Snapshot ptychography on array cameras.

We use convolutional neural networks to recover images optically down-sampled by 6.7 × using coherent aperture synthesis over a 16 camera array. Where conventional ptychography relies on scanning and oversampling, here we apply decompressive neural estimation to recover full resolution image from a single snapshot, although as shown in simulation multiple snapshots can be used to improve signal-to-noise ratio (SNR). In place training on experimental measurements eliminates the need to directly calibrate the measurement system. We also present simulations of diverse array camera sampling strategies to explore how snapshot compressive systems might be optimized.

Modeling and characterization of OASIS inflatable primary antenna by dual modality metrology.

OASIS (Orbiting Astronomical Satellite for Investigating Stellar Systems) is a space-based observatory with a 14 m diameter inflatable primary antenna that will perform high spectral resolution observations at terahertz frequencies. The large inflatable aperture, non-traditional surface configuration, and the double layered membrane structure afford unique challenges to the modeling and testing of the primary antenna. A 1-meter prototype of the primary antenna (A1) was built to validate our technical approach. A laser radar coordinate measuring system was adopted to measure the shape of A1. In addition, deflectometry was performed to monitor the stability of A1 during the radar measurement. Test cases pertaining to specific operational conditions expected for the 14 m OASIS primary were explored. The measured data were then compared to the Fichter model and Finite-element Analyzer for Inflatable Membranes (FAIM).

Holographic display having a wide viewing zone using a MEMS SLM without pixel pitch reduction.

A one-micron pixel pitch is believed to be required for spatial light modulators (SLMs) to realize holographic displays possessing a wide viewing zone. This study proposes the use of a microelectromechanical systems (MEMS) SLM for not only displaying holographic patterns but also scanning laser beam. During the rotation of MEMS mirrors in the MEMS SLM, the timing of laser pulses illuminating the MEMS SLM is controlled to change the reflection direction of light modulated by the MEMS SLM in order to enlarge the viewing zone. In this technique, the width of the viewing zone depends on the rotation angle of MEMS mirrors, and not on the pitch of pixels (MEMS mirrors). We experimentally demonstrated the enlargement of the viewing zone angle to ∼40° using the MEMS SLM with a pixel pitch of 13.68 µm.

Single-chip holographic beam steering for lidar by a digital micromirror device with angular and spatial hybrid multiplexing.

A digital micromirror device (DMD) based holographic beam steering technique is reported that multiplexes fine-steering binary amplitude gratings with a coarse-steering programmable blazed grating. The angular spatial light modulation (ASLM) technique encodes the spatial pattern of the binary amplitude grating at the same plane as the angular modulation set by a phase map of the DMD-based beam steering technique. The beam steering technique is demonstrated at 532 nm and implemented into a 905 nm lidar system. The results of the lidar system tests are presented, achieving a 44° field-of-view, 0.9°×0.4° (H×V) angular resolution, 1 m max distance, 1.5 kHz sampling, and 7.8 FPS video. Scalability techniques are proposed, including max distance increases to over 100 m.

Gigapixel and 1440-perspective extended-angle display by megapixel MEMS-SLM.

Orders-of-magnitude increases are desired in the pixel count and density of spatial light modulators (SLMs) for next-gen displays. We present in-plane and simultaneous angular-spatial light modulation by a micro electro mechanical system (MEMS)-based SLM, a digital micromirror device (DMD), to generate gigapixel output by time and angular multiplexing. Pulsed illumination synchronized to the micromirror actuation achieves pixel-implemented and diffraction-based angular modulation, and source multiplexing increases angular selectivity. We demonstrate 1440-perspective image output across a 43.9∘×1.8∘ FOV, 8-bit multi-perspective videos at 30 FPS, and multi-focal-plane image generation. We discuss scalability to terapixels and implications for near-to-eye displays.

Occlusion-capable optical-see-through near-eye display using a single digital micromirror device.

Occlusion of a real scene by displayed virtual images mitigates incorrect depth cues and enhances image visibility in augmented reality applications. In this Letter, we propose a novel optical scheme for the occlusion-capable optical-see-through near-eye display. The proposed scheme uses only a single spatial light modulator, as the real-scene mask and virtual image display simultaneously. A polarization-based double-pass configuration is also combined, enabling a compact implementation. The proposed scheme is verified by optical experiments which demonstrate a 60 Hz red-green-blue video display with a 4-bit depth for each color channel and per-pixel dynamic occlusion of a 90.6% maximum occlusion ratio.

Fast laser beam steering into multiple diffraction orders with a single digital micromirror device for time-of-flight lidar.

The sampling rate and angular resolution of diffraction-based beam steering employing a digital micromirror device (DMD) can be simultaneously enhanced by at least an order of magnitude by synchronizing multiple nanosecond laser sources and pulses during each DMD actuation. A time-of-flight single-chip DMD lidar with three sources measures a range at a 3.34 kHz sampling rate and a 3.4° angular resolution across a 48° field of view. Employing multiple diffraction orders of the DMD improves the sampling rate at least by a factor of 2 and up to the number of diffraction orders supported by the DMD. An improved sampling rate of 6.68 kHz with a 9.6° angular resolution is experimentally demonstrated by illuminating micromirrors multiple times within a single transition period of the micromirrors.

