therefore, this research aims to develop a phase and polarization modulation method based on phase-only LCOS SLMs to simultaneously control both the holographic image and its polarization state. Phase-only modulation of light can tailor the output image by using computer-generated holograms onto LCOS SLMs. This is very useful for generate arbitrary multi-beam data writing light field. To fully control the polarization state of the data writing light field, the amplitude and relative phase of two orthogonal polarization components needs to be independently modulated. However, the phase-only modulation cannot directly affect the polarization of light. Therefore, three methods are proposed to achieve the phase and polarization control using LCOS SLMs. Also, two customized LCOS SLMs were designed and fabricated by using in-house-developed die-level assembly technique. They are used in all experiments of this research. First method is parallel coding and two-beam combining. Two orthogonal input beams are parallelly and independently encoded with the same target image information but with the different amplitude information by using two phase holograms on two LCOS SLMs. Then, two modulated beams are now considered as two polarization components and be spatially superposed to form target polarization state. The first-order diffraction efficiency change controlled by using phase modulation depth on hologram is used to design a technique to encode amplitude information onto the hologram. This technique is used in all three methods for amplitude modulation of polarization components. This method requires high precision alignment process in beam combining. In the second method, to avoid beam combining in polarization control, instead of modulating two beams, the object of modulation is changed to two polarization components of a single input beam. By using the characteristic of polarization sensitivity of phase-only LCOS SLM, two polarization components of single beam are sequentially and independently coded with information target image and amplitude using two LCOS SLMs. Because the spatial status to components of single beam remain unchanged in the modulation, the phase and polarization control is achieved automatically. The third method is a compact system using only single LCOS SLM device. The principle of this method is two polarization components coding like in the second method, but the fundamental difference is in a polarization components rotation technique in compact system. Using this polarization rotation technique, two light components can be independently coded by separately using two holograms on the two halves of LCOS SLM. The prototype of the compact system is developed and fabricated, and the effectiveness of the system has been experimentally verified. To sum up, the phase and polarization modulation methods based on LCOS SLM has been explored and developed. They can provide dynamical control of both polarization sate and image of light field using only LCOS. The proposed methods can provide a more promising way to largely increase the data writing speed in the 5D optical data storage technology.

The iterative Fourier transform algorithm (IFTA) is widely used in various optical communication applications based on liquid crystal on silicon spatial light modulators. However, the traditional iterative method has many disadvantages, such as a poor effect, an inability to select an optimization direction, and the failure to consider zero padding or phase quantization. Moreover, after years of development, the emergence of various variant algorithms also makes it difficult for researchers to choose one. In this paper, a new intelligent hybrid algorithm that combines the IFTA and differential evolution algorithm is proposed in a novel way. The reliability of the proposed algorithm is verified by beam splitting, and the IFTA and symmetrical IFTA algorithms, for comparison, are introduced. The hybrid algorithm improves the defects above while considering the zero padding and phase quantization of a computer-generated hologram, which optimizes the directional optimization in the diffraction efficiency and the fidelity of the output beam and improves the results of these two algorithms. As a result, the engineers’ trouble in the selection of an algorithm has also been reduced.

For augmented reality applications, the micro display panels are generally used, as a straightforward method for display engines. But there are the light efficiency and vergence accommodation conflict problems, which affect the performance and application of the AR glasses, HMD and HUDs. One way to solve the problem is to use holography display instead of direct display, which exploit the diffraction light instead of reflection light of the liquid crystal panel. One of the big problems is the form factor of holographic systems which use SLM. Most of current SLMs are composed of a driver board with FPGA and a liquid crystal on silicon panel. The FPGA driver board is big and very power consuming, which makes it better for general SLM systems that cares more about changing the driving algorithm flexibly rather than make it a wearable gadget. A compact SLM system is designed specifically for AR applications, which replaced the normally used FPGA system with a driver IC and greatly reduce they whole system size and power consumption while realize the same function for holographic display. The driver IC could receive the RGB signal or MIPI signal and transform the standard picture signal to a high frame rate color sequential signal, also the gray scale could be tuned through on chip registers either beforehand or instantly, which makes it good for liquid crystals working in different wavelength. The driver board is 2*6 cm2 with a type-C connector which could easily transmit image data from a laptop or a cellphone. This form factor is almost the same with monocular glasses. The power consumption of the driver IC is around 250mW for the driver IC comparing to the normally 5W power of FPGAs. Also, the frame rate could be from 60 to 120 Hz. A simple Fourier holography optical system is used to demonstrate the holographic display, with a lens tear apart from a smart glass on the market. The 3D holographic is displayed in the lens.

