SiPM for Automotive 3D Imaging LiDAR SystemsSensL Technologies Ltd., 6800 Airport Business Park, Cork, Ireland

www.sensl.comsales@sensl.com+353 21 240 7110 (International)+1 650 641 3278 (USA)

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The Silicon Photomultiplier (SiPM) is a low-light sensor which is used in high-volume security and nuclear medicine applications. The SiPM is now considered the solution to the sensor challenge of LiDAR for autonomous vehicles. LiDAR has the benefit of enabling high-resolution object identification at long range. The challenge is to achieve this with low-reflectivity targets and in complex environments. These challenges can be overcome by using a combination of a single photon-counting sensor and a multi-shot histogramming technique. To fully understand the challenges, SensL has developed a software model using Matlab that can simulate a variety of situations and system configurations. This is used to predict the performance of a system given a set of input parameters. SensL has developed a new N-on-P process that enhances the SiPM sensitivity to longer wavelength photons, which has been used to create a 1x16 linear array specifically for scanning LiDAR systems. A 3D ToF LIDAR demonstrator system was built, based upon this sensor, to assess the performance and validate the software model.

The Challenges of Automotive, Long Distance LiDARA LiDAR system for automotive applications (autonomous vehicles and ADAS) needs to combine:

• ranging to long distance

• with low reflectivity targets

• and in bright sunlight (or other harsh environmental conditions)

In addition, it must :

• be fully solid state (no moving parts)

• have a large FoV (90o to 120o)

• be lost cost (<$250)

SensL LiDAR Demonstrator Overview• The ArrayMR-0116A20, 1 x 16 element SiPM array

has been developed specifically for scanning LiDAR

applications.

• It is made using the R-Series process with enhanced

NIR sensitivity.

• It is used in the SensL LiDAR demonstrator system.

x = 171 μmy1 = 491 μmy2 = 59 μmy3 = 8.74 mm

Abstract

SensL have built a long range LiDAR demonstrator system that is based upon the 1×16 SiPM array as receiver. The demonstrator is an electro-mechanical scanning, 3D ToF imaging LiDAR system, that uses direct time of flight (ToF). It is comprised of:

Summary

SensL LiDAR Model

Long Distance (>200m)

Low reflectivity targets (10%)

Bright sunlight (100klux)

Results from the Model LiDAR with an SiPM Multi-Shot Method

Ave

rage

Num

ber

of R

etur

ned

Pho

tons

• SiPM sensors have emerged as a preferred sensor for automotive LiDAR applications

• SiPM have a demonstrable benefit over APDs for both performance and system advantages

• SensL have developed updated R-Series SiPM sensors with 9% PDE @ 905nm

• SensL have used the R-Series process to create a 1x16 array for our Gen3 LiDAR demonstrator

• Gen3 is now in test to further validate our model and test the limits of long range LiDAR

SensL LiDAR Array SensL LiDAR Demonstrator Results

Parameter Simulated ValueAmbient light 100 kluxTarget reflectivity 5 %Angle of view 0.1o x 0.1o

Aperture 1”Bandpass filter ±25 nmLaser power 25 WLaser pulse width 4 ns

SensL has created a model using MATLAB to simulate SiPM-based ranging system with variety of conditions that can then be verified with the LiDAR test bench.

• The model consists of two main parts:

Analytic: calculates the photon flux incident on each SiPM cell due to noise (ambient light) and signal (laser light) from a reflecting target in the Field of View (FoV) of the cell itself.

Monte Carlo: sensor output waveforms can be simulated and compared to experimental data. Readout techniques are implemented allowing the estimation of performance benchmarks i.e. ranging accuracy. The sensor parameters and information on the readout circuitry are included.

• APD and PIN photodiode models have been developed for comparison.

• Readout technique is selectable, e.g. single shot or multi-shot.

The model was used to evaluate the amount of light incident on the sensor as a function of ranging distance. (The input parameters are summarized in the table below).• The laser pulse return diminishes as 1/d2

• Solar ambient photon noise is constant with distance

Different sensor types were then included in the model to calculate the SNR as a function of ranging distance:• PIN and APD sensors have high QE and dynamic range,

but no/low gain• The SiPM has limited dynamic range, but high gain allows

detection of weak signals.• SNR defined as peak photo current / sigma of the ambient

noise• All input parameters are included in the table below.

• There are a number of factors that are specific to the use of SiPM sensors for ranging that enable the >100m ranging with low reflectivity targets.

• The first is to limit the ambient light as much as possible this is done in two ways:

- Limit the angle of view

- Use a narrow band-pass filter (see figure below)

Typical LiDAR Signal Return

(905±25) nm

Previously, SiPM sensors have been optimized for detection of light peaking in the blue or green, and these sensors have limited sensitivity to the 905nm light used in LiDAR.

SensL has created a new, fully CMOS process for creating SiPM sensors with sensitivity pushed out to longer wavelengths giving enhanced NIR sensitivity. The latest R-Series sensors have 9% PDE at 905nm.

• A physical, scanning LiDAR demonstrator system has been built by SensL using the 1x16 SiPM array.

• It has been used to validate the results from the software model.

• Below are the simulation and experimental results for a 3% target as a function of distance. It can be seen that there is good agreement.

• The imaging capability of the system has also been tested. The video is available from the QR code bottom right.

• Eye-safe 905 nm laser diode array

• Electro-mechanical rotating mirror for horizontal scanning of a 80o × 5o at 30 fps

• Collection optics

• 1×16 SiPM array as receiver and associated readout and control electronics.

Animation exploring how the SiPM can be used to meet the

challenges of long-distance LiDAR.

Video showing the performance of SensL’s Gen3 LiDAR demonstrator

system.

Can you get still get ranging information when the signal is comparable to the background...? ...Yes! Use the multishot method

• Time stamp each detected photon and add to histogram• Combination of signal, solar, dark count photons• Build up the histogram over a number of pulses (~20)• Photons correlated with a target will form a distinct peak

• This technique improves the SNR over the single shot method, in proportion to the square root of the number of samples.

• This increase in SNR allows for longer distance ranging.• This technique can be implemented while retaining a 30 fps frame

rate.• The plot below shows the simulated SNR for single and multi-

shot LiDAR with the SiPM. The multi-shot case uses 20 shots per measurement.