Optical waveguides – With optical coupler – Particular coupling structure
Reexamination Certificate
1999-05-21
2001-10-16
Bovernick, Rodney (Department: 2874)
Optical waveguides
With optical coupler
Particular coupling structure
C385S030000, C385S040000, C385S041000, C385S042000, C385S047000
Reexamination Certificate
active
06304697
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an optical device, and more particularly to, an optical device provided with a directional coupling type optical waveguide.
BACKGROUND OF THE INVENTION
In recent years, optical fiber communication systems capable of conducting the high-quality transmission of large-capacity information have come into practical use. As the component part of such a communication system, a directional coupling type optical device that can control optical signal at a high speed and uses optical waveguides capable of being miniaturized by integration has been developed.
FIG.1
shows the generalized composition of a conventional optical device thus developed. This optical device is composed of a first optical waveguide
11
and a second optical waveguide
12
on a LiNbO
3
substrate
10
. The first optical waveguide
11
and the second optical waveguide
12
have the same width, thickness and refractive index, and are disposed in parallel close to each other, thereby forming a directional coupler
13
in this parallel part. The coupling length that the movement of light between optical waveguides in the directional coupler
13
becomes 100% is defined as a perfect coupling length Lc. The directional coupler
13
is formed with a coupling length that is half of the perfect coupling length Lc. Also, a total reflection film (or total reflection plate)
14
is disposed opposed to the end faces of the first and second optical waveguides forming the directional coupler
13
. Further, on the first and second optical waveguides
11
,
12
forming the directional coupler
13
, control electrodes
15
,
16
are formed through buffer layers (not shown), and voltage can be applied to its both ends.
When voltage is not applied to the control electrodes
15
,
16
, the optical energy of incident light
17
supplied to the first optical waveguide
11
of this optical device gradually moves to the second optical waveguide
12
in the directional coupler
13
. Then, when propagating by half of the perfect coupling length Lc to reach the total reflection film
14
, half of the energy of incident light is moved to the second optical waveguide
12
. At this time, the first and second optical waveguides
11
,
12
have a same optical intensity, and have phases inverse to each other. It reflects totally on the total reflection film
14
, then propagating through the directional coupler
13
in the reverse direction. Also in this case, the optical energy gradually moves to the second optical waveguide
12
. When returning to the incidence point of the directional coupler
13
, all the optical energy is moved to the second optical waveguide
12
. As a result, emitting light
18
with the same optical intensity as incident light
17
is obtained from the second optical waveguide
12
.
However, this optical device is composed of the first and second optical waveguides
11
,
12
on the LiNbO
3
substrate
10
. The substrate
10
has an electro-optic effect, where the refractive index at the periphery of voltage-applied part varies by an electric field caused by the application of voltage. Thus, applying voltage to the control electrodes
15
,
16
, causes the refractive index of the first and second optical waveguides
11
,
12
formed under the electrodes to be changed.
In this state, the coupling state between the optical waveguides changes due to the discordance of phase speed between the waveguide modes of the optical waveguides forming the directional coupler
13
.
Thus, light
18
can be controlled so as not to be emitted from the second optical waveguide
12
.
Namely, by applying voltage to the electrode on the optical waveguide forming the directional coupler provided on the substrate with the electro-optic effect, when supplying incident light from one optical waveguide, light can be controlled so as to be emitted from another optical waveguide or so as not to be emitted therefrom.
This means that the on/off control of emitted light can be performed.
Also, the optical device to perform such control can be miniaturized since it only has to have half of the perfect coupling length.
Such optical devices using the electro-optic effect are, for example, disclosed in Japanese patent application laid-open Nos. 63-234227(1988) and 3-256028(1991).
However, these optical devices have to use a very specific substrate with the electro-optic effect, e.g., LiNbO
3
substrate. Therefore, there is a problem that especially in combining and integrating various kinds of optical devices, the manufacturing cost increases.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the invention to provide an optical device in which integration can be attained at a low manufacturing cost.
According to the invention, an optical device, comprises:
a first optical waveguide disposed on a substrate having a thermo-optical effect;
a second optical waveguide that, at its one end, has part which is disposed close to and in parallel with part of the first optical waveguide by a predetermined length on the substrate, and that, at the parallel part, is evanescent-coupled with light propagating through the first optical waveguide;
light reflecting means that is disposed opposed to the end faces, at the one end, of the first and second optical waveguides and that totally reflects light emitted from the end faces; and
distribution ratio altering means that heats around the evanescent-coupled parallel part of the first and second optical waveguides to alter a distribution ratio of lights emitted from the other ends of the first and second optical waveguides to which incident light supplied to the first optical waveguide at the other end is distributed.
According to another aspect of the invention, an optical device, comprises:
a first optical waveguide disposed on a substrate having a thermo-optical effect;
a second optical waveguide that, at its one end, has part which is disposed close to and in parallel with part of the first optical waveguide by a predetermined length on the substrate, and that, at the parallel part, is evanescent-coupled with light propagating through the first optical waveguide;
light reflecting means that is disposed opposed to the end faces, at the one end, of the first and second optical waveguides and that totally reflects light emitted from the end faces;
emitted light detecting means that is disposed opposed to the end face of the second optical waveguide at the other end and that detects the intensity of light emitted from the end face of the second optical waveguide at the other end; and
distribution ratio altering means that heats around the evanescent-coupled parallel part of the first and second optical waveguides to alter a distribution ratio of lights emitted from the other ends of the first and second optical waveguides to which incident light supplied to the first optical waveguide at the other end is distributed.
According to another aspect of the invention, an optical device, comprises:
a first optical waveguide disposed on a substrate having a thermo-optical effect;
a second optical waveguide that, at its one end, has part which is disposed close to and in parallel with part of the first optical waveguide by a predetermined length on the substrate, and that, at the parallel part, is evanescent-coupled with light propagating through the first optical waveguide;
light reflecting means that is disposed opposed to the end faces, at the one end, of the first and second optical waveguides and that transmits part of light emitted from the end faces and reflects the remaining part of light;
received light intensity detecting means that detects the intensity of light transmitted through the light reflecting means; and
distribution ratio altering means that heats around the evanescent-coupled parallel part of the first and second optical waveguides to alter a distribution ratio of lights emitted from the other ends of the first and second optical waveguides to which incident light supplied to the first optical waveguide at the other end is distributed.
According to another
Bovernick Rodney
NEC Corporation
Rojas Omar
Young & Thompson
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