Optical waveguides – With optical coupler – Particular coupling structure
Reexamination Certificate
2002-06-18
2004-04-06
Glick, Edward J. (Department: 2882)
Optical waveguides
With optical coupler
Particular coupling structure
C385S014000, C385S042000, C385S039000, C398S170000, C398S173000
Reexamination Certificate
active
06718098
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a two-way optical communication module for combining/splitting a transmission light and a reception light using a directional optical coupler.
2. Description of the Related Art
FIGS. 12-14
show a conventional two-way optical communication module disclosed in Japanese Patent Application Laid-Open No. Hei 5-289120.
FIG. 12
is a diagram for showing an overall configuration, FIG.
13
[
1
] is an expanded view for showing part of
FIG. 12
, FIG.
13
[
2
] is a cross-sectional view for showing FIG.
13
[
1
], and
FIG. 14
is a graph for showing wavelength characteristics of a directional optical coupler. The following will describe the module with reference to these figures.
As shown in
FIG. 12
, on the surface of an optical wave-guide board
200
and near its one side are provided parallel an optical wave-guide
251
coupled optically to a light emitting element
210
, an optical wave-guide
252
coupled optically to a light receiving element
220
, and an optical wave-guide
254
coupled optically to a light receiving element
230
. Near the other side of the optical wave-guide board
200
and on its surface, on the other hand, is provided a trunk optical wave-guide
250
coupled optically to an optical fiber
500
. The trunk optical wave-guide
250
is divided into two branches, one of which provides an optical wave-guide
253
and the other of which provides an optical wave-guide
254
.
The optical wave-guide
253
is further divided into two branches, one of which provides an optical wave-guide
251
and the other of which provides an optical wave-guide
252
. At a Y-form junction of the trunk optical wave-guide
250
and the optical wave-guides
253
and
254
is provided a beam combiner/splitter (wave-guide type directional optical coupler or Mach-Zehnder type combiner/splitter)
220
, which splits a light coming in through the optical fiber
500
into two components of a short-wavelength band &lgr;
11
and a long-wavelength band &lgr;
12
to transmit them through the optical wave-guides
253
and
254
respectively.
Further, at a Y-form junction of the optical wave-guides
251
,
253
, and
253
is provided a directional optical coupler
400
which gives a larger coupling loss in the long wavelength band &lgr;
12
to the optical wave-guide
252
than the others, thus preventing a leakage light of the long wavelength band &lgr;
12
going through the optical wave-guide
253
from coming into the light receiving element
220
.
Further, the optical wave-guide
251
has the light emitting element
210
disposed at its injection end (that is, an end surface of the optical wave-guide board
200
), while the optical wave-guide
252
has, as opposed thereto, a light receiving surface of the light receiving element
220
disposed at its emission end (that is, the end surface of the optical wave-guide board
200
). Also, the optical wave-guide
254
has, as opposed thereto, a light receiving surface of the light receiving element
230
disposed at its emission end (that is, the end surface of the optical wave-guide board
200
).
The following will detail the directional optical coupler
400
with reference to
FIGS. 13 and 14
.
As shown in
FIG. 13
, an interconnection of the optical wave-guides
253
and
251
is bent in a reverse trapezoid shape to provide a core line
410
and a light-incident end of the optical wave-guide
252
is bent in a trapezoid shape to provide a core line
420
near and parallel to the core line
410
, thus implementing the directional optical coupler
400
.
In one example of a configuration of the core lines
410
and
420
, a width b is 6 [&mgr;m] and a height a is 6 [&mgr;m] to form a rectangle, a length L is 1.81 [&mgr;m], and a distance d between the core lines
410
and
420
is 3.6 [&mgr;m]. Also, the refractive index of the core lines
410
and
420
is 1.468 and that of a clad
450
is 1.457.
FIG. 14
shows a wavelength characteristic of the directional optical coupler
400
. A dotted line P-
1
in
FIG. 14
indicates a relationship of a coupling loss and a wavelength between the optical wave-guides path
253
and
251
, while a solid line P-
2
indicates that between the optical wave-guides
253
and
252
. Since the directional optical coupler
400
has such wavelength characteristics as shown in
FIG. 14
, by selecting a wavelength band centering around a value of 1.31 [&mgr;m] as the short-wavelength band &lgr;
11
and a wavelength band centering around a value of 1.55 [&mgr;m] as the long-wavelength band &lgr;
12
, it is possible to prevent a light of the long-wavelength band &lgr;
12
from entering to the optical wave-guide
252
, that is, the light receiving element
220
.
In a conventional two-way optical communication module, a light of the short-wavelength band &lgr;
11
and that of the long-wavelength band &lgr;
12
emitted from the optical fiber
500
pass through the trunk optical wave-guide
250
and then enter the beam combiner/splitter
220
to be split in wavelength into the short-wavelength and long-wavelength bands &lgr;
11
and &lgr;
12
. As a result, the light of the long-wavelength band &lgr;
12
goes along the optical wave-guide
254
and enters the light receiving element
230
. The light of the short-wavelength band &lgr;
11
and a light of the long-wavelength band &lgr;
12
which has leaked from the beam combiner/splitter
220
, on the other hand, go along the optical wave-guide
253
and pass through the directional optical coupler
400
so that only the light of the short-wavelength band &lgr;
11
may go along the optical wave-guide
252
to enter the light receiving element
220
. In this case, the light of the short-wavelength band &lgr;
11
originated from the light emitting element
210
passes through the optical wave-guide
251
, the directional optical coupler
400
, the optical wave-guide
253
, the beam combiner/splitter
220
, and the trunk optical wave-guide
250
and then enters the optical fiber
500
.
This conventional two-way optical communication module, however, permits a light of the short-wavelength band &lgr;
11
emitted from the light emitting element
210
to be divided and radiated when passing through the directional optical coupler but does not take into account how to control the lights thus divided and radiated. That is, in the detailed drawings of the directional optical coupler
400
shown in
FIG. 13
, one half of the light of the short-wavelength band &lgr;
11
issued from the optical wave-guide
251
is guided to the optical wave-guide
253
, whereas the other half of the light is transferred in power to the core line
420
to be radiated from the cut end of the optical wave-guide
252
. Thus radiated light is reflected irregularly in the two-way optical communication module to provide a stray light, which then enters the light receiving element
220
for the short-wavelength band &lgr;
11
, thus deteriorating the reception sensitivity characteristics.
As shown in FIG.
13
[
1
], the directional optical coupler
400
has such a construction that the distance between the two close core lines
410
and
420
made of the optical wave-guides becomes larger toward the cut end of the optical wave-guide
252
. In this construction, therefore, the optical wave-guides are elongated, thus giving rise to a disadvantage of a difficulty to make compact the optical wave-guide board
200
.
SUMMARY OF THE INVENTION
In view of the above, it is an object of the present invention to provide two-way optical communication module with improved reception sensitivity characteristics.
In order to achieve above mentioned object, a two-way optical communication module according to present invention comprising: a light emitting element for emitting a light with a first wavelength; a first optical wave-guide including, a curved wave-guide portion coupled to said light emitting element, and a straight wave-guide portion coupled to
Glick Edward J.
McGinn & Gibb PLLC
NEC Corporation
Suchecki Krystyna
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