This PDF file contains the front matter associated with SPIE Proceedings Volume 12089, including the Title Page, Copyright information, Table of Contents and Conference Committee list.

We present a 16×16 single-photon avalanche diode (SPAD) image array prototype for super-resolution imaging under photon-starved environments. To take advantage of photon sparsity, we introduce a 16-to-1 multiplexing scheme at the column level which shares the same quenching circuitry among 16 SPAD pixels. This includes column-level address encoding to support super-resolution microscopy (SRM) despite multiplexing. The quenching circuit uses a 16 input pseudo-NMOS OR gate to decrease SPAD recovery time and circuitry area. The imager array was implemented in a 180nm high-voltage CMOS process and consists of SPADs with a pixel pitch of 21.3 μm and a fill factor of 17.4 % to provide high system detection efficiency. The total die area is 1.5×2.5 mm2 with a photosensitive SPAD array area of 340×340 μm2. At an excess bias of 3.6 V, we measured a photon detection probability up to 22 % at a wavelength of 520 nm. The mean dark count rate of the arrayed detectors is approximately 20 Hz/μm2. We measured a detector dead time of 4ns, which enables lifetime measurement at our target laser repetition rate of 80MHz. To demonstrate SRM with our multiplexing scheme, we localized gold nanoparticle displacement at 40nm, which is 3.7 times smaller than our pixel pitch.

Jet Propulsion Laboratory is developing a Europa Lander astrobiology mission concept to search for biosignatures within Europa’s subsurface. However, Europa’s rugged terrain presents a number of physical hazards for landing. MIT Lincoln Laboratory is designing a radiation-hardened real-time direct-detection LIDAR system at 532nm to aid with autonomous hazard avoidance and landing site selection for this Europa Lander concept. The detector for this system is a 2048x32 array of silicon Geiger-mode APDs and covers the required field-of-view in one dimension, removing the need for 2D stitching and enabling real-time data processing. Detector design, improvements for radiation tolerance and component characterization results are presented.

We present a room temperature single photon source based on a color center in hexagonal boron nitride for satellite-based quantum networks. The resonator-coupled emitter is characterized by a narrowband tuneable spectrum, high photon purity, and high quantum efficiency. The photon source is currently integrated on a 3U CubeSat to qualify it for use in a future satellite-based global quantum-encrypted network. The satellite also performs a fundamental test of quantum gravity.

Using short-wave infrared wavelength advantages, we demonstrate one-photon fluorescence confocal microscopy of adult mouse brains with penetration depths up to 1.7mm. This is achieved by labeling quantum dots with 1300 nm excitation and 1700 nm emission and detecting them with a single-photon superconducting nanowire detector.

The recent development of single-photon avalanche diode (SPADs) arrays as imaging sensors with both picosecond binning capabilities and single photon sensitivity has led to the rapid development of time-of-flight imaging systems. When used in conjunction with a synchronised light source these sensors produce a 3D image. Here, we apply this 3D imaging ability to the problem of drone identification, orientation, and, segmentation. The proliferation of semi-autonomous aerial multi-copters i.e. drones, has raised concerns over the ability of existing aerial detection systems to accurately characterise such vehicles. Here, we fuse the 3D imaging of SPAD sensors with the classification capabilities of a bespoke convolutional neural network (CNN) into a system capable of determining drone pose in flight. To overcome the lack of publicly available training data we generate a photorealistic dataset to enable the training of our network. After training, we are able to predict the roll, pitch, and yaw of the several different drone types with an accuracy greater than 90%.

With recent advances in quantum technologies for applications such as communication, cryptography, computing, metrology and sensing, the performance and scalability of single-photon detection as a vital key component is becoming increasingly important. At the same time, ongoing efforts in the development of high-performance photonic integrated circuits (PIC) benefit the miniaturization and scalability of these quantum technologies. Waveguide-integrated superconducting nanowire single-photon detectors (WI-SNSPDs) allow to combine excellent performance metrics, such as high detection efficiency, low dark-count rates and low timing jitter below 20 ps with the scalability and functionality that PIC platforms such as Si₃N₄ provide. We have previously demonstrated broadband efficient single-photon detection with a single device over a range from visible to mid-infrared wavelengths and ultra-fast detector recovery times allowing for up to GHz count rates. Here, we present the utilization of WI-SNSPDs for discrete-variable quantum cryptography receivers with the complete photonic circuitry embedded together with the single-photon detectors on a single silicon chip, where the secret-key rates greatly benefit from the short recovery times of the detectors especially for metropolitan distances. We further realize a fully packaged 64 channel WI-SNSPD matrix for use in a wavelengthdivision multiplexed QKD setup.

