Optical fiber array

Details Optical fiber array Optical fiber array

1998-12-21

2001-05-15

Font, Frank G. (Department: 2877)

Optical waveguides

With disengagable mechanical connector

Optical fiber/optical fiber cable termination structure

C385S077000

Reexamination Certificate

active

06231244

ABSTRACT:

BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT
The present invention relates to an optical fiber array.
Due to the increasing density of optical fibers, more and more fibers are used for planar waveguides (PLC). To avoid the increase in size of waveguide elements associated with the increasing number of fibers and to further increase the density, efforts are being made to reduce the conventional standard type waveguide pitch (250 &mgr;m) down to about a half, that is, 127 &mgr;m.
To account for the increasing density of optical fibers and the decreasing waveguide pitch, efforts are also being made to reduce down to 127 &mgr;m the inter-fiber pitch of fiber arrays connected to optical fibers.
As a conventional technique for reducing the pitch of fibers, a configuration has been proposed and examined wherein two sets of optical fibers
14
of standard tape fibers
13
are mutually overlapped in such a way that the upper and lower fibers
14
are alternately aligned in V-shaped grooves
16
in a V-shaped groove substrate
10
as shown in
FIG. 7
(Document: see 1997 Electronic Information Communication Society Electronics Society Convention, C-3-113 “PLC Splitter Module Using 127 &mgr;m-pitch Optical Fiber Array”).
This configuration, however, requires taper to overlap as shown in
FIG. 6
, and unless the distance between the covered optical fibers
13
and the end of the substrate
11
where the naked fibers
14
are held is set at a predetermined value or more, this taper angle increases to cause losses or defects such as open circuits. Thus, to minimize the losses, the bend radius of the naked fibers
14
is set at 20 mm or less.
In the fiber array according to the above conventional document, the V-shaped grooves and a step portion
12
are formed in the V-shaped groove substrate
10
so as to mount covered optical fibers in the step portion as shown in FIG.
7
.
In such a fiber array having such a V-shaped groove substrate
10
, since normal tape fibers have a 250-&mgr;m pitch, for example, the fiber interval at both ends of an 8-core tape fiber is 1.75 mm. Due to the manufacturing error of about 0.1 mm, when the covered optical fibers
13
are arranged in such a way as to contact the step portion
12
, the naked fibers
14
are distinctly tapered to cause an open circuit. If the naked fibers
14
is shifted slightly backward from their original positions, the open circuit can be avioded because the taper is decreased. However, this requires increase in adhesive stress and adjustment. The fibers have to be shifted about 2 mm backward to secure a bend radius of 20 mm of the fibers. There is some apprehension that this cause deterioration in properties of the optical fibers due to the adhesive stress in this part.
FIG. 5
shows an example of a half-pitch fiber array in which the conventional pitch of 250 &mgr;m is reduced to about a half.
In this figure, a covered fiber housing substrate
15
is stuck and fixed to a lower substrate (V-shaped groove substrate)
10
having V-shaped grooves, from above a step portion
12
in the V-shaped groove substrate
10
. Then, tape fibers (covered fibers)
13
a
and
13
b
are inserted through a covered fiber housing groove
17
formed in the covered fiber housing substrate
15
, in such a way as to overlap each other, and the upper and lower fibers are alternately aligned in the V-shaped grooves. Then, an upper substrate (a fiber presser substrate)
11
is installed and fixed from above the V-shaped grooves in the V-shaped groove substrate
10
to form an optical fiber array
22
.
In
FIG. 5
, to reduce the taper angle of the overlapping fibers, the fibers are shifted slightly backward from their original positions.
Since, however, an adhesive is filled in the overlapping fiber portion
21
, the thermal expansion of the adhesive causes stress in the fibers to degrade the characteristics of the optical fiber array
22
, for example, to cause losses in the optical fiber array.
In addition, shifting the fibers slightly backward requires adjustments, and shifting them backward, for example, about 4.9 mm enables a sufficient bend radius of the fibers to be obtained to avoid losses. If, however, adjustments are insufficient and the shifting distance is short, the bend radius of the fibers decreases to increase the taper angle, while if the shifting distance is excessively long, the amount of adhesive filled in the overlapping fiber portion increases possibility to degrade the characteristics of the optical fiber array
22
.
SUMMARY OF THE INVENTION
This invention is provided to solve these problems, and its object is to provide an optical fiber array that can accurately set the positional relationship between non-covered optical fibers and covered optical fibers to avoid the degradation of the characteristics of the array and open circuits in the fibers.
The present invention provides an optical fiber array comprising an upper substrate and a lower substrate in which V-shaped grooves are formed, optical fibers being inserted and arranged in the V-shaped grooves and being solidified using an adhesive, wherein the lower substrate comprises a V-shaped groove section having V-shaped grooves in which the optical fibers are aligned and arranged, a covered optical fiber support section for supporting covered optical fibers, and a free buffer section located between the V-shaped groove section and the covered optical fiber support section and that is prevented from restricting the alignment and arrangement of the optical fibers, and wherein the free buffer section continues with the covered optical fiber support section via a step.
According to this invention, a taper is preferably formed on the surface of the upper substrate opposed to the free buffer section of the lower substrate, and this invention is preferably applied to a half-pitch optical fiber array in which two sets of tape fibers are mutually overlapped.
In addition, a taper is preferably formed in the portion of the free buffer section that is connected to the V-shaped grooves because it serves to avoid the concentration of stress on the fibers at the edges of the V-shaped grooves.


REFERENCES:
patent: 6118917 (2000-09-01), Lee et al.
patent: 0926 520 (1999-06-01), None
patent: 9-133833 (1997-05-01), None

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