Optical Vapor Cell Filter for Laser Air Data Signal Isolation
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Solution Overview
Problem
Existing laser air-data systems face challenges in accurately measuring air data metrics due to the presence of background light, which can overwhelm the Doppler-shifted reflected signal and hinder the determination of airspeed and other atmospheric metrics.
Innovation Solution
The system employs a background-light rejection filter and a vapor cell filter to separate the Doppler-shifted reflected portion from the background light, allowing for the estimation and excision of background light from the beam sampling portion, thereby isolating the Doppler-shifted signal for accurate air data calculation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of stationary object
If background light is present in the optical receiver, then the reception volume can be increased to improve measurement coverage, but the signal-to-noise ratio deteriorates due to overwhelming background light
Solution Approach 1:
The patent segments the received light into different wavelength components using a vapor cell filter that selectively transmits only the specific wavelength of the projected laser beam while blocking background light at other wavelengths. This segmentation allows the system to maintain a large reception volume while preserving signal-to-noise ratio by isolating the Doppler-shifted signal from background interference.
Solution Approach 2:
The vapor cell filter acts as an intermediary element between the optical receiver and the detection system. It mediates the interaction between the Doppler-shifted reflected signal and background light by selectively transmitting only the desired wavelength range, thereby enabling large reception volumes without compromising measurement precision.
2Adaptability or versatility
If the wavelength spectrum of the reflected portion is broadened due to Doppler shifting, then more atmospheric metrics can be measured, but the difficulty of detecting and measuring the specific Doppler-shifted signal increases
Solution Approach 1:
The patent applies local quality by using a vapor cell filter with a narrow transmission bandwidth that is precisely tuned to the specific Doppler-shifted wavelength. This allows the system to handle broad wavelength spectra containing multiple atmospheric metrics while maintaining easy detection by focusing measurement energy on the specific wavelength region of interest where the Doppler-shifted signal is present.
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 effectively reduces the impact of background light, enabling more accurate measurement of air data metrics such as airspeed, air particle concentration, and air temperature, by isolating the Doppler-shifted signal and improving the signal-to-noise ratio.
Implementation Method 1
Such relative motions cause Doppler wavelength shifting (and corresponding Doppler frequency shifting) of photons reflected by aerosols and air molecules that are moving relative to the aircraft
Implementation Method 2
The light received by the optical receiver is transmitted through the vapor cell filter from a first end to a second end. The vapor cell filter has a narrow stop-band characterized by a characteristic wavelength.
Implementation Method 3
The background-light rejection filter is configured to separate the light received by the optical receiver as filtered by the vapor cell filter into a beam sampling portion and a complementary non-beam portion.
Implementation Method 4
A light projector is configured to project a beam of light into a projection volume of an atmosphere
Implementation Method 5
each typically a monochromatic beam of light
Implementation Method 6
For aerosols, Mie scattering typically predominates
Implementation Method 7
For air molecules, Rayleigh scattering typically predominates
Implementation Method 8
A reflected portion of each of the projected beams of light is then backscattered by aerosols (small particles that are suspended in the atmosphere)
Data Source
AI summary
Apparatus and associated methods relate to improving measurement of metrics of air data of an atmosphere outside an aircraft. Such measurements are improved by estimating a daylight portion of light received by an optical receiver configured to receive a reflected portion of the projected beam backscattered by the atmosphere. Estimation of the daylight portion is performed using a daylight filter. The daylight filter receives the light received by the optical receiver after it has been filtered by a vapor cell filter and separates the light, as filtered, into a beam sampling portion and a complementary non-sampling portion. The non-beam sampling portion includes wavelengths immediately adjacent to the beam sampling portion. The non-beam sampling portion is used to estimate the daylight portion within the beam sampling portion, which also contains the reflected portion of the projected beam used for calculating the metrics of air data.