Narrow-Divergence VCSEL Proximity Sensing in Compact Modules
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Solution Overview
Problem
Current proximity sensing technologies face limitations in accuracy and miniaturization due to high divergence light sources, which result in reduced sensitivity and increased complexity, especially in applications like mobile phone camera auto-focus systems, where the detector is close to the source and prone to errors from protective window reflections.
Innovation Solution
The use of very low divergence Vertical Cavity Surface Emitting Lasers (VCSEL) with a narrow beam divergence of 0.5 to 10 degrees, achieved through extended cavity lengths and external mirrors, along with optical microlenses and baffles, to improve proximity sensing accuracy and reduce the sensor footprint.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a divergent light source (LED or standard VCSEL) is used for proximity sensing, then the sensor can be miniaturized with the detector close to the source, but the beam divergence causes protective window reflections to propagate back to the detector, severely limiting detection accuracy and range
Solution Approach 1:
The patent changes the beam divergence parameter from typical VCSEL values (15 degrees) to ultra-low divergence (0.5 to 10 degrees) by extending the resonant cavity length. This parameter change allows the detector to be positioned close to the source while preventing window reflections from reaching the detector, thus resolving the contradiction between miniaturization and measurement precision
Solution Approach 2:
The patent extends the VCSEL resonant cavity in the vertical dimension, adding external mirrors to create a longer optical path within a compact physical footprint. This dimensional extension reduces beam divergence without increasing the overall sensor volume, enabling both miniaturization and improved measurement accuracy
2Volume of moving object
If the detector is positioned close to the light source to achieve miniaturization, then the sensor footprint is reduced, but reflections from the protective window propagate back to the detector, causing errors and limiting detection range
Solution Approach 1:
By changing the beam divergence parameter to ultra-low values (0.5 to 10 degrees) through cavity extension, the patent ensures that reflected light from the protective window does not return to the detector even when positioned close to the source. This resolves the contradiction between miniaturization and harmful reflection interference
Solution Approach 2:
The patent converts the potentially harmful window reflections into a beneficial configuration where the narrow beam ensures reflections miss the detector entirely. The same geometric relationship that causes harm in divergent systems becomes beneficial in the narrow beam system, allowing close positioning without interference
3Ease of manufacture
If standard VCSEL beam divergence (15 degrees) is used, then the device can be manufactured with standard components, but the sensitivity of proximity sensors is limited and detection range is reduced
Solution Approach 1:
The patent changes the beam divergence parameter from standard VCSEL values to ultra-low divergence by extending the resonant cavity with external mirrors. This modification improves sensing sensitivity and detection range while maintaining compatibility with standard VCSEL manufacturing processes, resolving the contradiction between ease of manufacture and sensing reliability
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 enhances proximity sensing accuracy and sensitivity, allowing for more precise distance measurements and longer range detection in a compact form factor, while minimizing interference from protective window reflections, and enables applications beyond camera focus, such as health monitoring.
Implementation Method 1
an optical source including a VCSEL device operable to generate a narrow divergence source beam... The use of very low divergence Vertical Cavity Surface Emitting Lasers (VCSEL) with a narrow beam divergence of 0.5 to 10 degrees, achieved through extended cavity lengths and external mirrors
Implementation Method 2
an optical detector to sense light reflected back from the object illuminated by the narrow divergence source beam
Data Source
Figure 1
Figure 2
Figure 3~3(b)
AI summary
A proximity sensor which uses very narrow divergent beams from Vertical Cavity Surface Emitting Laser (VCSEL) for the illumination source is disclosed. Narrow divergent beams in the range 0.5 to 10 degrees can be achieved to provide high proximity sensing accuracy in a small footprint assembly. One approach to reducing the beam divergence is to increase the length of the VCSEL resonant cavity using external third mirror. A second embodiment extends the length of the VCSEL cavity by modifying the DBR mirrors and the gain region. Optical microlenses can be coupled with the VCSEL to collimate the output beam and reduce the beam divergence. These can be separate optical elements or integrated with the VCEL by modifying the substrate output surface profile or an added a transparent layer. These methods of beam divergence reduction are incorporated into various embodiment configurations to produce a miniature proximity sensor suitable for cell phones and tablets.