Coherent LiDAR Receiver Optics for High-Pulse-Energy Fiber Lasers
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Solution Overview
Problem
Conventional fiber-based lidar receivers are unable to handle high pulse-energy laser transmissions exceeding 1.0 mJ, leading to component damage and degradation of the laser beam phase front, limiting the effective measurement distance of these systems.
Innovation Solution
A lidar receiver design that includes a quarter-wave plate to convert the circular polarization and convert the circular polarization to a second linear polarization, a beam splitter to separate and reflect the atmospheric backscatter, and a beam splitter to convert the circular polarization to a second linear polarization, and a beam splitter to separate and reflect the circular polarization, and a beam splitter to separate and reflect the atmospheric backscatter, and a quarter-wave plate to convert the circular polarization to a second linear polarization, and a detector to combine the atmospheric backscatter, and a beam expander to spatially expand the output beam, and a mode-matching optical assembly to couple the atmospheric backscatter to an output optical fiber.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If conventional fiber-based receiver designs are used with high pulse-energy laser transmitters, then the laser pulse-energy can be increased to extend measurement distance, but the high laser pulse-energy will burn the fiber surfaces and glass core, causing attenuation and phase front degradation
Solution Approach 1:
The receiver system is segmented into distinct functional modules: a first optical assembly with dielectric mirrors to handle the high-energy laser beam, a beam splitter to separate the laser beam from atmospheric backscatter, and a second optical assembly with fiber optic components to detect the backscatter. This segmentation allows each component to be optimized for its specific function, protecting the fiber from direct exposure to high pulse-energy while maintaining detection capability.
Solution Approach 2:
A beam splitter is introduced as an intermediary component between the high-energy laser beam path and the fiber optic detection path. The beam splitter directs the atmospheric backscatter (low energy) into the fiber optic assembly while allowing the high-energy laser beam to pass through to the dielectric mirror assembly, thereby protecting the fiber from thermal damage while maintaining the detection function.
2Use of energy by moving object
If larger area fibers are used to distribute energy load, then the fiber can handle higher pulse-energy, but multi-mode operation is created which degrades the phase front required for coherent detection
Solution Approach 1:
The system separates the high-energy laser beam handling function from the coherent detection function by using different optical paths. The first optical assembly with dielectric mirrors handles the high-energy beam, while the second optical assembly with single-mode fiber maintains the phase front quality for coherent detection. This segmentation allows each subsystem to be optimized independently.
Solution Approach 2:
Different optical components are assigned different qualities suited to their specific functions: dielectric mirrors with high damage thresholds are used where high pulse-energy is present, while single-mode fiber with high phase front quality is used where coherent detection is required. The beam splitter creates spatial separation between these different quality requirements.
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
The design effectively handles high pulse-energy laser transmissions, minimizing component damage and maintaining the phase front, enabling coherent detection and extending the measurement range of these systems.
Implementation Method 1
a quarter-wave plate configured to receive atmospheric backscatter having a circular polarization and convert the circular polarization to a second linear polarization
Implementation Method 2
a beam splitter configured to reflect the atmospheric backscatter having the second linear polarization while allowing the high pulse-energy output beam having the first linear polarization to pass through the beam splitter
Implementation Method 3
a first optical assembly having a half-wave plate and a pair of dielectric laser mirrors to direct atmospheric backscatter reflected by the beam splitter to the half-wave plate. The half-wave plate is configured to optimize the second linear polarization of the atmospheric backscatter
Implementation Method 4
a second optical assembly having an output optical fiber and a mode-matching optical assembly for coupling the atmospheric backscatter emitted by the half-wave plate to the output optical fiber
Implementation Method 5
a detector having a fiber optic coupler coupled to the output optical fiber and the pulsed local oscillator laser beam and configured to provide at least one output signal that comprises a portion of the atmospheric backscatter and a portion of the pulsed local oscillator laser beam
Data Source
AI summary
A lidar receiver for use with a fiber laser transmitter that generates a high pulse-energy output beam and a pulsed local oscillator laser beam. The lidar receiver includes an atmospheric backscatter routing assembly having a thin-film beam splitter to reflect atmospheric backscatter while allowing the high pulse-energy output beam to pass through the beam splitter. The beam splitter has a dielectric coating to minimize absorption. The backscatter routing assembly includes a first optical assembly having a half-wave plate and dielectric laser mirrors to direct atmospheric backscatter reflected by the beam splitter to the half-wave plate. The dielectric laser mirrors are configured to minimize absorption. The backscatter routing assembly includes a second optical assembly having a mode-matching optical assembly and output optical fiber. The mode-matching optical assembly couples the atmospheric backscatter emitted by the half-wave plate to the output optical fiber. The output optical fiber is coupled to a detector.