Optical waveguides – With optical coupler – Input/output coupler
Reexamination Certificate
2002-04-23
2004-11-30
Patel, Nimeshkumar D. (Department: 2879)
Optical waveguides
With optical coupler
Input/output coupler
C385S039000, C385S046000, C385S014000
Reexamination Certificate
active
06826332
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an arrayed waveguide grating used as a wavelength division multiplexer/demultiplexer in optical communications, and method for correcting center wavelength.
BACKGROUND OF THE INVENTION
In recent optical communications, wavelength division multiplexing communications are vigorously researched and developed and its practical use is advanced as a method for greatly increasing transmission capacity of the optical communications. In the wavelength division multiplexing communications, for example, a plurality of lights having wavelengths different from each other are multiplexed and transmitted. In such wavelength division multiplexing communications, a light transmitting device which transmits only the predetermined wavelengths is indispensable.
FIG. 11
shows one example of the light transmitting device. This light transmitting device is an arrayed waveguide grating (AWG) of a planar lightwave circuit (PLC). The arrayed waveguide grating includes a waveguide forming area having a waveguide construction formed on a silicon substrate
1
as shown in FIG.
11
.
The waveguide construction of the arrayed waveguide grating comprises at least one optical input waveguide
2
and a first slab waveguide
3
connected to an emitting side of at least one optical input waveguide
2
. An arrayed waveguide
4
constructed by a plurality of channel waveguides
4
a
arranged side by side is connected to an emitting side of the first slab waveguide
3
. A second slab waveguide
5
is connected to an emitting side of the arrayed waveguide
4
. A plurality of optical output waveguides
6
arranged side by side are connected to an emitting side of the second slab waveguide
5
.
The above arrayed waveguide
4
propagates light transmitted from the first slab waveguide
3
. Lengths of the adjacent channel waveguides
4
a
are different by &Dgr;L from each other. For example, the optical output waveguides
6
are arranged in accordance with the number of signal lights of wavelengths different from each other. A plurality of channel waveguides
4
a
such as 100 channel waveguides
4
a
are normally arranged. However, in
FIG. 11
, the number of optical output waveguides
6
, the number of channel waveguides
4
a
and the number of optical input waveguides
2
are respectively schematically shown to simplify FIG.
11
.
For example, an unillustrated optical fiber is connected to the optical input waveguide
2
so as to introduce the wavelength multiplexed light. The wavelength multiplexed light is transmitted to the first slab waveguide
3
through one of the optical input waveguides
2
. The wavelength multiplexed light transmitted to the first slab waveguide
3
is widened by a diffraction effect, and is transmitted to the arrayed waveguide
4
, and is propagated in the arrayed waveguide
4
.
The light propagated in the arrayed waveguide
4
reaches the second slab waveguide
5
, and the lights are condensed each other and outputted to each of optical output waveguide
6
. However, since the lengths of the adjacent channel waveguides
4
a
of the arrayed waveguide
4
are different from each other, a phase shift is caused for the individual light after the light is propagated in the arrayed waveguide
4
. A phasefront of the condensed light is inclined in accordance with this shift amount, and a condensing position is determined by an angle of this inclination.
Therefore, the condensing positions of the lights of different wavelengths are different from each other. The lights (demultiplexed lights) of different wavelengths can be outputted from the different optical output waveguides
6
every wavelength by forming the optical output waveguides
6
in the respective light condensing positions.
Namely, the arrayed waveguide grating has an optical demultiplexing function for demultiplexing from the multiplexed light, having wavelengths different from each other. A center wavelength of the demultiplexed light is proportional to the difference (&Dgr;L) between the lengths of the adjacent channel waveguides
4
a
of the arrayed waveguide
4
and an effective refractive index (equivalent refractive index) n of the arrayed waveguide
4
.
The arrayed waveguide grating satisfies the relation of (formula 1).
n
s
·d
·sin &phgr;+
n
c
·&Dgr;L=m·&lgr;
(formula 1)
Here, n
s
is an equivalent refractive index of each of the first slab waveguide and the second slab waveguide, and n
c
is an equivalent refractive index of the arrayed waveguide. Further, &phgr; is a diffraction angle, m is a diffraction order, d is the distance between the adjacent channel waveguides
4
a
at the end of the arrayed waveguide
4
, and &lgr; is a center wavelength of light outputted from each optical output waveguide.
Here, when the center wavelength at the diffraction angle &phgr;=0 is set to &lgr;
0
, &lgr;
0
is represented by (formula 2). The wavelength &lgr;
0
is generally called a center wavelength of the arrayed waveguide grating.
λ
0
=
n
c
·
Δ
L
m
(
Formula
2
)
Since the arrayed waveguide grating has the above characteristics, the arrayed waveguide grating can be used as a wavelength multiplexer/demultiplexer for the wavelength multiplexing transmission.
For example, as shown in
FIG. 11
, when a multiplexed light of wavelengths &lgr;1, &lgr;2, &lgr;3, - - - , &lgr;n (n is an integer not less than 2) is inputted from one of the optical input waveguides
2
, the light having the different wavelengths is widened in the first slab waveguide
3
and reach the arrayed waveguide
4
. Thereafter, the lights of the respective wavelengths are condensed to different positions in accordance with the wavelengths as mentioned above through the second slab waveguide
5
. The lights of the respective wavelengths are transmitted to the optical output waveguides
6
different from each other, and are outputted from emitting ends of the optical output waveguides
6
through the respective optical output waveguides
6
.
The above light of each wavelength is taken out through an unillustrated optical fiber for an optical output by connecting this optical fiber to the emitting end of each optical output waveguide
6
. When the optical fiber is connected to each optical output waveguide
6
and the above optical input waveguide
2
, for example, an optical fiber array fixedly arranging a connecting end face of the optical fiber in a one-dimensional array shape is prepared. The optical fiber arrays are fixed to connecting end face sides of the optical output waveguides
6
and the optical input waveguides
2
, and then the optical fibers, the optical output waveguides
6
and the optical input waveguides
2
are connected.
In the above arrayed waveguide grating, transmittion characteristics of the light outputted from each optical output waveguide
6
, i.e., the wavelength dependency of transmitted light intensity of the arrayed waveguide grating are provided as shown in FIG.
12
A. As shown in
FIG. 12A
, in the light transmitting characteristics of the light outputted from each optical output waveguide
6
, each center wavelength (for example, &lgr;1, &lgr;2, &lgr;3, - - - , &lgr;n) is set to a center and light transmittance is reduced as the wavelength is shifted from each corresponding center wavelength.
FIG. 13
is a view overlapping and showing an example of an output spectrum from each optical output waveguide
6
.
It is not necessarily limited that the above light transmitting characteristics have one local maximum value as shown in FIG.
12
A. For example, as shown in
FIG. 12B
, there is also a case in which the light transmitting characteristics have not less than two local maximum values.
Further, since the arrayed waveguide grating utilizes the principle of reciprocity (reversibility) of light, the arrayed waveguide grating has the function of an optical demultiplexer, and also has the function of an optical multiplexer. For example, in contrast to
FIG. 11
, the optical multiplexing is performed by makin
Hasegawa Junichi
Kashihara Kazuhisa
Nekado Yoshinobu
Ono Yoshimi
Saito Tsunetoshi
Dong Dalei
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Patel Nimeshkumar D.
The Furukawa Electric Co. Ltd.
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