SiPM Photodetector Photon Distribution Non-Uniformity
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Solution Overview
Problem
Silicon photomultiplier (SiPM) systems face challenges in accurately counting photons due to 'dead time' and non-uniform photon distribution, leading to degraded photon counting accuracy and energy resolution, as the recovery time of APDs affects detection efficiency and gain, and increasing APD arrays or shortening dead time introduces noise or reduces gain.
Innovation Solution
A photodetector design incorporating two arrays of APD cells with separate pulse height analyzers and a signal processing unit that determines non-uniformity, allowing only uniform photon distribution signals to be counted, thereby improving accuracy by suppressing variations and correcting output signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the number of APD arrays is increased to improve photon detection efficiency, then the detection efficiency is improved, but the area of each APD is reduced which degrades the gain
Solution Approach 1:
The SiPM is divided into multiple APD arrays (first and second arrays) with different aperture ratios. This segmentation allows each array to contribute differently to photon detection, optimizing both detection efficiency and gain by having specialized sub-arrays rather than uniformly increasing the total number of APDs.
Solution Approach 2:
Different APD arrays are assigned different aperture ratios tailored to specific detection needs. The first APD array has a first aperture ratio optimized for certain conditions, while the second APD array has a second aperture ratio optimized for other conditions, allowing local optimization of both detection efficiency and gain characteristics.
2Productivity
If the dead time is shortened to improve counting rate, then the productivity is improved, but noise increases or gain decreases
Solution Approach 1:
The photodetector is segmented into multiple APD arrays that can operate with different timing characteristics. This allows the system to process photons in parallel across different arrays, effectively increasing the counting rate without requiring individual APDs to have extremely short dead times, thereby avoiding noise and gain degradation.
Solution Approach 2:
Instead of reducing dead time in a single dimension (time), the invention adds a spatial dimension by using multiple APD arrays with different aperture ratios. This dimensional approach allows simultaneous photon detection across multiple channels, increasing effective counting rate without compressing the dead time to problematic levels.
3Quantity of substance
If photons enter non-uniformly to increase detection capacity, then the quantity of photons detected increases, but the energy resolution is degraded due to dead time losses
Solution Approach 1:
The SiPM is segmented into multiple APD arrays with different aperture ratios, allowing different portions of the detector to handle different photon flux conditions. This segmentation enables the system to detect higher total photon quantities while maintaining energy resolution by distributing the detection load across arrays optimized for different conditions.
Solution Approach 2:
Different APD arrays are configured with different aperture ratios suited to local detection requirements. Arrays with higher aperture ratios can handle higher photon flux without excessive dead time losses, while arrays with lower aperture ratios maintain precision for lower flux conditions, allowing the system to detect more photons overall without sacrificing energy resolution.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enhances photon counting accuracy by filtering out non-uniform photon distribution effects, maintaining detection efficiency, and reducing noise, thus improving the overall performance of SiPM systems.
Implementation Method 1
A silicon photomultiplier (SiPM) is a photodetector element including two-dimensionally arranged avalanche photodiodes (hereafter referred to as 'APDs'), which operate in a mode called 'Geiger mode' when a reverse-bias voltage higher than a breakdown voltage of the APDs is applied thereto.
Implementation Method 2
The gain of an APD operating in Geiger mode is very high, 1×10^5 to 1×10^6. Therefore, a very weak light emission of a single photon can be measured using the APD.
Data Source
AI summary
A photodetector according to an embodiment includes: a photodetector element unit including a first cell array including a plurality of first cells arranged in an array and a second cell array including a plurality of second cells arranged in an array, each of the first and second cells including a photoelectric conversion element, the second cell array being arranged to be adjacent to the first cell array; a first pulse height analyzer unit analyzing a pulse height of an electrical signal outputted from the first cell array; a second pulse height analyzer unit analyzing a pulse height of an electrical signal outputted from the second cell array; and a signal processing unit determining non-uniformity of a distribution of photons entering the first and second cell arrays using an output signal of the first pulse height analyzer unit and an output signal of the second pulse height analyzer unit.