Phase flicker can degrade the performance of holographic applications at the device and application levels. On the device side, the meaningful phase modulation resolution is proved to be limited by the overlapping between adjacent phase levels caused by flicker. Here, the tolerance of the overlapping for different modulation levels is provided. The frame rate of the device is also constrained by the phase flicker. The balance between low flicker and fast LC response for fast frame rate is quantitatively analyzed. On the application side, the effects of real phase flicker on the performance of blazed gratings and image holograms are investigated using the temporal phase flicker profiles measured from a phase-only liquid crystal on silicon (LCOS) device; they are shown to be comparable with that introduced by quantization level and amplitude noise, respectively.

Optical see-through head-mounted displays are actively developed in recent years. An appropriate method for mutual occlusion is essential to provide a decent user experience in many application scenarios of augmented reality. However, existing mutual occlusion methods fail to work well with a large field of view (FOV). In this Letter, we propose a double-parabolic-mirror structure that renders hard-edge occlusion within a wide FOV. The parabolic mirror increases the numerical aperture of the system significantly, and the usage of paired parabolic mirrors eliminates most optical aberrations. A liquid crystal on silicon device is introduced as the spatial light modulator for imaging a bright see-through view and rendering sharp occlusion patterns. A loop structure is built to eliminate vertical parallax. The system is designed to obtain a maximum monocular FOV of H 114 ∘ × V 95 ∘ with hard-edge occlusion, and a FOV of H 83.5 ∘ × V 53.1 ∘ is demonstrated with our bench-top prototype.

We present the design for a bidirectional coherent optical Rectifying Linear Unit (ReLU) device capable of phase thresholding and appropriately rectifying forward-propagating optical-neuron activity and gating optically back-propagating error that will enable the construction of an all-optical deep learning system. The ReLU device can be fabricated in large arrays using high-speed liquid-crystal-on-Silicon (LCoS) smart-pixel technology capable of implementing arrays of feature planes needed for convolutional neural networks. Interferometric detection of the phase of a split-off fraction of the forward-propagating neuron input is used to set the state of the bidirectional switch and gate both the rest of the forward-propagating neuron input as well as the back-propagating error signals. We show how the array of convolutional adaptive interconnections needed for deep learning can be physically implemented and learned in an all-optical multistage dynamic holographically-interconnected architecture using lenslet arrays addressing thick Fourier-plane dynamic holograms. This optical architecture is self-aligned, phase-calibrated, and aberration compensated by using phase-conjugate mirrors to record the dynamic-holographic interconnections in each layer. This system has the potential to achieve a computational throughput approaching that of supercomputer clusters at a much lower energy cost by synergistically combining the analog computational properties of coherent Fourier optics with the hardware fault-tolerance provided by error-driven deep-learning algorithms.

Liquid crystal on-silicon (LCoS) display is one of the most representative micro-display technologies, and is widely adopted in virtual reality (VR) and augmented reality (AR) devices thanks to a relatively simple structure using a semiconductor manufacturing process to realize high-resolution displays. However, the structural complexity to handle color frames by field sequential color (FSC) scheme hinders more widespread adoptions of the LCoS displays. In this article, to resolve the problem, we propose a novel FSC driver architecture using resistive random access memory (ReRAM) that diminishes the driver's structural complexity with matrix-vector multiplications. The proposed architecture leverages fast matrix-vector multiplications with a memristor crossbar array to expedite the FSC operation that extracts the individual red, green, and blue color sub-frames from an entire image. We present the hardware performance of our architecture that is implemented using the crossbar array and peripheral circuits. Compared to the conventional static random access memory (SRAM)-based architecture, we confirm that the proposed design is much superior in terms of chip size, leakage power, and frame rate in various image resolutions. Specifically, the chip size and leakage power are reduced by up to 96% and 99%, respectively, and the frame rate is improved by up to 36%. We also analyze image quality loss caused by ReRAM read and write noise.

