Optical waveguides – With optical coupler – Particular coupling structure
Reexamination Certificate
2000-09-22
2002-12-03
Ullah, Akm E. (Department: 2874)
Optical waveguides
With optical coupler
Particular coupling structure
C385S015000, C385S024000, C385S037000
Reexamination Certificate
active
06490395
ABSTRACT:
CROSS-REFERENCES TO RELATED APPLICATIONS
The present application claims priority under 35 U.S.C. §119 to Japanese Patent Application No. 11-270201, filed Sep. 24, 1999, entitled “Arrayed Waveguide Grating”, Japanese Patent Application No. 2000-021533, filed Jan. 31, 2000, entitled “Arrayed Waveguide Grating”, and Japanese Patent Application No. 2000-219205, filed Jul. 19, 2000, entitled “Arrayed Waveguide Grating”. The Contents of these applications are incorporated herein by reference in their entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an arrayed waveguide grating (AWG) which is used as, for example, an optical multiplexer or demultiplexer. Further, the present invention relates to a method for compensating an optical transmitting center wavelength of light which travels through an arrayed waveguide grating.
2. Discussion of the Background
In the field of optical communications, active researches and developments of the WDM (Wavelength Division Multiplexing) optical communications have been made over the recent years in order to dramatically increase transmission capacity. According to the WDM optical communications, for example, plural fluxes of light having different wavelengths are transmitted in multiplexing. The WDM optical communications system includes an optical transmitting device that transmits only the beams of light having predetermined wavelengths in order to extract the light beam of each wavelength from the multiplexed beams at a light receiving side.
FIG. 11
shows an arrayed waveguide grating (AWG) of a planar lightwave circuit (PLC) by way of one example of the optical transmitting device. The arrayed waveguide grating has a waveguide pattern as illustrated in FIG.
11
. The waveguides include cores and claddings composed of silica-based glass or the like. The waveguides are provided on a substrate
1
which is made of silicon or the like.
In the waveguide pattern of the arrayed waveguide grating, a first slab waveguide
3
is connected to an exit side of one or more optical input waveguides
2
provided in a side-by-side relation. A plurality of arrayed waveguides
4
provided side by side are connected to an exit side of the first slab waveguide
3
. A second slab waveguide
5
is connected to an exit side of the arrayed waveguides
4
. A plurality of optical output waveguides
6
provided side by side are connected to an exit side of the arrayed waveguides
4
.
The arrayed waveguides
4
serve to transmit the light traveling through the first slab waveguide
3
. The arrayed waveguides
4
are formed to have different lengths. The lengths of the arrayed waveguides
4
adjacent to each other are different by (&Dgr;L). Note that the optical input waveguides
2
and the optical output waveguides
6
are provided corresponding to the number of signal lights which have wavelength different from each other and which are demultiplexed or multiplexed by, for example, the arrayed waveguide grating. Normally, the arrayed waveguides
4
include a lot of waveguides, for example, 100 waveguides. Referring to
FIG. 11
, however, simply countable numbers of the optical input waveguides
2
, the arrayed waveguides
4
and the optical output waveguides
6
are shown therein for simplicity of illustration.
Since optical fibers (not shown) of, for example, a transmission side are connected to the optical input waveguides
2
, the WDM light is introduced. The light entering the first slab waveguide via the optical input waveguides
2
expands due to a diffraction effect thereof and enters the respective arrayed waveguides
4
, thus traveling through the arrayed waveguides
4
.
The light traveling through the arrayed waveguides
4
arrives at the second slab waveguide
5
. Then, these fluxes of light are converged on and outputted to the optical output waveguides
6
. However, all the arrayed waveguide
4
have their lengths different from each other. Accordingly, there occur phase shifts between the individual beams of light after traveling through the arrayed waveguides
4
. A phase front of the converged flux of light inclines corresponding to a quantity of this phase shift, and a position of the convergence is determined based on an angle of this inclination.
Therefore, the converging positions of the beams of light having different wavelengths become different from each other. The optical output waveguides
6
are provided in those different converging positions. Accordingly, the demultiplexed beams of light having different wavelengths may be outputted from the optical output waveguides
6
provided in the positions different according to the respective wavelengths.
Namely, the arrayed waveguide grating incorporates an optical demultiplexing function of demultiplexing the beams of light having one or more wavelengths from the multiplexed beams of light inputted from the optical input waveguide
2
and having the plurality of wavelengths different from each other, and outputting the thus demultiplexed beams of light from each of the optical output waveguides
6
. A center wavelength of the demultiplexed beams of light is proportional to an effective refractive index (n
c
) of the optical waveguide
4
as well as to the difference (&Dgr;L) in length between the arrayed waveguides
4
.
The arrayed waveguide grating exhibits the characteristics described above and is therefore used as a WDM demultiplexer for a WDM transmission. For example, as shown in
FIG. 11
, when WDM light beams having wavelengths (&lgr;
1
, &lgr;
2
, &lgr;
3
, . . . , &lgr;
n
) (n is an integer 2 or larger) are inputted from one single line of optical input waveguide
2
, the light beams having these wavelengths are expanded through the first slab waveguide
3
and arrive at the arrayed waveguides
4
. The light beams travel via the second slab waveguide
5
, as described above, converge on the different positions according to the wavelengths and enter the different optical output waveguides
6
. The light beams then travel through the corresponding optical output waveguides
6
and are outputted from the exit ends of these optical output waveguides
6
.
Then, the optical fibers (not shown) for outputting the light are connected to the exit ends of the optical output waveguides
6
. Therefore, the light beams having the above wavelengths are taken out via these optical fibers. Note that when connecting the optical fibers to the optical output waveguides
6
and to the optical input waveguides
2
, for instance, an optical fiber array in which the optical fibers are fixedly disposed in a one-dimensional array is prepared and fixed to connection end surface sides of the optical output waveguides
6
and of the optical input waveguides
2
. Thus, the optical fibers are connected to the optical output waveguides
6
and to the optical input waveguides
2
.
In this arrayed waveguide grating, the light beams outputted from the optical output waveguides
6
exhibit an optical transmitting characteristic (a wavelength characteristic of an intensity of the transmitting light of the arrayed waveguide grating) as shown in FIG.
12
. Referring to
FIG. 12
, an optical transmission becomes smaller as the wavelength shifts from the corresponding optical transmitting center wavelength (e.g., &lgr;
1
, &lgr;
2
, &lgr;
3
, . . . , &lgr;
n
). It should be noted that the optical transmitting characteristic does not necessarily have one maximal value and might have two or more maximal values in some cases.
Further, the arrayed waveguide grating utilizes the principle of the light reciprocity (reversibility), and therefore has a function of an optical demultiplexer and a function of an optical multiplexer as well. That is, in a direction reverse to the direction in
FIG. 11
, the light beams having a plurality of diferrent wavelengths enter the optical output waveguides
6
corresponding to the respective wavelengths, then travel through the transmission path in the reverse direction. These light beams are multiplexed in the arrayed waveguides
4
and exit through one
Kashihara Kazuhisa
Nakajima Takeshi
Nara Kazutaka
Saito Tsunetoshi
Doan Jennifer
The Furukawa Electric Co. Ltd.
Ullah Akm E.
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