LiDAR has become a critical requirement for Advanved Driver Assistance Systems (ADAS) as the automotive industry moves towards improved driver safety and autonomous cars. Silicon Photomultipliers (SiPM) and Single Photon Avalanche Diodes (SPAD) sensors are emerging as the most promising sensor technology for long range, >100m, direct time-of-flight LiDAR that needs to function in bright daylight and with low reflectance targets.
SensL is developing a new range of SiPM, the R-Series, that have improved detection efficiency at longer wavelengths used in LiDAR. In parallel to the sensor development, SensL is working to understand the fundamental advantages SiPM and SPAD sensor arrays provide long-range, ADAS LiDAR systems.
It will be shown that to achieve long range LiDAR with eye-safe lasers, a sensor with single photon sensitivity is required. This is due to the low number of returned photons from distances greater than 100m. When ambient daylight conditions are taken into account, the small returned signal at these distances can be easily lost in the noise and histogramming multiple laser pulses will be shown to provide the only method which allows for accurate time of flight ranging operation.
The histogramming technique and the architecture used to implement it will be described. A portable long-range LiDAR demonstrator using SiPM sensors has been developed and will be presented including range accuracy versus distance and low reflective targets. This will be compared to a detailed Monte Carlo model which will be shown to accurately describes SiPM and SPAD array operation in LiDAR ranging.
Avalanche photodiodes are very well suited and extensively used for low light application. In this paper we present a devise using avalanche photodiodes in conjunction with a pulsed laser-source to be used as an optical altimeter. The extreme sensitivity of a dedicated silicon SPAD array is combined with a versatile standard CMOS readout circuit to achieve unique performances. This imaging device is able to perform ranging with four centimeters accuracy over five kilometers distance. It is also capable of delivering quantum limited images. Development of the readout circuit will be disclosed as well as measurement results performed on the final device.
The European Space Agency (ESA) foresees several robotic missions aimed for the preparation of the future Human Exploration of Mars. To accomplish the mission objectives Imaging LIDARs are one of the identified technologies that shall provide essential information to the spacecraft Guidance, Navigation and Control (GN&C) system. ESA awarded two technology development contracts to two industrial teams for the development and demonstration of novel technologies for Imaging LIDAR sensors. Both teams designed and are manufacturing an Imaging LIDAR breadboard targeting one specific application. The objective of using novel technologies is to reduce substantially the mass and power consumption of Imaging LIDAR sensors. The Imaging LIDAR sensors shall have a mass <10kg, power consumption <60Watt, measure distances up to 5000m, with a field of view (FOV) of 20x20 degrees, range resolutions down to 2 cm, and a frame rate higher than 1 Hz.
3D LIDAR imaging is a key enabling technology for automatic navigation of future spacecraft, including landing,
rendezvous and docking and rover navigation. Landing is typically the most demanding task because of the range of
operation, speed of movement, field of view (FOV) and the spatial resolution required. When these parameters are
combined with limited mass and power budget, required for interplanetary operations, the technological challenge
becomes significant and innovative solutions must be found. Single Photon Avalanche Photodiodes (SPADs) can reduce
the laser power by orders of magnitude, array detector format can speed up the data acquisition while some limited
scanning may extend the FOV without pressure on the mechanics. In the same time, SPADs have long dead times that
complicate their use for rangefinding. Optimization and balance between the instrument subsystems are required. We
discuss how the implementation of real-time control as an integral part of the LIDAR allows the use of SPAD array
detectors in conditions of high dynamics. The result is a projected performance of more than 1 million 3D pixels/s at a
distance of several kilometers within a small mass/power package. The work is related to ESA technology development
for future planetary landing missions.
Current state of the art high resolution counting modules, specifically designed for high timing resolution applications,
are largely based on a computer card format. This has tended to result in a costly solution that is restricted to the
computer it resides in. We describe a four channel timing module that interfaces to a computer via a USB port and
operates with a resolution of less than 100 picoseconds. The core design of the system is an advanced field
programmable gate array (FPGA) interfacing to a precision time interval measurement module, mass memory block and
a high speed USB 2.0 serial data port. The FPGA design allows the module to operate in a number of modes allowing
both continuous recording of photon events (time-tagging) and repetitive time binning. In time-tag mode the system
reports, for each photon event, the high resolution time along with the chronological time (macro time) and the channel
ID. The time-tags are uploaded in real time to a host computer via a high speed USB port allowing continuous storage
to computer memory of up to 4 millions photons per second. In time-bin mode, binning is carried out with count rates
up to 10 million photons per second. Each curve resides in a block of 128,000 time-bins each with a resolution
programmable down to less than 100 picoseconds. Each bin has a limit of 65535 hits allowing autonomous curve
recording until a bin reaches the maximum count or the system is commanded to halt. Due to the large memory storage,
several curves/experiments can be stored in the system prior to uploading to the host computer for analysis. This makes
this module ideal for integration into high timing resolution specific applications such as laser ranging and fluorescence
lifetime imaging using techniques such as time correlated single photon counting (TCSPC).
