MEMS Wavelength Selectable Switch for LiDAR Noise Filtering
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Solution Overview
Problem
LiDAR systems in autonomous vehicles face challenges in maintaining a high signal-to-noise ratio due to temperature-induced shifts in the laser wavelength, which compromise the effectiveness of optical filters.
Innovation Solution
A MEMS-based Wavelength Selectable Switch (WSS) is repurposed to act as a filter, allowing for real-time measurement and adjustment of the output wavelength, thereby optimizing the filtered bandwidth to improve the signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the optical filter is set with a wider spectral range to accommodate laser wavelength shifts due to temperature changes, then the laser signal is not cut off, but the solar noise acceptance range is widened and the signal-to-noise ratio is compromised
Solution Approach 1:
The patent employs a tunable optical filter whose transmission characteristics can be dynamically adjusted in real-time. The filter's central wavelength and bandwidth are made variable, allowing the system to adapt to laser wavelength shifts while maintaining a narrow passband to reject solar noise. This dynamic tuning capability resolves the contradiction by enabling the filter to be wide enough to accommodate wavelength drift yet narrow enough to reject noise at any given moment.
Solution Approach 2:
The patent changes the spectral parameters (central wavelength and bandwidth) of the optical filter in response to temperature-induced laser wavelength shifts. By monitoring the laser wavelength and adjusting the filter parameters accordingly, the system maintains optimal signal-to-noise ratio while ensuring the laser signal remains within the passband. This parameter adaptation allows the filter to dynamically balance between signal transmission and noise rejection.
2Object-affected harmful factors
If a fixed optical filter is used to reject solar noise, then the signal-to-noise ratio is maintained, but the filter cannot accommodate wavelength shifts caused by temperature variations
Solution Approach 1:
The patent replaces the fixed optical filter with a tunable filter that can dynamically adjust its transmission characteristics. This dynamic filter maintains narrow bandwidth for effective solar noise rejection while being capable of tracking and adapting to wavelength shifts caused by temperature variations. The real-time tunability allows the system to preserve both noise rejection performance and wavelength accommodation capability.
Solution Approach 2:
The patent implements a feedback mechanism where the laser wavelength is monitored (e.g., through wavelength detection) and this information is fed back to control the optical filter's transmission characteristics. This closed-loop feedback ensures that the filter remains properly aligned with the laser wavelength while maintaining a narrow passband for noise rejection, thereby simultaneously achieving adaptability and noise rejection.
3Object-affected harmful factors
If the optical filter bandwidth is narrowed to improve signal-to-noise ratio, then solar noise is rejected better, but the filter may cut off the laser signal due to wavelength shifts
Solution Approach 1:
The patent uses a dynamically tunable optical filter that can adjust its bandwidth and central wavelength in real-time. The filter maintains a narrow passband for effective solar noise rejection while simultaneously tracking the laser wavelength to ensure the signal remains within the passband. This dynamic adjustment prevents the filter from cutting off the laser signal while maintaining narrow bandwidth for noise rejection.
Solution Approach 2:
The patent employs feedback control where the laser wavelength is continuously monitored and used to adjust the optical filter's transmission characteristics. This feedback mechanism ensures that the filter bandwidth remains narrow for noise rejection while the central wavelength is kept aligned with the laser emission wavelength, preventing signal cutoff. The feedback loop dynamically balances noise rejection and signal transmission 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
The implementation of the MEMS-based WSS filter in LiDAR systems enhances the signal-to-noise ratio by selectively filtering out unwanted wavelengths, leading to improved accuracy and reliability in object detection and ranging.
Implementation Method 1
The WSS is controllable to provide a selected wavelength band to a selected output of the WSS
Implementation Method 2
A light condenser directs reflected light from the light emitter to an input of the WSS
Implementation Method 3
where it is detected by a photodetector
Data Source
AI summary
A MEMS-based Wavelength Selectable Switch (WSS), used classically for demultiplexing fiber optic communications, is re-purposed to act as a filter. A light emitter provides a light beam with its wavelength detected by a wavelength detector. A light condenser directs reflected light from the light emitter to an input of the WSS. The WSS is controllable to provide a selected wavelength band to a selected output of the WSS, where it is detected by a photodetector. Other wavelengths are discarded by the WSS at other outputs. A controller is configured to control the WSS to select the selected wavelength band based on a detected wavelength from the wavelength detector.