Wavelength-Steered 3D Imaging Lidar for SmallSat Coverage
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Solution Overview
Problem
Existing lidar systems for small satellites lack sufficient spatial coverage and resolution, suffer from spatial speckle noise due to small footprint sizes, and are limited by linear detector array size, leading to inefficiencies in size, weight, power, and cost.
Innovation Solution
A lidar system utilizing a fast-tunable seed laser, high-power fiber amplifier, high-performance transmission gratings, and a linear-mode, photon-sensitive detector array, enabling rapid beam steering across multiple tracks with reduced power and size, and incorporating time-division multiplexing to achieve gapless swath mapping with sub-meter resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If existing lidar systems are used for small satellites, then the system can perform basic ranging, but spatial coverage and resolution are insufficient
Solution Approach 1:
The patent segments the illumination into multiple independent laser beams, each targeting a specific track or footprint on the surface. By dividing the total coverage area into discrete beams that can be independently controlled and steered, the system achieves both high resolution within each beam footprint and extensive spatial coverage across multiple tracks simultaneously
Solution Approach 2:
The patent introduces wavelength as an additional dimension for beam steering control. By rapidly tuning the laser wavelength and using diffraction gratings to convert wavelength changes into angular deviations, the system can steer multiple beams across different tracks without mechanical moving parts, thereby expanding spatial coverage while maintaining sub-meter resolution
2Weight of stationary object
If small footprint sizes and small receiver apertures are used, then the lidar system is more compact, but spatial speckle noise increases significantly
Solution Approach 1:
The patent segments the received signal by using multiple detector elements (such as linear detector arrays or superpixels) that independently detect light from different spatial locations. By segmenting the detection process, the system can apply independent processing to each segment, reducing the impact of speckle noise through spatial diversity while maintaining compact aperture sizes
Solution Approach 2:
The patent employs periodic modulation of the laser beam (such as dithering or oscillating the beam position) and corresponds periodic sampling in the detection process. This periodic action allows the system to distinguish between speckle noise and actual surface features through temporal filtering and signal processing, reducing noise impact while keeping the system compact
3Area of stationary object
If linear detector array size is increased to expand footprint swath, then the coverage area increases, but device complexity and cost increase
Solution Approach 1:
The patent employs dynamic beam steering to redirect a single laser beam across multiple tracks sequentially or in rapid succession. By making the beam position dynamic rather than static, the system can cover a large footprint swath using a single detector element or a small array, avoiding the complexity of large-scale detector arrays while maintaining extensive coverage
Solution Approach 2:
The patent makes the single laser beam and single detector element multi-functional by enabling them to serve multiple tracks and coverage areas through rapid steering and tuning. The same beam and detector that measure one location can quickly transition to measure another location, providing universal coverage capability without requiring dedicated detectors for each track, thereby reducing overall device complexity
4Ease of manufacture
If laser peak power is reduced to 4 kW, then commercial fiber amplifiers can be used, but illumination intensity decreases
Solution Approach 1:
The patent segments the total illumination requirement into multiple lower-power laser beams distributed across different tracks. Instead of concentrating all power into a single high-power beam, the system uses multiple parallel beams at reduced power levels, which can be generated by commercial fiber amplifiers. The combined effect of multiple beams provides sufficient total illumination while enabling the use of commercially available, easier-to-manufacture amplifier components
Solution Approach 2:
The patent merges the output of multiple low-power laser beams to achieve the cumulative illumination effect equivalent to a single high-power beam. By combining signals from multiple commercial fiber amplifiers operating at 4 kW each, the system achieves the necessary total illumination intensity for accurate ranging while maintaining ease of manufacture through the use of commercially available amplifier technology
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 system achieves unprecedented precision and accurate 3-D imaging with reduced power, size, and cost, enabling new SmallSat missions by improving spatial resolution and reducing speckle noise, allowing for efficient mapping of surfaces like the Moon's polar regions.
Implementation Method 1
the first transmitter grating diffracts and steers the collimated laser beam from the fiber amplifier by wavelength via the primary mirror to a surface, to an arbitrary subset of up to 2000 resolvable footprints
Implementation Method 2
the returned laser pulses are detected by a high-quantum-efficiency, single-photon-sensitive mercury cadmium telluride (HgCdTe) avalanche photo diode (APD) linear detector array
Data Source
AI summary
The present invention relates to a lidar system including: laser transmitter and receiver systems, the laser transmitter system including: a wavelength-tunable seed laser which emits pulses at selected wavelength points, and switches between wavelengths within a switching time of <200 ns; a fiber amplifier which amplifies the laser pulses up to 200 kW to a transmitter grating; and a transmitter telescope including primary and secondary mirrors. The laser beam is directed from the transmitter grating to the secondary then primary mirrors, and the first transmitter grating is imaged on the primary mirror to minimize laser beam wander thereon. The transmitter grating diffracts and steers the laser beam by wavelength to a surface, to an arbitrary subset of <2000 resolvable footprints along a cross-track direction at a beam pointing angle switching time of <200 ns, such that footprints illuminated by the laser beam on the surface are imaged in 3D.