Optical waveguides – With optical coupler
Reexamination Certificate
2000-09-13
2002-04-23
Ullah, Akm E. (Department: 2874)
Optical waveguides
With optical coupler
Reexamination Certificate
active
06377723
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an optical waveguide circuit, which is used as a wavelength filter and an optical wavelength synthesizing and dividing device, etc., used for light transmissions, and a method for compensating the light transmission wavelength. In particular, the invention relates to an optical waveguide circuit which compensates for a fluctuation in temperature of the light transmission wavelength, and a method for compensating the light transmission wavelength thereof.
BACKGROUND OF THE ART
Recently, as a method to remarkably increase a transmission capacity in optical transmissions, studies and research have actively been carried out with respect to optical wavelength division multiplexing transmissions, and actual uses thereof have been commenced. The optical wavelength division multiplexing transmission is, for example, to transmit a plurality of lights having different wavelengths from each other while multiplexing the same. In such a system for optical wavelength division multiplexing transmission, it is indispensable to provide, in the system, an optical wavelength synthesizing and dividing device to pick up lights of each wavelength from the plurality of lights to be transmitted, at the light receiving side. Also, an optical wavelength synthesizing and dividing device used for optical wavelength division multiplexing transmissions is constructed so as to be provided with a light transmission device, which transmits only lights of predetermined wavelengths, or an optical reflection device, etc., which reflects only lights of predetermined wavelengths.
As one example of a light transmission device, there is a planar light waveguide circuit (PLC: Planar Light-wave Circuit) shown in, for example, FIG.
13
. An optical waveguide circuit shown in the same drawing is called an arrayed waveguide diffraction grating (AWG: Arrayed Waveguide Grating). The arrayed waveguide diffraction grating
11
is such that a waveguide construction formed of a glass material is constructed on a substrate
1
formed of silicon, etc.,
In the waveguide construction, an input side slab waveguide
3
which acts as a first slab waveguide is connected to the emitting side of one or more optical input waveguides
2
, and an array waveguide
40
which consists of a plurality of optical waveguides
4
is connected to the emitting side of the input side slab waveguide
3
. An output side slab waveguide
5
which acts as the second slab waveguide is connected to the emitting side of the array waveguide
40
while a plurality of optical output waveguides
6
juxtaposed to each other are connected to the emitting side of the output side slab waveguide
5
.
The array waveguide
40
propagates light emitted from the input side slab waveguide
3
, which consists of optical waveguides
4
whose lengths are different from each other, wherein the lengths of optical waveguides adjacent to each other have a difference of &Dgr;L. Also, optical input waveguides
2
and optical output waveguides
6
are those that are provided, corresponding to the number of signal lights having wavelengths different from each other, which are divided by, for example, an arrayed waveguide diffraction grating
11
. Further, the array waveguide
40
is formed of a number of optical waveguides
4
, for example, 100 waveguides. However, in the same drawing, the number of respective optical waveguides
2
,
4
, and
6
are simplified and illustrated for simplification of the drawing.
For example, transmission side optical fibers (not illustrated) are connected to the optical input waveguides
2
to cause wavelength-multiplexed lights to be introduced. Lights introduced into the input side slab waveguide
3
through the optical input waveguides
2
are propagated by its diffraction effect and are made incident into the respective optical waveguides
4
of the array waveguide
40
, whereby the lights are propagated in the respective optical waveguides
4
(array waveguide
40
).
Lights propagated in the array waveguide
40
reach the output side slab waveguide
5
, and are collected to and outputted to the optical output waveguides
6
. Also, since the lengths of optical waveguides
4
which form the array waveguide
40
are different from each other, shifts arise in the phase of the individual light phase after the lights are propagated in the array waveguide
40
. Accordingly, the wave plane of a convergent light is inclined in compliance with a shift amount of the phase, and a position, at which the convergent light is caused to converge, is determined by an angle of the inclination.
Further, where it is assumed that the angle (diffraction angle) is &thgr; at which a light is caused to converge when a light is made incident into the output side slab waveguide
5
from the array waveguide
40
, there is a relationship between the &thgr; and the wavelength &lgr; of the convergent light as shown in the following expression.
n
s
&thgr;+n
c
&Dgr;L=m&lgr;
(1)
In expression (1), n
s
is a refractive index of the output side slab waveguide
5
, and n
c
is a refractive index (effective refractive index) of optical waveguides
4
which forms an array waveguide
40
. Also, m is the number of diffractions, whose figure is an integral number. In expression (1), where the wavelength is &lgr; when, for example, &thgr;=0 is established, the following expression (2) can be established.
l
—
0=
nc&Dgr;L/m
(2)
Therefore, the converging positions of lights having different wavelengths become different from each other, whereby it is possible to output lights having different wavelengths from different optical output waveguides
6
corresponding to the respective wavelengths.
An arrayed waveguide diffraction grating
11
has an optical dividing feature which, on the basis of the principle described above, divides lights having a plurality of wavelengths from those having the correspsonding plurality of wavelengths, different from each other, which are inputted from the optical input wavelengths
2
, and outputs these from the respective optical output waveguides
6
. And, a light transmission feature of the respective lights outputted from the respective optical output waveguides
6
becomes a feature as shown in, for example, FIG.
14
(
a
). That is, the light transmission feature of the abovementioned respective lights has a light transmission feature in which the light transmission ratio is reduced in compliance with the wavelength being deviated from the center wavelength of the transmission of the respective lights centering around the center wavelengths of the respective light transmissions different from each other, in at least a predetermined wavelength area. In addition, the center wavelengths of the respective light transmissions in the light transmission feature are proportionate to a different (&Dgr;L) in the length of optical waveguides
4
forming an array waveguide
40
, and effective refractive index nc of the optical waveguides
4
.
In addition, the abovementioned light transmission feature does not necessarily have a relative maximum figure. For example, as shown in (b) in the same drawing, there may be a light transmission feature which has two relative maximum figures. Also, the wavelength showing the light transmission feature is not necessarily one for a specified optical output waveguide
6
, and the wavelengths can be established, respectively, for the numbers m of diffraction which are different from each other in expression (1), wherein there exist a plurality of wavelengths for each of the numbers of diffraction. Therefore, where, for example, an arrayed waveguide diffraction grating is used for waveguide multiplexed light transmission, the number m of diffraction is determined so that the light transmission feature corresponds to the use wavelength of wavelength multiplexed optical transmission, whereby an arrayed waveguide diffraction grating
11
is designed.
Since the arrayed waveguide diffraction grating
11
has a feature as described above, it
Ohta Toshihiko
Saito Tsunetoshi
The Furukawa Electric Co. Ltd
Ullah Akm E.
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