Fig. 1. Non-line-of-sight (NLOS) imaging aims at recovering the shape and albedo of objects hidden from a camera or a light source. Using ultra-fast pulsed illumination and single photon detectors, the light transport in the scene is sampled for visible objects (left). The global illumination components of these time-resolved measurements (A,E) contain sufficient information to estimate the shape of hidden objects (B,C). Using a novel formulation for NLOS light transport that models partial occlusions of hidden objects (D) via visibility terms (F), we demonstrate higher-fidelity reconstructions (C) than previous approaches to NLOS imaging (B).Imaging objects obscured by occluders is a significant challenge for many applications. A camera that could "see around corners" could help improve navigation and mapping capabilities of autonomous vehicles or make search and rescue missions more effective. Time-resolved single-photon imaging systems have recently been demonstrated to record optical information of a scene that can lead to an estimation of the shape and reflectance of objects hidden from the line of sight of a camera. However, existing nonline-of-sight (NLOS) reconstruction algorithms have been constrained in the types of light transport effects they model for the hidden scene parts. We introduce a factored NLOS light transport representation that accounts for partial occlusions and surface normals. Based on this model, we develop a factorization approach for inverse time-resolved light transport and demonstrate high-fidelity NLOS reconstructions for challenging scenes both in simulation and with an experimental NLOS imaging system.

Silicon single-photon avalanche detectors are becoming increasingly significant in research and in practical applications due to their high signal-to-noise ratio, complementary metal oxide semiconductor compatibility, room temperature operation, and cost-effectiveness. However, there is a trade-off in current silicon single-photon avalanche detectors, especially in the near infrared regime. Thick-junction devices have decent photon detection efficiency but poor timing jitter, while thin-junction devices have good timing jitter but poor efficiency. Here, we demonstrate a light-trapping, thin-junction Si single-photon avalanche diode that breaks this trade-off, by diffracting the incident photons into the horizontal waveguide mode, thus significantly increasing the absorption length. The photon detection efficiency has a 2.5-fold improvement in the near infrared regime, while the timing jitter remains 25 ps. The result provides a practical and complementary metal oxide semiconductor compatible method to improve the performance of single-photon avalanche detectors, image sensor arrays, and silicon photomultipliers over a broad spectral range.

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We experimentally demonstrate a broadband electro-absorption modulator exploiting indium tin oxide (ITO) as the active switching material. Si strip waveguides are fabricated and covered with 8 nm of HfO2 and 15 nm of ITO to form metal-oxide-semiconductor capacitor (MOS-C) based modulators. The mobile carrier density in the ITO film is controlled using a postanneal treatment to tune its permittivity ε to a near-zero value at the operation wavelength of 1550 nm. Using simulations and experiments, we demonstrate that realizing an epsilon-near-zero (ENZ) can enhance the modulation performance as it increases the overlap of the guided mode with the active ITO layer. We then show even greater benefits of this approach with Si waveguides featuring a central slot filled with ITO. Leveraging the ENZ effect, we achieve a notable 3 dB modulation depth of optical signals in a nonresonant waveguide structure with a length of 20 μm. The results provide insight into the design of very compact modulators for chip-scale optical links.

An Er/Yb silicate strip loaded waveguide was fabricated for optical amplification purpose. A 2.4-lm-wide SiO 2 strip was deposited on top of the Er/Yb silicate active layer. Experiment data showed a 5.5 dB signal enhancement in a 7.8-mm-long waveguide pumped by a laser of 372 mW at 1480 nm. The signal is not saturated and can be further enhanced by increasing pumping power and decreasing waveguide loss. The strong red light emission at 660 nm was also observed due to excited state absorption and Yb 3þ participated energy transfer upconversion processes.

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With the advent of autonomous vehicles imminent, a solid-state approach to beam steering is necessary for more affordable lidar tracking systems. Capable of dynamic control of light with subwavelength components, electrically tunable metamaterials show potential in this field as well as other applications. Here, we demonstrate a nanopillar-based metamaterial composed of Ge and Al-doped ZnO (AZO), whose optical properties can be modulated by the field effect and whose fabrication process is compatible with complementary metal-oxide-semiconductor (CMOS) technology. From reflectance spectra, wavelength shifts up to 240 nm of the optical resonances are measured in our fabricated device with gate biases from −4 to 4 V. A high differential reflectance of more than 40% in this voltage range is experimentally shown. Then, through an effective medium approximation, we can describe the nanopillar array as a macroscopic metamaterial and calculate the phase shift of this device. With optimization of the nanopillar parameters, a large phase modulation approaching 270°is possible according to simulations, which is promising for beam steering applications.

Silicon single-photon avalanche diodes (SPADs) are core devices for single-photon detection in the visible and the near-infrared wavelength range and are widely used in many fields such as astronomy, biology, lidar, quantum optics, and quantum information. Due to limitations in their structural design and fabrication, however, the key parameters of detection efficiency and timing jitter cannot be optimized simultaneously. Here, we propose a nanostructured silicon SPAD that achieves high detection efficiency with excellent timing jitter over a broad spectral range. Our optical and electrical simulations show significant performance enhancement compared to conventional silicon SPAD devices. This nanostructured device can be easily fabricated and is thus well suited for practical applications.