Overlapped chirped fiber Bragg grating sensing fiber and methods and apparatus for parameter measurement using same

An optical sensing system comprising:

• an optical sensor including an optical fiber inscribed with overlapping, chirped-frequency fiber Bragg gratings at multiple locations along the optical fiber such that light reflected from a location on the optical fiber is reflected at multiple frequencies in a range of frequencies;
• control circuitry, coupled to the optical fiber, including OFDR circuitry and configured to:
• detect measurement reflection data from the optical fiber over the range of frequencies,
• determine a change in the detected measurement reflection data over the range of frequencies, and
• determine a parameter describing a state of the optical sensor based on the determined change in the detected measurement reflection data,
• wherein a reflection wavelength of at least one of the overlapping, chirped-frequency fiber Bragg gratings exceeds a wavelength scan range of the OFDR circuitry and allows spectral shifts greater than the wavelength scan range of the OFDR circuitry to be measured by the OFDR circuitry.

A method for making an optical sensor that includes an optical fiber for use with Optical Frequency Domain Reflectometry (OFDR) circuitry, the method comprising:

• inscribing a first chirped-frequency, light refracting pattern on the optical fiber at every measurement point along at least a portion of the length of the optical sensor;
• and
• inscribing a second chirped-frequency, light refracting pattern on the optical fiber that overlaps the first chirped-frequency, light refracting pattern at every measurement point along at least the portion of the length of the sensor, the second chirped-frequency, light refracting pattern having a same pattern as the first chirped-frequency, light refracting pattern,
• inscribing a third chirped-frequency, light refracting pattern on the optical fiber that overlaps the first and second chirped-frequency, light refracting patterns at every measurement point along at least the portion of the length of the sensor, the third chirped-frequency, light refracting pattern having a same pattern as the first and second chirped-frequency, light refracting patterns,
• wherein the optical fiber inscribed with the overlapping first, second, and third chirped-frequency, light refracting patterns reflects light from a location on the optical fiber at multiple frequencies in a range of frequencies, and
• wherein at least one of multiple reflection wavelengths of the overlapping first, second, and third chirped-frequency, light refracting patterns exceeds a wavelength scan range of the OFDR circuitry and allows spectral shifts greater than the wavelength scan range of the OFDR circuitry to be measured by the OFDR circuitry.

A method for an optical system that includes an optical fiber inscribed with overlapping, chirped-frequency fiber Bragg gratings at multiple locations along the optical fiber such that light reflected from a location on the optical fiber is reflected at multiple frequencies in a range of frequencies and OFDR circuitry coupled to the optical fiber, the method comprising:

• detecting measurement reflection data from the optical fiber over the range of frequencies,
• determining a change in the detected measurement reflection data over the range of frequencies, and
• determining a parameter describing a state of the optical fiber based on the determined change in the detected measurement reflection data,
• wherein a reflection wavelength of at least one of the overlapping, chirped-frequency fiber Bragg gratings exceeds a wavelength scan range of the OFDR circuitry and allows spectral shifts greater than the wavelength scan range of the OFDR circuitry to be measured by the OFDR circuitry.