Wavelength-Diverse FMCW Lidar for Speckle Noise Reduction
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Solution Overview
Problem
Lidar systems face challenges in increasing the signal-to-noise ratio (SNR) due to signal degradation from atmospheric particles like rain, snow, and fog, and noise from speckle patterns, which limit their performance, especially at longer ranges and in adverse weather conditions.
Innovation Solution
A multiple laser, single optical resonator lidar system is developed, where two lasers are optically coupled to a single optical resonator formed of electrooptic material, with one laser operating at a different wavelength than the other to reduce speckle noise and enhance power, and a controller manages the operating states of the lasers based on environmental conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single laser is used in a lidar system, then the device complexity is low, but the signal-to-noise ratio is limited due to speckle noise and power constraints
Solution Approach 1:
The patent combines multiple lasers operating at different wavelengths into a single lidar system, merging their optical paths through a shared resonator and beam combining optics. This integration approach increases the effective signal power and reduces speckle noise through wavelength diversity while maintaining a compact, unified system architecture rather than separate independent lidar units.
Solution Approach 2:
The patent employs composite optical structures including a shared resonator that supports multiple wavelengths, dichroic mirrors for wavelength-selective beam combining, and integrated optical paths. These composite optical components enable multiple lasers to operate simultaneously and contribute their signals coherently, achieving enhanced SNR without proportionally increasing system complexity.
2Reliability
If the laser power is increased to improve signal-to-noise ratio, then the SNR improves, but the speckle noise increases and atmospheric absorption worsens
Solution Approach 1:
The patent changes the wavelength parameter by employing multiple lasers operating at different wavelengths (e.g., 1550 nm and other wavelengths). This wavelength diversity allows the system to exploit atmospheric transmission windows that are less susceptible to absorption by rain, snow, and fog, thereby maintaining signal strength over extended ranges while reducing the impact of atmospheric harmful factors.
Solution Approach 2:
The patent converts the potentially harmful effect of speckle noise into a benefit by using wavelength diversity. Different wavelengths produce uncorrelated speckle patterns that, when combined, average out the noise through incoherent addition, transforming the speckle phenomenon from a degradation mechanism into a noise-reduction mechanism that enhances overall signal quality.
3Reliability
If multiple lasers operating at different wavelengths are used, then the SNR is enhanced by reducing speckle noise, but the device complexity increases
Solution Approach 1:
The patent implements a shared resonator that serves multiple functions: it provides optical feedback for multiple lasers simultaneously, establishes a common frequency reference, and enables wavelength-selective resonance for different laser lines. This multi-functional component reduces the need for separate resonators and control systems for each laser, thereby limiting the increase in device complexity despite using multiple wavelengths.
4Reliability
If the laser wavelength is selected for eye safety, then the SNR can be improved at longer ranges, but the power transmission through atmospheric particles is reduced
Solution Approach 1:
The patent implements dynamic wavelength selection capability, allowing the system to adaptively choose between different wavelength combinations based on environmental conditions, detection range requirements, and safety constraints. This dynamic flexibility enables the system to optimize the balance between eye safety, atmospheric transmission, and signal-to-noise ratio in real-time operating conditions.
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 enhances the SNR by reducing speckle noise and increasing power, allowing for improved performance in adverse weather conditions and extended ranges by selectively enabling or disabling lasers based on wavelength and environmental factors.
Implementation Method 1
A single modulator is configured to apply a time-varying voltage to the optical resonator. The time-varying voltage controls modulation of an optical property (e.g., index of refraction) of the electrooptic material to cause the first laser to generate a first frequency modulated optical signal
Implementation Method 2
A multiple laser, single optical resonator lidar system is developed, where two lasers are optically coupled to a single optical resonator
Implementation Method 3
A FMCW lidar system can include a laser source that generates a frequency modulated optical signal that includes a continuous series of optical chirps
Implementation Method 4
Measurement of a frequency shift and/or a phase shift for each reflected optical chirp relative to a reference optical chirp can provide a measure of a distance and/or a speed of the target
Data Source
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AI summary
Various technologies described herein pertain to multiple laser, single optical resonator lidar systems. A lidar system includes a single optical resonator optically coupled to at least a first laser and a second laser. The optical resonator is formed of an electrooptic material. The first laser and the second laser are optically injection locked to the optical resonator. A modulator applies a time-varying voltage to the optical resonator to control modulation of an optical property of the electrooptic material, which causes the first laser to generate a first frequency modulated optical signal comprising a first series of optical chirps and/or the second laser to generate a second frequency modulated optical signal comprising a second series of optical chirps. Further, front end optics transmits at least a portion of the first frequency modulated optical signal and/or the second frequency modulated optical signal into an environment from the lidar system.