Polarization-Encoded LIDAR Beam Paths for Mirror Misalignment
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Solution Overview
Problem
Conventional LIDAR systems suffer from signal degradation due to angular misalignment of scanning mirrors, especially at high speeds, leading to reduced coupling efficiency and limited range and velocity measurement capabilities, particularly in single-mode fiber systems.
Innovation Solution
Implementing polarization encoding and separation of illumination and collection beam paths using a polarization selective component, such as a quarter-wave plate and reflective optics, to interfere and deflect returning signals into separate optical detectors, allowing for larger multi-mode fibers and improved signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the mirror's angular velocity is increased to achieve higher frame rates, then the scanning speed is improved, but the target signal from distant objects is severely degraded due to angular misalignment causing walk-off at the fiber tip
Solution Approach 1:
The patent introduces a second spatial dimension by using two separate single-mode fibers (SMF1 and SMF2) oriented at different angular positions relative to the scanning mirror. This dimensional separation allows the system to capture signals that would otherwise walk off due to angular misalignment, maintaining signal quality at high frame rates by collecting light from multiple angular dimensions simultaneously
Solution Approach 2:
The patent makes the fiber bundle system multi-functional by having each fiber serve dual purposes: SMF1 collects signals for one angular dimension while SMF2 collects signals for another angular dimension. This multi-functionality allows the system to maintain high frame rates while preserving signal detection quality across different scanning angles and distances
2Volume of moving object
If single-mode fiber with small diameter is used for detection, then the system compactness is improved, but the coupling efficiency is decreased due to decentering of target signal at the fiber tip
Solution Approach 1:
The patent segments the detection function across multiple single-mode fibers (SMF1, SMF2, and potentially more) arranged in a bundle, where each fiber is positioned at a different angular orientation. This segmentation allows the system to maintain small fiber diameters for compactness while distributing the coupling function across multiple fibers to capture the full angular spread of reflected light, preventing energy loss
Solution Approach 2:
The patent merges the collection capability of multiple individually small single-mode fibers into a functional equivalent of a larger aperture by arranging them in a bundle with specific angular orientations. This merging preserves the compactness of individual fibers while achieving the light-gathering capability of a larger system, maintaining coupling efficiency without increasing fiber diameter
3Speed
If fast scanning mirrors are used to illuminate the scene quickly, then the scanning speed is improved, but the angular position mismatch between launch and collection times causes signal degradation
Solution Approach 1:
The patent adds an angular dimension to the detection system by using multiple fibers oriented at different angles, allowing the system to maintain high scanning speeds while compensating for the angular position mismatch that occurs during the round-trip time. Each fiber captures signals from a different angular perspective, ensuring accurate range and velocity measurements even at high scan rates
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
Enhances collection efficiency and signal quality, enabling longer range and higher framerate measurements by minimizing optical losses and crosstalk, particularly in multi-mode fiber systems.
Implementation Method 1
A quarter-wave plate transforms polarization of a laser beam provided by a single-mode optical fiber
Implementation Method 2
A polarization selective component refracts the collection beam path
Implementation Method 3
The local oscillator signal and target signal interfere to generate a combined signal
Data Source
Figure 1A~1B
Figure 2
Figure 3~4
AI summary
A light detection and ranging (LIDAR) apparatus includes optical source configured to emit a laser beam in a first direction (206), a polarization wave plate (214) to transform polarization state of the laser beam headed in the first direction toward a target environment, and a reflective optical component (216) to return a portion of the laser beam toward the optical source along a return path (210) and through the polarization wave plate (214) as a local oscillator signal. A polarization selective component (208) to separate light in the return path (210) based on the optical polarization, wherein the polarization selective component (208) refracts orthogonally polarized light along the return path (210) to a divergent path, wherein the polarization selective component (208) further enables interference between the local oscillator signal and the target signal to generate a combined signal. An optical detector configured to receive the combined signal from the second direction and lensing optics (212) configured to collimate the refracted light along a focal plane of the optical detector. The illumination beam path which is centered on a single-mode optical fiber (202) is passed through a lens (212) to collimate the light. Th e systems can combine the pulsed laser light from the target with reflected local light within the polarization selective component (208). The combined beam can then be focused with the collimating lens (212) toward a multi-mode fiber (204). The polarization selective component (208) refracts the beam from the collection path to an off-axis path that is at an angle a to the system's optical axis. This angle, determined by the birefringence properties of the prism, creates a vertical displacement d of the collected light on the focal plane of the lens. The polarization selective component (208) may be a Rochon prism that encodes the polarization of the illumination and collection optical paths. Alternatively, such polarization selective components (208) could include Wollaston or Senarmont prisms. A LIDAR system comprises a fast scanning mirror to direct the laser beam in a raster pattern to scan the environment.