Ming C. Wu

University of California, Berkeley | UCB · Computer Science Division

Self-training is an important technique for solving semi-supervised learning problems. It leverages unlabeled data by generating pseudo-labels and combining them with a limited labeled dataset for training. The effectiveness of self-training heavily relies on the accuracy of these pseudo-labels. In this paper, we introduce doubly robust self-traini...

Leveraging multi-modal fusion, especially between camera and LiDAR, has become essential for building accurate and robust 3D object detection systems for autonomous vehicles. Until recently, point decorating approaches, in which point clouds are augmented with camera features, have been the dominant approach in the field. However, these approaches...

Three-dimensional (3D) imaging sensors allow machines to perceive, map and interact with the surrounding world1. The size of light detection and ranging (LiDAR) devices is often limited by mechanical scanners. Focal plane array-based 3D sensors are promising candidates for solid-state LiDARs because they allow electronic scanning without mechanical...

A one-dimensional focusing grating coupler array based in silicon nitride (SiN) was proposed for trapped ion qubit manipulation. By applying inverse design optimization with a double-etched grating structure, a directionality of 98% was achieved. A small beam diameter of 2.5 µm on the target ion with a low crosstalk of -36 dB was attained. Addition...

We report on 32x32 silicon photonic switches realized through wafer bonding. Broadband operation is demonstrated over 1260-1320 nm range. The maximum on-chip loss is measured to be 4 dB and the cross-talk is -80 dB.

A fabrication tolerant Si grating coupler for 1.762 µm operation is optimized with inverse design, allowing for −30 dB crosstalk between a pair of ¹³³ Ba ⁺ trapped ion qubits within expected fabrication variation.

The III–V InP/InGaAsP/InGaAs material family is important for photonic devices due to its optical emission and absorption in the 1.55 and 1.3 μm telecommunication bands for optical interconnects. However, InGaAsP/InGaAs generally suffer from relatively high surface recombination velocity—compared to Si [Das et al., in 2020 47th IEEE Photovoltaic Sp...

Photonic delay-based reservoir computers (RC) have emerged as an attractive high-speed, low-power alternative to traditional digital hardware for AI. We demonstrate experimentally a novel hybrid RC scheme in which input data is first preprocessed through several convolutional layers, either trained or untrained, digitally to generate novel feature...

The rate of spontaneous emission from an optical emitter can be greatly enhanced using a metallic optical antenna at the penalty of efficiency. In this paper we propose a metal-dielectric antenna that eliminates the tradeoff between spontaneous emission enhancement and radiative efficiency by using nanoscopic dielectric structures at the antenna ti...

We report on 128×128-element two-dimensional silicon photonics focal plane switch arrays with microelectromechanical-system optical switches for random-access optical beam steering. A 70°×70° field-of-view and sub-MHz steering speed are experimentally demonstrated.

We report on novel dual-layer grating couplers that support polarization diversity in silicon photonics. High coupling efficiency (-0.22 dB or 95.1%) and low polarization dependence (0.1 dB) have been realized through inverse design.

We present a novel photonic integrated circuit (PIC) that monolithically integrates a racetrack colliding-pulse mode-locked laser with a pulse-picking electro-absorption modulator and a semiconductor optical amplifier on Indium Phosphide. We present detailed characterization of this PIC that includes optical pulse characterization, phase noise and...

We present a two-dimensional random-access optical beam steering system composed of a 20x20 focal plane switch array integrated on a silicon photonics chip with microelectromechanical-system (MEMS) optical switches. 32°x32°field-of-view is demonstrated.

We report on monolithically integrated wavelength cross-connects (WXCs) on an enhanced silicon photonic platform with integrated micro-electro-mechanical-system (MEMS) actuators. An 8 × 8 WXC with 8 wavelength channels comprising 16 echelle gratings and 512 silicon photonic MEMS switches is integrated on a 9.7 mm × 6.7 mm silicon chip. The WXC inhe...

Silicon photonics is a rapidly maturing platform for optical communication and sensing. As systems leveraging silicon photonics have grown in size and complexity, so too has the demand for high performance silicon photonics components. In order to meet these demands, we propose a hierarchical approach to design and optimization of silicon photonics...

Transition metal dichalcogenide (TMDC) monolayers are promising materials for next-generation nanoscale optoelectronics, including high-speed light sources and detectors. However, most past reports on TMDC light-emitting diodes are limited to operation in high vacuum, while most applications require operation under ambient conditions. In this work,...

Efficient high-speed nanoscale optical sources are required for low-power next-generation data communication. Here we propose an integrated antenna-LED on a single-mode optical waveguide. By leveraging inverse design optimization, we achieved a waveguide coupling efficiency of 94% and an antenna efficiency of 64%, while maintaining a high average e...

