Optical Angle Modulation Measurement Using Delayed Self-Heterodyne
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Solution Overview
Problem
Existing optical angle modulation measurement techniques face challenges in accurately measuring temporal waveforms due to light intensity modulation, calibration requirements, and interferometer stability issues, particularly when dealing with semiconductor lasers directly modulated by injection current.
Innovation Solution
The delayed self-heterodyne method employs a heterodyne interferometer with a photodetector and phase demodulator to demodulate the beat signal, allowing for the measurement of optical angle modulation temporal waveforms without being affected by light intensity modulation and without the need for calibration or interferometer stabilization, by setting the delay time to a negligibly small value compared to the time scale of optical frequency or phase changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If optical angle modulation is measured using conventional interferometric methods, then measurement capability is provided, but light intensity modulation affects measurement accuracy and calibration is required
Solution Approach 1:
The invention extracts only the phase information from the interferometric signal while discarding the intensity information. By using phase demodulation techniques on the beat signal, the measurement system obtains optical frequency and phase modulation data without being influenced by concurrent light intensity modulation, thus eliminating the harmful effect of intensity variations on measurement accuracy
Solution Approach 2:
The invention introduces a phase demodulator as an intermediary component between the photodetector and the measurement output. This phase demodulator acts as a mediator that converts the interferometric beat signal into pure phase information, filtering out the unwanted intensity modulation effects and providing clean measurement data
2Measurement precision
If conventional interferometric measurement methods are used, then optical angle modulation can be detected, but calibration procedures are required which complicate the measurement process
Solution Approach 1:
The invention enables the measurement system to be self-calibrating by using the laser's own coherent light as both the measurement beam and the reference beam. The delayed self-heterodyne configuration allows the system to automatically establish its reference without requiring external calibration standards or procedures, making the system self-sufficient and eliminating complex calibration steps
3Device complexity
If interferometer optical path length is not stabilized, then device complexity is reduced, but measurement accuracy deteriorates due to path length fluctuations
Solution Approach 1:
The invention dynamically adjusts the delay time parameter of the optical path difference to be negligibly small compared to the modulation period. This dynamic parameter selection allows the system to operate without active stabilization while maintaining measurement accuracy, as the short delay minimizes the impact of path length fluctuations during the measurement window
4Measurement precision
If delay time is set to negligibly small value, then measurement of temporal waveform is enabled, but the delay medium length must be very short
Solution Approach 1:
The invention changes the critical parameter of delay time from a fixed value determined by physical length to a dynamically optimized value that is negligibly small compared to the modulation period. This parameter optimization enables temporal waveform measurement capability while minimizing the required delay medium length, allowing the use of compact optical components
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 enables accurate measurement of optical angle modulation temporal waveforms, simplifying the measurement process and improving the accuracy of optical sensing systems by separating optical frequency and phase modulation components effectively.
Implementation Method 1
a heterodyne interferometer 3 which is fed with laser light to be measured
Implementation Method 2
output light of the heterodyne interferometer 3
Implementation Method 3
a light detector 4 which is configured to receive output light of the heterodyne interferometer 3 to perform heterodyne detection
Data Source
Figure 1~3
Figure 4~5
Figure 6~7
AI summary
The present invention provides an apparatus and a method which enable, in optical angle modulation measurement of laser light to be measured by a delayed self-heterodyne method, accurate measurement of a temporal waveform of optical angle modulation, without any influence by light intensity modulation, without necessity of calibration, and without necessity of stabilizing an interferometer. In an optical angle modulation measurement apparatus by a delayed self-heterodyne method, a heterodyne interferometer that is fed with laser light to be measured; a photodetector that receives output light of the heterodyne interferometer and performs heterodyne detection of the output light to output a beat signal; a phase demodulator that is configured to demodulates a phase of a beat signal; and a temporal waveform analyzer that is configured to obtain a temporal waveform of optical angle modulation, from the phase of the beat signal are provided. In an optical angle modulation measurement method by a delayed self-heterodyne method, laser light to be measured which is optical-angle modulated is input to a heterodyne interferometer, heterodyne detection of the output light is performed by a photodetector, and a temporal waveform of optical angle modulation is obtained by demodulating a phase of the beat signal.