A standard method for distance determination is light detection and ranging (LiDAR), which relies on the emission and detection of reflected laser pulses. When LiDAR systems become common for every vehicle, many simultaneous laser signals will produce mutual LiDAR interference between LiDAR systems. In this paper, we analyze the possibility to recognize mutual interference in time-correlated single photon counting (TCSPC) LiDAR with particular focus on flash systems. We evaluate the LiDAR interference appearance by deriving the expected event distribution for ego and aggressor signal. From that, we calculate the probability of photon detection within each measured signal. This paper shows the high potential of different pulse repetition frequencies to reduce LiDAR interference. Using signal-to-noise ratio (SNR), we define the extinction distance, beyond which the aggressor signal completely extinguishes the ego signal. Applied on different background and laser event rates, we find the connection between ideal LiDAR system designs and lowest probability for unrecognized LiDAR interference. Furthermore, we show the relationship to a specific LiDAR design, which must fulfill eye safety condition and receives lower intensities with increasing target distances. Finally, we present different solutions for the recognition and reduction of LiDAR interference based on our previous results.

We have developed a 32x24 pixel sensor array based on single-photon avalanche diodes (SPADs). Beside conventional 2- dimensional imaging, this sensor allows for precise timing of single-photon arrival times which can be exploited in a variety of technical and scientific approaches like 3D image acquisition, quantum imaging and quantum random number generation. Thus, such a sensor is eligible for many fields of application such as autonomous driving, remote and non-lineof- sight sensing, safety, robotics and more recently random number generation for statistical applications or data encryption. The novel sensor contains CMOS integrated backside illuminated SPADs which are connected to an underlying read-out IC by wafer-to-wafer bonding. Their single-photon sensitivity (quantum efficiency QE=60 % @ 580 nm) and high-speed performance (readout frequency 𝑓 = 25 kHz, temporal resolution 𝑡TDC = 312.5 ps) make the sensor a promising choice for, e.g. quantum imaging with photon-pairs where a 2-dimensional spatial and temporal resolution are as crucial as a low noise level. SPADs also offer exciting opportunities for random number generation by using the randomness of photon generation paired with time-resolved detection and post-processing. Another potential application of the sensor is light detection and ranging for which we integrated the sensor into a demonstrator system for direct time-of-flight measurements. It is capable of coincidence detection using 4 SPADs in each pixel, which allows for background light suppression in outdoor situations. This combination of single-photon sensitivity, precise photon arrival timing and our recent developments in wafer-to-wafer bonding technology gives access to a new generation of optical sensors for a variety of applications.

Performance of systems for optical detection depends on the choice of the right detector for the right application. Designers of optical systems for ranging applications can choose from a variety of highly sensitive photodetectors, of which the two most prominent ones are linear mode avalanche photodiodes (LM-APDs or APDs) and Geiger-mode APDs or single-photon avalanche diodes (SPADs). Both achieve high responsivity and fast optical response, while maintaining low noise characteristics, which is crucial in low-light applications such as fluorescence lifetime measurements or high intensity measurements, for example, Light Detection and Ranging (LiDAR), in outdoor scenarios. The signal-to-noise ratio (SNR) of detectors is used as an analytical, scenario-dependent tool to simplify detector choice for optical system designers depending on technologically achievable photodiode parameters. In this article, analytical methods are used to obtain a universal SNR comparison of APDs and SPADs for the first time. Different signal and ambient light power levels are evaluated. The low noise characteristic of a typical SPAD leads to high SNR in scenarios with overall low signal power, but high background illumination can saturate the detector. LM-APDs achieve higher SNR in systems with higher signal and noise power but compromise signals with low power because of the noise characteristic of the diode and its readout electronics. Besides pure differentiation of signal levels without time information, ranging performance in LiDAR with time-dependent signals is discussed for a reference distance of 100 m. This evaluation should support LiDAR system designers in choosing a matching photodiode and allows for further discussion regarding future technological development and multi pixel detector designs in a common framework.

Advances in laser diode technology enable the generation of eye-safe laser pulses with short pulse duration and high peak power. This opens up new opportunities for Light Detection and Ranging (LiDAR)-systems based on the direct time-of-flight (dTOF) principle because their range performance is mainly limited by the requirement of eye-safe laser pulse energy. Another limiting factor for dTOF LiDAR is the sensitivity to background noise. Shorter pulse width enables better parasitic light suppression inside the LiDAR system for improved performance in high background flux scenarios. With the improvements caused by using short laser pulses, new challenges emerge. Shorter pulse duration and limited achievable timing resolution of time discrimination circuits inside of dTOF detectors lead to histogram data distributions in which the laser originated time stamps can only fill few time bins. The time stamp histogram of the detected and clocked laser photons shows a sharp exponential decline. The slope is strongly dependent on the occurring laser event rate inside the system. In an extreme case, all laser generated events fall into one time bin. Because of the coarse discrete arrangement of those laser generated events, a need for new algorithmic approaches arises. This work illustrates the dependency between the occurring laser photon rate in the system and its distribution inside the measurement data. Influence of the time discrimination circuit's time bin width is discussed with regards to resulting histogram shapes.

Single-Photon Avalanche Diode (SPAD)-based 'Light Detection And Ranging' (LiDAR) systems often use the first photon measurement principle to acquire ranging information. While those systems provide accurate distance measurements, they can easily saturate in high background scenarios. Recent improvements in SPAD quenching circuit technology open up the opportunity for SPAD LiDAR systems to detect multiple photons while measuring with a single laser pulse, partially circumventing this challenge. The theoretical framework for the distribution of higher order single photon detections is presented and discussed how the sensor's typical quenching times influence it. Measurements with a SPAD circuitry capable of detecting multiple events in a single measurement are presented. Differences to first-photon and continuous detection implementations are discussed and advantages in high background light scenarios are shown.

For some applications, a reliable detection of the distance of objects is necessary, even under strong environmental conditions. Commonly this includes sunlight, but fog, rain and snow cause interferences as well. For fast and reliable three-dimensional monitoring of the environment, LiDAR is a key sensor technology. A light source, often in the near-infrared, emits a short light pulse and the time-of-flight of the photons reflected by an object is measured. This allows to calculate the distance by using the speed of light. In order to be able to ensure reliable detection despite possible interferences, we have set up a new measurement concept based on the existing time-gating. Thus, an area is covered by step-wise shifting of the measuring window. By accumulating different delays, the true distance to the object can be determined. An advantage of the method is that no information about the approximate position of the object has to be known in advance. In this paper we present measurement results with this method, which were taken in different environmental conditions. The method can be implemented in addition to already existing concepts and can therefore supplement them.