Fiber optic sensing device and method of making and operating the same

A fiber optic sensing device, comprising:

• a core having a first index of refraction and a plurality of grating elements each having an index of refraction different from the first index of refraction, the core comprising:
• a first portion, wherein the distance between adjacent grating elements is at a first distance;
• a second portion, wherein the distance between adjacent grating elements is at a second distance different than the first distance;
• and
• a third portion, wherein the distance between adjacent grating elements is at the first distance;
• wherein the second portion is disposed between the first and third portions;
• a light source configured to illuminate the core;
• and
• a detector system configured to estimate at least one parameter based upon at least one diffraction peak generated from the plurality of grating elements.

A method, comprising:

• providing a source of light to a fiber optic sensor cable having a plurality of grating elements;
• reflecting a first wavelength of light via a first pair of grating elements such that waves of the first wavelength of light are in phase with one another;
• reflecting a second wavelength of light via a second pair of grating elements such that waves of the second wavelength of light are in phase with one another;
• and
• reflecting the first wavelength of light via a third pair of grating elements, wherein at least one grating element of the second pair of grating elements is located between at least one grating element of the first pair of grating elements and at least one grating element of the third pair of grating elements such that waves of the first wavelength of light are in phase with one another.

A method of sensing a plurality of parameters, comprising:

• providing a light source to a fiber optic sensor cable having first and third pair of grating elements configured to reflect a first wavelength of light and a second pair of grating elements configured to reflect a second wavelength of light, wherein at least one grating element of the second pair of grating elements is located between at least one grating of the first and third pair of grating elements;
• detecting light emitted from the fiber optic sensor cable;
• detecting diffraction peaks from the light emitted from the fiber optic sensor cable;
• and
• correlating the diffraction peaks to changes in monitored parameters.

A method of fabricating a fiber optic sensing device, comprising:

• providing a core having a first index of refraction;
• providing a first pair of grating elements configured to reflect a first wavelength of light in phase, wherein the distance between adjacent grating elements of the first pair is at a first distance;
• providing a second pair of grating elements configured to reflect a second wavelength of light in phase, wherein the distance between adjacent grating elements of the second pair is at a second distance;
• providing a third pair of grating elements configured to reflect the first wavelength of light in phase, wherein at least one grating element of the second pair of grating elements is located between at least one grating element of the first pair and at least one grating element of the third pair;
• and
• disposing a cladding circumferentially about the core.

A method of fabricating a fiber optic sensor cable, comprising:

• providing a core having a first index of refraction;
• mechanically altering the core to form altered portions within the core, wherein an index of refraction of each of the altered portions is different than the first index of refraction;
• and
• disposing a cladding circumferentially about the core.

A distributed sensor system for sensing a parameter in a harsh environment, comprising:

• a plurality of sensors disposed on a distributed cable, wherein each of the plurality of sensor comprises:
• a core having a first index of refraction;
• and
• a plurality of mechanically altered portions each having an index of refraction different than the first index of refraction.

A fiber optic sensor cable, comprising:

• a core;
• and
• a cladding disposed circumferentially about the core;
• wherein the core comprises first, second, and third portions, the second portion being located between the first and third portions, the first and third portions having a first index of refraction and the second portion having a second index of refraction different from the first index of refraction.