Dual-Loop Sagnac Fiber Sensor for Rotational Noise
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Solution Overview
Problem
Sagnac interferometer optical fibre current sensors are adversely affected by rotational movement, which can cause large phase shifts in polarisation modes, making it difficult to accurately measure current flow.
Innovation Solution
A sensing unit with a dual-loop sensing coil is designed, where the loops are interconnected and inclined to each other, allowing light to propagate in opposite directions, minimizing sensitivity to rotational movement while maintaining high current sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single sensing coil is used in a Sagnac interferometer, then the device structure is simple, but rotational movement causes large phase shifts that adversely affect measurement accuracy
Solution Approach 1:
The sensing coil is divided into two separate loops (first loop and second loop) that are interconnected. Each loop encloses different conductor portions, and light propagates in opposite directions through each loop. This segmentation allows the system to differentiate between phase shifts caused by current and those caused by rotational movement, thereby improving measurement accuracy while maintaining reasonable structural complexity.
2Object-affected harmful factors
If the sensing coil loops are disposed in a common plane, then rotational sensitivity is minimized, but the device requires precise alignment
Solution Approach 1:
The two loops are configured with asymmetric characteristics - they enclose different conductor portions and light propagates in opposite directions through each loop. This asymmetric design creates different sensitivity patterns to rotational movement, allowing the system to nullify rotational effects through differential measurement while providing tolerance for alignment variations during manufacturing.
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 dual-loop sensing coil configuration effectively nullifies the effects of rotational movement, providing accurate current measurements by reducing phase shifts caused by rotational movements while maintaining high sensitivity to current changes.
Implementation Method 1
Sagnac interferometer optical fibre current sensor
Implementation Method 2
spun single mode birefringent ('Hi-Bi') optical fibre
Implementation Method 3
interferometric sensor having an optic fiber which forms a sensing loop optical path
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
A sensing coil for a Sagnac interferometer current sensor is disclosed, the sensing coil (14) being composed of an optical fibre (for example a spun polarising Hi-Bi fibre) that is arranged in use to transmit a single elliptical polarisation state and the sensing coil comprising at least two interconnected loops (15 and 16 or 26 and 27 or 28 and 29). At least one of the loops is arranged in use to enclose a current conductor (11, 12 or 25) and the loops are interconnected such that light propagating in a first direction (23 or 30) in the first loop will propagate in a second, opposite, direction (24 or 31) in the other or, if more than one, in each other loop, whereby the sensing coil provides minimal sensitivity to rotational movement. Also disclosed are a sensing unit (Fig. 5) that incorporates the sensing coil and a current sensor (Fig. 1) that incorporates the sensing unit.