VECSEL Self-Mixing Interferometry Sensor for Extended Detection Range
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Solution Overview
Problem
VCSEL-based SMI laser sensors have a limited detection range due to their short coherence length, restricting their application to short-range uses and making them unsuitable for longer-range applications like automotive systems.
Innovation Solution
A VECSEL-based SMI laser sensor with an external cavity structure, where the coherence length is increased by extending the cavity length, allowing for a significantly longer detection range and improved power density, enabling applications beyond short-range use.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If VCSEL is used as laser light source in SMI laser sensor, then low-cost production and surface-emitting properties are achieved, but detection range is limited to several millimeters due to short coherence length
Solution Approach 1:
The laser cavity is segmented into two parts: a short internal cavity (VCSEL) and a long external cavity. The internal cavity maintains the VCSEL's manufacturing advantages while the external cavity extends the coherence length. This segmentation allows the system to benefit from both the ease of VCSEL production and the extended detection range provided by the external cavity.
Solution Approach 2:
An external cavity acts as an intermediary between the VCSEL and the target object. This external cavity extends the optical path length and coherence length without requiring a complete redesign of the VCSEL structure, thereby maintaining low-cost production while achieving extended detection range of several meters.
2Ease of manufacture
If VCSEL with short coherence length is used, then low-cost production is enabled, but application to long-range uses like automotive systems becomes impossible
Solution Approach 1:
By segmenting the cavity into internal and external portions, the system maintains VCSEL manufacturing simplicity while adapting to long-range applications through the extended external cavity, enabling versatility across both short-range and long-range applications.
Solution Approach 2:
The coherence length parameter is changed by extending the external cavity length, while maintaining the VCSEL's manufacturing parameters unchanged. This allows the same VCSEL structure to be adapted for different application ranges by simply adjusting the external cavity configuration.
3Length of stationary object
If external cavity length is extended in VECSEL, then coherence length and detection range are increased, but device complexity increases
Solution Approach 1:
The external cavity serves as a simple intermediary component that extends coherence length without requiring complex internal modifications to the VCSEL structure. This approach increases detection range while minimizing the increase in overall device complexity.
Solution Approach 2:
The cavity extension function is extracted from the VCSEL internal structure and placed in an external cavity. This separation allows the VCSEL to maintain its simple, manufacturable structure while the external cavity provides the coherence length extension, thereby limiting the increase in device complexity.
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
The extended coherence length and power density of the VECSEL-based sensor enhance the detection range to several meters, enabling applications in automotive and other fields, such as parking aids and blind-angle supervision, while maintaining a low-cost production process.
Implementation Method 1
vertical external cavity surface emission laser (VECSEL) having a gain medium arranged in a layer structure on a front side of a first end mirror
Implementation Method 2
at least one photodetector monitoring the laser radiation of the laser light source
Implementation Method 3
the detection range of this sensor is limited to several millimeters... the maximally accessible range of such a device is limited to half the coherence length lc of the laser radiation
Data Source
AI summary
The present invention relates to a laser sensor for self-mixing interferometry. The laser sensor comprises at least one semiconductor laser light source emitting laser radiation and at least one photodetector (6) monitoring the laser radiation of the laser light source. The laser light source is a VECSEL having a gain medium (3) arranged in a layer structure (15) on a front side of a first end mirror (4), said first end mirror (4) forming an external cavity with an external second end mirror (5). The proposed laser sensor provides an increased detection range and can be manufactured in a low-cost production process.