Optical wavelength multiplexing and dividing device

Details Optical wavelength multiplexing and dividing device Optical wavelength multiplexing and dividing device

2000-04-05

2002-07-02

Sanghavi, Hemang (Department: 2874)

Optical waveguides

With optical coupler

Plural

C385S037000

Reexamination Certificate

active

06415072

ABSTRACT:

TECHNICAL FIELD
The present invention relates to an optical wavelength multiplexing and dividing device that is used in, for example, an optical wavelength multiplex transmission. Background of the invention.
Recently, in a wavelength multiplex optical transmission system, an attempt has been carried out, in which the number of optical transmissions is increased by increasing the degree of multiplex in wavelengths. In order to achieve the objective, it is necessary to prepare an optical wavelength multiplexing and dividing device that is able to multiplex and divide a plurality of signal lights whose wavelength interval is lnm or less. For example, in a wavelength multiplexed transmission at a wavelength band of 1.55 &mgr;m, an optical wavelength multiplexing and dividing device is demanded, which is able to multiplex and divide a plurality of signal lights whose wavelength interval is 0.8 nm (100 GHz interval in terms of frequency).
A diffraction grating is available as an example of the optical wavelength multiplexing and dividing device. In an optical wavelength multiplexing and dividing device in which a prior art diffraction grating is employed, there is a limitation in the number of diffractions that can be used, wherein sufficient dispersion cannot be obtained. Therefore, although it was impossible to decrease the wavelength interval to 1 nm or less, Japanese Laid-Open Patent Publication No. 65588-1989 proposed an optical wavelength multiplexing and dividing device which improves the wavelength resolution by using an array type waveguide diffraction grating as a diffraction grating and can narrow the wavelength interval.
As shown in FIG.
6
(
a
), the proposed optical wavelength multiplexing and dividing device has a waveguide chip in which a waveguide pattern is formed on a substrate
1
. The optical wavelength multiplexing and dividing device is constructed as follows; that is, the abovementioned waveguide pattern is composed so the input type slab waveguide
3
which functions as a first slab waveguide is connected to the outgoing side of optical input waveguides
2
juxtaposed in a plurality, a plurality of juxtaposed array waveguides
4
are connected to the outgoing side of the input side slab waveguide
3
, an output side slab waveguide
5
which functions as a second slab wave guide is connected to the outgoing side of a plurality of array waveguides
4
, and a plurality of juxtaposed optical output waveguides
6
are connected to the outgoing side of the output side slab waveguide
5
.
The array waveguides
4
are composed so as to have different lengths from each other, and propagate light introduced from the input side slab waveguide
3
. In addition, the optical input waveguides
2
and optical output waveguides
6
are provided so as to correspond to the number of a plurality of signal lights having different wavelengths from each other, which are divided by, for example, an optical wavelength multiplexing and dividing device. Although the array waveguides
4
are usually provided in a plurality, for example, 100 in number, the number of these respective waveguides
2
,
4
and
6
is simply illustrated in FIG.
6
(
a
) for the sake of simplification of the drawing.
Transmission side optical fibers (not illustrated) are connected to the optical input waveguides, in which wavelength-multiplexed light is introduced. The light introduced through the optical input waveguides
2
into the input side slab waveguide
3
is widened by its diffraction effect and is made incident into a plurality of array waveguides
4
for propagation therein. The light propagated in the respective array waveguides
4
reaches the output side slab waveguide
5
, wherein the light is condensed and outputted into the optical output waveguides
6
. In the light propagation, since the lengths of the respective array waveguides
4
are different from each other, a deviation in the individual optical phases arises after the light propagates in the respective array type waveguides
4
, whereby the wave plane of the converged light is inclined in line with the deviation amount, and the angle of inclination determines a light condensing position. Therefore, by forming the optical output waveguides
6
at the light condensing position, light having different wavelengths can be outputted wavelength by wavelength from the optical output waveguides
6
.
For example, as shown in FIG.
6
(
b
), a signal (signal light)
1
, having a wavelength &lgr;, which is condensed through the output side slab waveguide
5
is condensed at the incident ends
7
of the output side waveguides
6
shown with a mark #
1
, and a signal
2
having a wavelength (&lgr;+&Dgr;&lgr;), which is condensed through the output side slab waveguide
5
is condensed at the incident ends
7
of the output side waveguides
6
shown by a mark #
2
. A signal
3
having a wavelength (&lgr;+2&Dgr;&lgr;), which is condensed through the output side slab waveguide
5
is condensed at the incident ends
7
of the output side waveguides
6
shown by a mark #
3
. Thus, light is made incident from the respective input ends
7
into the optical output waveguides
6
, and is outputted from the outgoing ends
8
of the optical output waveguides
6
through the respective optical output waveguides
6
.
Therefore, as shown in
FIG. 7
, by connecting optical fibers
10
for optical output to the outgoing ends
8
of the respective optical output waveguides
6
, it is possible to separate and pick up light of the abovementioned respective wavelengths through the optical fibers. Further, in the abovementioned optical wavelength multiplexing and dividing device, the arraying pitch Ø of the outgoing ends
8
of the optical output waveguides
6
is formed to be approx. 250 &mgr;m, which is equal to the diameter Ø of the optical fibers
10
so that the optical fibers
10
can be easily connected to the outgoing ends
8
of the optical output waveguides
6
. And the arraying pitch of the outgoing ends
8
of the optical output waveguides
6
is formed greater than that of the incident ends
7
of the optical output waveguides
6
.
In an optical wavelength multiplexing and dividing device of the array type waveguide diffraction grating, since the wavelength resolution is proportional to a difference (&Dgr;L) in length of the respective array waveguides
4
which constitute diffraction gratings, it becomes possible to multiplex and divide wavelength-multiplexed light of a narrow wavelength interval, which could not be achieved by any prior art diffraction grating, by designing the &Dgr;L to be a large value.
However, in an optical wavelength multiplexing and dividing device of such an array waveguide diffraction grating, a deviation arises in the wavelength characteristics of an optical wavelength multiplexing and dividing device due to unevenness in the film thickness of a produced waveguide pattern, waveguide widths, refractive index, etc. If such a deviation occurs, signal light of the respective wavelengths, which is condensed through the output side slab waveguide
5
, is not normally condensed at the incident ends
7
of the optical output. waveguides
6
shown at, for example, #
1
, #
2
and #
3
, and the light is condensed at a deviated position shown at
9
in FIG.
6
(
b
). The deviation of the condensing position reaches ±0.5 nm or so at most in terms of wavelength, wherein since light of the respective wavelengths is condensed at a position far from the incident ends
7
of the optical output waveguides
6
, it is impossible to make the light of the respective wavelengths into the optical output waveguides
6
.
In addition, as a means for reducing the problem of the deviation in wavelengths divided by such an optical wavelength multiplexing and dividing device, such a method is proposed, which shifts a wavelength condensed at the incident ends
7
of the optical output waveguides
6
by combining a temperature controlling device to a waveguide chip and utilizing a temperature dependency of the refractive

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