We present a design for an analog phase shifter based on Silicon Photonic MEMS technology. The operation principle is based on a two-step parallel plate electrostatic actuation mechanism to bring a vertically movable suspended tapered waveguide in a first step into proximity of the bus waveguide and to tune the phase of the propagating coupled mode...

We report on 4x20 silicon photonic MEMS switch that is capable of multicasting. The switch is built on passive optical crossbar network with gap-adjustable directional couplers. The switch has high on-off extinction ratio (59 dB), low insertion loss (< 4.0 dB), small footprint (1.2x4.5 mm²), and fast response (9.8 µs). The switching voltage is 9.6...

Miniaturization of frequency-comb sources could open a host of potential applications in spectroscopy, biomedical monitoring, astronomy, microwave signal generation, and distribution of precise time or frequency across networks. This review article places emphasis on an architecture with a semiconductor mode-locked laser at the heart of the system...

Optical-phased arrays (OPAs) enable complex beamforming, random-access beam pointing, and simultaneous scan and tracking of multiple targets by controlling the phases of two-dimensional (2D) coherent emitters. So far, no OPA can achieve all desirable features including large 2D arrays, high optical efficiency, wideband operation in wavelengths, fas...

Fast optical switches have been proposed as a promising alternative to enable continual scaling of data centers with increasing size and data rates. Silicon photonics is a compelling platform for large-scale integrated photonic switches, leveraging advanced manufacturing foundries for electronic integrated circuits. In the past decade, the port cou...

We report on a laser frequency sweep linearization method by iterative learning pre-distortion for frequency-modulated continuous-wave (FMCW) light detection and ranging (LiDAR) systems. A pre-distorted laser drive voltage waveform that results in a linear frequency sweep is obtained by an iterative learning controller, and then applied to the FMCW...

We report on 240x240 silicon photonic MEMS switches on 4cm x 4cm dies realized by wafer-scale integration and reticle stitching. The maximum on-chip loss is measured to be 9.8dB and the crosstalk is below -70dB.

We review the recent developments in large-scale silicon photonic switches, focusing on MEMS-based switches that enables high port-count (128x128), low optical loss (0.05 dB/port), low crosstalk, broadband operation, sub-microsecond response time, and low power consumption.

Optical antennas can enhance the modulation bandwidth and output power of nanoscale LEDs. Here we analyze a wavelength division multiplexer that uses high Q optical antennas in parallel to further increase the total optical power.

Low propagation loss Ge23Sb7S70 waveguides (0.56 dB/cm) are fabricated in a wafer scale process. Simulation of a 2 cm long, 1.2 μm wide waveguide with 100 ps/nm/km peak dispersion predicts coherent supercontinuum generation at 1.55 μm pump wavelength. Octave-spanning supercontinuum using a dispersive wave is experimentally demonstrated using picojo...

Optical antennas can enhance the spontaneous emission rate from nanoemitters by orders of magnitude, enabling the possibility of an ultrafast, efficient, nanoscale LED. Semiconductors would be the preferred material for such a device to allow for direct high-speed modulation. However, efficient nanoscale devices are challenging to implement because...

We demonstrate the first-ever silicon photonics enabled hyper-wideband RF spread-spectrum link. A hybrid III/V-silicon photonic mode-locked laser encoded with a four-channel silicon photonic phase encoder is used to generate optical carriers that coherently demodulate a received RF signal spanning an instantaneous bandwidth greater than 85% of the...

The cascaded integration of optical waveguides with third-order optical nonlinearity ( $\chi ^{(3)}$ susceptibilitiy) with lithium niobate (LiNbO $_{3}$ ) waveguides is demonstrated on the same chip. Thin-film (LiNbO $_{3}$ ) and chalcogenide (ChG) glass (Ge $_{23}$ Sb $_{7}$ S $_{70}$ ) waveguides are integrated on silicon (Si) substrates....

A novel injection locking architecture is demonstrated to simultaneously improve the axial mode linewidth and stabilize the repetition rate of a monolithically integrated modelocked laser. First, linewidth reduction is demonstrated via multitone injection locking. Then, the passive mode-locked laser is used as a source to make a coupled optoelectro...

Long-range shape measurement with high accuracy is needed for precision manufacturing of large-scale parts such as turbines, compressors, and trains. We have developed a high-accuracy ranging system based on frequency-modulated continuous-wave (FMCW) technology. Our system has two unique features. First, it achieves high-accuracy range measurement...

Transition-metal dichalcogenide monolayers have naturally terminated surfaces and can exhibit a near-unity photoluminescence quantum yield in the presence of suitable defect passivation. To date, steady-state monolayer light-emitting devices suffer from Schottky contacts or require complex heterostructures. We demonstrate a transient-mode electrolu...

We report on 50x50 silicon photonic MEMS switches with reduced polarization dependence. The switches make use of two-level waveguide crossbars and MEMS-actuated adiabatic couplers. Simulations indicate that by eliminating all polarization-dependent elements (e.g., waveguide crossings), low polarization-dependent losses (<1 dB) can be realized. An e...

