Optical fiber collimator and optical fiber collimator array

Optical waveguides – With optical coupler – Input/output coupler

Reexamination Certificate

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C385S031000, C385S033000

Reexamination Certificate

active

06795613

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to an optical fiber collimator and an optical fiber collimator array in which a gradient index rod lens is used.
An optical collimator device includes first and second optical fiber collimators. The first optical fiber collimator converts a light emitted from an optical fiber into a parallel light. The second optical fiber collimator converges the parallel light into a collimator lens and couples the light to an optical fiber. The first optical fiber collimator will hereinafter be referred to as an optical fiber collimator on an incidence side, and the second optical fiber collimator will be referred to as an optical fiber collimator on a reception side. In general, the collimators on the incidence and reception sides have substantially the same structure.
Optical function devices such as an optical filter, optical isolator, and optical switch are inserted between two collimator lenses of the optical collimator device. The optical collimator device exerts a predetermined action onto the light propagated through the optical fiber on the incidence side by the optical function device, and subsequently couples the light to the optical fiber of the optical fiber collimator on the reception side.
FIG. 1
is a schematic constitution diagram of an optical fiber collimator
20
for use in a conventional optical collimator device. The optical fiber collimator
20
includes a gradient index rod lens
21
, single mode optical fiber
22
, capillary
23
which holds the optical fiber
22
, and glass tube
24
which holds the capillary
23
and rod lens
21
. Anti-reflection films
25
,
26
are formed on both end faces of the rod lens
21
, and an anti-reflection film
27
is also formed on the end face (single mode fiber (SMF) end face) of the optical fiber
22
. The anti-reflection films
25
to
27
are usually dielectric multilayered films.
The anti-reflection films
25
to
27
prevent the incident light from the optical fiber
22
from being reflected and returned to a light source side. Moreover, a loss of the incident light caused by the reflection is suppressed. In the optical fiber collimator
20
, the end faces of the optical fiber
22
and rod lens
21
are obliquely polished. The oblique polishing can prevent the reflected light from the end faces of the optical fiber
22
and rod lens
21
from being incident upon the optical fiber
22
again and returning to the light source side. If the rod lens
21
is coupled to the optical fiber
22
without taking any anti-reflection countermeasure, the following disadvantage occurs.
FIG. 2
shows only a rod lens
21
A and optical fiber
22
A of an optical fiber collimator
20
A which does not have any anti-reflection film. In the optical fiber collimator
20
A, both end faces
21
a
,
21
b
of the rod lens
21
A are flat surfaces vertical to an optical axis, and the anti-reflection films are not formed on the end faces
21
a
,
21
b
. The SMF end face of the optical fiber
22
A is a flat surface vertical to a core center axis, and the anti-reflection film is not formed also on the SMF end face.
In the optical fiber collimator
20
A not subjected to the anti-reflection countermeasure, the reflection by each of the SMF end face and the end faces
21
a
,
21
b
of the rod lens
21
A occurs substantially by 5%, and a loss of about 14% is generated as a whole. As a result, a coupling efficiency is −0.6 dB or less, and standard required characteristics such as a characteristic of −0.2 dB or more cannot be obtained.
The reflected light on the SMF end face and the reflected lights on the end faces
21
a
,
21
b
of the rod lens
21
A are directly incident as return lights upon the optical fiber
22
A again, and return to the light source side. Therefore, the anti-reflection countermeasure is required as in the optical fiber collimator
20
shown in FIG.
1
. As shown in
FIGS. 1 and 3
, anti-reflection films
25
,
26
,
27
each having a reflectance of 0.2% or less are disposed on the both end faces of the rode lens
21
and the SMF end face of the optical fiber
22
. The anti-reflection films
25
,
26
,
27
reduce the whole reflection loss to about 0.6%. Furthermore, the SMF end face and one end face of the rod lens
21
are obliquely polished. By the anti-reflection countermeasure of the oblique polishing, the reflected return lights from the SMF end face and the both end faces of the rod lens
21
are remarkably reduced.
However, the conventional optical fiber collimator
20
shown in
FIG. 1
has the following problems.
(A) It is necessary to form the anti-reflection film
27
on the SMF end face of the optical fiber
22
, but it is not easy to form the anti-reflection film
27
on the SMF end face which has a long dimension and small diameter.
(B) The oblique polishing of at least one end face of the rod lens
21
and the SMF end face of the optical fiber
22
requires long time, causes the reduction of a yield, and deteriorates productivity.
(C) Since the capillary
23
and glass tube
24
are required, the number of components and the number of assembly processes increase, and cost increases.
(D) To perform an optical adjustment so that the optical axis of the rod lens
21
agrees with a core center of the optical fiber
22
, it is necessary to consider the deflection of the light by the light reflection in the SMF end face of the optical fiber
22
and one end face of the rod lens
21
as the oblique surfaces. Therefore, the optical adjustment becomes complicated.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an optical fiber collimator and optical fiber collimator array in which manufacturing and assembling processes are simplified, productivity is enhanced, cost is reduced, and optical adjustment is facilitated.
According to one aspect of the present invention, there is provided an optical fiber collimator including a gradient index rod lens and an optical fiber optically connected to the rod lens. The optical fiber collimator includes an anti-reflection film formed on one end face of the rod lens. The anti-reflection film has a refractive index which continuously changes from a value substantially equal to a center refractive index of the rod lens to a value substantially equal to the refractive index of the optical fiber along a film thickness direction of the anti-reflection film. The optical fiber collimator further includes a refractive index matching medium which has a refractive index substantially equal to that of the optical fiber and which couples the anti-reflection film to an end face of the optical fiber.
According to another aspect of the present invention, there is provided a method for manufacturing an optical fiber collimator including a gradient index rod lens and an optical fiber optically connected to the rod lens. The method comprises a step of forming an anti-reflection film on one end face of the rod lens. The anti-reflection film has a refractive index which continuously changes from a value substantially equal to a center refractive index of the rod lens to a value substantially equal to the refractive index of the optical fiber along a film thickness direction of the anti-reflection film. The method further comprises a step of using a refractive index matching medium having a refractive index substantially equal to that of the optical fiber to bond the anti-reflection film to the end face of the optical fiber.
According to further aspect of the present invention, there is provided an optical fiber collimator array comprising a plurality of optical fiber collimators. Each of the plurality of optical fiber collimators includes a gradient index rod lens and an optical fiber optically connected to the rod lens. Each optical fiber collimator includes an anti-reflection film formed on one end face of the rod lens. The anti-reflection film has a refractive index which continuously changes from a value substantially equal to a center refractive index of the rod lens to a value substantially equal to the refractive in

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