Hollow-Core Optical-Fiber Filter for RFOG Phase Noise Reduction
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Solution Overview
Problem
Semiconductor lasers in resonator-fiber-optic gyros (RFOGs) suffer from significant phase noise, which degrades the performance of rotation rate measurements.
Innovation Solution
The implementation of frequency stabilized reference lasers with hollow-core optical-fiber filters that reduce phase noise by phase-locking slave lasers to a master laser and using hollow-core optical-fiber filters to further minimize phase fluctuations beyond the servo bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If semiconductor lasers are used in RFOGs, then cost is reduced, but phase noise increases degrading measurement performance
Solution Approach 1:
A hollow-core 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 spectrum by transmitting only the desired wavelength while blocking noise components, thereby enabling the use of low-cost semiconductor lasers without degrading the rotation rate measurement accuracy.
Solution Approach 2:
The hollow-core optical fiber filter provides localized spectral filtering at a specific wavelength region. By designing the photonic bandgap structure with specific geometric parameters, the filter creates a narrow transmission window that selectively passes the laser wavelength while rejecting phase noise, thus improving measurement precision locally at the critical wavelength without affecting other system components.
2Adaptability or versatility
If hollow-core photonic bandgap fiber is used with micro-fiber insertion, then filter tunability is achieved, but device complexity increases
Solution Approach 1:
The filter structure incorporates a movable micro-fiber that can be positioned at different locations within the hollow-core photonic bandgap fiber. By dynamically adjusting the micro-fiber position, the filter's transmission characteristics and central wavelength can be tuned, providing adaptability while maintaining a relatively simple overall structure compared to other tunable filter designs.
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 results in low-noise, coherent optical beams that enhance the accuracy of rotation rate measurements by reducing laser frequency noise and preventing non-linear effects, thereby improving the performance of RFOGs.
Implementation Method 1
phase-locking slave lasers to a master laser
Implementation Method 2
hollow-core optical-fiber filters that reduce phase noise by phase-locking slave lasers to a master laser and using hollow-core optical-fiber filters to further minimize phase fluctuations beyond the servo bandwidth
Implementation Method 3
The basic principle of RFOG operation is that the effective resonator path length in a clockwise (CW) and counter-clockwise (CCW) direction is different when the rotation of the fiber ring resonant cavity has a nonzero component in a resonator axis. By measuring the CW and CCW resonance frequency difference, which is proportional to Sagnac phase shift due to rotation, the RFOG can accurately measure the rotation rate.
Implementation Method 4
a fiber ring resonant cavity to enhance the signal to noise ratio in the measurement of a rotation-induced Sagnac effect within the resonant cavity
Implementation Method 5
Xiaozhen Wang et al.: 'Tunable Fabry-Perot filter using hollow-core photonic bandgap fiber and micro-fiber for a narrow-linewidth laser'
Data Source
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AI summary
A hollow-core optical-fiber filter is provided. The hollow-core optical-fiber filter includes a hollow-core 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 hollow-core optical-fiber filter also includes a first reflective end-cap positioned at the first end-face and a second reflective end-cap positioned at the second end-face. When an optical beam from a laser is coupled into one of the first end-face or the second end-face, an optical output from the opposing end-face has a narrow linewidth and low frequency noise fluctuations.