Avalanche Photodiode Sensor with Segmented Optical Filter
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Optoelectronic sensors face challenges in maintaining measurement accuracy due to wavelength drift caused by temperature changes, which affects the filtering of useful light and allows extraneous light to interfere, leading to reduced sensitivity and accuracy.
Innovation Solution
A sensor system with a narrow-band bandpass filter and multiple optical filters with narrower passbands than the tolerance wavelength range, where each filter is assigned to an avalanche photodiode element, allowing for selective detection of useful light and suppression of extraneous light, and a control unit that adjusts the wavelength range of the transmitted light to compensate for drifts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a narrow-band bandpass filter is used to suppress extraneous light, then the suppression of extraneous light is improved, but the tolerance to wavelength drift deteriorates
Solution Approach 1:
The filter system is divided into multiple optical filters, each with a different central wavelength and narrow bandwidth. Instead of using a single wide-band filter, the system segments the wavelength coverage into multiple narrow bands, allowing each filter to provide strong extraneous light suppression while the collective array maintains tolerance to wavelength drift through diversity.
Solution Approach 2:
Multiple optical filters with different central wavelengths are combined in parallel, each assigned to a separate avalanche photodiode element. The merging of these filters creates a composite filtering system that achieves both narrow bandwidth (for extraneous light suppression) and wide coverage (for drift tolerance) simultaneously.
2Measurement precision
If multiple optical filters with narrower passbands are used, then the signal-to-noise ratio is improved, but the device complexity increases
Solution Approach 1:
The detection system is segmented into multiple independent channels, each consisting of an optical filter paired with an avalanche photodiode element. This segmentation allows each channel to operate with optimized narrow-band filtering for high signal-to-noise ratio, while the modular structure manages complexity through repetition of standardized units.
Solution Approach 2:
Each optical filter is designed with locally optimized properties (specific central wavelength and narrow bandwidth) tailored to its assigned avalanche photodiode element. This local quality optimization ensures maximum signal-to-noise ratio for each detection channel while the overall system maintains simplicity through consistent design patterns across channels.
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
This approach significantly improves the signal-to-noise ratio, enabling more accurate measurements and longer range detection or the use of less powerful light sources, while maintaining high sensitivity to useful light signals.
Implementation Method 1
The incident light triggers a controlled avalanche (avalanche effect). As a result, the charge carriers generated by incident photons are multiplied and a photocurrent is produced
Implementation Method 2
The incident light triggers a controlled avalanche... the charge carriers generated by incident photons are multiplied
Implementation Method 3
arranging a bandpass filter tuned to the wavelength range of the useful light in the reception path of the SPAD receiver
Implementation Method 4
in a phase method, the transmitted light is amplitude-modulated and a phase shift between the transmitted and received light is determined, the phase shift also being a measure of the light propagation time
Data Source
Figure 1~2
Figure 3~4
AI summary
An optoelectronic sensor 10, for example a single-beam photoelectric sensor, is described, comprising a light transmitter 12 for generating transmitted light 14 and a transmitting optic 16 for detecting objects 20 in a monitoring area 18. The sensor 10 includes a light receiver 24 with a plurality of avalanche photodiode elements 24a, each of which can be biased above a breakdown voltage and thus operated in a Geiger mode, a receiving optic 26, 28 with a first optical filter 28, 28a tuned to the wavelength range, and a control and evaluation unit 30 designed to acquire information about the objects 20 from a received signal of the light receiver 24. The wavelength range shifts during operation of the sensor 10 due to drifts within a tolerance wavelength range.The first filter 28, 28a has a passband that is narrower than the tolerance wavelength range. The filter 28 has at least two, generally n, and here purely by way of example, four filter areas 28a. The filter areas 28a have a narrower passband than the tolerance wavelength range and the filter areas divide the tolerance wavelength range approximately equally among themselves. The light receiver 24 comprises as many groups with at least one light receiving element 24a as there are filter areas 28a, and one of these groups receives a strong signal. A control and evaluation unit 30 then selects the group with the strong signal and ignores the signals of the other groups.The control and evaluation unit preferentially selects the received signal of the at least one avalanche photodiode element based on its level or temperature information from its own light transmitter, which significantly influences the shift of the wavelength.