Optical waveguides – With optical coupler – Input/output coupler
Reexamination Certificate
2003-01-29
2004-11-02
Palmer, Phan T. H. (Department: 2874)
Optical waveguides
With optical coupler
Input/output coupler
C385S046000, C385S024000
Reexamination Certificate
active
06813415
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a wavelength multiplexing/demultiplexing apparatus that is used in wavelength division multiplexing (WDM) communications for multiplexing a plurality of light with different wavelengths to demultiplex, for each wavelength, the multiplexed light that has been transmitted through a single optical fiber, or for multiplexing a plurality of light with different wavelengths to input the multiplexed light to a single optical fiber, and in particular, relates to a technique for reducing a loss in the wavelength multiplexing/demultiplexing apparatus using an optical waveguide of a substrate shape that is formed by enclosing, by a cladding, a core having a refractive index higher than that of the cladding.
2. Description of the Related Art
A configuration example of a wavelength multiplexing/demultiplexing apparatus using a conventional optical waveguide is shown in
FIG. 10
, in which (a) is a plan view, and (b), (c) and (d) are cross sectional views taken along lines A—A, B—B and D—D in the plan view, respectively.
As illustrated in (b) of
FIG. 10
, the optical waveguide in the conventional wavelength multiplexing/demultiplexing apparatus comprises a cladding
102
and a core
103
respectively formed on a substrate
101
. The core
103
has a refractive index higher than that of the cladding
102
and is enclosed by the cladding
102
.
Patterns
2
-
6
shown in (a) of
FIG. 10
are formed by core patterns, wherein
2
is an input waveguide,
3
is an input slab,
4
are channel waveguides,
5
is an output slab and
6
are output waveguides. Here, a connection point between the input waveguide
2
and the input slab
3
is denoted by
301
, an interface between the input slab
3
and the channel waveguides
4
is denoted by
302
, an interface between the channel waveguides
4
and the output slab
5
is denoted by
502
, and an interface between the output slab
5
and the output waveguides
6
is denoted by
504
. Further, in (b) of
FIG. 10
, thickness and width of the core
103
constituting the input waveguide
2
are denoted by t and w2, respectively. Still further, in (d) of
FIG. 10
, spacing between each core
103
constituting each of the channel waveguides
4
at the interface
302
is denoted by P
1
, and width of each core
103
is denoted by w
4
. In addition, in (a) of
FIG. 10
, spacing between each core
103
constituting each of the channel waveguides
4
at the interface
502
is denoted by P
2
. Note, each core
103
has the same thickness t at all positions in the input waveguide
2
, the input slab
3
, the channel waveguides
4
, the output slab
5
and the output waveguides
6
. Further, it is assumed that the channel waveguides
4
are configured so as to be gradually longer from the lower side to the upper side in (a) of
FIG. 10
, and the length of each channel waveguides
4
is adjusted so that a difference between optical path from the input slab
3
and the output slab
5
in the adjacent core patterns is maintained to be fixed
The conventional wavelength multiplexing/demultiplexing apparatus is designed so that the interface
302
between the input slab
3
and the channel waveguides
4
is a circular arc interface centered at the point
301
with a curvature radius r1, the interface
502
between the channel waveguides
4
and the output slab
5
is a circular arc interface centered at a point
501
with a curvature radius r2, and the curvature radiuses of r1 and r2 of respective circular arc interfaces are equal to each other. Further, it is typical that the spacing P
1
between the cores comprising the channel waveguides
4
at the input slab
3
side is equal to the spacing P
2
between the cores comprising the channel waveguides
4
at the output slab
5
side.
In such a conventional wavelength multiplexing/demultiplexing apparatus, if each light with each wavelength &lgr;1, &lgr;2 and &lgr;3 is multiplexed to be input to the input waveguide
2
, for example, the multiplexed light is demultiplexed for each wavelength &lgr;1, &lgr;2 and &lgr;3 to be output from each of the output waveguides
6
. Conversely, if each light with each wavelength &lgr;1, &lgr;2 and &lgr;3 is input to each of the output waveguides
6
, each light with each wavelength &lgr;1, &lgr;2 and &lgr;3 is multiplexed to be output from the input waveguide
2
.
Incidentally, in the wavelength multiplexing/demultiplexing apparatus constituted as described above, as shown in (c) of
FIG. 10
, gaps G exist in a position where each of the channel waveguides
4
is connected to the input slab
3
. Each of the gaps G is a factor responsible for a loss of light that is incident on the input waveguide
2
and propagated through the input slab
3
to be coupled to each of the channel waveguides
4
. Therefore, it is preferable that each gap G is as narrower as possible.
On the other hand, in the channel waveguides
4
, since it is necessary to define a phase difference between the light passing through each waveguide, it is required that interference between the waveguides does not occur. For this purpose, the channel waveguides
4
need to be formed so as to maintain spacing constant or above therebetween except at connection points with the input slab
3
. Conventionally, by maintaining the spacing P
1
constant between the channel waveguides at the connection points with the input slab
3
, the spacing of the channel waveguides at other portions is also maintained constant.
As one of methods of reducing the gaps G while maintaining the spacing P
1
constant or above, there is known a method of forming tapered portions
401
on the portion where the input slab
3
and the channel waveguides
4
are connected with each other, as shown in (a) of FIG.
10
. In this way, in the conventional wavelength multiplexing/demultiplexing apparatus, the gaps G are made narrower to reduce a connection loss between the input slab
3
and the channel waveguides
4
. Note, in the configuration example in (a) of
FIG. 10
, tapered portions
402
are also formed on the point where the channel waveguides
4
and the output slab
5
are connected with each other.
In the conventional wavelength multiplexing/demultiplexing apparatus as described above, if a waveguide with a core having the thickness t in 7 &mgr;m is used, for example, it is required that the core spacing P
1
between the channel waveguides
4
at the input slab
3
side is about 18 &mgr;m or more. At this time, in order to reduce the loss, the gaps G between the channel waveguides
4
may be as narrower as possible. However, due to the width of photomasking for processing and overetching in a transverse direction at the time of processing, it becomes difficult to form the gaps G into about 3 &mgr;m or less according to the known technique described above. As a result, there is a problem in that, even in the case where the tapered portions
401
are formed, the loss of 1 dB or more causes at the portion where the input slab
3
and the channel waveguides
4
are connected with each other.
There are known techniques for reducing the loss in the conventional wavelength multiplexing/demultiplexing apparatus disclosed in Japanese Patent No. 2861996 and Japanese Unexamined Patent Application No. 2000-131541. Such known techniques are for reducing the loss at the connection points between the output slab and the output waveguides by performing mode matching at the connection points between the output slab and the output waveguides. Further, more typically, these techniques are for reducing connection loss at the portion where the input slab and the input waveguide are connected with each other or the portion where the output slab and the output waveguides are connected with each other. However, the known techniques described above do not refer to the mode matching at the connection points between the input slab and the channel waveguides as described above, and thus the problem about the loss reduction at such a portion has not yet been solved.
SUMMARY OF THE INVENTI
Naruse Terukazu
Tabuchi Haruhiko
Fujitsu Limited
Palmer Phan T. H.
Staas & Halsey , LLP
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