Wavelength demultiplexer

Details Wavelength demultiplexer Wavelength demultiplexer

2000-10-17

2003-04-01

Ngo, Hung N. (Department: 2874)

Optical waveguides

With optical coupler

Particular coupling structure

C385S014000, C385S043000

Reexamination Certificate

active

06542670

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a wavelength demultiplexer used for optical communications.
2. Description of Related Art
In recent years, there have been considerable advances in the research and development of wavelength demultiplexers for realizing FTTH (fiber to the home) systems.
As one such wavelength demultiplexer, which is shown in
FIG. 6
, a reflection-type wavelength demultiplexer provided with a dielectric multilayer filter has been proposed (see, for example, 1995 Denshi Jouhou Tsuushin Gakkai Electronics Society Taikai C-229, or Shingaku Gihou EMD 96-36, CPM 96-59, OPE 96-58, LQE 96-60 (1996-08)).
FIG. 6
is a schematic top view showing waveguide portions and a dielectric multilayer filter 16 of a reflection-type wavelength demultiplexer provided with a Y-branching waveguide
14
(referred to as “wavelength demultiplexer A” in the following), disclosed in these documents.
When wavelength multiplexing light SP including first wavelength light S
1
and second wavelength light S
2
is input into an optical waveguide
18
for wavelength multiplexing light, the dielectric multilayer filter
16
transmits the first wavelength light S
1
and inputs it into the Y-branching waveguide
14
, and reflects the second wavelength light S
2
, which is input into a reflection-light waveguide
20
, thus demultiplexing the wavelength multiplexing light SP.
The Y-branching waveguide
14
includes a main waveguide
22
, a tapered waveguide
24
for widening the waveguide width, and first and second branching waveguides
26
and
28
. After the first wavelength light S
1
that has been input into the Y-branching waveguide
14
has been propagated through the main waveguide
22
and the tapered waveguide
24
for widening the waveguide width, it branches into the first and the second branching waveguides
26
and
28
, and is output to the outside.
However, for the configuration of optical communication modules using such reflection-type wavelength demultiplexers, the waveguides are formed so that the input direction and the output direction of the wavelength demultiplexer coincide with one another (that is, they are parallel to each other). As will be explained in the following, the input direction and the output direction correspond to a first propagation direction L
1
. This means, that the main waveguide
22
is connected to the dielectric multilayer filter
16
in a second propagation direction L
2
, in order to reduce the emission loss of input first wavelength light S
1
. The center line of the main waveguide
22
bends smoothly until it runs in the first propagation direction L
1
. First and second branching waveguides
26
and
28
, whose center lines are arranged symmetrically to one another, are connected to this main waveguide
22
. At a third port P
3
and a fourth port P
4
, the center lines of the first and second branching waveguides
26
and
28
, too, run in the first propagation direction L
1
.
However, the wavelength demultiplexer A disclosed in the above-noted documents has the disadvantage that it has a structure that is long with respect to the first propagation direction L
1
.
To remove this disadvantage, a reflection-type wavelength demultiplexer has been proposed in which the dielectric multilayer filter
16
is arranged obliquely against the input direction LA (referred to as “wavelength demultiplexer B” in the following), as shown in FIG.
7
. Like
FIG. 6
,
FIG. 7
is a top view showing the wavelength demultiplexer B.
However, the production efficiency for the wavelength demultiplexer B is poor. The following explains the reasons for this.
FIG. 8
is a top view of a series of three chips arranged next to each other under the same orientation on a wafer for forming wavelength demultiplexers B. Grooves
36
for inserting a dielectric multilayer film (in the drawings, these grooves are indicated by hatching) are formed on the surface of the chips, but these grooves
36
are arranged at an angle, so that they are not on a common straight line and the grooves
36
on the chips of one series of reflection-type wavelength demultiplexers cannot be formed by dicing in one step. Consequently, as mentioned above, the production efficiency for the wavelength demultiplexer B is poor.
On the other hand, the production efficiency for the wavelength demultiplexer A is higher than that for the wavelength demultiplexer B. The reason for this is explained in the following. Like
FIG. 8
,
FIG. 9
is a top view, of a series of three chips arranged next to each other under the same orientation on a wafer for forming wavelength demultiplexer A. Grooves
36
for inserting a dielectric multilayer film (in the drawings, these grooves are indicated by hatching) are formed on the surface of the chips, but these grooves
36
are formed on a common straight line, so that the grooves
36
on the chips of one series of reflection-type wavelength demultiplexers can be formed by dicing in one step. Consequently, as mentioned above, the production efficiency for the wavelength demultiplexer A is high.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a wavelength demultiplexer whose overall length in the first propagation direction is short, whose production efficiency is high, and whose emission loss is smaller than that of the above-described conventional configurations.
In order to attain this object, a wavelength demultiplexer of the present invention includes a wavelength demultiplexing portion and a Y-branching waveguide. The wavelength demultiplexing portion demultiplexes a specific wavelength of light from wavelength multiplexing light that has been input into the wavelength demultiplexer in a first propagation direction and then outputs the specific wavelength of light in a second propagation direction that is different from the first propagation direction. The Y-branching waveguide outputs the specific wavelength of light, which has been input into the Y-branching waveguide in the second propagation direction, in the first propagation direction. The Y-branching waveguide includes a main waveguide, a tapered waveguide, a first branching waveguide, and a second branching waveguide. The main waveguide is connected to the wavelength demultiplexing portion. The tapered waveguide is connected to the main waveguide and widens the waveguide width. The first branching waveguide and the second branching waveguide are both connected to the tapered waveguide.
In this configuration, the main waveguide is a straight waveguide whose center line is oriented in the second propagation direction. After bending the center line of the first branching waveguide along a smooth first curved line away from the second branching waveguide, a tangential direction of the first curved line coincides with the first propagation direction. After bending the center line of the second branching waveguide along a smooth second curved line away from the first branching waveguide, and after bending it along a smooth third curved line, which is connected to the second curved line in the tangential direction of the second curved line, into a direction towards the first branching waveguide, the tangential direction of the third curved line coincides with the first propagation direction.
Moreover, when a shape of the Y-branching waveguide is seen as a “Y”, at least one of a first condition and a second condition is satisfied.
The first condition is that an entire first end face of the main waveguide is connected to a portion of a second end face of the tapered waveguide arranged in opposition to the first end face.
The second condition is that an entire third end face of the first branching waveguide and an entire fourth end face of the second branching waveguide are connected to a portion of a fifth end face of the tapered waveguide, respectively, the fifth end face being arranged in opposition to the third end face and the fourth end face.
With this configuration, the first branching waveguide and the second branching waveguid

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