A 256 x 256 single photon avalanche diode (SPAD) sensor integrated in a 3D-stacked 90nm 1P4M/40nm 1P8M process is reported for flash light detection and ranging (LIDAR) or high speed direct time of flight (ToF) 3D imaging. The sensor bottom tier is composed of a 64x64 matrix of 36.72 m pitch modular photon processing units which operate from shared 4x4 SPADs at 9.18 m pitch and 51% fill-factor. A 16 x 14-bit counter array integrates photon counts or events to compress data to 31.4 Mbps at 30 fps readout over 8 I/O operating at 100 MHz. The pixel-parallel multi-event TDC approach employs a programmable internal or external clock for 0.56 ns to 560 ns time bin resolution. In conjunction with a perpixel correlator, the power is reduced to less than 100 mW in practical daylight ranging scenarios. Examples of ranging and high speed 3D TOF applications are given. Index Terms-3-D imaging, CMOS, direct time of flight (dTOF), histogramming, image sensor, light detection and ranging (LiDAR), single photon avalanche diodes (SPADs), time-to-digital converter (TDC), TDC sharing architecture, TOF.

Nonlinear optical devices and their implementation into modern nanophotonic architectures are constrained by their usually moderate nonlinear response. Recently, epsilon-near-zero (ENZ) materials have been found to have a strong optical nonlinearity, which can be enhanced through the use of cavities or nano-structuring. Here, we study the pump dependent properties of the plasmon resonance in the ENZ region in a thin layer of indium tin oxide (ITO). Exciting this mode using the Kretschmann-Raether configuration, we study reflection switching properties of a 60 nm layer close to the resonant plasmon frequency. We demonstrate a thermal switching mechanism, which results in a shift in the plasmon resonance frequency of 20 THz for a TM pump intensity of 70 GW cm−2. For degenerate pump and probe frequencies, we highlight an additional two-beam coupling contribution, not previously isolated in ENZ nonlinear optics studies, which leads to an overall pump induced change in reflection from 1% to 45%.

Imaging systems with temporal resolution play a vital role in a diverse range of scientific, industrial, and consumer applications, e.g., fluorescent lifetime imaging in microscopy and time-of-flight (ToF) depth sensing in autonomous vehicles. In recent years, single-photon avalanche diode (SPAD) arrays with picosecond timing capabilities have emerged as a key technology driving these systems forward. Here we report a high-speed 3D imaging system enabled by a state-of-the-art SPAD sensor used in a hybrid imaging mode that can perform multi-event histogramming. The hybrid imaging modality alternates between photon counting and timing frames at rates exceeding 1000 frames per second, enabling guided upscaling of depth data from a native resolution of 64 × 32 to 256 × 128 . The combination of hardware and processing allows us to demonstrate high-speed ToF 3D imaging in outdoor conditions and with low latency. The results indicate potential in a range of applications where real-time, high throughput data are necessary. One such example is improving the accuracy and speed of situational awareness in autonomous systems and robotics.

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An ultra-compact 1.4mm×1.4mm, 128×120 SPAD image sensor with a 5-wire interface is designed for time-resolved fluorescence microendoscopy. Dynamic range (DR) is extended by noiseless frame summation in SRAM attaining 126dB time resolved imaging at 15fps with 390ps gating resolution. The sensor SoC is implemented in STMicroelectronics 40nm/90nm 3D-stacked BSI CMOS process with 8µm pixels and 45% fill factor.