Patent ID: 8611708

Claim:
An optical assembly having one or more operating wavelengths and comprising a housing and an optical fiber that has a longitudinal axis and that extends from the interior to the exterior of the housing, wherein: (a) the optical fiber has a core and a cladding surrounding the core, and the cladding has at least one region having a refractive index n clad ; (b) in a portion of the optical fiber external to the housing, the cladding is surrounded by a polymer coating having a refractive index n poly that is less than n clad by an amount sufficient for light of at least one said operating wavelength to be confined within the cladding as a guided mode of the cladding; (c) an optical medium is included that is effective to guide light of at least one said operating wavelength along the fiber axis from the interior to the exterior of the housing substantially outside of the fiber core; and (d) the optical assembly includes a transition region external to the housing, where at least one optical mode guided by said optical medium transitions to at least one optical mode confined by the polymer coating as a guided mode of the cladding; wherein the optical medium effective to guide light from the interior to the exterior of the housing comprises the fiber cladding and at least one material region external to the cladding that has a refractive index less than n clad , such that the guided light is confined in a cladding mode, and, wherein the material region having a refractive index less than n clad includes at least one space filled with air.