Optoelectronic Sensor with Free-Form Lens and SPAD Matrix
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Solution Overview
Problem
Optoelectronic sensors with digital SPAD matrices face challenges in accurately detecting objects due to interference from extraneous light and diffraction patterns, leading to incorrect detections and reduced sensitivity, especially in complex environments.
Innovation Solution
The sensor employs an elongated light spot geometry adapted to the SPAD matrix, where only activated avalanche photodiode elements contribute to measurements, with a control unit selecting and deactivating pixels based on the light spot's position, using receiving optics with free-form surfaces for homogenization and microlenses to enhance irradiance and reduce noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional spherical or aspherical transmitting and receiving lenses are used, then the system structure is simple, but the light spot is round with inhomogeneous irradiance and creates interference patterns that reduce detection accuracy
Solution Approach 1:
The patent replaces conventional spherical or aspherical lenses with a receiving lens having a free-form surface (non-spherical, non-rotationally symmetric curvature). This free-form surface is specifically designed to transform the round light spot into an elongated light spot, eliminating diffraction patterns and interference while improving detection accuracy. The free-form surface represents a departure from traditional curved surfaces to achieve superior optical performance.
2Reliability
If all avalanche photodiode elements in the SPAD matrix are activated, then the coverage area is maximized, but interference from extraneous light and dark noise increases, reducing signal-to-noise ratio
Solution Approach 1:
The patent implements selective activation of avalanche photodiode elements based on the elongated light spot's position and shape. Instead of activating all SPAD elements uniformly, the system activates only those elements that receive usable light within the elongated light spot footprint. This localized activation strategy maintains adequate coverage while minimizing interference from extraneous light and dark noise in inactive elements, thereby improving signal-to-noise ratio.
3Measurement precision
If the light spot is made narrow to improve resolution, then the power density increases, but the light spot becomes more susceptible to diffraction patterns and interference from extraneous light
Solution Approach 1:
The free-form surface of the receiving lens is specifically designed to generate an elongated light spot that avoids the diffraction patterns and interference effects that plague narrow circular spots. The elongated geometry distributes the light energy over a larger area in one dimension while maintaining narrow dimensions in the other, thereby achieving high resolution without the harmful diffraction effects associated with circular apertures.
4Reliability
If multiple SPADs are evaluated together to counteract interference, then the signal strength increases, but the ability to resolve individual object positions decreases
Solution Approach 1:
The patent segments the SPAD matrix into individually controllable elements and selectively activates only those elements that receive light within the elongated light spot footprint. This segmentation allows the system to maintain high signal strength from multiple activated SPADs while preserving the ability to resolve individual object positions through the spatial distribution pattern of activated elements. The control unit processes signals from individual activated elements to determine precise object positions.
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 signal-to-noise ratio, increases range and response time, enhances ambient light tolerance, and ensures precise object detection by minimizing interference and optimizing the utilization of avalanche photodiode elements.
Implementation Method 1
The incident light triggers a controlled avalanche breakdown (avalanche effect). This multiplies the charge carriers generated by the incident photons, resulting in a photocurrent that is proportional to the light intensity received
Implementation Method 2
a single charge carrier released by a single photon can trigger an uncontrolled avalanche
Data Source
Figure 1~2
Figure 3a~3b
Figure 4a~5b
AI summary
An optoelectronic sensor (10) for detecting an object (20) in a monitoring area (18) is described, comprising a light transmitter (12) for emitting a light signal (16) into the monitoring area (18) and a light receiver (26) which has a plurality of avalanche photodiode elements (28) for detecting received light from the monitoring area (18), each biased with a voltage above a breakdown voltage and thus operating in a Geiger mode, wherein the light receiver (26) is digitally configured and thus enables individual or groups of avalanche photodiode elements (28, 28a) to be activated or deactivated, and a control and evaluation unit (30) is described, which is configured to evaluate a received signal from the light receiver (26) and to activate those avalanche photodiode elements (28a) where a light spot (44) of the light signal (22) emitted or reflected by the object (20) is expected. is.The light spot (44) is elongated.