Balanced Heterodyne Detection of Scattered Laser Light in Bright Backgrounds
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing laser warning receivers struggle to detect scattered laser light effectively in bright incoherent backgrounds, particularly at large scattering angles and in environments with natural daylight, due to challenges in distinguishing scattered laser light from broadband noise and requiring prior knowledge of the laser wavelength.
Innovation Solution
A coherent detection method using a balanced heterodyne detection system with a non-cooperative tunable laser as a local oscillator, combined with a signal processing algorithm, to discriminate scattered laser light from incoherent background noise without optical filtering, enabling detection even before the laser hits the receiver.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If direct detection methods are used to detect scattered laser light, then the system can identify laser light when it directly hits the receiver, but the system fails to detect scattered laser light at large scattering angles in bright incoherent backgrounds
Solution Approach 1:
The patent introduces coherent detection as an intermediary method between the optical sensor and signal processing. By using a local oscillator laser to mix with the scattered laser light and convert it to an electrical signal, the system creates an intermediate representation that preserves coherence information, enabling subsequent digital signal processing to discriminate the laser signal from background noise effectively.
Solution Approach 2:
The patent replaces traditional optical filtering mechanisms with electronic/digital signal processing. Instead of using physical optical filters that require precise wavelength tuning, the system uses coherent detection followed by digital signal processing algorithms (autocorrelation, spectral analysis) to discriminate laser light from background, substituting mechanical optical filtering with electronic processing.
2Measurement precision
If narrow-band optical filtering is used to detect laser light, then the system can suppress background noise, but the system requires prior knowledge of the laser wavelength which is a burdensome demand
Solution Approach 1:
The patent implements self-service by having the system automatically determine the laser wavelength through coherent detection and spectral analysis. The local oscillator laser is tuned to match the signal laser wavelength, and the system uses autocorrelation and spectral power density analysis to identify the wavelength without requiring external information or manual tuning, allowing the system to self-calibrate.
Solution Approach 2:
The patent replaces the mechanical/optical approach of pre-tuned narrow-band filters with an electronic/digital approach. Instead of requiring the optical system to be pre-configured for specific wavelengths, the system uses coherent detection to convert optical signals to electrical signals, then employs digital spectral analysis to automatically identify the wavelength, eliminating the need for a-priori wavelength knowledge.
3Measurement precision
If ultra-sensitive detectors and nighttime operation are used to detect scattered laser light, then the system can achieve sufficient noise suppression, but the system cannot operate in bright incoherent backgrounds during daytime
Solution Approach 1:
The patent uses coherent detection as an intermediary that converts optical signals to electrical signals while preserving coherence information. This intermediate conversion allows the system to process the signal in the electrical domain where coherence can be exploited through digital signal processing, enabling operation in bright backgrounds where direct optical detection fails.
Solution Approach 2:
The patent changes the detection parameter from direct optical intensity measurement to coherent signal mixing. By multiplying the scattered laser light with a local oscillator laser and detecting the beat signal at the difference frequency, the system transforms the detection problem from measuring weak optical intensity in bright backgrounds to measuring coherent electrical signals, which can be easily distinguished from incoherent background noise.
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 method achieves nearly perfect detection of weakly scattered laser light with zero false alarms, rejecting incoherent background light and demonstrating high sensitivity across a broad wavelength range, suitable for military and civilian applications.
Implementation Method 1
A coherent detection method using a balanced heterodyne detection system with a non-cooperative tunable laser as a local oscillator
Implementation Method 2
collecting a raw optical signal by the optical sensor
Data Source
AI summary
A system and method for coherent detection for identification of scattered laser light in a detection region. The system may have an optical sensor that collects a raw optical signal. The optical signal may be mixed with a local oscillator signal to generate a mixed baseband signal. Various processing may be performed on the mixed baseband signal. The system may use the mixed baseband signal to detect whether or not scattered laser light is in the raw optical signal.