Wide-angle MEMS-based imaging lidar by decoupled scan axes.

We present an optical architecture for a scanning lidar in which a digital micromirror device (DMD) is placed at an intermediate image plane in a receiver to decouple the trade-offs between scan angle, scan speed, and aperture size of the lidar's transmitter and receiver. In the architecture, the transmitter with a galvo mirror and the receiver with a DMD scan the horizontal and vertical fields of view, respectively, to enable an increased field of view of 50°, centimeter transmitter beam diameter, and video frame rate range finding captures. We present our optimized system and discuss the adjustable parameter trade-offs.

Angular and spatial light modulation by single digital micromirror device for multi-image output and nearly-doubled étendue.

The "Angular Spatial Light Modulator" (ASLM) achieves simultaneous angular and spatial light modulation at a plane by combining Digital Micromirror Device (DMD) based programmable blazed grating beam steering and binary pattern sequencing. The ASLM system multiplies the number of effective output pixels of the DMD for increased spatial and/or angular degrees of freedom, and nearly-doubles the étendue output of the DMD. We implement multiple illumination and projection schemes to demonstrate ASLM-based extended FOV display, light-field projection, and multi-view display. We also implement time-multiplexed pupil segmented illumination to extend the pattern steering to two dimensions.

Design of discretely depth-varying holographic grating for image guide based see-through and near-to-eye displays.

For the see-through and near-to-eye displays, light throughput and uniformity of luminance over the field of view are improved by employing an optical image guide with discretely depth-varying surface relief holographic gratings. In the design process, a newly developed mathematical model, in conjunction with rigorous coupled wave analysis of diffraction efficiency, eliminates massive and time consuming iteration of non-sequential ray tracing but rapidly identifies the depth-varying structure and optimum optical performance. The depth-varying grating based approach achieved a 1.37x improvement in light throughput compared to the conventional depth un-varying design, 315 cd/m2/lm, along with improved uniformity over the field of view of 35 (H) x 20 (V) degrees with an eye box size of 17 (H) x 14 (V) mm.

Single chip lidar with discrete beam steering by digital micromirror device.

A novel method of beam steering enables a large field of view and reliable single chip light detection and ranging (lidar) by utilizing a mass-produced digital micromirror device (DMD). Using a short pulsed laser, the micromirrors' rotation is frozen in mid-transition, which forms a programmable blazed grating. The blazed grating efficiently redistributes the light to a single diffraction order, among several. We demonstrated time of flight measurements for five discrete angles using this beam steering method with a nano second 905nm laser and Si avalanche diode. A distance accuracy of < 1 cm over a 1 m distance range, a 48° full field of view, and a measurement rate of 3.34k points/s is demonstrated.

Fast fabrication of polymer out-of-plane optical coupler by gray-scale lithography.

We report a fabrication process of a polymer, and mirror-based out-of-plane optical coupler. In the process, a pre-formed mirror blank made of a buffer coat material is re-exposed by a laser direct writing tool with low numerical aperture of 0.1. The fabrication process is inherently fast because of the low numerical aperture (NA) process. The surface figure of the mirror is controlled under 0.04 waves in root-mean-square (RMS) at 1.55 µm wavelength, with mirror angle of 45 ± 1 degrees. Nominal insertion loss of 8.5dB of the mirror-based coupler was confirmed with polymer waveguides fabricated simultaneously.

Cavity-enhanced eigenmode and angular hybrid multiplexing in holographic data storage systems.

Resonant optical cavities have been demonstrated to improve energy efficiencies in Holographic Data Storage Systems (HDSS). The orthogonal reference beams supported as cavity eigenmodes can provide another multiplexing degree of freedom to push storage densities toward the limit of 3D optical data storage. While keeping the increased energy efficiency of a cavity enhanced reference arm, image bearing holograms are multiplexed by orthogonal phase code multiplexing via Hermite-Gaussian eigenmodes in a Fe:LiNbO3 medium with a 532 nm laser at two Bragg angles. We experimentally confirmed write rates are enhanced by an average factor of 1.1, and page crosstalk is about 2.5%. This hybrid multiplexing opens up a pathway to increase storage density while minimizing modification of current angular multiplexing HDSS.

Cavity techniques for holographic data storage recording.

Conventionally, reading and writing of data holograms utilizes a fraction of the light power because of a trade off in write and read efficiencies. This system constraint can be mitigated by applying a resonator cavity. Cavities enable more efficient use of the available light leading to enhanced read and write data rates with no additional energy cost. This enhancement is inversely related to diffraction efficiency, so these techniques work well for large capacity holographic data storage having low diffraction efficiency. The enhancement in write data transfer rate is evaluated by writing plane wave holograms and image bearing holograms in Fe:LiNbO3 with a 532 nm wavelength laser. We confirmed 1.2 times enhancement in write data rate, out of a 1.4 theoretical maximum for materials absorption of 16%.

