Laser Radar System Gigahertz Frequency Shift
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Solution Overview
Problem
Conventional laser radar systems face challenges in achieving large frequency shifts between signal and local oscillator light, making it difficult to perform high-resolution distance and movement characteristic measurements of targets with short pulse widths, especially due to limited frequency differences and difficulties in downsizing or integrating heterodyne detection systems.
Innovation Solution
A laser radar system that utilizes a semiconductor laser to output light at different frequencies, an optical splitter to separate these lights into signal and local oscillator light, an optical modulator to create pulsed light, and an optical heterodyne receiver to perform heterodyne detection on scattered light, allowing for a longer signal light path length than the local oscillator light path length, enabling gigahertz-level frequency shifts and high-resolution measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional optical frequency shifters are used to perform heterodyne detection, then the system can achieve frequency shifting, but the frequency shift is limited and gigahertz-level shifts cannot be realized
Solution Approach 1:
The patent changes the fundamental parameter of frequency shifting from using optical frequency shifters (acousto-optic modulators) to directly modulating the semiconductor laser's output frequency. By controlling the laser's injection current, the system achieves gigahertz-level frequency shifts between the first light and second light, overcoming the conventional limitation of limited frequency shifting capability.
2Measurement precision
If heterodyne detection is performed on pulsed light with short pulse widths, then high-resolution distance measurement is achieved, but large frequency shifts of gigahertz-level or more are required which cannot be realized with conventional techniques
Solution Approach 1:
The system directly modulates the semiconductor laser's oscillation frequency by controlling the injection current, enabling frequency shifts of gigahertz-level or more. This parameter change approach allows the system to generate the large frequency differences required for heterodyne detection on nanosecond-order pulsed signals, achieving both high measurement precision and reliable frequency shifting.
Solution Approach 2:
The patent employs periodic frequency modulation of the semiconductor laser, switching between first frequency and second frequency in alternating periods. The optical modulator similarly creates periodic pulsed light signals. This periodic action enables the system to generate the necessary frequency differences for detecting short pulse widths while maintaining signal integrity for high-resolution measurements.
3Device complexity
If direct detection method is used, then the system configuration is simple, but thermal noise is dominant and reception sensitivity is degraded
Solution Approach 1:
The patent implements dynamic frequency modulation, where the semiconductor laser's frequency is continuously varied between first and second frequencies during operation. This dynamic approach enables heterodyne detection by creating a time-varying frequency difference between signal light and local oscillator light, thereby achieving high reception sensitivity while maintaining practical system complexity through the use of directly modulated laser sources.
4Measurement precision
If a modulator is used to shift frequency of transmission light or local oscillator light, then heterodyne detection with high sensitivity is achieved, but downsizing or integration becomes difficult
Solution Approach 1:
The patent merges the frequency shifting function directly into the semiconductor laser by utilizing its direct frequency modulation capability through injection current control. This integration eliminates the need for separate external modulators and frequency shifters, thereby achieving heterodyne detection with high sensitivity while enabling system downsizing and simplifying the overall configuration.
Solution Approach 2:
The semiconductor laser performs its own frequency shifting function by directly modulating its output frequency in response to injection current changes. This self-service capability eliminates the need for external frequency shifting devices, reducing system complexity and enabling easier integration while maintaining the high reception sensitivity required for heterodyne detection on pulsed light.
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 configuration allows for high-resolution distance and movement characteristic measurements of targets with short pulse widths, overcoming the limitations of conventional systems by achieving larger frequency shifts and enabling the detection of nanosecond-order pulse signals, while also facilitating system downsizing and integration.
Implementation Method 1
a semiconductor laser to output first light having a first frequency in a first period and second light having a second frequency in a second period
Implementation Method 2
an optical splitter to split the first light and the second light outputted from the semiconductor laser into signal light and local oscillator light
Implementation Method 3
an optical modulator to modulate the signal light into pulsed light
Implementation Method 4
an optical antenna to radiate the pulsed light modulated by the optical modulator into space and to receive, as reception light, scattered light of the pulsed light from a target
Implementation Method 5
an optical heterodyne receiver to perform, using the local oscillator light, heterodyne detection on the reception light
Implementation Method 6
measurement circuitry to measure a propagation time of the scattered light from the target
Data Source
AI summary
A laser radar system according to the present invention includes: a light source to output light having a first frequency in a first period and light having a second frequency in a second period; an optical splitter to split the lights, outputted from the light source, into signal light and local oscillator light; an optical modulator to modulate the signal light into pulsed light; an optical antenna to output the pulsed light into space and to receive, as reception light, the scattered light from a target; an optical heterodyne receiver to perform heterodyne detection on the reception light by using the local oscillator light; and a measurement unit to measure the distance to the target or the movement characteristics of the target by using the reception signal detected by the optical heterodyne receiver, wherein the optical heterodyne receiver performs the heterodyne detection on the first frequency of the reception light by using the second frequency of the local oscillator light. With this configuration, a large amount of frequency shift can be provided between the signal light and the local oscillator light, and thus, the distance to the target can be measured with high resolution by using short pulsed-light.