Active Polarization LIDAR Pixel for Speckle-Resilient FMCW Sensing
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Solution Overview
Problem
FMCW LIDAR systems face challenges in accuracy due to speckle patterns from coherent light reflecting off diffuse surfaces, which reduce power coupling and broaden signal spectra, affecting range and velocity measurements.
Innovation Solution
Implementing coherent LIDAR pixels with active polarization control, where light is split into two arms with adjustable amplitude and phase, allowing for arbitrary polarization manipulation and coupling into dual-polarization optical couplers, enhancing signal reception and processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If coherent light is used for FMCW LIDAR measurements, then range and velocity information can be obtained, but speckle patterns are generated that reduce power coupling and broaden signal spectra
Solution Approach 1:
The patent implements dynamic polarization control by adjusting the relative phase and amplitude between two orthogonal polarization modes (TE and TM) in real-time. This dynamic adjustment allows the system to adapt the polarization state to match the reflected light from targets, thereby maximizing power coupling and minimizing speckle pattern effects while maintaining coherent light benefits for accurate range and velocity measurements.
Solution Approach 2:
The system changes the polarization parameters (phase difference and amplitude ratio between TE and TM modes) to optimize signal quality. By controlling these parameters, the patent transforms the polarization state to reduce speckle broadening and improve power coupling efficiency, directly addressing the reliability issue while preserving measurement precision.
2Reliability
If polarization control components are added to manipulate light polarization states, then signal quality and power coupling are improved, but device complexity increases
Solution Approach 1:
The patent combines the polarization control function with the existing waveguide structure by integrating phase shifters and amplitude controllers directly into the waveguide paths for TE and TM modes. This merging approach eliminates the need for separate external polarization control components, thereby improving signal quality and power coupling without proportionally increasing device complexity.
Solution Approach 2:
The waveguide structure serves multiple functions: it guides light transmission and simultaneously provides the medium for polarization control through integrated phase shifters and amplitude controllers. This multi-functionality reduces the need for additional dedicated polarization control components, addressing the complexity issue while achieving improved signal quality.
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 improves signal quality by maximizing beat signal amplitude and sensitivity to specific polarizations, leading to enhanced accuracy in range and velocity measurements in FMCW LIDAR systems.
Implementation Method 1
a 2x2 splitter configured to divide the coherent light into two orthogonal polarization modes, each having equal amplitude
Implementation Method 2
a phase shifter to adjust a relative phase between the TE and TM modes
Implementation Method 3
independent amplitude controllers to independently adjust amplitudes of the TE and TM modes
Implementation Method 4
a grating coupler to couple the manipulated coherent light into free space
Implementation Method 5
an optical mixer to combine the local oscillator signal with the reflected light to produce beat signals
Data Source
Figure 1A
Figure 1B
Figure 2
AI summary
A light detection and ranging (LIDAR) pixel includes a polarization controller, a grating coupler, and an optical mixer. The polarization controller includes a phase shifter that sets a phase of light in a first arm of the polarization controller and a second arm of the polarization controller.