Hollow-core optical fibers
A hollow-core optical fiber may include a hollow-core extending along a central longitudinal axis of the hollow-core optical fiber; a substrate; a first cladding positioned between the central longitudinal axis and an inner surface of the substrate, the first cladding surrounding the central longitudinal axis of the hollow-core optical fiber and having a Bragg structure configured to provide a photonic bandgap operable to confine an optical signal with a wavelength λ propagating in the hollow-core of the hollow-core optical fiber; and a second cladding positioned between the central longitudinal axis of the hollow-core optical fiber and the inner surface of the substrate, the second cladding surrounding the central longitudinal axis of the hollow-core optical fiber and including a plurality of cladding elements configured to provide an anti-resonant effect at the wavelength λ, the anti-resonant effect operable to confine the optical signal at the wavelength λ in the hollow-core.
1 . A hollow-core optical fiber comprising:
a hollow core extending along a central longitudinal axis of the hollow-core optical fiber;
a substrate, the substrate comprising a tubular shape and an inner surface surrounding the central longitudinal axis of the hollow-core optical fiber;
a first cladding positioned between the central longitudinal axis of the hollow-core optical fiber and the inner surface of the substrate, the first cladding surrounding the central longitudinal axis of the hollow-core optical fiber and comprising a Bragg structure, the Bragg structure configured to provide a photonic bandgap operable to confine an optical signal with a wavelength λ propagating in the hollow core of the hollow-core optical fiber, the Bragg structure further configured to provide an anti-resonant effect at the wavelength λ, the anti-resonant effect operable to confine the optical signal at the wavelength λ in the hollow core of the hollow-core optical fiber; and
a second cladding positioned between the central longitudinal axis of the hollow-core optical fiber and the inner surface of the substrate, the second cladding surrounding the central longitudinal axis of the hollow-core optical fiber and comprising a plurality of cladding elements, the plurality of cladding elements configured to provide an anti-resonant effect at the wavelength λ, the anti-resonant effect operable to confine the optical signal at the wavelength λ in the hollow core of the hollow-core optical fiber; each of the plurality of cladding elements extending in a direction parallel to the central longitudinal axis of the hollow-core optical fiber and comprising a glass sheet configured as a spiral.
2 . The hollow-core optical fiber of claim 1 , wherein the second cladding is positioned between the first cladding and the central longitudinal axis of the hollow-core optical fiber.
3 . The hollow-core optical fiber of claim 1 , wherein the first cladding is in direct contact with the second cladding.
4 . The hollow-core optical fiber of claim 1 , wherein the first cladding is in direct contact with the inner surface of the substrate.
5 . The hollow-core optical fiber of claim 1 , wherein the Bragg structure comprises alternating concentric first layers and second layers, the first layers comprising a first refractive index at the wavelength λ and the second layers comprising a second refractive index at the wavelength λ, the second refractive index differing from the first refractive index.
6 . The hollow-core optical fiber of claim 5 , wherein the Bragg structure comprises 3 or more first layers.
7 . The hollow-core optical fiber of claim 5 , wherein the Bragg structure comprises 30 or fewer first layers.
8 . The hollow-core optical fiber of claim 5 , wherein each first layer has a thickness from 0.1 μm to 4.0 μm.
9 . The hollow-core optical fiber of claim 5 , wherein a difference between the first refractive index and the second refractive index is greater than 0.10.
10 . The hollow-core optical fiber of claim 5 , wherein the first layers comprise glass and the second layers comprise air.
11 . The hollow-core optical fiber of claim 10 , wherein the first layers are interconnected.
12 . The hollow-core optical fiber of claim 11 , wherein the first layers are interconnected by a plurality of ribs extending parallel to the central longitudinal axis of the hollow-core optical fiber.
13 . The hollow-core optical fiber of claim 12 , wherein each of the plurality of ribs has a width from 0.1 μm to 5 μm.
14 . The hollow-core optical fiber of claim 11 , wherein the first layers are interconnected by a plurality of tubes extending parallel to the central longitudinal axis.
15 . The hollow-core optical fiber of claim 14 , wherein each of the plurality of tubes are positioned on radii of the hollow-core optical fiber that do not pass through the plurality of cladding elements.
16 . The hollow-core optical fiber of claim 1 , wherein each cladding element is spaced apart from adjacent cladding elements in a circumferential direction about the central longitudinal axis.
17 . The hollow-core optical fiber of claim 1 , wherein each of the plurality of cladding elements extends in a direction parallel to the central longitudinal axis of the hollow-core optical fiber and each of the plurality of cladding elements comprises a capillary.
18 . The hollow-core optical fiber of claim 1 , wherein the wavelength λ is in a range from 350 nm to 8000 nm.
19 . The hollow-core optical fiber of claim 1 , wherein the first cladding and the second cladding are configured such that a confinement loss of a fundamental mode of the optical signal propagating in the hollow-core optical fiber is less than 10 −2 dB/km at the wavelength λ.