Circular Polarization Diversity Element for Programmable Lidar Scanning
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Solution Overview
Problem
Conventional Lidar systems face challenges with polarization diversity for circularly polarized light, require fine optical axis adjustments, are unsuitable for high-temperature environments, and lack programmable scanning capabilities for efficient light beam manipulation.
Innovation Solution
A circular polarization-type polarization diversity element and light beam digital scanning element using polarization switches and gratings, enabling programmable scanning with arbitrary frequency and pattern, and a Lidar system configuration that eliminates the need for complex optical axis adjustments and is resistant to high temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a conventional polarization diversity scheme using linear polarized light separation is used, then linear polarized light can be effectively controlled, but circularly polarized light cannot be handled
Solution Approach 1:
The patent changes the polarization parameter from linear to circular by introducing a quarter-wave plate that converts linearly polarized light to circularly polarized light. This allows the polarization diversity element to handle both linear and circular polarized light, resolving the contradiction between linear polarization effectiveness and circular polarization capability.
Solution Approach 2:
The patent creates a universal polarization diversity element that can handle multiple polarization states (linear and circular) by combining a quarter-wave plate with the conventional polarization separation system. This multi-functional design allows the same device to process different polarization types without requiring separate systems.
2Object-affected harmful factors
If a coaxial system with MEMS mirror is used, then external light interference is reduced, but light power reception is limited by small aperture
Solution Approach 1:
The patent transitions from a reflective coaxial system to a transmissive four-dimensional scanning system using polarization gratings and wave plates. This dimensional change allows light to pass through the scanning element rather than reflect off it, enabling larger aperture areas for better light collection while maintaining resistance to external light interference through the polarization-based scanning mechanism.
3Measurement precision
If fine adjustments for optical axis assembly are required, then optical performance can be optimized, but manufacturing complexity increases
Solution Approach 1:
The patent employs polarization-based scanning elements that inherently maintain optical alignment through their polarization-maintaining properties. The system self-aligns through the polarization state management, eliminating the need for complex manual optical axis adjustments during assembly. This self-aligning characteristic significantly simplifies manufacturing while maintaining optical performance.
4Productivity
If semiconductor laser and light receiving element are used, then light emission and detection can be achieved, but performance degrades at high temperatures
Solution Approach 1:
The patent introduces polarization-maintaining optical fibers as intermediaries between the light source and scanning elements, and between the scanning elements and detector. These fibers act as temperature-compensating mediators that maintain stable light transmission through temperature variations, protecting the sensitive semiconductor components from direct thermal exposure while maintaining light emission and detection capabilities.
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
Enables effective polarization diversity for circularly polarized light, facilitates mass production, allows Lidar to be mounted on vehicles, and achieves fast, programmable scanning with high precision and efficiency.
Implementation Method 1
a polarization switching element (91) made of blue phase liquid crystal
Implementation Method 2
two polarization gratings (92) having different pitch values in a direction parallel to the optical axis
Implementation Method 3
separating an incoming light into two orthogonal linearly polarized light beams with a polarizing beam splitter
Implementation Method 4
two wedge blocks (93) made of a material having a high refractive index, sandwiching the polarization switching element (91) in a point-symmetrical manner
Data Source
Figure 1
Figure 2
Figure 3~4A
AI summary
In the prior art, a scanning element used for Lidar in the self-driving car technology employed a mirror or the like continuously rotated by MEMS, and due to the inertia of the mirror or the like, the scanning element was suited for a raster scan that scans a scene in one stroke, but was incapable of discontinuous movement from one arbitrary point to another, and programmable scanning with an arbitrary frequency in an arbitrary pattern, as fast as the raster scan. In the present invention, there was fabricated Lidar, which is composed of a polarization diversity scheme and a scanning element, wherein the polarization diversity scheme uses two polarization gratings, each polarization grating having a thickness such that it becomes a half-wave plate, wherein birefringent directors of each polarization grating rotate with a period A, wherein these polarization gratings are disposed with a desired interval from each other, wherein a half-wave plate is inserted in either one of two paths of separated, exiting right-handed or left-handed circularly polarized light beam, depending on a rotation direction of the circularly polarized light, to thereby enable conversion of light beams into parallel proximate circularly polarized light beams with the same rotational direction, and wherein the scanning element has a multistage structure of polarization switch-polarization grating sets connected in combination, with a polarization switch and a polarization grating being defined as one set.