High PMD Fiber Optic Gyroscope for Simplified Alignment
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Solution Overview
Problem
Fiber-optic gyroscopes face limitations in sensitivity and manufacturing complexity due to the use of polarization maintaining fibers, which require precise alignment and result in signal attenuation, and standard single-mode fibers require expensive Lyot depolarizers, limiting their length and sensitivity.
Innovation Solution
Employing a high polarization mode dispersion (PMD) single-mode optical fiber operating in a coupled regime, where the group propagation time differential (DGD) is higher than the decoherence time of the source, to achieve polarization scrambling and maintain sensitivity without the need for precise alignment or depolarizers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a polarization maintaining fiber is used to preserve polarization state, then the polarization state is maintained along the fiber, but precise alignment is required and signal attenuation occurs
Solution Approach 1:
The invention extracts the polarization maintenance function from the fiber itself by using a standard single-mode fiber combined with an input polarizer. Instead of relying on the fiber to maintain polarization, the system extracts only the necessary polarization state at the input and accepts any polarization state at the output, eliminating the need for precise alignment while maintaining reliable operation.
Solution Approach 2:
The invention inverts the conventional approach by not requiring the fiber to maintain polarization throughout its length. Instead, it allows the polarization state to evolve freely along the fiber and only enforces polarization control at the input end, reversing the traditional problem-solution paradigm.
2Ease of manufacture
If a standard single-mode fiber is used without polarization maintenance, then manufacturing is simplified, but the fiber length is limited due to polarization-related sensitivity loss
Solution Approach 1:
The invention extracts the polarization control requirement from the entire fiber length and concentrates it only at the input end through the use of a polarizer. This allows standard single-mode fibers to be used without polarization maintenance along the fiber, enabling much longer fiber lengths (several kilometers) while maintaining gyroscope sensitivity.
3Reliability
If Lyot depolarizers are added to standard single-mode fiber to maintain sensitivity, then sensitivity is preserved, but device complexity and cost increase
Solution Approach 1:
The invention extracts the polarization control function from complex depolarizing components and implements it simply through an input polarizer. By controlling only the input polarization state and accepting any output polarization, the system maintains sensitivity without requiring Lyot depolarizers or other complex polarization management components.
Solution Approach 2:
The invention replaces expensive, complex polarization maintenance components with a simple, inexpensive input polarizer. This single component provides the necessary polarization control without the need for costly depolarizers or precise alignment mechanisms, significantly reducing device complexity and cost.
4Reliability
If polarization maintaining fiber is used, then polarization is preserved, but signal attenuation reduces the maximum usable fiber length
Solution Approach 1:
The invention extracts the polarization stability requirement from the entire fiber path and implements it only at the input through a polarizer. This allows the use of standard single-mode fibers with lower attenuation coefficients, enabling much longer fiber lengths (several kilometers) while maintaining polarization stability at the critical measurement point.
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 simplifies manufacturing, increases fiber length and sensitivity, and maintains constant sensitivity by ensuring half the light passes through the polarizer, while avoiding the use of expensive depolarizers and reducing alignment constraints.
Implementation Method 1
Employing a high polarization mode dispersion (PMD) single-mode optical fiber operating in a coupled regime... to achieve polarization scrambling
Implementation Method 2
The fiber-optic gyroscopes are more and more used for rotation measurements... A fiber-optic gyroscope is a Sagnac-ring interferometer
Implementation Method 3
a first beam splitter (2) (referred to as the source-receiver splitter)... a second splitter (4) (referred to as the coil splitter)... capable of splitting the incident beam into a first and a second beam
Implementation Method 4
a spatial single-mode filter and a polarizer capable of receiving the incident beam from the source and of transmitting said linearly polarized spatial single-mode incident beam
Implementation Method 5
a detector capable of detecting the interference of the output beam... the first and second beams interfere with each other and these interferences are read at the detector
Data Source
AI summary
Disclosed is a fiber optic interferometer including: a wideband optical source having a decoherence time τDC; a coil including N turns of a fiber optic with length L; an optical element separating the incident beam into first and second beams coupled to first and second ends of the fiber respectively, so the first beam travels through the fiber optic in a first direction and the second beam travels through the fiber optic in a counter propagating direction; and a detector detecting the intensity of the output beam. The fiber optic is a high polarization mode dispersion type, and the length L of the fiber optic coil is more than twice the fiber correlation length, so the fiber operates in a coupled PMD mode, and the propagation differential group delay between two orthogonal polarization states, accumulated over the length of the fiber, is greater than the decoherence time of the source.