Hollow-core optical fibers

Abstract

An anti-resonant hollow-core fiber comprising a first tubular, cladding element which defines an internal cladding surface, a plurality of second tubular elements which are attached to the cladding surface and together define a core with an effective radius, the second tubular elements being arranged in spaced relation and adjacent ones of the second tubular elements having a spacing therebetween, and a plurality of third tubular elements, each nested within a respective one of the second tubular elements.

1 - 53 . (canceled) 
     
     
         54 . An anti-resonant hollow-core fiber comprising a first tubular, cladding element which defines an internal cladding surface, a plurality of second tubular elements which are attached to the cladding surface and together define a core with an effective radius, the second tubular elements being arranged in spaced relation and adjacent ones of the second tubular elements having a spacing therebetween, and a plurality of third tubular elements, each nested within a respective one of the second tubular elements to provide nested tubular arrangements. 
     
     
         55 . The fiber of  claim 54 , wherein (i) the nested tubular arrangements are arranged in symmetrical relation at the cladding surface, and/or (ii) one or more of the tubular elements have different sectional shape. 
     
     
         56 . The fiber of  claim 54 , wherein (i) the first tubular element is circular in section, and/or (ii) the second tubular elements are circular in section or have a longer dimension in a radial direction than a tangential direction, optionally elliptical or oval in section. 
     
     
         57 . The fiber of  claim 54 , wherein the tubular elements are formed of glass, optionally silica, optionally the tubular elements are formed of glass having a refractive index of at least about 1.4, optionally about 1.4 to about 3, optionally about 1.4 to about 2.8. 
     
     
         58 . The fiber of  claim 54 , wherein the second tubular elements are attached to the first tubular element each only at a single location on the cladding surface, optionally the third tubular elements are attached to the respective second tubular elements at the locations at which the second tubular elements are attached to the cladding surface. 
     
     
         59 . The fiber of  claim 54 , wherein (i) a ratio of the spacing of the adjacent second tubular elements and a wall thickness of the second tubular elements is greater than about 0.5, optionally greater than about 0.8, optionally greater than about 1, and optionally greater than about 2, or (ii) a ratio of the spacing of the adjacent second tubular elements and a wall thickness of the second tubular elements is less than about 12, optionally less than about 10, optionally less than about 8, and optionally less than about 6. 
     
     
         60 . The fiber of  claim 54 , wherein the second and third tubular elements have substantially the same wall thickness. 
     
     
         61 . The fiber of  claim 54 , wherein (i) a ratio of a radial spacing between radially-inner walls of the second and third tubular elements to the core radius is between about 0.3 and about 1.0, optionally between about 0.35 and about 0.95, (ii) a ratio of a radial spacing between radially-inner walls of the second and third tubular elements to the core radius is between about 0.05 and about 0.4, optionally between about 0.1 and about 0.3, optionally between about 0.2 and about 0.3, or (iii) a ratio of a radial spacing between radially-inner walls of the second and third tubular elements to the core radius is between about 0.8 and about 1.2, optionally between about 0.9 and 1.2, optionally between about 1.0 and about 1.2. 
     
     
         62 . The fiber of  claim 54 , wherein the fiber has (i) a fundamental loss of less than 0.15 dB/km at wavelengths of between about 1.0 μm and about 2.5 μm, (ii) a fundamental loss of about 1 dB/km at wavelengths of up to about 2.7 μm, (iii) a fundamental loss of less than 1 dB/m at wavelengths of up to about 5 μm, or (iv) a fundamental loss of less than 4 dB/m at wavelengths of up to about 7 μm. 
     
     
         63 . The fiber of  claim 54 , wherein the fiber has a fundamental loss of less than about 1 dB/km at wavelengths of down to about 0.8 μm. 
     
     
         64 . The fiber of  claim 54 , wherein a fraction of an optical power guided by the fiber in a material of the tubular elements is less than about 1×10 −3 , optionally less than about 1×10 −4 . 
     
     
         65 . The fiber of  claim 54 , wherein the core radius is optionally less than about 50 μm, optionally less than about 40 μm, optionally less than about 30 μm, optionally less than about 25 μm, optionally less than about 20 μm, optionally less than about 15 μm, optionally less than about 13 μm. 
     
     
         66 . The fiber of  claim 54 , wherein the fiber includes (i) six nested arrangements of tubular elements, or (ii) three, four or five nested arrangements of tubular elements. 
     
