# US 10,481,182 B2 · Optical sensor with spun birefringent sensing fiber > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 10,481,182 B2 - Document ID: US10481182B2 - Status: Granted - Kind: B2 - Application number: 15/434,747 - Filed: 2017-02-16 - Published: 2017-06-08 - Granted: 2019-11-19 - Earliest claimed: 2014-08-19 - Assignees: ABB Schweiz AG - Applicants: ABB Schweiz AG - Inventors: Georg Müller; Klaus Bohnert; Andreas Frank; Lin Yang - Web page: https://patentgrep.com/patent/US10481182B2 ## CPC - G01R 15/245: {using magneto-optical modulators, e.g. based on the Faraday or Cotton-Mouton effect} - G01R 15/246: {based on the Faraday, i.e. linear magneto-optic, effect} - G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12) ## Abstract There is described an optical fiber current sensor having an opto-electronic module part for detecting an optical phase shift induced by the measurand field in a sensing fiber, a sensor head including the sensing fiber, wherein the sensing fiber is a spun highly-birefringent fiber having a length L=∫ ds defined by the line integral along the space curve given by the sensing fiber coil such that the length L of the sensing fiber is sufficiently long to suppress thermal signal instabilities due to the spun character of the sensing fiber while the effective number of fiber windings is low enough to maintain a maximum sensitivity over the full measurement range of the fiber-optical sensor. ## Claims ### Claim 1 An optical fiber current sensor having an opto-electronic module part for detecting a magneto-optic phase shift induced in a sensing fiber by a magnetic field of the current, and a sensor head including the sensing fiber, wherein the sensing fiber is a spun highly-birefringent fiber having a length L=∫ ds defined by the line integral along the space curve described by the sensing fiber, wherein a sensing length is defined as L′=L for a transmission optical sensor and as L′=2L for a sensing fiber being terminated by a reflector and L ′ > L EB ⁢ λ Δλ with L EB = L LB 1 + x 2 - x ≈ 2 ⁢ xL LB and x being the spinning ratio of the spun highly-birefringent fiber, λ Δλ the ratio of center wavelength λ over the spectral width Δλ of the light in the sensing fiber, and LLB being the linear beat length which is a length section of equivalent unspun highly-birefringent fiber that produces a birefringent phase shift of 2π, and wherein D = a 2 + b 2 2 < D max , with Dmax being 50 cm or smaller and Dmax being a length characterising the available volume for the sensor head, and a and b being the two largest edge lengths of a cuboid of minimal size enclosing the sensing fiber, wherein the magneto-optic phase shift accumulated in the fiber is reduced by having at least one of the following features: (i) one or more sections of the sensing fiber forming loops enclosing the current but being counter-wound with respect to other sections of the sensing fiber forming loops enclosing the current, (ii) one or more sections of the sensing fiber being at least partly magnetically shielded, and (iii) one or more sections of the sensing fiber forming loops not enclosing the current. ### Claim 2 (depends on 1) The sensor of claim 1, wherein the sensor head is connected by a polarization maintaining fiber to the optoelectronic module. ### Claim 3 (depends on 1) The sensor according to claim 1, wherein the sensor is not a transmission optical sensor using counter-propagating light waves. ### Claim 4 (depends on 1) The sensor according to claim 1, wherein the sensing fiber being terminated by a reflector. ### Claim 5 (depends on 1) The sensor according to claim 1, wherein the sensor is a transmission optical sensor using co-propagating light waves. ### Claim 6 (depends on 1) The sensor according to claim 1, wherein the sensing fiber has one or more sections forming loops enclosing the current or being designed for enclosing the current or a current conductor carrying the current. ### Claim 7 (depends on 1) The sensor according to claim 1, wherein the one or more sections of the sensing fiber forming loops enclosing the current are designed for enclosing the current or a current conductor carrying the current; and/or the one or more sections of the sensing fiber forming loops not enclosing the current are designed for not enclosing the current or a current conductor carrying the current. ### Claim 8 (depends on 1) The sensor according to claim 1, wherein the number of counter-wound loops enclosing the current differs from the number of not counter-wound loops enclosing the current. ### Claim 9 (depends on 1) The sensor according to claim 1, having an effective winding number N eff = 1  I  ⁢  ∫ H → · d ⁢ s →  with N eff < C ⁢ L π ⁢ ⁢ D wherein ∫{right arrow over (H)}·d{right arrow over (s)} is the line integral of magnetic field vector H along the space curve defined by the sensing fiber over the sensing fiber length L, I being the current and |I| the absolute value of the current to be measured, and C being a numerical factor with 0