Method for determining distributed birefringence variations in a polarization-maintaining optical fiber

A system for determining distributed birefringence variations in a polarization-maintaining optical fiber (PM fiber), the system being optically connected to the PM fiber, the system comprising:

• a controller;
• a detector communicatively connected to the controller;
• and
• a probe signal generating module,
• the system being configured to:
• cause a pump signal to be sent into the PM fiber at a first moment in time to generate a Brillouin dynamic grating (BDG) in the PM fiber along a first polarization direction at an interaction region of the PM fiber, the pump signal being polarized in the first polarization direction;
• cause a first chirped probe optical pulse to be sent into the PM fiber at a second moment in time subsequent to the first moment in time, the first chirped probe signal being polarized in the second polarization direction, the second polarization direction being orthogonal to the first direction;
• receive, at the detector, a first reflected signal at a third moment in time, the first reflected signal being a first portion of the first chirped probe optical pulse reflected by the BDG receive, at the detector, a second reflected signal at a fourth moment in time, the second reflected signal being a second portion of the first chirped probe optical pulse reflected by the BDG at the interaction region of the PM fiber;
• and
• determine a variation of birefringence of the PM fiber at the interaction section based on the second, third and fourth moments in time, the variation of birefringence being indicative of a variation of physical disturbance of the PM fiber between times of reflections on the BDG of the first and second reflected signals.