Optical waveguides – Planar optical waveguide
Reexamination Certificate
1998-12-24
2001-06-05
Font, Frank G. (Department: 2877)
Optical waveguides
Planar optical waveguide
C385S132000, C385S143000, C385S031000
Reexamination Certificate
active
06243524
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an optical waveguide, a method for fabricating the same, and a coupling structure of the optical waveguide to a light-receiving device.
BACKGROUND OF THE INVENTION
Heretofore, as an example for a coupling structure of an optical waveguide to a light-receiving device, the one shown in
FIG. 1
is usual.
In the coupling structure, an optical waveguide
4
made of a quartz-base material and having a structure wherein a long core
2
having a high index of refraction and a square or rectangular section is enclosed with a cladding
3
having a low index of refraction is formed on a base
1
made of a silicon substrate or the like, an end plane
2
a
of the core
2
is opposed to a light-receiving plane
6
of a photodiode (PD: light-receiving device)
5
, the end plane
2
a
of the core
2
is positioned in such that the center thereof coincides substantially with the center of the light-receiving plane
6
of the photodiode
5
, and then, the photodiode
5
is fixed to on the base
1
.
Since it is required to position the center of the end plane
2
a
of the core
2
in such that the former center coincides substantially with the center of the light-receiving plane
6
of the photodiode
5
in the above described structure, there is such a manner that markers (register marks) indicating positions of the optical waveguide
4
and the photodiode
5
, respectively, have been previously prepared on the base
1
, and the optical waveguide
4
and the photodiode
5
are fixed after having been in register, respectively, in the case where the optical waveguide
4
and the photodiode
5
are fixed on the base
1
.
Meanwhile, since it is required to fix the optical waveguide
4
and the photodiode
5
on the base
1
made of a silicon substrate and the like in the above-mentioned conventional coupling structure of optical waveguide to light-receiving device, there have been a problem of requiring an extra material of the base
1
, so that it is difficult to downsize the whole structure, and another problem of a difficulty t o lower costs for the structure, because the base
1
must be used in the structure so that it becomes expensive.
Furthermore, such a manner that markers for indicating positions of the optical waveguide
4
and the photodiode
5
have been previously formed on the base
1
, respectively, and then, the optical waveguide
4
and the photodiode
5
are fixed so as to maintain register in the respective markers is applied in the above described structure. In this case, however, variations in positions of the respective markers formed on the base
1
are significant, and further variations in positioning of the optical waveguide
4
and the photodiode
5
in case of securing them on the markers thus formed are also remarkable. As a result, there is a problem of magnifying further relative positional displacements in the core
2
of the optical waveguide
4
with respect to the light-receiving plane
6
of the photodiode
5
, resulting in defective products due to the positional discrepancies, in turn, it becomes a cause for reducing an yield of products.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide an optical waveguide which can be downsized and is excellent in productivity, a method for fabricating the same, and a coupling structure of the optical waveguide to a light-receiving device.
According to the first feature of the invention, an optical waveguide composed of a core part and a cladding part disposed so as to enclose the core part, comprises a cavity having an inner surface which inclines relative to a light axis of the core section, the cavity crossing partly or perfectly the core section; and a material for filling the cavity, the material having a refractive index higher than the core section.
In the preferred embodiment, the cavity is any one of conical, pyramidal, and wedge-shaped cavities in the above described optical waveguide.
In the preferred embodiment, the material is a resin in the above described optical waveguide.
In the preferred embodiment, the resin is an ultraviolet-curing resin in the above described optical waveguide.
According to the second feature of the invention, a method for fabricating an optical waveguide composed of a core section, and a cladding section disposed so as to enclose the core section, comprises the steps of:
defining a cavity the inner surface of which inclines with respect to the core section of the optical waveguide on one of principal planes parallel to the core section so as to traverse partly or perfectly a section of the core; and
filling the cavity with a material having a higher index of refraction than that of the core section.
According to the third feature of the invention, a coupling structure of the optical waveguide to a light-receiving device, comprises a light-receiving plane of the light-receiving device being disposed to face a cavity of the optical waveguide composed of a core section, and a cladding section disposed so as to enclose the core section, wherein the cavity the inner surface of which inclines with respect to the core section of the optical waveguide is defined on one of principal planes parallel to the core section so as to traverse partly or perfectly a section of the core, and the cavity is filled with a material having a higher index of refraction than that of the core section; and the light-receiving device being fixed to the optical waveguide.
In a preferred embodiment, a coupling structure of the optical waveguide to a light-receiving device in the above described coupling structure, wherein register markers for positioning the optical waveguide and the light-receiving device are prepared respectively, and the markers for the optical waveguide and the markers for the light-receiving device are allowed to be in register, thereby to position the light-receiving device with respect to the optical waveguide.
In the optical waveguide according to the invention, a cavity the inner surface of which inclines with respect to the core section of the optical waveguide is defined on one of principal planes parallel to the core section so as to traverse partly or perfectly a section of the core; and the cavity is filled with a material having a higher index of refraction than that of the core section.
If the cavity is not filled with a material having a higher index of refraction than that of the core section, a refraction factor of the core section becomes higher than that (about 1.00) of air, so that a part of the light propagating through the core section is reflected by the interface between the core section and the cavity, and the light other than that reflected proceeds towards the direction of the cavity peak while being refracted in accordance with Snell laws of refraction. Accordingly, the light is difficult to be output outside the cavity.
On the other hand, when the cavity is filled with a material having a higher index of refraction than that of the core section, the light propagating through the core section enters into the cavity without being reflected by the interface between the core section and the cavity, and proceeds to the direction opposite to the cavity peak while being refracted. Thereafter, the light is reflected by the inner surface of the cavity, and is output towards the outside of the cavity.
Thus, it becomes possible to lift the light propagating through the core section along the direction perpendicular substantially to the core section.
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Font Frank G.
McGuireWoods LLP
NEC Corporation
Nguyen Sang H.
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