An optical fiber comprising: a hollow core region having a longitudinal axis, said core region configured to support and guide the propagation of signal light in a transverse core mode comprising a first polarization state and a second orthogonal polarization state, said transverse core mode propagating in said core region in essentially the direction of said axis, and a cladding region including an inner cladding region (14.1) that surrounds the hollow core region and an outer cladding region (14.2) that surrounds the inner cladding region (14.1), the inner cladding region (14.1) includes a localized hollow waveguide region configured to support and guide the propagation of light in a transverse waveguide mode, said transverse waveguide mode propagating in said waveguide region in a direction essentially parallel to said axis, said core and waveguide regions (12, 16) being further configured so that (i) at least one of said core region and said waveguide region is birefringent, (ii) the first polarization state is resonantly coupled to said waveguide mode, and (iii) the second polarization state is not resonant and has substantially less coupling to said waveguide region than the first polarization state, wherein said core region includes a multiplicity of micro-defects disposed at or near the periphery thereof, said core region micro-defects being positioned in a non-rotationally symmetric pattern within the cross-section of said core region so that signal mode energy therein is distributed therein more along a first transverse axis than along a second orthogonal axis, and wherein said waveguide region includes a multiplicity of micro-defects disposed at or near the periphery thereof, said waveguide region micro-defects being positioned in a non-rotationally symmetric pattern within the cross-section of said waveguide region so that coupled mode energy therein is distributed therein more along said second orthogonal transverse axis than along said first transverse axis. a hollow core region having a longitudinal axis, said core region configured to support and guide the propagation of signal light in a transverse core mode comprising a first polarization state and a second orthogonal polarization state, said transverse core mode propagating in said core region in essentially the direction of said axis, and a cladding region including an inner cladding region (14.1) that surrounds the hollow core region and an outer cladding region (14.2) that surrounds the inner cladding region (14.1), the inner cladding region (14.1) includes a localized hollow waveguide region configured to support and guide the propagation of light in a transverse waveguide mode, said transverse waveguide mode propagating in said waveguide region in a direction essentially parallel to said axis, said core and waveguide regions (12, 16) being further configured so that (i) at least one of said core region and said waveguide region is birefringent, (ii) the first polarization state is resonantly coupled to said waveguide mode, and (iii) the second polarization state is not resonant and has substantially less coupling to said waveguide region than the first polarization state, wherein said core region includes a multiplicity of micro-defects disposed at or near the periphery thereof, said core region micro-defects being positioned in a non-rotationally symmetric pattern within the cross-section of said core region so that signal mode energy therein is distributed therein more along a first transverse axis than along a second orthogonal axis, and wherein said waveguide region includes a multiplicity of micro-defects disposed at or near the periphery thereof, said waveguide region micro-defects being positioned in a non-rotationally symmetric pattern within the cross-section of said waveguide region so that coupled mode energy therein is distributed therein more along said second orthogonal transverse axis than along said first transverse axis.