Low Power Laser Sensing With Modulated CW Source
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Solution Overview
Problem
Current laser designation systems face challenges in accurately homing targets using low-power laser signals due to low signal-to-noise ratios, particularly when the intercepting platform is far from the target, and existing solutions like multi-pixel matrix sensors are costly and less sensitive compared to quadrant sensors.
Innovation Solution
A method and laser sensor unit that utilize a modulated CW laser source with a quadrant sensor, sampling at a rate greater than the modulation frequency, and employing digital filtering to integrate energy at the modulation frequency band, enabling detection of low-power laser signals and distinguishing them from background noise, while also being capable of processing high-power signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a quadrant sensor is used for laser detection, then measurement precision and sensitivity are improved, but the ability to detect low-power laser signals in noisy environments deteriorates due to low signal-to-noise ratios
Solution Approach 1:
The laser source is modulated at a specific frequency, causing the laser signal to vary periodically. The sensor system uses synchronous detection at this modulation frequency to distinguish the periodic laser signal from non-periodic or differently-frequency background noise, thereby improving signal detection reliability in noisy environments while maintaining measurement precision
Solution Approach 2:
The system employs feedback through synchronous detection where the detection process uses the known modulation frequency as a reference. The sensor output is processed with a reference signal at the same frequency, creating a feedback mechanism that enhances the signal-to-noise ratio by reinforcing the periodic laser signal components while suppressing non-synchronized noise
2Measurement precision
If multi-pixel matrix sensors are used to improve signal detection, then detection capability is improved, but device complexity and cost increase
Solution Approach 1:
The quadrant sensor structure is designed to perform multiple functions: it detects both the position and intensity of laser spots, and with the addition of modulation detection, it also filters signals by frequency. This multi-functionality allows a single sensor type to replace what would otherwise require multiple specialized sensors, reducing overall system complexity while maintaining detection capability
Solution Approach 2:
The system changes the temporal parameter of the laser signal by applying frequency modulation. This transforms the detection problem from one requiring spatial filtering (multiple pixels) to one solvable by temporal filtering (frequency discrimination), allowing simple quadrant sensors to achieve the detection capability previously requiring complex multi-pixel matrix systems
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
Enables accurate detection and tracking of low-power laser signals, improving the signal-to-noise ratio for guiding platforms towards targets with reduced system size, weight, and cost, leveraging existing quadrant sensor technology.
Implementation Method 1
The energy received in each of the sectors of the sensor is converted into corresponding signal intensity
Data Source
AI summary
The presently disclosed subject matter includes a laser system and a respective method of detecting a signal reflected from a target illuminated by a modulated CW light source configured to generate a modulated laser signal at a predefined modulation frequency. A signal comprising true laser signal portions reflected from said target, and noise is received; the signal is filtered for selecting laser signal portions at a modulation frequency band; and the true signal portions in the signal are detected, if the energy at the modulation frequency band is greater than a given threshold.