Automotive ADAS (Advanced Driver Assistance Systems) will be based upon a fusion of sensor technologies, including cameras, ultrasound, radar and LiDAR (light detection and ranging). These technologies will work in concert to provide all of the sensing requirements necessary to build up the full picture of the environment, both near and far.
LiDAR is emerging as the technique that is needed to provide high-accuracy and resolution at long distance targets, in bright light with a variety of reflective surfaces.
Time of Flight Techniques
Several methods for LiDAR exist, but the one best suited to use with the SensL SiPM has been found to be direct Time of Flight (ToF) with Leading Edge Discrimination (LED). TCSPC (Time Correlated Single Photon Counting) and SPSD (Single Photon Synchronous Detection) with direct ToF may also be considered.
Time the photon transit time to determine distance
No range ambiguity
Timing accuracy determined by ability to detect the photon arrival
Low laser power requirement
Leading Edge Discrimination (LED)
Timing the arrival of the returned laser pulse leading edge
SiPM sensitivity to single photons allows low detection threshold
Short laser pulse width enables low laser power requirement
Fast SiPM response, high gain and bandwidth result in low jitter
Sensor Options for LiDAR
A wide range of sensor technologies have been explored in use in LiDAR applications. Each has its unique system implementation challenges. Silicon Photomultipliers offer many advantages over other technologies.
Techniques for ambient light rejection for SiPM sensors:
Aperture limit – minimize sensor field of view to overlap with pulsed source. Highest resolution and signal to noise is achieved by making laser spot coincident with sensor spot.
Bandpass optical filter – ±25nm bandpass will reduce ambient light from 1000W/m2 to 38W/m2.
Shorten laser pulse – provides a higher optical peak power.
“SiPM Sensors for ToF Ranging Applications” (Poster)
Poster from the SPIE Photonics West 2016 conference, giving an overview of SensL’s work on using SiPM sensors for ranging applications.
“Direct Time-of-Flight Ranging with SensL SiPM” (Application Note)
An application note that gives a brief overview of SensL’s work using SiPM sensors for direct ToF ranging applications, at both short and long distances.
“SiPMs in Direct ToF Ranging Applications” (White Paper)
A white paper that gives a detailed description of how SensL SiPMs can be employed for direct ToF ranging, including a description of a MATLAB model developed by SensL for simulating various sensor and environmental configurations. It is used to isolate the contribution of each individual factor on the system signal to noise ratio.
“Ranging Demonstrator Description” (Tech Note)
A detailed description of the Ranging Demonstrator hardware built by SensL to demonstrate the ranging performance of the SiPM sensors.