The operation and performance of multi-pixel, Geiger-mode APD structures referred to as Silicon Photomultiplier (SPM) are reported. The SPM is a solid state device that has emerged over the last decade as a promising alternative to vacuum PMTs. This is due to their comparable performance in addition to their lower bias operation and power consumption, insensitivity to magnetic fields and ambient light, smaller size and ruggedness. Applications for these detectors are numerous and include life sciences, nuclear medicine, particle physics, microscopy and general instrumentation. With SPM devices, many geometrical and device parameters can be adjusted to optimize their performance for a particular application. In this paper, Monte Carlo simulations and experimental results for 1mm<sup>2</sup> SPM structures are reported. In addition, trade-offs involved in optimizing the SPM in terms of the number and size of pixels for a given light intensity, and its affect on the dynamic range are discussed.
Previous generation low light detection platforms have been based on the photomultiplier tube (PMT) or the silicon single photon counting module (SPCM) from Perkin Elmer<sup>1</sup>. A new generation of silicon CMOS compatible photon counting sensors are being developed offering high quantum efficiency, low operating voltage, high levels of robustness and compatibility with CMOS processing for integration into large format imaging arrays. This latest generation yields a new detector for emerging applications which demand photon counting performance providing high performance and flexibility not possible to date. We describe a 4-channel photon detection platform, which allows the use of 4 separate photon counting detectors in either free space or fibre-coupled mode. The platform is scalable up to 16 channels with plug in modules allowing active quenching or Peltier cooling as required. A graphical user interface allows feedback and control of all device parameters. We show a novel ability to integrate separate detection modules to extend the dynamic range of the system. This allows a PIN or APD mode detector to be used alongside sensitive photon counting detectors. An advanced FPGA and microcontroller interface has been designed which allows simultaneous time binning of counting rates and readout of the analog signals when used with linear detectors. This new architecture will be discussed, presenting a full characterization of count rate, quantum efficiency, time binning and sensitivity across the broad spectrum of light flux applicable to PIN diodes, APDs and Geiger-mode photon counting sensors.
In the field of fluorescent microscopy, neuronal activity, diabetes and drug treatment are a few of the wide ranging biomedical applications that can be monitored with the use of dye markers. Historically, in-vivo fluorescent detectors consist of implantable probes coupled by optical fibre to sophisticated bench-top instrumentation. These systems typically use laser light to excite the fluorescent marker dies and using sensors, such as the photo-multiplier tube (PMT) or charge coupled devices (CCD), detect the fluorescent light that is filtered from the total excitation. Such systems are large and expensive. In this paper we highlight the first steps toward a fully implantable in-vivo fluorescence detection system. The aim is to make the detector system small, low cost and disposable. The current prototype is a hybrid platform consisting of a vertical cavity surface emitting laser (VCSEL) to provide the excitation and a filtered solid state Geiger mode avalanche photo-diode (APD) to detect the emitted fluorescence. Fluorescence detection requires measurement of extremely low levels of light so the proposed APD detectors combine the ability to count individual photons with the added advantage of being small in size. At present the exciter and sensor are mounted on a hybrid PCB inside a 3mm diameter glass tube.This is wired to external electronics, which provide quenching, photon counting and a PC interface. In this configuration, the set-up can be used for in-vitro experimentation and in-vivo analysis conducted on animals such as mice.
Geiger Mode avalanche photodiodes offer single photon detection, however, conventional biasing and processing circuitry make arrays impractical to implement. A novel photon counting concept is proposed which greatly simplifies the circuitry required for each device, giving the potential for large, single photon sensitive, imaging arrays. This is known as the DigitalAPD. The DigitalAPD treats each device as a capacitor. During a write, the capacitor is periodically charged to photon counting mode and then left open circuit. The arrival of photons causes the charge to be lost and this is later detected during a read phase. Arrays of these devices have been successfully fabricated and a read out architecture, employing well known memory addressing and scanning techniques to achieve fast frame rates with a minimum of circuitry, has been developed. A discrete prototype has been built to demonstrate the DigitalAPD with a 4x4 array. Line rates of up to 5MHz have been observed using discrete electronics. The frame burst can be transferred to a computer where the arrival of single photons at any of the 16 locations can be examined, frame by frame. The DigitalAPD concept is highly scalable and is soon to be extended to a fully integrated implementation for use with larger 32x32 and 100x100 APD arrays.