Optical waveguide device and optical waveguide method

Details Optical waveguide device and optical waveguide method Optical waveguide device and optical waveguide method

2001-11-09

2003-11-04

Lee, John D. (Department: 2874)

Optical waveguides

With optical coupler

Particular coupling structure

C385S046000

Reexamination Certificate

active

06643432

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims priority of Japanese Patent Application No. 2001-040571, filed on Feb. 16, 2001, the contents being incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical waveguide device for trapping incident light in an area and transmitting the energy in a direction to output it.
2. Description of the Related Art
Splitting and combining of optical power (energy) are important basic functions in many optical waveguide devices including waveguides. In this case, reduction of energy loss between input and output and improvement of transmission loss uniformity among output ports are important objectives. Meanwhile, reduction of dimensions of optical waveguide devices is another requirement necessary to reduce manufacturing cost and facilitate use of the device in a broader range of applications.
Concrete examples of conventional optical waveguide splitting and combining devices are presented below.
First, a Multi-Mode Interference device (MMI) is cited as shown in FIG.
7
.
The device is constituted by including an input waveguide
101
for converting incident light into a single optical mode, a plurality of output waveguides
102
for splitting power and to output it, and a waveguide
103
formed with a constant width along the propagation direction of light, connecting the input waveguide
101
and the output waveguides
102
, and causing the propagation of a plurality of optical modes along the propagation direction of light.
Incident light, which is converted into a single optical mode by the input waveguide
101
, is converted into a plurality of optical modes in the waveguide
103
, and the power thereof is divided equally over the output waveguides
102
to be outputted. The field intensity in an end portion of the waveguide
103
on the side of the output waveguides
102
(in
FIG. 7
, marked by ellipse E) is distributed in a form having peaks at locations corresponding to the positions of the output waveguides
102
. The distribution is shown in FIG.
7
.
Next, a Star Coupler device is cited as shown in FIG.
8
.
The device is constituted by including the input waveguide
101
as in the MMI device, a plurality of output waveguides
104
in a tapered form decreasing in width toward the output portions, radially provided for splitting power and to output it, and a passage
105
for connecting the input waveguide
101
and the output waveguides
104
and allowing light to freely propagate therethrough toward the output waveguides
104
.
Incident light converted into a single optical mode by the input waveguide
101
freely propagates in the passage
105
and the power thereof is split in the output waveguides
104
to be outputted. The field intensity in an end portion of the passage
105
on the side of the output waveguides
104
(in
FIG. 8
, marked by ellipse E) is distributed smoothly in substantially a bell shape with a peak in the center region as shown in FIG.
8
.
Next, a Y-branch device is cited as shown in FIG.
9
.
The device is constituted by including the input waveguide
101
as in the MMI device, two output waveguides
106
, each provided radially to split power and output it, and a tapered waveguide
107
for connecting the input waveguide
101
and the output waveguides
106
and having a very small taper angle to be adiabatic, that is, to make an optical mode invariable along the light propagation direction.
Incident light, which is converted into a single optical mode by the input waveguide
101
, propagates along the waveguide
107
without changing optical mode, and the power thereof is split in the output waveguides
106
to be outputted. The field intensity at an end portion of the waveguide
107
on the side of the output waveguides
106
(in
FIG. 9
, marked by ellipse E) is distributed smoothly in substantially a bell shape with a peak in the center region as shown in FIG.
9
.
However, the above-described conventional optical waveguide devices have the following disadvantages.
MMI devices are excellent in obtaining uniform optical coupling among the output waveguides
102
constituting the output ports, but the length of the waveguide
103
increases quadratically with the number of ports, which inevitably results in excessive device dimensions not practical for fabrication if a sufficient number of output ports is provided.
Star coupler devices can be reduced in size to be compact even with a number of output ports being provided, but require adjustment of the width of the passage
105
for obtaining uniformity in optical coupling among the output ports. In this case, extremely large width is required, which results in an increased length of the passage
105
, and it is also necessary to provide tapers at each of the output waveguides
104
, thus further increasing the size of the entire device.
The Y-branch devices realize an adiabatic state avoiding optical mode conversion, which requires reduction of the taper angle, and thus it requires extreme increases in length.
As described above, the conventional optical waveguide devices can satisfy the requirement of uniform optical coupling among the output ports, but it is extremely difficult for them to satisfy the requirement of reduction in size of the entire devices while satisfying the above requirement at present.
SUMMARY OF THE INVENTION
The present invention is made in view of the aforementioned problems, and its objective is to provide an optical waveguide device and an optical waveguide method with high reliability and high precision, which sufficiently meet both requirements of uniform optical coupling among the output ports and reduction in the entire device size, and being suitable for various kinds of useful applications.
The inventor reaches the modes of the invention presented below as a result of detailed study.
An optical waveguide device of the present invention comprises a single optical mode input waveguide, a plurality of output waveguides, and a tapered waveguide for connecting the aforementioned input waveguide and aforementioned output waveguides, gradually increasing in width from the aforementioned input waveguide toward the aforementioned output waveguides, and is characterized in that the aforementioned tapered waveguide has a sufficiently large taper angle so that optical power guided by lower order optical modes couple into higher order optical modes while the light propagates along the tapered waveguide.
Here, it is preferable that the width at a narrow end of the aforementioned tapered waveguide is larger than the width of the aforementioned input waveguide, but is set to a value small enough to support a discrete spectrum of a certain number of optical modes.
Further, it is preferable that the aforementioned tapered waveguide has a linear taper plane in section made by optimizing the taper angle by a numerical analysis method so that a field intensity profile at the wide end of the tapered waveguide is maximally flat.
Furthermore, it is preferable that the aforementioned output waveguides are provided in such a direction that the axes thereof point to the narrow end of the aforementioned tapered waveguide.
Further, it is preferable that the aforementioned output waveguides are placed on a wave front of an electromagnetic wave at the wide end of the aforementioned tapered waveguide.
Still further, it is preferable that each of the aforementioned output waveguides has a width optimized by a numerical analysis method to obtain substantially equal power coupling efficiency.
Furthermore, it is preferable that the aforementioned output waveguides are tapered, gradually increasing in width toward the wide end of the aforementioned tapered waveguide.
In this case, it is preferable that each of the aforementioned output waveguides has a sufficiently large taper angle so that higher order optical modes couple into lower order optical modes while the light propagates along each of the output waveguides.
Further, it is preferable that

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