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
We show both on phantoms and in-vivo the full potential of fast time-gated acquisitions exploiting an innovative custom-developed digital silicon photomultiplier, overcoming consolidated limitations showed by single-photon avalanche diodes linked to their small sensitive area.
A multimodal instrument for breast imaging was developed, combining ultrasound (morphology), shear wave elastography (stiffness), and time domain multiwavelength diffuse optical tomography (blood, water, lipid, collagen) to improve the non-invasive diagnosis of breast cancer.
KEYWORDS: Silicon photomultipliers, Silicon photonics, Digital photography, Analog electronics, Positron emission tomography, Photodetectors, Near infrared spectroscopy, LIDAR, Single photon, Silicon
An innovative general-purpose Digital Silicon-PhotoMultiplier (dSiPM) with 32 × 32 SPADs, designed in 160 nm BCD technology, is presented. The main goals of this device are to enhance the dynamic range, still keeping the single-photon resolution, and minimize the timing jitter. Both an analog and a digital approach are used to distinguish between 1 to ~300 incoming photons. A voltage-controlled current generator converts the pixel’s digital output pulse in a current pulse, tunable in amplitude (10 μA ÷ 350 μA) and duration (from 1 ns to the SPAD holdoff time). The digital option is useful in low photon flux applications. Instead, in high photon flux applications, the digital output misses information, due to an overlap among the photon pulses, so the analog option is to be preferred. Moreover, a double threshold algorithm is implemented in order to reduce the timing jitter of the output. Basically, the concept behind this procedure is to refer the timing measurement to the crossing of the lower threshold, while the higher threshold is only used as a validation for the measurement. Finally, a Time-to-Digital Converter (TDC), with a resolution of 75 ps, is integrated to provide the timing information. The SPAD frontend design works in a free running photon detection modality, and there is the possibility to enable or disable the pixels individually. Thanks to its programmable number of photon resolution and the improved timing performance, the detector can be exploited in many different scientific applications.
Light Detection and Ranging (LiDAR) is a technique that can be applied to identify the position of objects in an industrial environment, which usually suffer by strong background illumination. In this work we present a novel architecture of a Single Photon Avalanche Diode (SPAD) array optimized for a direct Time Of Flight (dTOF) single-point rangefinder system, with a distance range of about 2 m and a resolution of a few centimeters. The ASIC has been implemented in a 0.16 µm Bipolar-CMOS-DMOS (BCD) technology and includes 10 × 40 pixels, 80 Time-to-Digital Converters (TDCs), and a histogram builder. The peculiarity of this work is the ability of performing a Region-Of-Interest (ROI) selection of just those pixels illuminated by the laser spot, as well as a smart sharing of timing electronics. ROI selection is performed through SPADconnected up/down counters, that are decremented whenever the connected SPAD is triggered within the time window where the laser spot is expected, whereas they are incremented when the connected SPAD is triggered within a time window where the laser pulse is not present. If the counter stores a negative value, the pixel is considered to be within the laser spot, and just those pixels might trigger a TDC during the following 500 samples frame. Each TDC is shared among 5 non-adjacent pixels that should not be hit at the same time, considering the expected laser spot dimension. The implemented TDCs have 75 ps resolution and 19.2 ns Full Scale Range (FSR).
To improve non-invasively the specificity in the diagnosis of breast cancer after a positive screening mammography or doubt/suspicious ultrasound examination, the SOLUS project developed a multimodal imaging system that combines: Bmode ultrasound (US) scans (to assess morphology), Color Doppler (to visualize vascularization), shear-wave elastography (to measure stiffness), and time domain multi-wavelength diffuse optical tomography (to estimate tissue composition in terms of oxy- and deoxy-hemoglobin, lipid, water, and collagen concentrations). The multimodal probe arranges 8 innovative photonic modules (optodes) around the US transducer, providing capability for optical tomographic reconstruction. For more accurate estimate of lesion composition, US-assessed morphological priors can be used to guide the optical reconstructions. Each optode comprises: i) 8 picosecond pulsed laser diodes with different wavelengths, covering a wide spectral range (635-1064 nm) for good probing of the different tissue constituents; ii) a large-area (variable, up to 8.6 mm2 ) fast-gated digital Silicon Photomultiplier; iii) the acquisition electronics to record the distribution of time-of-flight of the re-emitted photons. The optode is the basic element of the optical part of the system, but is also a stand-alone, ultra-compact (about 4 cm3 ) device for time domain multi-wavelength diffuse optics, with potential application in various fields.
We present the design of a new fast-gated 16 x 16 silicon SPAD array developed in a 0.16 μm BCD technology with builtin 6 ps resolution TDCs (Time-to-Digital Converters), optimized for Non-Line-Of-Sight imaging. The high temporal resolution is achieved by sharing one high-performance TDC among 16 SPADs, without losing spatial resolution, thanks to an identification logic capable of detecting and rejecting collisions. In the SPAD frontend, a low-threshold comparator minimizes temporal jitter, while an active quenching circuit reduces afterpulsing. An event-driven readout scheme optimizes data transfers, however a standard frame-driven photon-counting only mode is also available. The goal is to enable quasi real-time NLOS scene reconstruction by parallelizing the acquisition across multiple spots. Thanks to its high temporal resolution, the detector can be exploited also in other scientific applications, such as clinical diagnostic (with Time-Domain Near Infrared Spectroscopy) and LiDAR (Light Detection and Ranging).
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.