Patent ID: 7356233

Claim:
A bandgap microstructure optical fiber comprising: a core region having a longitudinal axis, a cladding region surrounding said core region, said core and cladding regions configured to support and guide the propagation of light in at least first and second transverse modes of said core region in the direction of said axis, said cladding region including an inner cladding region, the cross-section of said inner cladding region perpendicular to said axis having a periodic spatial variation of its refractive index configured to guide said light by bandgap confinement, said inner cladding region including at least one perturbation region that perturbs the periodicity of said index therein, said at least one perturbation region being configured to resonantly couple at least said second transverse mode of said core region to at least one transverse mode of said perturbation region, and said perturbation region being configured to suppress at least said second transverse mode.