Optical-Fiber Filter for RFOG Phase Noise Reduction
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Solution Overview
Problem
Semiconductor lasers in resonator-fiber-optic gyrosscopes (RFOGs) suffer from significant phase noise, degrading the performance of rotation rate measurement systems.
Innovation Solution
The implementation of optical-fiber filters with reflective coatings at both ends, which reduce phase noise by forming a high-finesse resonant cavity, coupled with a frequency stabilized reference laser to phase-lock slave lasers, thereby minimizing phase fluctuations beyond the servo bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If semiconductor lasers are used as light sources in RFOGs, then cost is reduced, but phase noise increases significantly degrading measurement performance
Solution Approach 1:
An optical-fiber filter is introduced as an intermediary component between the semiconductor laser and the fiber ring resonant cavity. This filter acts as a mediator that cleans up the laser output by reducing phase noise and narrowing linewidth, thereby enabling the use of low-cost semiconductor lasers without sacrificing RFOG measurement performance
Solution Approach 2:
The harmful phase noise component is extracted and removed from the laser output using the optical-fiber filter. The filter selectively passes the desired narrow linewidth signal while attenuating the broadband phase noise, effectively separating the useful signal from the harmful noise
2Measurement precision
If laser phase noise is reduced using conventional filtering methods, then measurement precision improves, but device complexity and cost increase
Solution Approach 1:
The optical-fiber filter is constructed entirely from optical fiber components with reflective coatings, utilizing the fiber itself as the filtering medium. This self-service approach eliminates the need for separate complex filtering subsystems, as the fiber resonant cavity structure inherently provides the necessary noise filtering functionality
Solution Approach 2:
The optical-fiber filter serves multiple functions simultaneously: it acts as a wavelength selector, a phase noise reducer, a linewidth narower, and a coupling element between the laser and resonant cavity. This multi-functionality consolidates what would otherwise require multiple separate components into a single integrated solution
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 optical-fiber filters produce a narrow linewidth optical beam with low frequency noise, enhancing the performance of RFOGs by reducing laser frequency noise and maintaining high power handling capability, manufacturability, and cost-effectiveness.
Implementation Method 1
an optical-fiber filter includes an optical fiber having a first end-face and an opposing second end-face. The first end-face and the second end-face are coated with reflective coatings. When an optical beam emitted from a laser is coupled into one of the first end-face or the second end-face, an optical beam output from the opposing end-face has a narrow linewidth and low frequency noise fluctuations
Data Source
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AI summary
An optical-fiber filter is provided. The optical-fiber filter includes an optical fiber having a first end-face and an opposing second end-face. The first end-face and the second end-face set a fiber length. The first end-face and the second end-face are coated with reflective coatings. When an optical beam emitted from a laser is coupled into one of the first end-face or the second end-face, an optical beam output from the opposing end-face has a narrow linewidth and low frequency noise fluctuations.