High-temperature hydrogen-resistant scattering enhancement in optical fiber
Described herein are systems, methods, and articles of manufacture for a spatially nonuniform scattering profile along its length, whose backscattering signal can be used for sensing even after fiber attenuation increases due to the conditions in the sensing environment. In one embodiment, the fiber has been pre-exposed to the conditions that produce attenuation, and the spatially nonuniform profile compensates for this. Subsequent exposure then results in very little or at least acceptable levels of additional attenuation. An exemplary fiber comprises a fiber length and an optical back scatter along the fiber length greater than a Rayleigh back scattering over the fiber length, wherein the optical back scatter does not decrease along the fiber length by more than 3 dB after exposure to a hydrogen-rich first environment having a given pressure and temperature. An exemplary method comprises drawing a fiber, applying a UV coating, post-processing the fiber using an interferogram, measuring optical back scatter enhancement dependence based on a UV dosage, incrementally increasing the reflectivity, exposing the fiber to a hydrogen-rich first environment.
1 . An optical fiber, comprising:
a fiber length; and
an optical back scatter that increases along the fiber length, wherein the optical back scatter from the first end to the opposing end is incrementally increased in discrete lengths to increase the optical back scatter by approximately 1-2 dB in each discrete length, wherein the optical back scatter is greater than a Rayleigh back scattering over the fiber length, wherein the optical back scatter does not decrease along the fiber length by more than 3 dB after exposure to a hydrogen-rich environment at 150° C. and 75 psi.
2 . The optical fiber of claim 1 , wherein the optical fiber in the hydrogen-rich environment features an attenuation of greater than 4 dB/km.
3 . The optical fiber of claim 1 , wherein the optical back scatter is 5 dB greater than the Rayleigh back scattering over the fiber length.
4 . An optical fiber, comprising:
a fiber length, a first end, and an opposing end; and
an optical back scatter that increases along the fiber length such that the optical fiber is exposed to molecular hydrogen at 150° C. and 75 psi, the optical back scatter from the first end of the optical fiber is within 3 dB to the optical back scatter at the opposing end of the optical fiber, wherein the optical back scatter from the first end to the opposing end is incrementally increased in discrete lengths to increase the optical back scatter by approximately 1-2 dB in each discrete length, and wherein the optical back scatter is within 3 dB of the optical back scattering from any point in between the front end and the opposing end.
5 . The optical fiber of claim 4 , wherein the optical fiber features an attenuation of greater than 4 dB/km.
6 . A method, comprising:
drawing a fiber;
applying a UV coating during the drawing of the fiber;
post-processing the fiber using an interferogram;
measuring optical back scatter enhancement dependence based on a UV dosage;
incrementally increasing the optical back scatter from the first end to the opposing end in discrete lengths to increase the optical back scatter by approximately 1-2 dB in each discrete length; and
exposing the fiber to a hydrogen-rich first environment.
7 . The method of claim 6 , further comprising:
placing the fiber in a second environment, wherein the second environment features at least one of a lower hydrogen pressure than the first environment or a lower temperature than the first environment, such that the fiber will have a smaller decrease in optical back scattering over time compared to the fiber prior to exposure to the hydrogen-rich first environment.
8 . The method of claim 6 , wherein the optical fiber in the hydrogen-rich first environment features an attenuation of greater than 4 dB/km, and wherein the attenuation is no greater than 6 dB/km when the optical fiber is exposed to the second environment.
9 . The method of claim 6 , wherein the optical back scatter from an end of the fiber is within 3 dB to the optical back scatter at an opposite end of the fiber.
10 . The method of claim 6 , wherein the post-processing step includes using a 248 nm pulsed chirped interferogram.
11 . The method of claim 6 , wherein the hydrogen-rich first environment features a temperature of 150° C. and a hydrogen pressure of 75 psi.