The CMOS image sensor was invented at Caltech’s Jet Propulsion Laboratory to miniaturize cameras on interplanetary spacecraft. While it took some years for NASA to full adopt the technology, 23 CMOS cameras were on-board the NASA Perseverance Mars lander, rover and helicopter due to their miniature size, mass, power and excellent performance. In this talk, we will trace the path of CMOS image sensors from then until now, including the CMOS Quanta Image Sensor (QIS) for photon counting. The CMOS QIS will be compared to SPAD photon counting sensors and the merits of both will be discussed. Future trends in CMOS image sensors will be discussed and we can speculate about what is on the horizon.

This conference presentation was prepared for SPIE Defense + Commercial Sensing, 2023.

Scalable, low power, high speed data transfer between cryogenic and room temperature environments is essential for the realization of practical, large-scale systems based on superconducting technologies. Optical fiber presents a 100–1,000x lower heat load than conventional electrical wiring, relaxing the requirements for thermal anchoring, and allows for very high bandwidth densities by carrying multiple signals through the same physical fiber. By operating a CMOS modulator in the forward bias regime at a temperature of 3.6 K, we have demonstrated the optical readout of a superconducting nanowire single-photon detector (SNSPD) without the need for an interfacing device.

Superconducting nanowire single-photon detectors (SNSPDs) have long been the detector of choice for photon-counting applications in the near-infrared that demand high efficiency, high timing resolution and low dark counts. Extending the operation of these detectors to mid-infrared wavelengths above 2 µm would enable a host of applications in the fields of chemical and remote sensing, LIDAR and quantum optics. Pushing the range of these detectors deeper into the mid-infrared would also be of interest to the astronomical and dark matter communities. In this work we demonstrate long-wavelength sensitivity in SNSPDs by careful material and device optimization. We also show work towards efficient, low jitter devices in the mid-infrared.

Spectral diffusion is a ubiquitous process caused by bath fluctuations which randomizes the spectral mode of single-photon emitters at cryogenic temperatures. Accurately measuring spectral diffusion on a single-emitter level is still a challenging task owing to the required high spectral and temporal resolution with an additionally high temporal dynamic range. In this talk, I highlight our recent progress towards understanding spectral diffusion in nascent quantum emitters using photon-correlation Fourier spectroscopy (PCFS). PCFS can measure the bandwidth and kinetics of spectral fluctuations down to nanosecond timescales. Using PCFS, I show how quantum emitters in 2D hexagonal boron nitride exhibit multi-timescale discrete spectral jumping that can be attributed to a bath with at least two characteristic fluctuation relaxation time constants.Broadly, I propose PCFS as a particularly suitable tool for the detailed study of decoherence processes and spectral diffusion.

Time-gated diffuse correlation spectroscopy (TG-DCS) was used in neuro-intensive care settings for monitoring of patients with severe traumatic brain injury. Here, I will present recent results of clinical translation of TG-DCS at the neuro-intensive care unit by implementing measurements at 1064 nm due to high sensitivity of superconducting nanowire single photon detectors. We obtained a significant correlation (ρ = 0.76) between TG-DCS and invasive thermal diffusion flowmetry. We also demonstrate high temporal resolution to obtain pulsatile flow measurements. Overall, the results demonstrate the first clinical translation capability of the TG-DCS system at 1064 nm using a superconducting nanowire single-photon detector.

Functional near-infrared spectroscopy (fNIRS) and diffuse correlation spectroscopy (DCS) have shown promise as non-invasive optical methods for cerebral functional imaging. DCS approaches currently have limited sensitivity in adults. fNIRS sensitivity is also limited, particularly in high-detector-density applications. Sensitivity can be improved using temporal discrimination (TD), where the laser excitation is of short (~400ps) duration and the detector rejects early photons that have not penetrated into the brain while maintain high sensitivity to those that have. We report here on the development of a novel 32x32 Single-Photon Avalanche photo-Detector (SPAD) array and Read-Out Integrated Circuit (ROIC) that can operate in either the visible or NIR enabling high-channel-count TD-fNIRS or TD-DCS systems.

Multispectral fluorescence lifetime microscopy (FLIM) is a valuable tool for biomedical and environmental applications. A multidimensional acquisition scheme (space, time, spectrum) provides high information content and the drawback of long acquisition/processing times. Compressive Sensing (CS) combined with Single-Pixel Camera (SPC) acquisition scheme has been proposed as a strategy to reduce the number of measurements. We present a multispectral FLIM system based on SPC, CS and data fusion (DF) with a high-resolution camera to strongly reduce the acquisition time. We adopted a novel method for TCSPC to increase the count-rate. The system is characterized and validated on a cellular sample.

Picosecond resolution time-correlated mode has emerged as a candidate technology for a variety of depth imaging applications in the visible, near-infrared and short-wave infrared regions. This presentation will examine this approach in a range of challenging sensing scenarios including: imaging though highly scattering underwater conditions; free-space imaging through obscurants such as smoke or fog; and depth imaging of complex scenes containing multiple surfaces.

Single-photon detector (SPAD) arrays are multi-pixel sensors that have single-photon sensitivity and pico-second temporal resolution. However, to fully exploit the capabilities of SPAD array sensors, it is crucial to establish the quality of depth images they are able to generate in a wide range of scenarios. What is the best-case depth resolution and what are realistic images generated by SPAD arrays? In this work, we establish a robust yet simple numerical procedure that rapidly establishes the fundamental limits to depth imaging with SPAD arrays under real-world conditions. Our approach accurately generates realistic depth images in a wide range of scenarios, allowing the performance of an optical depth imaging system to be established without the need for costly and laborious field testing. This procedure has applications in object detection and tracking for autonomous systems and could be easily extended to systems for underwater imaging or for imaging around corners.

This conference presentation was prepared for SPIE Defense + Commercial Sensing, 2023.