Optical apparatus having improved resistance to thermal damage
View Patent ↗An optical assembly is provided that can mitigate thermal damage that could otherwise occur in the region near where the optical fiber emerges from a high-power optical device package. The optical assembly includes an optical medium to guide stray light, along the fiber axis but substantially outside of the fiber core, from the interior to the exterior of a housing. The assembly further includes a transition region external to the housing, where at least one optical mode guided by the optical medium transitions to at least one optical mode confined by a polymer coating as a guided mode of the cladding. In embodiments, the optical medium is provided by the fiber cladding together with overlying materials of relatively low refractive index that help to confine the stray light within the cladding.
1. 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.
2. The optical assembly of claim 1 , wherein the optical assembly further comprises a ferrule passing through a wall of the housing, the optical fiber passes through a bore in the ferrule, and the external material region comprises at least an inner portion of the ferrule.
3. The optical assembly of claim 2 , wherein the external material region further comprises a layer of adhesive material in the bore between the optical fiber and said inner ferrule portion.
4. The optical assembly of claim 3 , wherein the transition region comprises a mass of said adhesive material in contact with the ferrule and with the polymer coating.
5. The optical assembly of claim 1 , wherein the at least one material region overlies the cladding that has a refractive index at least n clad , such that the guided light is confined in a mode at least partially of the overlying material region.
6. The optical assembly of claim 5 , wherein the optical assembly further comprises a ferrule passing through a wall of the housing, the optical fiber passes through a bore in the ferrule, and the external material region comprises at least an inner portion of the ferrule.
7. The optical assembly of claim 6 , wherein the external material region further comprises a layer of adhesive material in the bore between the optical fiber and said inner ferrule portion.
8. The optical assembly of claim 5 , wherein the fiber cladding has a diameter, the transition region comprises a portion of the external material region that tapers from a higher initial diameter to the cladding diameter, and the taper is gradual enough to effectuate said transition between the guided optical modes.
9. The optical assembly of claim 1 , further comprising a cladding mode power stripper optically coupled to the optical fiber at a position downstream of the transition region.
10. The optical assembly of claim 1 , wherein the polymer coating having a refractive index n poly is the innermost of two or more polymer layers.