Thermally Coupled VCSEL Optical Filter for Stable ToF Wavelength Matching
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Solution Overview
Problem
Existing detector arrangements for time-of-flight measurements face challenges in compensating for production spread and thermal drift of VCSEL arrays, leading to variations in emission wavelengths and reduced sensitivity due to thermal shifts.
Innovation Solution
A detector arrangement is designed with VCSELs and optical filters sharing a common substrate, optimized for equal reflectivity and thermal coupling, enabling compensation for production spread and thermal drift, and incorporating a driver to control laser pulse length for improved sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If VCSEL arrays are used for infrared illumination in time-of-flight applications, then compact design and gesture recognition capability are achieved, but variations in emission wavelengths occur due to temperature differences between laser and photodetector
Solution Approach 1:
The patent merges the laser and optical filter onto a common substrate, creating a thermally coupled system where both components experience the same temperature variations. This thermal coupling ensures that wavelength shifts in the laser are compensated by corresponding shifts in the optical filter's passband, maintaining measurement precision despite temperature changes and enabling compact integration.
2Manufacturing precision
If VCSEL arrays are processed on the same wafer with photodetectors, then production spread is minimized, but thermal drift still causes wavelength variations
Solution Approach 1:
The patent combines the laser and optical filter on the same substrate, creating a thermally coupled system. This ensures both components experience identical temperature variations, causing their wavelength characteristics to shift together and maintain alignment, thereby compensating for thermal drift effects.
Solution Approach 2:
The patent designs the optical filter with a reflectivity that can be adjusted to match the laser's emission characteristics. By tuning the optical filter's parameters (reflectivity, passband width) to correspond with the laser's emission wavelength and profile, the system maintains optimal performance despite temperature-induced wavelength shifts.
3Measurement precision
If the optical filter has equal reflectivity to the laser mirror, then thermal coupling and wavelength matching are optimized, but sensitivity may be reduced due to reflected light interference
Solution Approach 1:
The patent applies different reflectivity characteristics to different parts of the optical system. The optical filter has high reflectivity at wavelengths outside its passband to block ambient light, while maintaining appropriate transmission within its passband. This spatially varying reflectivity profile optimizes both wavelength matching and detection sensitivity by allowing desired light through while blocking interfering reflections.
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 solution enhances sensitivity and reduces thermal drift, allowing for precise time-of-flight measurements and compact design by ensuring consistent emission and reception of laser light, even in varying temperature conditions.
Implementation Method 1
The optical filter is further arranged to filter the received light such that laser light reflected from the object and received from the first direction passes the optical filter
Implementation Method 2
The at least one laser is arranged to emit laser light in a first direction. The laser light is emitted through the first mirror of the at least one laser
Implementation Method 3
The first mirror of the at least one laser and the first mirror of the at least one optical filter have an equal reflectivity
Implementation Method 4
The laser and optical filter are thermally coupled in a way such that the temperatures of the laser and the optical filter during operation of the laser arrangement are essentially the same in order to compensate for thermal shift of the emission wavelength
Data Source
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AI summary
The invention describes a laser arrangement (100) for time-of-flight measurements comprising at least one laser and at least one optical filter arranged adjacent to the at least one laser, wherein the at least one laser and the at least one optical filter each comprise a substrate (101) a first mirror (105), a second mirror (109) and an active layer (107) arranged between the first mirror (105) and the second mirror (109), wherein the at least one laser is arranged to emit laser light (121) in a first direction, wherein the optical filter is arranged to receive received light (123), wherein the received light (123) comprises laser light (121) reflected from an object (300), the at least one optical filter has, in direction of the received light propagation, the first mirror (105), the active layer (107) and the second mirror (109), wherein the second mirror (109) of the at least one optical filter has a reflectivity same as or lower than the reflectivity of the first mirror (105) of the at least one optical filter, wherein the optical filter is further arranged to filter the received light (123) such that laser light (121) reflected from the object (300) and received from the first direction passes the optical filter. The invention further describes a detector arrangement (10) for time-of-flight measurements, a time-of-flight camera (200), a method of determining a depth image and a corresponding computer program product.