Evaluation of channel capacities of OAM-based FSO link with real-time wavefront correction by adaptive optics.

We have evaluated the channel capacity of OAM-based FSO link under a strong atmospheric turbulence regime when adaptive optics (AO) are employed to correct the wavefront phase distortions of OAM modes. The turbulence is emulated by the Monte-Carlo phase screen method, which is validated by comparison with the theoretical phase structure function. Based on that, a closed-loop AO system with the capability of real-time correction is designed and validated. The simulation results show that the phase distortions of OAM modes induced by turbulence can be significantly compensated by the real-time correction of the properly designed AO. Furthermore, the crosstalk across channels is reduced drastically, while a substantial enhancement of channel capacity can be obtained when AO is deployed.

Diffraction Efficiency of MEMS Phase Light Modulator, TI-PLM, for Quasi-Continuous and Multi-Point Beam Steering.

The recent development of the Micro Electromechanical System (MEMS) Phase Light Modulator (PLM) enables fast laser beam steering for lidar applications by displaying a Computer-Generated Hologram (CGH) without employing an iterative CGH calculation algorithm. We discuss the application of MEMS PLM (Texas Instruments PLM) for quasi-continuous laser beam steering by deterministically calculated CGHs. The effect on the diffraction efficiency of PLM non-equally spaced phase levels was quantified. We also address the CGH calculation algorithm and an experimental demonstration that steered and scanned the beam into multiple regions of interest points, enabling beam steering for lidar without sequential raster scanning.

Optical Enhancement of Diffraction Efficiency of Texas Instruments Phase Light Modulator for Beam Steering in Near Infrared.

Phase light modulator (PLM) by MEMS mirror array operating in a piston-mode motion enables a high-speed diffractive beam steering in a random-access and flexible manner that makes a lidar system more intelligent and adaptive. Diffraction efficiency is determined by the range of the piston motion of the MEMS array; consequently, a larger range of the piston motion is required for beam steering in infrared, such as for lidar. We demonstrated how the range of the piston motion is optically enhanced by a factor of two with a light-recycling optics based on Talbot self-imaging. The proposed optical architecture extends the usable range of the wavelength so that a MEMS-PLM designed for visible wavelength is applicable for a high-efficiency beam steering at an infrared wavelength of 1550 nm with an improved diffraction efficiency of 30%.

Real-Time CGH Generation by CUDA-OpenGL Interoperability for Adaptive Beam Steering with a MEMS Phase SLM.

Real-time, simultaneous, and adaptive beam steering into multiple regions of interest replaces conventional raster scanning with a less time-consuming and flexible beam steering framework, where only regions of interest are scanned by a laser beam. CUDA-OpenGL interoperability with a computationally time-efficient computer-generated hologram (CGH) calculation algorithm enables such beam steering by employing a MEMS-based phase light modulator (PLM) and a Texas Instruments Phase Light Modulator (TI-PLM). The real-time CGH generation and display algorithm is incorporated into the beam steering system with variable power and scan resolution, which are adaptively controlled by camera-based object recognition. With a mid-range laptop GPU and the current version of the MEMS-PLM, the demonstrated scanning speed can exceed 1000 points/s (number of beams > 5) and potentially exceeds 4000 points/s with state-of-the-art GPUs.

All-MEMS Lidar Using Hybrid Optical Architecture with Digital Micromirror Devices and a 2D-MEMS Mirror.

In a lidar system, replacing moving components with solid-state devices is highly anticipated to make a reliable and compact lidar system, provided that a substantially large beam area with a large angular extent as well as high angular resolution is assured for the lidar transmitter and receiver. A new quasi-solid-state lidar optical architecture employs a transmitter with a two-dimensional MEMS mirror for fine beam steering at a fraction of the degree of the angular resolution and is combined with a digital micromirror device for wide FOV scanning over 37 degree while sustaining a large aperture area of 140 mm squared. In the receiver, a second digital micromirror device is synchronized to the transmitter DMD, which enables a large FOV receiver. An angular resolution of 0.57°(H) by 0.23° (V) was achieved with 0.588 fps for scanning 1344 points within the field of view.

Ultra-high resolution resonant C-shaped aperture nano-tip.

We report a new optical near-field transducer comprised of a metallic nano-antenna extending from the ridge of a C-shaped metallic nano-aperture. Finite-difference time domain simulations predict that the C-aperture nano-tip (CAN-Tip) provides high intensity (650x), high optical resolution (~λ/60), and background-free near-field illumination at a wavelength of 980 nm. The CAN-Tip has an aperture resonance and tip antenna resonance which may be tuned independently, so the structure can be made resonant at ultraviolet wavelengths without being unduly small. This near-field optical resolution of 16.1 nm has been experimentally confirmed by employing the CAN-Tip as an NSOM probe.