Optical Fiber Sensor Phase Measurement Range Extension
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Solution Overview
Problem
Conventional homodyne interferometer systems are prone to errors due to laser signal intensity fluctuations and have limited measurement range, making it difficult to maintain a precise phase difference between reference and signal light, especially under temperature variations and environmental changes.
Innovation Solution
A wavelength-stabilized laser source is used to generate phase-modulated laser pulses, which are divided and applied to a motion sensor with moving mirrors, forming a Michelson Interferometer, allowing for the calculation of precise phase differences through Time Division Multiplexing and optical signal processing to eliminate measurement inaccuracies and extend the measurement range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional homodyne interferometer system is used, then the system structure is simple, but measurement precision deteriorates due to laser signal intensity fluctuations and environmental factors
Solution Approach 1:
The patent uses periodic square wave signals to modulate the phase of laser light, creating distinct time-separated measurement states. The phase modulator applies periodic phase shifts (0, 90, 180, 270 degrees) to the reference light, enabling the system to periodically sample different interference conditions and calculate phase difference through time-division multiplexing, thereby eliminating intensity fluctuation errors.
Solution Approach 2:
The patent introduces a phase modulator as an intermediary component that actively controls the phase of reference light. This intermediary device mediates between the laser source and the interferometer, adding known phase shifts to the reference beam that enable accurate phase difference calculation even when intensity varies, thus resolving the precision problem without complicating the overall system.
2Manufacturing precision
If conventional homodyne interferometer system is used, then the component requirements are relaxed, but measurement range is limited to ±90 degrees (half wavelength)
Solution Approach 1:
By applying periodic phase modulation with multiple discrete phase states (0, 90, 180, 270 degrees), the system can determine phase difference through time-division multiplexing of interference patterns. This periodic sampling approach allows unambiguous phase measurement over the full 0-360 degree range and beyond, extending measurement range to multiple wavelengths while maintaining relaxed component tolerance requirements.
Solution Approach 2:
The patent transitions from spatial interference pattern analysis to temporal phase modulation analysis. Instead of relying on spatial positioning of interference fringes, the system uses time-domain phase modulation with square wave signals, adding a temporal dimension to the measurement process. This dimensional change enables extended measurement range without compromising manufacturing precision requirements.
3Measurement precision
If phase difference is maintained within narrow range for accurate measurement, then measurement precision improves, but system adaptability to environmental changes deteriorates
Solution Approach 1:
The patent implements a feedback mechanism where the system continuously measures interference patterns under varying conditions and uses the time-division multiplexed phase information to calculate and compensate for environmental drifts. The phase modulator's periodic action provides reference information that enables the system to adapt to temperature variations while maintaining measurement precision through computational correction.
Solution Approach 2:
The periodic phase modulation creates a structured measurement sequence that samples the interference pattern at multiple known phase states. This periodic sampling provides redundant information that enables the system to distinguish between intentional phase shifts and environmental drifts, maintaining measurement precision even when operating conditions change, thus improving adaptability without sacrificing accuracy.
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 solution reduces measurement errors caused by laser signal drifts and environmental factors, enabling a wider measurement range and more accurate phase detection without requiring precise component dimensioning, thus reducing system costs and extending dynamic range.
Implementation Method 1
The laser pulse is divided into two (2) by an optical coupler, one of which is applied to a t/2 optical delay line and then is supplied to a motion sensor
Implementation Method 2
one of which is applied to a t/2 optical delay line
Implementation Method 3
The motion sensor has a weight on which laser pulse reflecting mirrors are stationed at both sides, and the weight moves according to the externally applied force
Implementation Method 4
The two reflected laser pulses are combined again by the optical coupler and forms a Michelson Interferometer
Implementation Method 5
The TDM optical signal is transformed into an electric signal by Optic to Electricity Converter (O/E)
Implementation Method 6
a laser pulse having a period T and a pulse width 3t (t1, t2 and t3) is generated, and is phase modulated to be t1 phase is equal to t2 and to be 90 degree (independently orthogonal) phase difference between t2 and t3
Data Source
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AI summary
Problem Homodyne interferometer system has advantages of a simple configuration and no power for operating the sensor. However, to get the stable operation, all the components shall be made with excellent dimension accuracy and the detection range is limited in a half light wavelength (±90 degree of light phase). Means for solving the problem An optical fiber sensor is provided in the present invention wherein an input of an optical interferometer is a periodical optical pulse, phase of the first half and the latter half of the reference pulse is 90 degree (independently orthogonal) phase difference, two (2) interferometric outputs i1 and i2 which the phase difference is 90 degree from each other, are obtained by being interfered the reference pulse and the signal pulse, θ is calculated by referring the amplitude of reference pulse (r) and the signal pulse (s) to remove the light intensity fluctuations, two (2) values of cos θ 1 and cos θ 2 are calculated and determined the positions on the cosine curve, by obtaining θ 1 and θ 2 values, Δ θ 1 and Δ θ 2, which are the phase increment or decrement of both θ 1 and θ 2 in T period is summed and becomes the sensor output signal that removes the measurement range limitation of ± 90 degree (a half wavelength of light) of light phase.