Optical waveguides – With optical coupler – Input/output coupler
Reexamination Certificate
2002-11-21
2004-07-06
Bovernick, Rodney (Department: 2874)
Optical waveguides
With optical coupler
Input/output coupler
C385S047000
Reexamination Certificate
active
06760517
ABSTRACT:
BACKGRUOND OF THE INVENTION
The present invention relates to an optical coupling device for two-way optical communications over a single optical fiber and, more particularly, to an optical coupling device disposed opposite the end face of the optical fiber, through which received light output from the optical fiber is guided to light receiving means and transmission light emitted from light emitting means is launched into the fiber end face.
For two-way optical communications over a single optical fiber, it is necessary to guide at either end of the fiber transmission light emitted from a light emitting element into the optical fiber and light output therefrom into a light receiving element. A general configuration of such an optical coupling device is one that optically couples the light emitting element and the light receiving element to either end face of the optical fiber through utilization of transmission and reflection of light by means of a half mirror or prism.
FIG. 1
is a diagrammatic showing of an example using a prism as the optical coupling element in combination with an optical fiber
12
, a light emitting element
14
and a light receiving element
13
. In this example, the optical coupling device is formed by a prism
11
, through which light is transmitted and received.
The prism
11
in this example is of rectangular equilateral triangle in section. The optical fiber
12
is disposed with its one end face adjacent a first one (
11
a
) of two planes of the prism
11
which form the right angles between them, and the light receiving element
13
is disposed with its condenser lens
17
a
adjacent the second plane
11
b
of the prism
11
. Disposed outside a third plane
11
c
of the prism
11
which forms an oblique side is the light emitting element
14
.
With such an arrangement, received light
21
output from the end face of the optical fiber
12
is launched into the prism
11
through the plane
11
a
, then reflected by the plane
11
c
to the plane
11
b
, and launched therefrom into the light receiving element
13
. On the other hand, transmission light
22
emitted from the light emitting element
14
enters the prism
11
through the plane
11
c
, that is, it passes through the plane
11
c
to the plane
11
a
, thereafter being launched into the end face of the optical fiber
12
.
The use of the prism
11
as described above permits favorable positioning of light emitting means (light emitting element
14
) for launching the transmission light
22
into the optical fiber
12
and light receiving means (light receiving element
13
) for receiving the received light output from the optical fiber
12
.
With the
FIG. 1
configuration, letting the diameter of the optical fiber
12
be represented by A
0
and the spread diameter of the transmission light
22
on the end face of the optical fiber
12
be represented by A
1
, the quantity of transmission light
22
to be launched into the optical fiber
12
bears a relationship, A
0
2
/A
1
2
, to the quantity of transmission light
22
having entered the prism
11
through the plane
11
c
and passed through the prism
11
—this suggests a considerably low coupling efficiency.
On the other hand, letting the diameter of the condenser lens
17
a
be represented by B
0
and the spread diameter of the received
21
at the position of the condenser lens
17
a
be represented by B
1
, the quantity of received light
21
incident on the condenser lens
17
a
bears a relationship, B
0
2
/B
0
2
, to the quantity of received light
21
reflected by the plane
11
c
of the prism
11
, which suggests a low coupling efficiency at the receiving side, too, as is the case with the transmitting side. The problem of low coupling efficiency still remains unsolved as well in the case of using the prism
11
coated over the entire area of its oblique plane
11
c
with a polarization reflecting film to form a polarization beam splitter.
The coupling efficiency could be increased, for example, by the placement of a condenser lens between the end face of the optical fiber and the prism
11
, but the introduction of such an optical system separate of the prism
11
inevitably gives rise to a problem that the device becomes bulky and expensive accordingly.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an optical coupling device for two-way optical communications which is small and inexpensive.
According to the present invention, the optical coupling device for two-way optical communications over a signal optical fiber, comprising:
a prism having a first plane containing an area opposite the end face of said optical fiber, a second plane containing an area opposite light receiving means and a third plane containing an area opposite light emitting means; and
a cylindrical member embedded in said prism in that area of said first plane opposite the end face of said optical fiber and having a refractive index larger than that of said prism;
wherein received light launched into said prism from said optical fiber is output to said light receiving element via said cylindrical member, and transmission light launched into said prism from said light emitting element is output to said optical fiber via said cylindrical member.
REFERENCES:
patent: 4915489 (1990-04-01), Minko
patent: 5440655 (1995-08-01), Kaplow et al.
Isoda Takeshi
Mine Keiji
Nakagawa Hiroshi
Bovernick Rodney
Gallagher & Lathrop
Hosiden Corporation
Lathrop, Esq. David N.
Stahl Mike
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