AMORPHOUS FLUORINATED POLYIMIDE OPTICAL-FIBER COATING
An optical fiber includes a glass structure to guide light along a longitudinal axis of the optical fiber, and an amorphous coating disposed on and surrounding the glass structure. The amorphous coating includes at least one fluorinated polyimide. A repeating unit each fluorinated polyimide includes two imide groups and at least one fluorinated aliphatic spacer group. Each imide group is attached to a terminus of a fluorinated aromatic group. The amorphous coating has a low refractive index, high-temperature stability, and low optical absorption, making the optical fiber suitable for high-power applications subject to high temperatures. The amorphous quality of the coating is compatible with fiber drawing and provides the necessary mechanical strength for the optical fiber when in use.
1 . An optical fiber, comprising:
a glass structure to guide light along a longitudinal axis of the optical fiber; and
an amorphous coating disposed on and surrounding the glass structure, the amorphous coating including at least one fluorinated polyimide, a repeating unit of each of the at least one fluorinated polyimide including:
two imide groups, each of the two imide groups attached to a terminus of a fluorinated aromatic group, and
at least one fluorinated aliphatic spacer group.
2 . The optical fiber of claim 1 , wherein the repeating unit further includes an additional fluorinated aromatic group.
3 . The optical fiber of claim 1 , wherein each of the at least one fluorinated polyimide is fully fluorinated.
4 . The optical fiber of claim 1 , wherein a molar ratio of C—F bonds to C—H bonds is at least 9:1 for each of the at least one fluorinated polyimide.
5 . The optical fiber of claim 1 , wherein the at least one fluorinated polyimide constitutes at least 15 weight percent of the amorphous coating.
6 . The optical fiber of claim 1 , wherein a backbone of each of the at least one fluorinated polyimide includes at least one fluorinated aliphatic spacer group within the repeating unit.
7 . The optical fiber of claim 6 , wherein the repeating unit further includes at least one other fluorinated aliphatic spacer group that is not located on the backbone.
8 . The optical fiber of claim 1 , wherein each of the at least one fluorinated aliphatic spacer group includes a difluoromethylene group.
9 . The optical fiber of claim 1 , wherein each of the at least one fluorinated aliphatic spacer group includes at least one difluoromethylene group in a backbone of the fluorinated polyimide.
10 . The optical fiber of claim 1 , wherein each of the at least one fluorinated aliphatic spacer group includes a chain of difluoromethylene groups attached to each other along a backbone of the fluorinated polyimide.
11 . The optical fiber of claim 10 , wherein the chain of difluoromethylene groups includes between 2 and 10 difluoromethylene groups.
12 . The optical fiber of claim 1 , wherein the two imide groups are attached to the same fluorinated aromatic group.
13 . The optical fiber of claim 1 , wherein the two imide groups are attached to the same fluorinated aromatic ring.
14 . The optical fiber of claim 1 , wherein the two imide groups are attached to two respective fluorinated aromatic groups separated from each other by at least one fluorinated aliphatic spacer group.
15 . The optical fiber of claim 1 , wherein the amorphous coating further includes an adhesion promoter and a thermal stabilizer.
16 . The optical fiber of claim 1 , wherein the amorphous coating has a lower refractive index than a portion of the glass structure in direct contact with the amorphous coating.
17 . The optical fiber of claim 1 , wherein a refractive index of the amorphous coating is less than 1.35 throughout a wavelength range from 1 to 2 micrometers.
18 . The optical fiber of claim 1 , wherein the glass structure includes:
a solid glass core; and
a solid glass cladding surrounding and having (a) a lower refractive index than the solid glass core and (b) a higher refractive index than the amorphous coating, the amorphous coating being deposited on the solid glass cladding.
19 . The optical fiber of claim 1 , wherein the glass structure includes:
a hollow glass tube, the amorphous coating being deposited on a radially-outward facing surface of the hollow glass tube; and
a plurality of glass cladding elements (a) distributed about the longitudinal axis of the optical fiber to surround and define a hollow core thereof, (b) positioned inside the hollow glass tube, and (c) connected to and supported by the hollow glass tube.
20 . A chemical mixture for forming an amorphous coating on an optical fiber, comprising:
at least one fluorinated polyimide, a repeating unit of each of the at least one fluorinated polyimide including:
two imide groups, each of the two imide groups attached to a terminus of a fluorinated aromatic group, and
at least one fluorinated aliphatic spacer group;
an adhesion promoter;
a thermal stabilizer; and
a solvent.
21 . The chemical mixture of claim 20 , wherein the solvent is fluorinated.
22 . The chemical mixture of claim 20 , wherein the solvent is fully fluorinated.
23 . The chemical mixture of claim 20 , wherein the fluorinated polyimide constitutes between 10 and 50 weight % of the chemical mixture, the adhesion promotor constitutes between 0.5 and 5 weight % of the chemical mixture, the thermal stabilizer constitutes between 0.1 and 2 weight % of the chemical mixture, and the solvent constitutes between 40 and 90 weight % of the chemical mixture.