Patent ID: 7403681

Claim:
A wavelength selective optical device connecting a first optical fiber with an end face to a second optical fiber, comprising: a collimating lens having a first end surface located such that a divergent light emitted from the end face of a first optical fiber is incident, and having a second end surface, the collimating lens arranged to emit the incident divergent light as a parallel light beam emitted from the second end surface; and an optical filter arranged to face the second end surface of the collimating lens so that the parallel light beam emitted from the collimating lens is incident on the optical filter, wherein the collimating lens and the optical filter are arranged such that a reflected light by the optical filter is incident back to the lens and input to the second optical fiber which is located at a location in which the reflected light is focused by the lens, wherein the collimating lens is provided with two gradient index rod lenses having different refractive index distribution constants relative to each other, wherein said two gradient index rod lenses have substantially the same outer diameter, and are bonded to each other so that optical axes of said two gradient index rod lenses are aligned, and wherein the refractive index distribution constants of said two gradient index rod lenses are √{square root over (A 1 )} and √{square root over (A 2 )}, respectively, and refractive indices on center axes are N 01 and N 02 , respectively, and respective lens lengths Z 1 and Z 2 of the lenses substantially satisfy: tan(√{square root over ( A 1)}· Z 1)·tan(√{square root over ( A 2)}· Z 2)= N 01·√{square root over ( A 1)}/( N 02·√{square root over ( A 2)}).