Capillary for optical fiber and ferrule for optical...

Details Capillary for optical fiber and ferrule for optical... Capillary for optical fiber and ferrule for optical...

2002-11-19

2004-07-13

Prasad, Chandrika (Department: 2839)

Optical waveguides

With disengagable mechanical connector

Optical fiber/optical fiber cable termination structure

C385S068000

Reexamination Certificate

active

06761490

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATION
This application claims the priority benefit of Japanese application serial no. 2001-352986, filed on Nov. 19, 2001.
BACKGROUND OF INVENTION
The present invention relates to a capillary for optical fiber, a ferrule for optical connector, and an optical-fiber-fixed capillary in which an optical fiber is inserted and fixed into an inner hole of a capillary for optical fiber, which are used for manufacturing optical devices.
Recent rapid development of optical communication networks has raised the need for large quantities of high performance, inexpensive optical devices. For a plug-type optical device or a receptacle-type optical device with a built-in optical fiber, in particular, a cylindrical optical-fiber-fixed capillary, called optical fiber stub, formed by inserting an optical fiber into an precise capillary to be fixed with an adhesive, and an optical connector plug are employed.
For example, as shown in
FIG. 12
, when one end face of an optical-fiber-fixed capillary is ground into a convex-sphere and the other end face is ground (or polished) into an inclined surface, the capillary comes to work as an optical fiber stub
6
. The optical fiber stub
6
is used for receiving an optical signal emitted from a laser diode
1
and focused by a lens
2
, transmitting the signal to an optical fiber
5
in a ferrule
4
for optical connector of an optical connector plug
3
, or for making the signal emitted from the optical fiber
5
in an inner hole
4
a
of the ferrule
4
for optical connector focus on a photodiode and the like which is not graphically represented.
An end face
7
b
of the optical fiber stub
6
is ground so that the reflection axis of the optical signal makes an angle of several degrees against the incident axis of the optical signal. This arrangement is made to prevent such a phenomenon from occurring at the end face
7
b
of the capillary
7
for optical fiber on the side of the laser diode
1
(or photodiode) that a reflected light comes into the laser diode
1
and becomes a noise. An end face
7
c
opposite to the end face
7
b
is ground to form a convex-sphere having a center on an end face
8
a
of an optical fiber
8
so that the optical fiber
8
is abutted on the optical connector plug
3
to be able to make PC (Physical Contact) connection.
As shown in
FIG. 12
, the connection between the optical connector plug
3
and the optical fiber stub
6
is made via PC connection, for which the end face
8
a
of the optical fiber
8
of the optical fiber stub
6
is abutted on a convex-spherical end face
5
a
of an optical fiber
5
of the optical connector plug
3
in a split sleeve
9
.
Such an optical signal connection as described above is made typically by connecting optical connectors used for high capacity optical communication. For connecting optical connectors, as shown in
FIG. 13
, a ferrule
11
for optical connector is employed to form an optical connector plug
10
, the ferrule
11
formed by processing an precise capillary, which has an inner hole
11
a with an inner diameter for allowing an optical fiber
12
to be inserted therein, into a prescribed shape. The optical fiber
12
is inserted into the inner hole
11
a
to be glued thereto with an adhesive and one end face of the ferrule
11
is machined into a convex-sphere. The connection between these optical plugs
10
are made via PC connection, in which respective end face
12
a
of the optical fiber
12
abut each other in a split sleeve
13
. A connection loss resulted from the PC connection mainly caused by an axial dislocation between the optical fibers
12
occurring at the connecting part. The axial dislocation occurs as the result from accumulated factors of the outer diameter difference between used ferrules
11
for optical connector, the circularity (or roundness) of the inner hole
11
a
at the end face and the cylindricity of an outer periphery
11
b
, the concentricity between the inner hole
11
a
of the ferrule
11
for optical connector and the outer periphery
11
b
, and the eccentricity of the optical fiber
12
in the inner hole
12
at the end face. Out of these factors, the concentricity between the inner hole
11
a
of the ferrule
11
for optical connector at the end face and the outer periphery
11
b
, and the eccentricity of the optical fiber
12
in the inner hole
11
a
at the end face are the major factors relating to the axial dislocation between the optical fibers to be abutted. With this reason, the concentricity of the ferrule
11
for optical connector is required to be 1.4 &mgr;m or less for an application to communication using a single mode optical fiber. Also, a ferrule having the inner hole
11
a
larger than the outer diameter of the optical fiber
12
to be inserted by 0 to 1 &mgr;m is employed for such a communication. The relation between the axial dislocation d of the optical fiber
12
and a connection loss (measuring unit: dB) is represented generally by the following equation (1) when the core diameter of the optical fiber is symbolized by w.
Loss=4.34(
d
/(
w
/2))
2
  (1)
Here, a consideration is made on the cause of connection loss by focusing on the concentricity between the inner hole
11
a
and the outer periphery
11
b
, and the eccentricity of the optical fiber
12
in the inner hole
11
a
. A case to be considered first is to use the ferrule
11
for optical connector, whose concentricity is 1.4 &mgr;m or less and the inner hole
11
a
has an inner diameter larger than the outer diameter of the optical fiber
12
by 1 &mgr;m. When the optical fiber becomes eccentric in the inner hole
11
a
by 0.5 &mgr;m in one ferrule on the assumption that the other ferrule to be abutted is subjected to the same eccentricity, the worst axial dislocation to be estimated is 2.4 &mgr;m, which is the dislocation value bringing a connection loss of 1.0 dB in maximum according to the above equation (1). Given this conclusion, the ferrule
11
for optical fiber must be revolved in a core adjusting operation in order to achieve a connection loss of 0.5 dB or less, which is specified as the standard value of an communication optical connector employing a quartz single mode optical fiber (JIS-C-5962). Actual core adjusting operation, however, tends to be extraordinary cumbersome. For example, the concentricity between the inner hole
11
a
and the outer periphery
11
b
is measured first at the end face of the ferrule
11
for optical connector, and an eccentric direction is marked on the side of a flange member
14
with 90 degree pitch (¼ revolution pitch), then assembling is made by aligning the eccentric direction of respective ferrule
11
for optical connection to be abutted. Or, in another example, while light is actually transmitted through the optical fiber and the intensity of the light is monitored with a power meter and the like, the ferrule
11
for optical fiber is revolved 90 degree at a time and the position for least connection loss is determined for assembling.
Meanwhile, the optical device represented by
FIG. 12
is also subjected to the same axial dislocation described above. In this case, when the optical connector plug
3
and the optical fiber stub
6
is connected or an aligning position is determined between the optical axis of an optical signal focused by the lens
2
(or an emitted optical signal) and the center of the optical fiber
8
in the inner hole
7
a
of the capillary
7
for optical fiber used for the optical fiber stub
6
, the end face
7
b
of the capillary
7
for optical fiber used for optical fiber stub
6
is ground (or polishing) to make an angle of several degrees and is fixed without a consideration for the eccentric direction of the optical fiber in the inner hole
7
a
, so that the core adjusting operation becomes structurally impossible. Therefore, as the optical connector plug and the optical fiber stub to be abutted have respective axial dislocation, the axial dislocation caused by the eccentricity of the optical fiber
8
in the inner ho

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