Collimator lens for optical fiber

DETAILED DESCRIPTION It is therefore, an object of the present invention to overcome the above-described prior art disadvantages and drawbacks and to provide an improved collimator for an optical fiber.
Another object of the present invention is to provide such collimator capable of easily performing axial alignment between a collimator lens axis and an optical axis defined by the light radiation from an end face of an optical fiber.
Still another object of the present invention is to provide the collimator lens which can be easily produced.
In accordance with the present invention, provided is a cylindrical member formed of an optically transparent material, which has refractive index n.
sub.
1, effective radius R, and effective axial length L.
The cylindrical member has one circular end provided with Fresnel lens pattern having a focal length F, and the other circular end face provided with a connecting portion connectable with a light emitting end face of an optical fiber.
The focal length F, the effective axial length L, the effective radius R and the refractive index n.
sub.
1 are so arranged as to be satisfied with the following formula (I) and (II): F/L=tan {sin.
sup.
-1 (NA/n.
sub.
1)}/tan {sin.
sup.
-1 (NA) } (I) R.
gtoreq.
L.
multidot.
tan {sin.
sup.
-1 (NA/n.
sub.
1 }) (II) in which NA is a numerical aperture of an optical fiber.