We will discuss recently-developed approaches to improve sensitivity of superconducting nanowire single photon detectors in the mid-infrared, showing saturated internal detection efficiency up to a wavelength of 10 microns. We will also show preliminary data from small 64-element SNSPD arrays with high internal detection efficiency in the midinfrared at 3.5 μm, and will discuss calibration techniques we are developing for measuring system detection efficiency in this region of the spectrum.

We present a compact camera module based on an array of 16 × 16 single-photon avalanche diodes (SPADs) with fastgating capabilities and hosting 16 shared time-to-digital converters (TDCs) with a least significant bit (LSB) of 6 ps. SPADs are gated with a rising-edge of less than 500 ps and show an average instrument response function (IRF) of 60 ps FWHM, including the TDCs, with less than 4 ps time-dispersion across a 30 ns gate window. Differential non-linearity (DNL) and integral non-linearity (INL) are as good as 0.04 LSB and 3.6 LSB, respectively. An event-driven readout protocol optimizes data transfer from the SPAD chip to the FPGA, handling the time-of-flight (TOF) pre-processing in order to minimize the dead-time of the TDCs, thus sustaining up to 1.6 · 10⁸ conversions per second. TOF data can be transferred towards a PC via USB-C with a maximum throughput of about 6 Gbit/s. Our camera meets the requirements of an optimized multi-pixel solution for non-line-of-sight (NLOS) imaging, as it combines fast-gating with narrow IRF: the sub-nanosecond activation of the SPADs is exploited to reject spurious light pulses, like the first bounce one from the relay wall, and properly acquire multiply-scattered photons arriving from the hidden target, while its narrow IRF allows for centimeter-accurate NLOS reconstructions. Furthermore, while the high throughput paves the way towards real-time NLOS acquisitions at video-rates, the compact form

Single photon counting is the most sensitive optical measurement method available. The counting range is limited by photoelectron (PE) pulse width and dark count operating in Geiger-mode typical in SPAD and SiPM sensors. The PE width is determined by the recharge process after typical picoseconds avalanche and the sensor time constant by its capacitance. We achieved sub-ns PE pulses using pF range capacitance coupled with each arrayed pixel and GHz electronics. Dark count was reduced by thermoelectric cooling. Current photon counting performance shows 580ps average PE width, saturation count 500Mcps and dark count <100cps/mm². Counting electronics can perform up to 1Gcps with ECL logic after 200ps resolution comparator. Time correlated single photon counting (TCSPC) is an important single photon application. Due to sensor deadtime issues, START-STOP period per excitation impulse becomes the determining factor for a measurement. Deadtime-less photon detection enables the counting of multiple photons within an excitation pulse, enabling simultaneous measure of fluorescence intensity and fluorescence lifetime. The PE pulse stream is captured by a digital oscilloscope and analyzed by MATLAB script, avoiding pulse pair resolution limitations using peak detection and statistical analysis. Time resolution is decided by the sampling rate even in overlapped PE signals. Experiments were performed using a commercial oscilloscope with 8M sampling/2ms at 4Gs=250ps, showing that higher bandwidth and sampling rate instruments improve the measurements. This approach is termed Time Correlated Multi-Photon Counting (TCMPC). When combined with a wide dynamic range photon counting sensor, it is a powerful tool for fluorescence analysis, laser induced photon spectroscopy (LIPS), photon flow cytometry and potentially photon communications in deep and free-space or even underwater.

