Patent ID: 7551819

Claim:
An optical coupler comprising: a first optical port; a second optical port; a third optical port; a fourth optical port; and a photonic-bandgap fiber comprising: a cladding comprising a material with a first refractive index and regions within the cladding, the regions having a second refractive index lower than the first refractive index; a first core substantially surrounded by the cladding, the first core optically coupled to the first optical port and to the second optical port; a second core substantially surrounded by the cladding, the second core optically coupled to the third optical port and to the fourth optical port, wherein at least a portion of the first core is generally parallel to and spaced from at least a portion of the second core such that the first core is optically coupled to the second core, wherein the first core, the second core, or both the first core and the second core is hollow; and a defect substantially surrounded by the cladding, the defect increasing a coupling coefficient between the first core and the second core.