Abstract
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.
Highlights
Signal-to-noise ratio (SNR) is a widely used metric for the ability of a photodetector to distinguish between an incident signal and its absence
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)
In contrast to a SPAD, this reverse-bias voltage is below the breakdown voltage of the APD and the multiplication results in an internal current gain, which is proportional to the incoming optical signal PS and noise power PN
Summary
Signal-to-noise ratio (SNR) is a widely used metric for the ability of a photodetector to distinguish between an incident signal and its absence. The authors derive their results using a Monte-Carlo based photonic simulator The difference between their results and the results detailed in this publication is that their simulations are based on a SPAD system which may accumulate multiple measurements while the compared APD system has to create its result from a single measurement and no analytical expressions of the SNR are given. The authors are not aware of any publication which considers the saturating behavior of SPAD SNR in ambient light scenarios and compares them to the respective APD behavior based on SNR values, including the readout circuitry, of commercially available diodes in ranging applications. Effects of their noise behavior in relation to their respective readout electronics are discussed briefly and mitigation strategies are sketched.
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