Fibre termination compound graded index lenses
AssigneeNortel Networks Limited
InventorsPaul A Firth, Adrian Janssen
Life of this patent
Estimating the term…
Abstract
It is known to couple a collimated beam of light into the end of an optical fibre with a graded index lens having an angled facet at the lens/fibre interface to reduce the amplitude of Fresnel retroreflected power. The expense incurred in providing angled facets is avoided by using a two-part compound lens. One part is a graded index lens part having an axial length shorter than a quarter period. To this is bonded a cylindrical uniform refractive index lens part whose index is matched with the effective refractive index of the fibre. This reduces the amplitude of the retroreflection power by causing the displacement of the Fresnel reflection from the lens focus.
Claims12
A two-part compound lens consisting of a plane-parallel ended first lens part united in end-to-end relationship with a plane-parallel ended second lens part, the compound lens having a lens axis which is co-directional with the normal to both ends of both lens parts, wherein the first lens part is a graded index lens of length d1 and quarter period s, and the second lens part is of uniform refractive index and of length d2, wherein d1=(2n−1)s−Δ, where n is a positive integer and s>Δ>0, Δ is a length of the first lens which is removed and substituted by the second lens part of length d2, d2 is a length possessing the property that collimated light incident axially upon that end face of the graded index first lens part that is remote from the end facet united with the second lens part, is brought to a substantial focus at that end facet of the second lens part that is remote from the end facet united with the first lens part.
A two-part compound lens consisting of a plane-parallel ended first lens part and a planar ended second lens part united in end-to-end relationship, wherein the first lens part of the compound lens has a lens axis normal to its ends and is a graded index lens of quarter period s length and of length d1, where d1=(2n−1)s−Δ, and where n is a positive integer and s>Δ>0, Δ is a length of the first lens which is removed and substituted by the second lens part of length d2 and wherein the planar ends of the second lens part of the compound lens are inclined at a small wedge angle, and are chosen to provide a lens part thickness of less than d2 at one side of the second lens part, and of greater than d2 at the other, where d2 is a length possessing the property that collimated light Incident axially upon the end face of the graded index first lens part that is remote from the end facet united with the second lens part, is brought to a substantial focus at a depth d2 into the material of the second lens part.
Dependencies are inferred from the claim text.