Hollow-core fibre and method of manufacturing thereof

1. A hollow-core anti-resonant-reflecting fibre (HC-AF) comprising:

a hollow-core region axially extending along the HC-AF;

an inner cladding region comprising a plurality of anti-resonant elements (AREs) and surrounding the hollow-core region; and

an outer cladding region surrounding the inner cladding region,

wherein the hollow-core region and the plurality of AREs are configured to provide phase matching of higher order hollow-core modes and ARE modes in a broadband wavelength range,

wherein the HC-AF is a non-bandgap type fibre,

wherein the plurality of AREs are non-nested AREs,

wherein the hollow-core region comprises a first transverse cross-sectional dimension (D),

wherein each of the plurality of AREs comprises a second transverse cross-sectional dimension (d), and

wherein a ratio of the first and second transverse cross-sectional dimensions (d/D) is approximated to a quotient of zeros of Bessel functions.

2. The HC-AF according to claim 1 , wherein the hollow-core region and the plurality of AREs are further configured to provide effectively endlessly single-mode (eESM) behavior.

3. The HC-AF according to claim 1 , wherein the hollow-core region and the plurality of AREs are further configured to provide at least a frequency of 10 THz in the broadband wavelength range.

4. The HC-AF according to claim 3 , wherein the hollow-core region and the plurality of AREs are further configured to provide at least a frequency of 20 THz in the broadband wavelength range.

5. The HC-AF according to claim 1 , wherein the hollow-core region and the plurality of AREs are further configured to provide phase matching for all wavelengths within a hollow-core transparency window of a transverse fundamental hollow-core mode.

6. The HC-AF according to claim 1 , wherein the refractive indices of the hollow-core region and the plurality of AREs are equal.

7. The HC-AF according to claim 1 , wherein each of the plurality of AREs comprises an elliptical transverse cross-section.

8. The HC-AF according to claim 7 , wherein each of the plurality of AREs comprises a circular transverse cross-section.

9. The HC-AF according to claim 1 , further comprising a plurality of longitudinal protrusions disposed between the inner cladding region and the outer cladding region.

10. The HC-AF according to claim 1 , wherein the plurality of AREs comprises a first plurality of AREs and a second plurality of AREs, wherein each of the first plurality of AREs has at least one physical characteristic that is different than each of the second plurality of AREs.

11. The HC-AF according to claim 1 , wherein:

the plurality of AREs comprises a first plurality of AREs and a second plurality of AREs;

each of the first plurality of AREs comprises a first transverse cross-sectional dimension (d 1 );

each of the second plurality of AREs comprises a second transverse cross-sectional dimension (d 2 ); and

the second transverse cross-sectional dimension (d 2 ) is no greater than the first transverse cross-sectional dimension (d 1 ).

12. The HC-AF according to claim 11 , further comprising a support tube disposed between the first plurality of AREs and the second plurality of AREs.

13. The HC-AF according to claim 1 , wherein

the ratio of the first and second transverse cross-sectional dimensions (d/D) is approximated to a quotient of zeros of Bessel functions of the first kind (u lm,ARE /u lm,core ), multiplied with a fitting factor in a range of about 0.9 to about 1.5, with m being the m-th zero of the Bessel functions of the first kind of order l, the zeros of the Bessel functions describing linearly polarized (LP lm ) ARE modes and linearly polarized (LP lm ) higher order hollow-core modes, respectively.

14. An optical device comprising:

a hollow-core anti-resonant-reflecting fibre (HC-AF), the HC-AF comprising:

a hollow-core region axially extending along the HC-AF;

an inner cladding region comprising a plurality of anti-resonant elements (AREs) and surrounding the hollow-core region; and

an outer cladding region surrounding the inner cladding region,

wherein the hollow-core region comprises a first transverse cross-sectional dimension (D) and each of the plurality of AREs comprises a second transverse cross-sectional dimension (d),

wherein the hollow-core region and the plurality of AREs are configured to provide phase matching of higher order hollow-core modes and ARE modes in a broadband wavelength range,

wherein the HC-AF is a non-bandgap type fibre,

wherein the plurality of AREs are non-nested AREs, and

wherein a ratio of the first and second transverse cross-sectional dimensions (d/D) is approximated to a quotient of zeros of Bessel functions.

15. The optical device according to claim 14 , wherein the ratio of the first and second transverse cross-sectional dimensions (d/D) is configured to provide effectively endlessly single-mode (eESM) behavior.

16. The optical device according to claim 14 , wherein the ratio of the first and second transverse cross-sectional dimensions (d/D) is configured to provide at least a frequency of 10 THz in the broadband wavelength range.

17. The optical device according to claim 14 , wherein the ratio of the first and second transverse cross-sectional dimensions (d/D) is configured to provide phase matching for all wavelengths within a hollow-core transparency window of a transverse fundamental hollow-core mode.

18. A method of manufacturing a hollow-core anti-resonant-reflecting fibre (HC-AF), the method comprising:

providing an inner cladding region comprising a plurality of anti-resonant elements (AREs) and an outer cladding region surrounding the inner cladding region;

coupling the plurality of AREs to an inner surface of the outer cladding region; and

forming a hollow-core region axially extending along the HC-AF and surrounded by the inner cladding region, wherein the hollow-core region comprises a first transverse cross-sectional dimension (D) and each of the plurality of AREs comprises a second transverse cross-sectional dimension (d),

wherein the hollow-core region and the AREs are configured to provide phase matching of higher order hollow-core modes and ARE modes in a broadband wavelength range,

wherein the HC-AF is a non-bandgap type fibre,

wherein the plurality of AREs are non-nested AREs, and

wherein a ratio of the first and second transverse cross-sectional dimensions (d/D) is approximated to a quotient of zeros of Bessel functions.

19. The method according to claim 18 , wherein the forming comprises forming the ratio of the first and second transverse cross-sectional dimensions (d/D) such that the broadband wavelength range covers at least a frequency of 10 THz.

20. The method according to claim 18 , further comprising filling the HC-AF with a gas, a liquid, or a material having a non-linear optical response.