LiDAR Wavelength Locking via Temperature Sweep Control
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Solution Overview
Problem
LiDAR systems that simultaneously measure water vapor density and wind speed face challenges in correctly selecting the appropriate absorption line wavelength, leading to potential locking at unintended wavelengths due to unstable laser oscillators.
Innovation Solution
The LiDAR system incorporates a temperature-controllable laser light source, a beam splitter, a modulator, a gas cell, a photodetector, and a target spectrum detector with temperature sweep and constant temperature control, along with a wavelength controller using a current control loop to accurately lock the wavelength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a gas cell with multiple absorption lines is used for wavelength locking, then the laser can be locked to an absorption line, but the laser oscillator may select a wrong absorption line when unstable, leading to locking at unintended wavelengths
Solution Approach 1:
The patent applies preliminary action by performing temperature sweep control before constant temperature control. The temperature sweep control preliminarily determines the correct absorption line by sweeping through a temperature range and identifying the absorption line with the lowest transmittance, ensuring the laser is locked to the correct wavelength before normal operation begins.
Solution Approach 2:
The patent uses feedback mechanisms in both temperature sweep control and constant temperature control. The system continuously monitors transmittance through the gas cell and adjusts the temperature accordingly. The feedback signal from the photodetector detecting transmitted laser light through the gas cell enables the system to identify and lock onto the correct absorption line.
2Measurement precision
If temperature sweep control is performed to determine the correct absorption line, then the wavelength selection accuracy is improved, but the measurement time and system complexity increase
Solution Approach 1:
The temperature sweep control is performed as a preliminary action during system initialization or when wavelength re-locking is needed. Once the correct absorption line is identified and the laser is locked, the system switches to constant temperature control for normal operation, minimizing the time spent in sweep mode while ensuring accurate wavelength selection.
Solution Approach 2:
The temperature sweep control can be performed periodically or triggered by specific conditions (such as after power-on or when wavelength drift is detected), rather than continuously. This periodic approach balances the need for accurate wavelength selection with the constraint of measurement time, performing the time-consuming sweep only when necessary.
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 configuration prevents the selection of wrong absorption lines and ensures the wavelength of the laser light is accurately locked, enhancing the reliability and accuracy of water vapor density and wind speed measurements.
Implementation Method 1
a laser light source that outputs laser light having the same wavelength as a wavelength (λON) that is absorbed in molecules in the atmosphere
Implementation Method 2
The differential absorption LiDAR according to Non-Patent Literature 1 adopts an HCN gas cell for the purpose of obtaining information on a wavelength that serves as an absolute reference. The differential absorption LiDAR according to Non-Patent Literature 1 irradiates a gas (HCN) of the gas cell with the laser light, and generates a feedback signal for wavelength locking from information on an absorption line spectrum obtained from transmitted light.
Implementation Method 3
a photodetector to detect transmitted laser light having transmitted through the gas cell, and convert the transmitted laser light into an electrical signal
Implementation Method 4
a wavelength controller to control a wavelength of the laser light source by current control loop
Implementation Method 5
the laser light source is temperature-controllable, and the LiDAR further includes a target spectrum detector to perform temperature sweep control and constant temperature control on the laser light source
Data Source
AI summary
A LIDAR according to the technology of the present disclosure includes: a laser light source to oscillate laser light; a beam splitter to split the laser light into two systems; a modulator to modulate a phase of the laser light sent from the beam splitter; a gas cell; a photodetector to detect transmitted laser light having transmitted through the gas cell, and convert the transmitted laser light into an electrical signal; and a wavelength controller to control a wavelength of the laser light source, the laser light source is temperature-controllable, and the LiDAR further includes a target spectrum detector to perform temperature sweep control and constant temperature control on the laser light source.