Optical sensor utilizing hollow-core photonic bandgap fiber with low phase thermal constant

A method for sensing comprising:

• providing a light signal;
• propagating a first portion of the light signal in a first direction through a portion of a photonic bandgap fiber having a hollow core and an inner cladding generally surrounding the core, wherein the photonic bandgap fiber has a phase thermal constant S less than 8 parts-per-million per degree Celsius;
• propagating a second portion of the light signal in a second direction through the photonic bandgap fiber, the second direction opposite to the first direction;
• optically interfering the first and second portions of the light signal after the first and second portions of the light signal propagate through the photonic bandgap fiber, thereby producing an optical interference signal;
• subjecting at least a portion of the photonic bandgap fiber to a perturbation;
• and
• measuring variations in the optical interference signal caused by the perturbation.

An optical system comprising:

• a light source having an output that emits a first optical signal;
• a directional coupler comprising at least a first port, a second port and a third port, the first port in optical communication with the light source to receive the first optical signal emitted from the light source, the first port in optical communication with the second port and with the third port such that the first optical signal received by the first port is split into a second optical signal that propagates to the second port and a third optical signal that propagates to the third port;
• a photonic bandgap fiber having a hollow core, an inner cladding generally surrounding the core, an outer cladding generally surrounding the inner cladding, and a jacket generally surrounding the outer cladding, the photonic bandgap fiber in optical communication with the second port and with the third port, wherein the second optical signal and the third optical signal counterpropagate through the photonic bandgap fiber and return to the third port and the second port, respectively, wherein the photonic bandgap fiber has a phase thermal constant S less than 8 ppm per degree Celsius;
• and
• an optical detector in optical communication with the directional coupler, the optical detector receiving the counterpropagating second optical signal and the third optical signal after having traversed the photonic bandgap fiber.