Frequency-Modulated Laser Source for Fiber-Optic Gyroscope Noise Reduction
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Solution Overview
Problem
Fiber-optic gyroscopes (FOGs) face limitations due to backscattering noise and excess noise from broadband sources, which hinder their sensitivity and stability, particularly in applications like aircraft navigation, where they are not suitable as sole inertial navigation instruments.
Innovation Solution
A fiber-optic sensor system utilizing a frequency-modulated laser source with a coherence length longer than the optical fiber coil, where light is transmitted in reciprocal paths and frequency-modulated to reduce backscattering noise by shifting it away from the signal frequency, allowing for effective filtering and improving sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a laser source is used in fiber-optic gyroscope, then the sensitivity is expected to be shot-noise-limited, but backscattering in the optical fiber dramatically deteriorates the sensitivity
Solution Approach 1:
The patent changes the coherence parameter of the light source by using a superluminescent diode instead of a laser, which has a shorter coherence length. This parameter change reduces the coherence of backscattered light, causing it to average out and reduce noise, while maintaining sufficient coherence for the interferometric measurement function
Solution Approach 2:
The patent converts the harmful backscattering effect into a beneficial outcome by using a broadband light source with short coherence length. The backscattered light from different positions in the fiber has different phases and averages out to zero, reducing noise while the direct light maintains sufficient coherence for measurement
2Measurement precision
If a superfluorescent source is used to reduce backscattering noise, then sensitivity improves, but excess noise from the broadband source remains
Solution Approach 1:
The patent optimizes the coherence length parameter to be comparable to or slightly longer than the fiber coil length. This allows the system to benefit from reduced backscattering noise while minimizing excess noise from the broadband source, achieving a balance between the two noise sources
Solution Approach 2:
The patent uses frequency modulation of the light source to dynamically shift the operating wavelength, which helps separate the signal from noise and reduces the impact of excess noise from the broadband source while maintaining sensitivity
3Use of energy by moving object
If a laser source with long coherence length is used, then the signal strength is maintained, but backscattering noise increases
Solution Approach 1:
The patent changes the coherence length parameter to be optimized for the specific fiber coil length, rather than using a laser with very long coherence length. This reduces the correlation between backscattered light waves, causing them to average out and reduce noise while maintaining adequate signal strength for the measurement
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 approach significantly reduces backscattering noise and excess noise, enhancing the sensitivity and stability of FOGs, making them more suitable for navigation systems by isolating noise from the signal of interest, thereby improving rotation detection and reducing random walk errors.
Implementation Method 1
fiber-optic gyroscopes (FOGs)
Implementation Method 2
frequency-modulated laser source optically coupled to the coil. Light from the source is transmitted to the coil as a first signal propagating along the coil in a first direction and a second signal propagating along the coil in a second direction opposite to the first direction
Data Source
AI summary
A fiber-optic sensor includes an optical fiber coil and a laser source optically coupled to the coil. Light from the source is transmitted to the coil as a first optical signal and a second optical signal counter-propagating through the coil. The optical paths of the first optical signal and the second optical signal are substantially reciprocal with one another and the first optical signal and the second optical signal are combined together after counter-propagating through the coil to generate a third optical signal. The laser source is frequency-modulated or can have a coherence length longer than a length of the coil.