Optical waveguides – With optical coupler – Plural
Reexamination Certificate
2002-02-08
2004-04-27
Palmer, Phan T. H. (Department: 2874)
Optical waveguides
With optical coupler
Plural
C385S020000, C385S037000, C385S046000
Reexamination Certificate
active
06728435
ABSTRACT:
CROSS-REFERENCES TO RELATED DOCUMENTS
The present application is related to and claims priority on Japanese Patent Applications 11-370,602, filed on Dec. 27, 1999, 2000-58646, filed on Mar. 3, 2000, 2000-102473, filed on Apr. 4, 2000, and 2000-285448, filed Sep. 20, 2000, the entire contents of each of which are hereby incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an arrayed waveguide grating type optical multiplexer/demultiplexer and an optical waveguide circuit which are used in the field of optical communications and similar fields.
2. Discussion of the Background
Recently, in optical communications research and development of optical wavelength division multiplexing communications has actively been pursued as a way to exponentially increase transmission volume, and the results are being put into practice. Optical wavelength division multiplexing communications uses, for example, a technique of wavelength division multiplexing on a plurality of light beams each having a different wavelength from one another to transmit them. For systems using such optical wavelength division multiplexing communications, an optical multiplexer/demultiplexer is necessary which demultiplexes light that has undergone wavelength division multiplexing to be transmitted to create a plurality of light beams each having a different wavelength from one another, and which multiplexes a plurality of light beams each having a different wavelength from one another.
An optical multiplexer/demultiplexer of this kind preferably has the following capabilities. Firstly, it should be capable of multiplexing and demultiplexing light with a wavelength interval as narrow as possible within a range of a preset wavelength. Secondly, it should be excellent in wavelength flatness in the vicinity of the central wavelength of light to be multiplexed/demultiplexed. Thirdly and lastly, it should have low crosstalk between one passing wavelength and another passing wavelength adjacent thereto (hereinafter referred to as adjacent crosstalk).
Of the desired capabilities listed above, the first capability is met by, for example, an arrayed waveguide grating (AWG) type optical multiplexer/demultiplexer. An arrayed waveguide grating type optical multiplexer/demultiplexer such as shown in
FIG. 19A
, for example, is obtained by forming on a substrate
11
an optical waveguide unit
10
that has a waveguide structure.
The above waveguide structure includes one or more optical input waveguides
12
arranged side by side, a first slab waveguide
13
connected to the output ends of the optical input waveguides
12
, an arrayed waveguide
14
connected to the output end of the first slab waveguide
13
, a second slab waveguide
15
connected to the output end of the arrayed waveguide
14
, and a plurality of optical output waveguides
16
arranged side by side and connected to the output end of the second slab waveguide
15
.
The arrayed waveguide
14
propagates light that is output from the first slab waveguide
13
, and is a plurality of channel waveguides
14
a
arranged side by side. Lengths of adjacent channel waveguides
14
a
are different from each other with the differences (&Dgr;L) preset. The optical input waveguides
12
and the optical output waveguides
16
have the same dimensions.
The number of optical output waveguides
16
is determined, for example, in accordance with how many light beams having different wavelengths from one another are to be created as a result of demultiplexing of signal light by the arrayed waveguide grating type optical multiplexer/demultiplexer. The channel waveguides
14
a
constituting the arrayed waveguide
14
are usually provided in a large number, for example
100
. However,
FIG. 19A
is simplified and the numbers of the channel waveguides
14
a
, the optical output waveguides
16
, and the optical input waveguides
12
in
FIG. 19A
do not reflect the actual numbers thereof.
FIG. 19B
schematically shows an enlarged view of an area of
FIG. 19A
surrounded by the chain line A. As shown in
FIG. 19B
, in the arrayed waveguide grating type optical multiplexer/demultiplexer of the background art, straight output ends of the optical input waveguides
12
are connected directly to the input end of the first slab waveguide
13
. Similarly, the straight entrance ends of the optical output waveguides
16
are connected directly to the output end of the second slab waveguide
15
.
The optical input waveguides
12
are connected to, for example, transmission side optical fibers (not shown), so that light having undergone the wavelength division multiplexing is introduced to the optical input waveguides
12
. The light, after traveling through the optical input waveguides
12
and being introduced to the first slab waveguide
13
, is diffracted by the diffraction effect thereof and is input to the arrayed waveguide
14
to travel along the arrayed waveguide
14
.
After traveling through the arrayed waveguide
14
, the light reaches the second slab waveguide
15
and then is condensed at the output end of the second slab waveguide
15
. Because of the preset differences in lengths between adjacent channel waveguides
14
a
of the arrayed waveguide
14
, light beams after traveling through the arrayed waveguide
14
have different phases from one another. The phase fronts of many light beams from the arrayed waveguide
14
are tilted in accordance with this difference and the each position where the each light beam is condensed is determined by the angle of this tilt. Therefore, the light beams having different wavelengths are condensed at different positions from one another. By forming the optical output waveguides
16
at these positions, the light beams having different wavelengths can be output from their respective optical output waveguides
16
provided for the different respective wavelengths.
For instance, as shown in
FIG. 19A
, light beam having undergone the wavelength division multiplexing and having wavelengths of &lgr;1, &lgr;2, &lgr;3, . . . , &lgr;n (n is an integer equal to or larger than 2) is input to one of the optical input waveguides
12
. The light beam is diffracted in the first slab waveguide
13
, reach the arrayed waveguide
14
, and travel through the arrayed waveguide
14
and the second slab waveguide
15
. Then, as described above, the light beams are respectively condensed at different positions determined by their wavelengths, enter different optical output waveguides
16
, travel along their respective optical output waveguides
16
, and are output from the output ends of the respective optical output waveguides
16
. The light beams having different wavelengths are output through optical fibers (not shown) connected to the output ends of the optical output waveguides
16
.
In this arrayed waveguide grating type optical multiplexer/demultiplexer, an improvement in wavelength resolution of a grating is in proportion to the differences in lengths (&Dgr;L) between the adjacent channel waveguides
14
a
of the arrayed waveguide
14
. When the optical multiplexer/demultiplexer is designed to have a large &Dgr;L, it is possible to multiplex/demultiplex light to accomplish wavelength division multiplexing with a narrow wavelength interval. However, in the background art there are limits to how narrow a wavelength interval can be multiplexed. The optical multiplexer/demultiplexer has a function of multiplexing/demultiplexing a plurality of signal light beams. A function of demultiplexing or multiplexing a plurality of optical signals with a wavelength interval of 1 nm or less is deemed necessary for optical wavelength division multiplexing communications of high density.
In order for the above arrayed waveguide grating type optical multiplexer/demultiplexer to practice the second desired capability of the optical multiplexer/demultiplexer, i.e., to achieve central wavelength flatness, and to broaden the 3 dB band width (3 dB pass band width) of optical central wavelengths output from the optica
Kashihara Kazuhisa
Nara Kazutaka
Palmer Phan T. H.
The Furukawa Electric Co. Ltd.
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