Chirped Diode Laser Speckle Mitigation in LIDAR
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Solution Overview
Problem
Conventional pulsed LIDAR systems face challenges such as low light reflection from distant targets, stringent detector requirements, and difficulty with crosstalk and sunlight interference, while coherent LIDAR systems struggle with high-speed and long-range imaging due to limitations in chirp duration and measurement time.
Innovation Solution
The use of feedback-controlled chirped diode lasers with precisely controlled frequency variations and the implementation of two chirped lasers with opposite frequency chirps, along with extended chirp durations spanning multiple pixels, allows for simultaneous range and range-rate measurements and increased 3D imaging rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If extended chirp durations are used to improve range precision, then measurement precision is improved, but imaging speed deteriorates
Solution Approach 1:
The patent implements multiple periodic chirps within a single pixel measurement window. Instead of using a single extended chirp, the system performs several shorter chirps sequentially (e.g., 3-5 chirps per pixel) and integrates the results. This periodic repetition allows the system to maintain high imaging speed while achieving the precision equivalent of longer measurement times, effectively resolving the contradiction between measurement precision and imaging speed.
2Reliability
If high output power is used to improve long-range detection, then detection capability is improved, but laser line width increases
Solution Approach 1:
The patent segments the high-power laser output into multiple lower-power chirps that are sequentially transmitted and integrated. By dividing the total energy into multiple discrete chirp events rather than transmitting one continuous high-power signal, the system maintains narrow line width characteristics while accumulating sufficient signal energy for long-range detection. Each individual chirp maintains spectral purity, and the integrated result achieves the required detection capability.
3Measurement precision
If multiple measurements per pixel are performed to mitigate speckle, then measurement precision is improved, but measurement time increases
Solution Approach 1:
The patent performs multiple measurements per pixel continuously through rapid sequential chirps without idle time between measurements. The system maintains continuous laser operation and continuous data acquisition, with each chirp immediately following the previous one. This continuous operation allows the system to accumulate multiple speckle-mitigating measurements within the original single-measurement time budget, achieving speckle reduction without increasing total measurement time per pixel.
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 approach enhances the 3D imaging rate beyond the speed of light limit, achieving higher pixel rates and improved range precision with reduced measurement time, while maintaining narrow laser line widths and high output powers for long-range applications.
Implementation Method 1
frequency modulated continuous wave (FMCW) technique, where the frequency of a continuous wave (CW) laser is 'chirped' or changed in accordance with a predetermined periodic frequency versus time function
Implementation Method 2
The photodetector 150 provides an output current proportional to the incident optical power
Implementation Method 3
The combined LO wave and the reflected light from the target are incident on a photodetector (PD) 150. The photodetector 150 effectively multiplies the amplitudes of the reflected light and the LO wave to create a coherent 'beat signal'
Data Source
AI summary
LIDAR systems, and methods of measuring a scene are disclosed. A laser source emits one or more optical beams. A scanning optical system scans the optical beams over a scene and captures reflections from the scene. A measurement subsystem independently measures the reflections from N subpixels within each scene pixel, where N is an integer greater than 1, and combines the measurements of the reflections from the N subpixels to determine range and/or range rate for the pixel.