Birefringence mitigation in an optical network

A method for obtaining optical frequency domain reflectometry (OFDR) data from an optical network and for mitigating birefringence, the optical network comprising plural optical subnetworks, the optical subnetworks each comprising (a) a reference arm comprising a first, single mode fiber segment optically connected to a first coupling point;

• and (b) a measurement arm distinct from the reference arm and comprising (i) a first optical circulator connected to the first coupling point via a second, single mode fiber segment;
• (ii) a second optical circulator for sending and receiving optical radiation to and from a sensor;
• and (iii) a single mode optical segment between the first optical circulator and the second optical circulator consisting essentially of a third, single mode fiber segment;
• the method comprising, with respect to each of the optical subnetworks;
• extracting current phase signal data from the OFDR interferometric interrogation data for the optical subnetworks;
• calculating a change in phase between the current phase signal data and previously acquired reference phase signal data from the OFDR interferometric interrogation data for the optical subnetworks;
• calculating a phase difference of a current phase signal data relative to previously acquired reference phase signal data for the MFB;
• and
• converting the compensated distribution from units of the OFDR interferometric interrogation data to units of twist to calculate MFB twist distribution data along the MFB;
• wherein birefringence is at least partially removed from the measurement arm;
• wherein each of the optical subnetworks includes a first polarization maintaining optical segment between the first optical circulator and the second optical circulator in which the polarization of the optical radiation is rotated once with respect to a second polarization maintaining optical segment, and comprising at least the second polarization maintaining optical fiber segment.

A device for mitigating birefringence in a first optical subnetwork using optical frequency domain reflectometry (OFDR) receiving optical radiation from a source and generating interrogation data, the first optical subnetwork comprising a reference arm and a measurement arm, the device for mitigating birefringence comprising, in the measurement arm:

• a first optical device which rotates polarization of the optical radiation;
• a second optical device which splits the rotated polarization optical radiation into a first polarization maintaining segment and into a second segment which further rotates polarization of the optical radiation;
• a third optical device which combines the optical radiation from the first polarization maintaining segment and the second segment for transmission to the sensor;
• and
• a return arm for receiving optical radiation from an optical circulator receiving optical radiation from the third optical device and passing the received optical radiation from the optical circulator to a polarization diversity detector (PDD) for producing the interrogation data.

A method for obtaining optical frequency domain reflectometry data using optical frequency domain reflectometry (OFDR) from an optical network and for mitigating birefringence, the optical network comprising plural optical subnetworks, the optical subnetworks each comprising (a) a reference arm comprising a first, single mode fiber segment optically connected to a first coupling point;

• and (b) a measurement arm distinct from the reference path and comprising a Michelson interferometer, the measurement arm comprising:
• (i) an outbound arm for sending optical radiation received from the source to a sensor and comprising plural optical devices which reduce polarization fading effects and mitigate birefringence through a state of polarization of the optical radiation;
• the method comprising, with respect to each of the optical subnetworks:
• acquiring OFDR interferometric interrogation data from a multifiber bundle (MFB);
• extracting current phase signal data from the OFDR interferometric interrogation data for the optical subnetworks;
• calculating a change in phase between the current phase signal data and previously acquired reference phase signal data from the OFDR interferometric interrogation data for the optical subnetworks;
• calculating a phase difference of the measurement arm relative to the reference arm;
• and
• converting the compensated distribution from units of the OFDR interferometric interrogation data to units of twist to calculate MFB twist distribution data along the MFB;
• wherein birefringence is at least partially removed from the measurement arm;
• wherein each of the optical devices includes a first optical device which rotates polarization of the optical radiation, a second optical device which splits the rotated polarization optical radiation into a first polarization maintaining segment and into a second segment which further rotates polarization of the optical radiation, and a third optical device which combines the optical radiation from the first polarization maintaining segment and the second segment for transmission to the sensor;
• and (ii) a return arm for receiving optical radiation from the third optical device and passing the received optical radiation to a polarization diversity detector (PDD) for producing the interrogation data.