As compared with the traditional back surface field (BSF) solar cells, the n -type passivated emitter rear and totally diffused rear-junction ( n -PERT-RJ) solar cells have much lower carrier recombination losses on their rear sides. In order to obtain more benefits (higher open-circuit voltages) from the currently passivated rear sides, the implementation of the point contact concept is an intuitive solution. In this article, we present industrial screen-printed point contacts that are metallized with aluminum (Al) pastes containing silicon additives (Si-add). To understand the impacts of the Si-add on the performance our n -PERT-RJ solar cells, the detailed loss analysis on the open-circuit voltage ( $V_{OC}$ ), short-circuit current density ( $J_{SC}$ ), and fill factor are performed separately. The effect of Si-add and pitch of laser contact openings (LCO) on the point contact characteristics are also investigated. In the last part, we introduce an innovative “point-line” contact concept on the rear side, which is composed of dot-shaped LCO and Al metal finger design, resulting in an n -PERT-RJ solar cell to reach $V_{OC}$ of 692 mV and peak efficiency of 22%. The 60% bifaciality of the device opens the way for an additional power output on module level, which further reduces the levelized cost of electricity. These features make the rear-side point contact design more flexible to be applied in industrial mass production.

We propose and experimentally demonstrate a 16-channel flexible optical passband filter array for colorless, directionless, contentionless, flexible reconfigurable optical add/drop multiplexer. Utilizing high-resolution diffraction grating for wavelength dispersion and liquid crystal on silicon for wavelength modulation, the filter array can realize adding/dropping 16 independent optical channels with tunable bandwidth and center wavelength. Furthermore, each channel is capable of tuning multiple wavelengths with different bandwidths. The proposed filter array realized remarkable performance, such as less than 6dB insertion loss, 50GHz to 5000GHz bandwidth tuning range, transmission bandwidth covering the full C band, and greater than 30dB optical isolation among the channels.

Liquid crystal on silicon (LCoS) based spatial light modulator (SLM) is widely used in many research areas, such as holography display, optical measurement, and optical tweezers, due to its programmable capability of phase modulation. However, a certain aberration term to the incident wavefront is introduced due to the spatial nonuniformity of the LCoS backplane, and the correction of this phase aberration is important to improve the accuracy of phase modulation by the SLM, which will then influence the SLM applications, e.g., the image quality in holography display, or the beam shaping for optical tweezers and free-space communications. Fortunately, the LCoS based SLM has the programmable capability of phase modulation; therefore, the spatial nonuniformity can be compensated by a wavefront correction. Conventionally, this aberration is corrected by adjusting the Zernike coefficients of the generated wavefront manually. However, this procedure is time-consuming and subjective, since there are dozens of coefficients to be adjusted, and the adjustment is evaluated manually by monitoring the interferogram. In this paper, we propose to use several phase retrieval techniques to measure the corresponding wavefront directly and employ the obtained wavefront to correct the aberration introduced by the spatial nonuniformity. A Twyman-Green interferometry is used, and an interferogram acquisition technique based on the self wavefront modulation of SLM is proposed. Besides, a method for determining the corresponding active area of the LCoS backplane and parameters of 2-D projective transformation is proposed to transform the active area to the fitted resolution of the SLM. RMS value of the aberration to approximately λ/32 can be obtained by the proposed method. Consequently, more accurate phase modulation by SLM for applications such as holography display and beam shaping is achievable. Effectiveness of the proposed method is validated by experiment, and the correction results by different phase retrieval techniques are evaluated and compared.