Repetition rate stabilization of an injection locked chip-scale mode-locked laser and progress towards carrier envelope offset frequency stabilization using chalcogenide waveguides for supercontinuum generation and a bulk PPLN for second harmonic generation are presented.

A thin-film periodically-poled lithium niobate (PPLN) on silicon wavelength converter is demonstrated for application in carrier-envelope offset stabilization. Supercontinuum generation, amplified at about 1900 nm wavelength, is used to generate second harmonic generation.

The rate of spontaneous emission can be enhanced using either a metallic antenna or a dielectric cavity. Here we adapt elements of both types for a novel metallo-dielectric structure that exhibits ultra-low mode volume, Veff = 4.53 × 10−6 휆3.

128×128 silicon photonic switch with 16,384 MEMS-actuated switching elements and row/column addressing scheme have been successfully integrated on a 16×17mm2 chip. The maximum (minimum) on-chip loss is 22.7 dB (4.8 dB).

We present a two-dimensional ultra large aperture optical phase array (OPA) with 160×160 elements enabled with optical microelectromechanical system (MEMS). The random access beamsteering up to 4.4°×4.6° scanning range at 1550nm is demonstrated.

We propose a broadband and efficient structure for single-mode spontaneous emission coupling of an electrically-injected slot antenna based nanoLED. Using FDTD simulations and inverse design, we achieved 93% waveguide coupling and 50.77% spontaneous emission coupling.

We report on a fully integrated 8×8 silicon photonic MEMS wavelength-selective switch with 8 wavelength channels on a 9.7mm × 6.7mm chip. Total on-chip loss including switches and echelle grating mux/demux is 13.3 dB.

We demonstrate bright electroluminescence in WSe2 monolayers using pulsed injection, without the use of split gates, chemical doping, or heterostructures. Electroluminescence quantum efficiency approaches that of photoluminescence, indicating efficient exciton formation with injected carriers.

Exploiting mechanical movement of surface micromachined waveguides on a passive silicon photonics platform provides scalable opportunities for efficient on-chip manipulation of optical signals in complex photonic integrated circuits for future photonic networks.

3D imaging technologies are applied in numerous areas, including self-driving cars, drones, and robots, and in advanced industrial, medical, scientific, and consumer applications. 3D imaging is usually accomplished by finding the distance to multiple points on an object or in a scene, and then creating a point cloud of those range measurements. Dif...

We present a comprehensive study for a new three-branch widely tunable semiconductor laser based on a self-imaging, lossless multi-mode interference (MMI) coupler. We have developed a general theoretical framework that is applicable to all types of interferometric lasers. Our analysis showed that the three-branch laser offers high side-mode suppres...

We report on the flip chip packaging of Micro-Electro-Mechanical System (MEMS)-based digital silicon photonic switching device and the characterization results of 12 × 12 switching ports. The challenges in packaging N <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> electrical and 2N optical in...

We report on high density optical packaging of high radix (64x64) silicon photonic MEMS switches using pitch-reducing optical fiber array. The footprint of 61-channel optical I/O is as small as 330μm x 280μm.

Silicon nitride spot-size converters were fabricated in a damascene process to improve the performance of supercontinuum generation in arsenic-free chalcogenide waveguides. Supercontinuum generation covering 950–1750 nm with 200 pJ pulses is demonstrated.

We review the state of the art of silicon photonic switches, with an emphasis on their scalabilities. We also describe a high-radix MEMS-actuated silicon photonic switch that is scalable to hundreds of ports.

We report resolution enhancement for non-linear swept-source lidar sensor using quasi-synchronous resampling, a new post-processing method. We report 6mm Fourier-limited resolution at 6m distance, and improvement of single-target resolution at 6m from 27.9mm to 0.42mm.

An integrated electronic-photonic phase-locked loop (PLL) modulates the frequency of a tunable laser for use in frequency-modulated continuous-wave (FMCW) lidar 3D imaging. The proposed lidar can perform 180k range measurements per second. The rms depth precision is 8 μm at distances of ±5 cm from the range baseline. The range window is 1.4 m, with...

Large-scale photonic switches are essential devices for energy- and cost-efficient optical communication networks in cloud and data-intensive computing. Silicon photonics is an attractive platform for high-density photonic integrated circuits with low manufacturing costs through the leveraging of existing advanced complementary metal-oxide-semicond...

We demonstrate helium-ion milled gold slot antennas with controllable 20-nm gap spacing that show large scattering polarization ratios of ~37x and resonance shifts with length. Antennas with larger gaps show comparable quality to gallium-milled antennas.

Coherent lidar is reported with precision 130um and multi-target resolution 6mm. The system is based on simultaneous modulation of the in-phase and quadrature components of the transmitted optical signal and uses simplified homodyne detection.