     
         67 . The fiber of  claim 54 , wherein the fiber (i) exhibits an effective single mode, optionally a differential between a fundamental mode and a lowest-loss high-order mode is at least one order or magnitude, optionally at least two orders of magnitude, optionally the nested arrangement of tubular elements supports a mode having an effective index (neff) which has a differential in the effective mode (Δneff) of less than about 0.001 to that of the higher-order mode in the core, and/or (ii) allows any mode field diameter (MFD) to be selected for any given wavelength, optionally in combination with a solid-core fiber, and optionally directly spliced thereto, wherein the hollow-core fiber has a mode field diameter which is matched to that of the solid-core fiber, optionally the solid-core fiber is a fiber from fiber laser, optionally an ytterbium-doped fiber laser. 
     
     
         68 . The fiber of  claim 54 , wherein a differential in a fundamental loss between the fiber when straight and when coiled to a diameter of 10 mm is less than two orders of magnitude, optionally less than one order of magnitude, optionally less than half an order or magnitude. 
     
     
         69 . The fiber of  claim 54 , further comprising a plurality of fourth tubular elements which are each nested within respective ones of the third tubular elements, optionally the second, third and fourth tubular elements have substantially the same wall thickness. 
     
     
         70 . The fiber of  claim 54 , wherein the second, outer tubular element of at least one of the nested tubular arrangements has a wall thickness t 1  which is different to that of a wall thickness t 2  of the second, outer tubular element of at least one of the other nested tubular arrangements, whereby the fiber is phase bi-refringent and polarizing-maintaining and/or polarizing, optionally the relationship of the wall thickness t 1  of the outer tubular element of the at least one of the nested tubular arrangements to the wall thickness t 2  of the outer tubular element of the at least one other of the nested tubular arrangements is 0.5t 2 <t 1 <t 2  or 1.5t 2 >t 1 >t 2 , optionally 0.4t 2 <t 1 <t 2  or 1.4t 2 >t 1 >t 2 , optionally 0.3t 2 <t 1 <t 2  or 1.3t 2 >t 1 >t 2 , optionally the relationship of the wall thickness t 1  of the outer tubular element of the at least one of the nested tubular arrangements to the wall thickness t 2  of the outer tubular element of the at least one other of the nested tubular arrangements is t 1 <0.9t 2  or t 1 >1.1t 2 , optionally the second, outer tubular elements of first and second of the nested tubular arrangements have a wall thickness which is different to that of the wall thickness of the second, outer tubular element of at least one other of the nested tubular arrangements, optionally the first and second tubular arrangements are disposed in generally opposed relation, optionally diametral relation, optionally comprising two, three, four, five, six, seven or eight nested tubular arrangements, optionally comprising four nested tubular arrangements, wherein a first pair of the nested tubular arrangements are arranged in a first substantially common direction and a second pair of the nested tubular arrangements are arranged in a second substantially common direction which is substantially orthogonal to the first substantially common direction, optionally the effective radius of the core of the fiber is at most about 15 times the wavelength λ of the source, optionally at most about 7 times, optionally at most about 5 times, optionally the wavelength λ is about 0.5, 0.8, 1.06, 1.55 or 2 μm. 
     
     
         71 . The fiber of  claim 70 , wherein one inner tubular element, optionally the innermost tubular element, of the at least other of the nested tubular arrangements has a sectional size and/or shape which is different to the counterpart one tubular element of the at least one of the nested tubular arrangements, whereby a spacing Z 1  between the one inner tubular element and an adjacent tubular element of the at least other of the nested tubular arrangements is different to a spacing Z 2  between the counterpart one tubular element and adjacent tubular element of the at least one of the nested tubular arrangements, optionally the one inner tubular element of the at least other of the nested tubular arrangements has a different sectional size, optionally the relationship of the spacing Z 1  of the at least one other of the nested tubular arrangements to the spacing Z 2  of the at least one of the nested tubular arrangements is Z 1 >1.2Z 2 , optionally Z 1 >1.5Z 2 , optionally Z 1 >2Z 2 , optionally Z 1 >2.5Z 2 . 
     
     
         72 . The fiber of  claim 70 , wherein the fiber exhibits (i) a phase bi-refringence of at least 1×10 − , (ii) a loss of at most about 0.1 dB/m, optionally at most about 0.01 dB/m, and/or (iii) a loss ratio of at least about 100, optionally at least about 200, optionally at least about 500, optionally at least about 1000, between orthogonal polarizations of the fundamental mode. 
     
     
         74 . Use of the fiber of  claim 54  in (i) an effective single mode, (ii) with any selected mode field diameter for any given wavelength, (iii) in a mode of reduced fundamental loss, (iv) as a polarizing-maintaining fiber, optionally maintaining an input polarization of a source signal, or (v) as a polarizing fiber, optionally introducing a polarization to a source signal, optionally producing linearly-polarized light from an unpolarized input.