Integrated Optical Filter Cavity for Stable Time-of-Flight Lasers
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Solution Overview
Problem
Existing laser arrangements for time-of-flight measurements face challenges in efficiently filtering ambient light and compensating for thermal shifts in laser wavelength, which affect the accuracy and sensitivity of depth imaging.
Innovation Solution
A laser arrangement comprising an optical filter adjacent to a laser, both with substrates and active layers between mirrors, where the mirrors have equal reflectivity, allowing the optical filter to effectively filter reflected laser light while compensating for thermal shifts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an optical filter is added adjacent to the laser to filter ambient light, then the sensitivity and accuracy of time-of-flight measurements are improved, but the device complexity increases
Solution Approach 1:
The patent combines the optical filter structure with the laser cavity structure, where the optical filter shares the same substrate and mirror architecture as the laser. This merging approach allows the optical filter to be integrated adjacent to the laser without requiring completely separate components, thereby improving measurement precision through effective ambient light filtering while minimizing the increase in device complexity through structural sharing
Solution Approach 2:
The optical filter structure is designed to serve multiple functions: it acts as both a laser cavity (emitting laser light) and an optical filter (filtering ambient light). The same mirrors and substrate serve dual purposes, allowing the system to perform both laser generation and wavelength-selective filtering functions with a single integrated structure, thus improving accuracy without proportionally increasing complexity
2Measurement precision
If the optical filter uses equal reflectivity mirrors to the laser, then the filter transmission for laser wavelength is optimized, but the ability to filter ambient light may be compromised
Solution Approach 1:
The optical filter is designed with spatially selective properties where it exhibits high transmission specifically at the laser wavelength while maintaining filtering capability for other wavelengths. The equal reflectivity mirrors are configured to create a resonance condition that is highly selective to the laser wavelength, allowing the filter to locally optimize transmission for the desired wavelength while globally maintaining ambient light rejection capabilities
Solution Approach 2:
The optical filter utilizes changes in optical parameters (reflectivity, transmission) as a function of wavelength. By designing the mirror reflectivities to be equal and the cavity to resonate at the laser wavelength, the system creates a sharp transmission peak at the desired wavelength while maintaining high reflection for ambient light wavelengths, thus achieving both optimized filter transmission and effective ambient light filtering through wavelength-dependent parameter variations
3Measurement precision
If the optical filter is integrated on the same substrate as the laser, then thermal shifts in laser wavelength are compensated, but the manufacturing precision requirements increase
Solution Approach 1:
The optical filter and laser are merged onto the same substrate, sharing common mechanical and thermal characteristics. This integration ensures that both components experience identical thermal expansion and wavelength shifts, allowing the filter to automatically track and compensate for laser wavelength drift due to temperature changes. The shared substrate physically couples the two components thermally, achieving wavelength stability without requiring complex active stabilization systems
Solution Approach 2:
The system exploits the temperature-dependent change in refractive index and physical dimensions of the substrate to achieve wavelength compensation. As temperature changes affect both the laser emission wavelength and the optical filter transmission peak equally, the filter remains tuned to the laser wavelength across temperature variations. This passive compensation mechanism reduces manufacturing precision requirements compared to active stabilization approaches
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 the sensitivity and accuracy of time-of-flight measurements by effectively filtering ambient light and stabilizing the laser wavelength against thermal variations, enabling reliable depth imaging.
Implementation Method 1
The optical filter filters 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 laser and optical filter each have a substrate and an active layer arranged between a first and second mirror
Data Source
AI summary
A laser arrangement for time-of-flight measurements includes an optical filter adjacent to a laser. The laser and optical filter each have a substrate and an active layer arranged between a first and second mirror. The laser emits laser light in a first direction through its first mirror. The optical filter receives the laser light reflected from an object through its first mirror. The laser's and the optical filter's first mirrors have an equal reflectivity. The laser's and the optical filter's second mirrors have an equal reflectivity, or the reflectivity of the optical filter's second mirror is reduced with respect to that of the laser. The optical filter filters the received light such that laser light reflected from the object and received from the first direction passes the optical filter.