Cladding mode degeneracy in bent W-fibres beyond cutoff

Experimental measurements of the transmission spectrum of slightly bent finite-cladding W-fibres beyond the cutoff wavelength of the fundamental mode exhibit closely-spaced double resonances between the core and cladding modes. Using a bent slab waveguide model, these double resonances can be attributed to the break in the degeneracy of the cladding modes of the straight fibre.