Single-photon avalanche diode (SPAD) based sensors and systems enable a variety of applications in biomedical, automotive, consumer, and security domains. While several established standard technologies, which can facilitate the design of SPAD-based systems are already in existence, challenges remain for the development of deep sub-micron monolithic integration of circuits and SPADs. In this work, we present SPADs along with pixel circuits in a standard GF 55 nm BCDL process. Two different designs demonstrate the flexibility allowed by the technology for a variety of applications. Both shallow and deep junction SPADs present excellent noise performance of less than 1 cps/μm2 at 3 V excess bias. An integrated passive-quench active-recharge (PQAR) circuit is used in conjunction with the SPADs, which enables a dead time of less than 2 ns, easily allowing for high dynamic range applications that require < 100 Mcps such as quantum communication and information technologies. The deep and shallow junction SPADs demonstrate an afterpulsing probability of < 0.5 % and < 2 % at 3V excess bias, respectively. The dead time is adjustable through analog control of the active-recharge circuit, allowing for afterpulsing reduction to below 0.1 % while maintaining Mcps operation. The shallow junction, which has a breakdown voltage of about 18 V and a peak sensitivity at 430 nm is particularly interesting for applications requiring low supply voltage, whereas the deep SPAD, which demonstrates < 4 % photon detection probability (PDP) at 940 nm, can be implemented in LiDAR sensors that require enhanced sensitivity at near-infrared (NIR) wavelengths. The measured timing jitter of both SPADs is < 50 ps FWHM at 3 V excess bias and 780 nm.

Arrays of Geiger-mode avalanche photodiodes (GmAPDs) are fabricated on a new type of engineered substrates with an epitaxial layer grown on silicon-on-insulator (SOI) wafers. The SOI-based structure facilitates rapid die-level bump bonding of the GmAPD array to a CMOS readout integrated circuit (ROIC) followed by substrate removal to make a backilluminated image sensor. To fabricate the engineered substrate, a commercial substrate with a 70-nm-thick SOI layer is implanted with BF2 ions to create a p+-doped passivation layer on the light illumination surface. Subsequently, a lightly p-doped silicon layer on which the GmAPD will be fabricated is grown using a homoepitaxy process. This approach allows for the use of chip-level hybridization to CMOS, avoiding the high cost and demanding wafer flatness and smoothness requirements of wafer-scale 3D integration processes. The new process yields cleaner wafers and allows for tighter control of detector layer thickness compared to the previous process. GmAPDs fabricated on 5-μm-thick epitaxial silicon have over 70% photon detection efficiency (PDE) when 532 nm light is focused into the center 3 μm of the device with an oxide layer that remains after substrate removal. With an anti-reflective coating, the PDE can be improved.

InGaAs/InP Single-Photon Avalanche Diodes (SPADs) can achieve high photon detection efficiency (PDE) with a thick absorber, but at the expense of higher dark count rate (DCR). PDE and DCR also depend on the electric field inside the structure, which can be tailored in the design phase and influences the overall performance. We present the design and the experimental characterization of two different 10 μm-diameter InGaAs/InP SPADs. The first one is intended for applications where low noise is the key requirement: at 225 K and 5 V excess bias, it features 1 kcps DCR, 25% PDE at 1550 nm and a timing jitter of 100 ps (FWHM). The second device is an InGaAs/InP SPAD optimized for PDE-enhanced applications, having a PDE up to 50% at 1550 nm, with a DCR of 20 kcps and a timing jitter of 70 ps (FWHM) at 225 K. Alternatively, it features a PDE of 37% at 1550 nm, with a DCR of just 3 kcps and a timing jitter of 100 ps (FWHM). When combined with a custom integrated circuit we developed, both devices show an afterpulsing probability as low as few percent with a gating frequency of 1 MHz and hold-off time of few microseconds at 225 K, allowing to achieve a photon count rate towards 1 Mcps.

We have developed 2048x32 arrays of silicon Geiger-mode avalanche photodiodes (GmAPDs) for a terrain mapping lidar to be used in planetary exploration missions. These devices support single photon detection with sub-ns timing. A key performance-limiting issue with arrays is optical crosstalk, in which hot-carrier light emission produced by an avalanche triggers spurious detection events in nearby pixels. To address this challenge, we have demonstrated a deep trench isolation process. This paper will report measurements of crosstalk between pixels in silicon GmAPD arrays, measurements both before and after the arrays are hybridized to a readout integrated circuit. Initial wafer probe measurements before hybridization show order-of-magnitude crosstalk reduction in a pair of test GmAPDs separated by 25 µm. These measurements use a novel technique based on analysis of the statistics of the time difference between the first detection events during a bias pulse. The results of our measurements are consistent with simulations of optical crosstalk modeled using optical ray tracing software.

In_0.52Al_0.48As based top-illuminated APDs with a dual-multiplication layer design is demonstrated. It can deliver high output photocurrent (12.7 mA) with high-responsivity (6.3 A/W) and high single-photon detection efficiency (48% @ 300K) with short jitter (65 ps) under 0.9 V_br and Geiger-mode operation, respectively.