Fiber Bragg grating and fabrication method
View Patent ↗A method of fabrication of a thermally stabilized Type I fiber Bragg grating-based temperature sensing device includes doping a fiber core material with germanium or germanium oxide for enhancing photosensitivity, co-doping the fiber core material with fluorine or chorine or for increasing a mean coordination number; and ultraviolet laser inscribing a periodic or quasiperiodic modulated refractive index structure in the fiber core using a laser energy operating at less than 1000 milliJoules per square centimeter per pulse. The resulting sensor is operable for more than 1000 hours at temperatures up to at least 550 degrees Celsius.
1. A method of fabrication of a thermally stabilized fiber Bragg grating-based temperature sensing device comprising: doping a fiber core material with germanium or germanium dioxide for enhancing photosensitivity; co-doping the fiber core material with fluorine or chlorine for increasing a mean coordination number; and laser inscribing a periodic or quasiperiodic modulated refractive index structure in the fiber core using an ultraviolet laser with a laser energy operating at less than 1000 millijoules per square centimeter per pulse.
2. The method of claim 1 wherein laser inscribing comprises using a laser operating at less than 500 milliJoules per square centimeter per pulse.
3. The method of claim 1 wherein laser inscribing comprises using a laser operating at less than 300 milliJoules per square centimeter per pulse.
4. The method of claim 1 wherein doping comprises doping of germanium in a range of 7 weight percent to 15 weight percent.
5. The method of claim 4 wherein co-doping comprises doping of fluorine in a range of 1 weight percent to 5 weight percent.
6. The method of claim 5 wherein co-doping comprises doping of fluorine at about 2.5 weight percent.
7. The method of claim 4 wherein co-doping comprises doping of chlorine in a range of 0.5 weight percent to 5 weight percent.
8. The method of claim 1 further comprising thermally annealing the fiber core material for widening the band gap of the fiber core material.
9. The method of claim 8 wherein annealing occurs at a temperature from 300 degrees Celsius to 570 degrees Celsius for a period of time from 1 hour to 100 hours.
10. A thermally stabilized fiber Bragg grating based sensor comprising: a fiber core including a plurality of Bragg grating elements wherein the grating elements comprise a periodic or a quasiperiodic modulated refractive index structure, the fiber core is doped with germanium or germanium oxide, the fiber core is co-doped with fluorine or chorine, and the sensor is operable for more than 100 hours at temperatures up to at least 550 degrees Celsius.
11. The sensor of claim 10 further comprising a fiber cladding surrounding the fiber core in the region of the Bragg grating elements.
12. The sensor of claim 11 wherein the cladding comprises silicon dioxide.
13. The sensor of claim 12 wherein the cladding is doped with germanium, fluorine or chorine, phosphorus, or combinations thereof.
14. The sensor of claim 10 comprising germanium in a range of 7 weight percent to 15 weight percent.
15. The sensor of claim 10 comprising fluorine in a range of 1 weight percent to 5 weight percent.
16. The sensor of claim 10 comprising fluorine at about 2.5 weight percent.
17. The sensor of claim 10 comprising chlorine in a range of 0.5 weight percent to 5 weight percent.
18. The sensor of claim 10 wherein the sensor is operable for more than 100 hours at temperatures in excess of 800 degrees Celsius.
19. The sensor of claim 10 wherein the fiber core comprises silicon dioxide.
20. The sensor of claim 10 wherein the sensor comprises a Type I fiber Bragg grating based sensor.