Optical sensor utilizing hollow-core photonic bandgap fiber with low phase thermal constant
View Patent ↗An optical sensor includes a directional coupler comprising at least a first port, a second port, and a third port. The first port is in optical communication with the second port and with the third port such that a 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. The optical sensor further includes a photonic bandgap fiber having a hollow core and an inner cladding generally surrounding the core. The photonic bandgap fiber is in optical communication with the second port and with the third port. 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. The photonic bandgap fiber has a phase thermal constant S less than 8 parts-per-million per degree Celsius.
1. An optical sensor comprising:
a directional coupler comprising at least a first port, a second port, and a third port, the first port in optical communication with the second port and with the third port such that a 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; and
a photonic bandgap fiber having a hollow core and an inner cladding generally surrounding the core, 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 parts-per-million per degree Celsius.
2. The optical sensor of claim 1 , wherein the phase thermal constant S is less than 6 part-per-million per degree Celsius.
3. The optical sensor of claim 1 , wherein the phase thermal constant S is less than 4 part-per-million per degree Celsius.
4. The optical sensor of claim 1 , wherein the phase thermal constant S is less than 1.4 part-per-million per degree Celsius.
5. The optical sensor of claim 1 , wherein the photonic bandgap fiber further comprises an outer cladding generally surrounding the inner cladding.
6. The optical sensor of claim 5 , wherein the photonic bandgap fiber further comprises a jacket generally surrounding the outer cladding.
7. The optical sensor of claim 6 , wherein the jacket comprises a polyimide layer having a thickness less than or equal to 5 microns.
8. The optical sensor of claim 7 , wherein the polyimide layer has a thickness of about 2.5 microns.
9. The optical sensor of claim 7 , wherein the jacket further comprises an amorphous carbon coating generally surrounded by the polyimide layer.
10. The optical sensor of claim 1 , wherein the inner cladding comprises a material having a first refractive index and a periodic array of regions having a second refractive index less than the first refractive index, the regions having a center-to-center distance of Λ.
11. The optical sensor of claim 1 , wherein the photonic bandgap fiber is a single-mode fiber.
12. The optical sensor of claim 1 , wherein the photonic bandgap fiber is a multi-mode fiber.
13. The optical sensor of claim 1 , wherein the photonic bandgap fiber is a single polarization fiber.
14. The optical sensor of claim 1 , wherein the photonic bandgap fiber further comprises an outer cladding generally surrounding the inner cladding and a jacket generally surrounding the outer cladding, wherein the outer cladding has an area A cl , a Young's modulus E cl , and a coefficient of thermal expansion α cl , wherein the jacket has an area A J , a Young's modulus E J , and a coefficient of thermal expansion α J , wherein a quantity
A
J
A
cl
E
J
E
cl
α
J
α
cl
is less than or equal to 2.5.
15. The optical sensor of claim 14 , wherein the quantity is less than or equal to 1.
16. The optical sensor of claim 1 , further comprising an optical detector in optical communication with the directional coupler to receive the second optical signal and the third optical signal after the second and third optical signals have traversed the photonic bandgap fiber.
17. The optical sensor of claim 1 , wherein the core contains air.
18. The optical sensor of claim 1 , wherein the photonic bandgap fiber is a coil.
19. The optical sensor of claim 18 , wherein the coil is wound with quadrupole winding.
20. 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.
21. The method of claim 20 , wherein the core contains air.
22. The method of claim 20 , wherein the perturbation comprises a rotation of the portion of the photonic bandgap fiber.
23. The method of claim 20 , wherein the perturbation comprises a change of pressure applied to the portion of the photonic bandgap fiber.
24. The method of claim 20 , wherein the perturbation comprises a movement of the portion of the photonic bandgap fiber.
25. 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.