Optical waveguide circuit and method of fabricating same

Details Optical waveguide circuit and method of fabricating same Optical waveguide circuit and method of fabricating same

1999-12-21

2002-03-19

Healy, Brian (Department: 2874)

Optical waveguides

Planar optical waveguide

C385S014000, C385S130000, C385S131000, C385S132000, C385S039000, C385S042000

Reexamination Certificate

active

06360047

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical waveguide circuit and method of fabricating same.
2. Description of the Prior Art
In the field of modern optical communication, wavelength division multiplexing (WDM) communication has been extensively investigated and developed as means for drastically increasing the transmission capacity. Realization of the WDM communication requires development of an optical waveguide circuit that enjoys high wavelength branching performance or a high isolation characteristic.
FIG. 10
shows an example of an existing optical waveguide circuit. An optical waveguide circuit
20
shown in
FIG. 10
is a wavelength multiplexing-branching filter of the Mach-Zehnder type, in which waveguide covres
20
b
and
20
c
, including a core and a clad, are formed on a substrate
20
a
. In the optical waveguide circuit
20
, a light beam with wavelengths &lgr;
1
and &lgr;
2
that is projected from an optical waveguide, such as an optical fiber, onto a port P
1
of the waveguide core
20
b
is branched into light beams with wavelengths &lgr;
1
and &lgr;
2
in an optical multiplexing-branching region Ab. The branch beams are guided individually to ports P
2
and P
3
of the waveguide cores
20
b
and
20
c
, and are emitted toward other optical waveguides such as optical fibers that are connected optically to the ports P
2
and P
3
.
In the optical waveguide circuit
20
, light incident upon the clad, not upon the core, at the port P
1
of the waveguide core
20
b
and a radiation mode of the light generated in the optical waveguide circuit
20
propagate in the clad as a clad mode. Thus, in a general region Aa behind the optical multiplexing-branching region Ab, the clad-mode light lands on the waveguide cores
20
b
and
20
c
and leaks into the ports P
2
and P
3
.
If the clad-mode light is generated in the optical waveguide circuit
20
, therefore, the isolation characteristic is lowered to cause cross talks and other adverse effects on the quality of optical communication.
SUMMARY OF THE INVENTION
The object of the present invention is to provide an optical waveguide circuit, capable of restraining clad-mode light from landing on a waveguide core or from leaking into other ports, and method of fabricating same.
In order to achieve the above object, according to the present invention, there is provided an optical waveguide circuit having a waveguide core of a desired shape formed on a substrate. In this optical waveguide circuit, light confinement portions having substantially the same refractive index as the waveguide core are arranged along one or both sides of the waveguide core.
In the present specification, the phrase “light confinement portions having substantially the same refractive index as the waveguide core” implies that the respective refractive indexes of the light confinement portions and the waveguide core are equal or approximate to each other. Thus, based on the difference in specific refractive index between a core and a clad that constitutes the waveguide core, the width of each light confinement portion is adjusted to a value such that a maximum light confinement effect can be obtained. For example, the width of each light confinement portion is set at about 1 &mgr;m or more, preferably at 3 to 20 &mgr;m, and most preferably at 5 to 9 &mgr;m.
The waveguide core and the light confinement portion are arranged at a distance of 30 &mgr;m or more from each other.
Further, the waveguide core has a branching portion at which an optical filter is located across the waveguide core.
In order to achieve the above object, according to the present invention, there is provided a manufacturing method for the optical waveguide circuit having a waveguide core of a desired shape on a substrate and light confinement portions arranged along one or both sides of the waveguide core. In this manufacturing method, the waveguide core and the light confinement portions are formed simultaneously.
According to the present invention, there may be provided an optical waveguide circuit and method of fabricating same, whereby clad-mode light can be restrained from landing on the waveguide core or from leaking into other ports. According to the method of the invention, moreover, the waveguide core and the light confinement portions are formed simultaneously, so that the optical waveguide circuit can be manufactured in simple processes at low cost.
The above and other objects, features, and advantages of the invention will be more apparent from the ensuing detailed description taken in connection with the accompanying drawings.


REFERENCES:
patent: 5151959 (1992-09-01), Mueller et al.
patent: 5206925 (1993-04-01), Nakazawa et al.
patent: 5303319 (1994-04-01), Ford et al.
patent: 6009218 (1999-12-01), Grand et al.
patent: 6157765 (2000-12-01), Bruce et al.

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