LIDAR System Noise Reduction
Optics
LIDAR System Noise Reduction (LAR-TOPS-323)
Polarized LIDAR with photon sieve boosts signal-to-noise ratio (SNR)
Overview
In order to overcome significant noise from solar background and backscatter this LIDAR system utilizes a laser light source that is azimuthally polarized or has Orbital Angular Momentum (OAM).
A photon sieve is used to produce a ring pattern on the focal plane corresponding from the light of the return signal and causes stray light that is not polarized to produce a clustered region at the center of the ring pattern that is distinct from the laser return.
The photon sieve can be used as the front end lens of a telescope or as an internal optical component after a traditional telescope. This technology can also be employed in encrypted communications and navigation.
The Technology
State of the art space-based LIDARs typically require a telescope with sufficient area to increase the return signal on the detector to levels above the noise floor of the detectors. Two major drivers of the signal-to-noise ratio (SNR) on the detectors are the laser output energy and the round trip distance traveled by the laser signal. The SNR on the detectors can be increased by increasing the telescope reflector area or by decreasing the system noise. If these techniques are not an option, this method can be used to separate stray light from polarized laser light in the LIDAR system and improve the SNR.
The method includes generating a beam of azimuthally polarized or OAM light utilizing an optical transmitter comprising a laser light source. The method includes providing an optical receiver including optical sensors at a focal plane with a photon sieve that produces a ring pattern on the focal plane corresponding to a laser return signal. The ring pattern comprises azimuthally polarized or OAM light that is transmitted by the transmitter and reflected towards the receiver. The photon sieve is utilized to cause stray light that is not polarized to cluster centrally, and away from the ring pattern created by the LIDAR signal. This technology could also be used with space based and terrestrial LIDAR for encrypted line of sight communications. The unique revolution frequencies of the LIDAR make any attempt to intercept the communication pointless for those who don't know the specific mode of the source.
The lidar system also has use cases for short range navigation for Urban Air Mobility (UAM) vehicles providing input as to whether there is significant enough clear air turbulence on a given path as to be dangerous to an aerial vehicle.
Benefits
- Significantly reduced detector noise such via solar background and traditional backscatter LIDAR
- Offers enhanced signal to noise ratio for a given configuration
- Makes smaller reflector LIDAR and/or systems with greater noise levels viable
Applications
- Remote sensing for autonomous sensing for navigation
- Provides additional communication security layer for sensitive content
- Aerosol monitoring of industrial sites
- Emissions monitoring of vehicles
Similar Results
Recirculating Advanced Coupled-cavity Etalon Receiver (RACER)
Advanced Coupled-cavity Etalon (ACE) significantly improves both in-band transmission and out-of-band rejection. In some cases, 12% more light is transmitted inside the passband and >3x more light is rejected outside the passband. Incorporating ACE into the recirculating etalon receiver (RER) improves performance significantly. ACE increases the wavelength resolution and enables closer channel spacing resulting in a very efficient, high resolution spectrometer. RACER has both high resolution and a high photon efficiency which allows flexibility for trading different combinations of reduced cross-talk and closer channel spacing.
Fine-pointing Optical Communication System Using Laser Arrays
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Space Optical Communications Using Laser Beams
This invention provides a new method for optical data transmissions from satellites using laser arrays for laser beam pointing. The system is simple, static, compact, and provides accurate pointing, acquisition, and tracking (PAT). It combines a lens system and a vertical-cavity surface-emitting laser VCSEL)/Photodetector Array, both mature technologies, in a novel way for PAT. It can improve the PAT system's size, weight, and power (SWaP) in comparison to current systems. Preliminary analysis indicates that this system is applicable to transmissions between satellites in low-Earth orbit (LEO) and ground terminals. Computer simulations using this design have been made for the application of this innovation to a CubeSat in LEO. The computer simulations included modeling the laser source and diffraction effects due to wave optics. The pointing used a diffraction limited lens system and a VCSEL array. These capabilities make it possible to model laser beam propagation over long space communication distances. Laser beam pointing is very challenging for LEO, including science missions. Current architectures use dynamical systems, (i.e., moving parts, e.g., fast-steering mirrors (FSM), and/or gimbals) to turn the laser to point to the ground terminal, and some use vibration isolation platforms as well. This static system has the potential to replace the current dynamic systems and vibration isolation platforms, dependent on studies for the particular application. For these electro-optical systems, reaction times to pointing changes and vibrations are on the nanosecond time scale, much faster than those for mechanical systems. For LEO terminals, slew rates are not a concern with this new system.
Optical Head-Mounted Display System for Laser Safety Eyewear
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Fast Optical Shutter, Chopper, Modulator, and Deflector
A laser or a light source is incident on a detector. It usually passes through a shutter that can open and then close to limit the amount of light hitting the detector. There are limitations on the speed, size and cost of such apertures. The design of this technology uses DLP mirror technology. It can rapidly deflect the incoming light beam onto an aperture, which blocks the beam path, or through the aperture, which allows it to go onto the detector. The DLP mirror in this shutter uses an aperture design that is nearly 3 orders of magnitudes faster (shorter exposure time) than similar-sized aperture using conventional commercial-off-the-shelf mechanical shutters and 1-2 orders of magnitude smaller and cheaper than higher-performing custom-made shutters that are used by a few labs around the world.
The DLP mirror is actuated via a computer controlled oscillator circuit. A laser beam directed to the mirror is either passed to a target detector, or diverted, based on the inputs from the circuit. In this manner, the DLP mirror / circuit can act as a fast shutter, modulator, or chopper for the light beam. One novel feature of this invention is the application of the DLP to divert a beam onto or off a detector for instrumentation systems.
