Optical waveguides – With optical coupler – Input/output coupler
Reexamination Certificate
2000-12-22
2002-09-24
Healy, Brian (Department: 2874)
Optical waveguides
With optical coupler
Input/output coupler
C385S024000, C385S014000, C385S018000, C385S046000, C359S199200, C359S199200, C359S199200
Reexamination Certificate
active
06456763
ABSTRACT:
CROSS-REFERENCES TO RELATED DOCUMENTS
The present document is related to and claims priority on Japanese Priority Documents 11-370,457, filed on Dec. 27, 1999, and 2000-176,691, filed on Jun. 13, 2000, the contents of both 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 used as an optical multiplexer/demultiplexer in, for example, wavelength division multiplexing optical communications, and to a method of manufacturing the same.
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 division multiplexing 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, a light transmissive device or the like is provided to enable the receiver of the optical communication to take out light beams separately on the basis of their wavelengths from the transmitted light beams that have undergone the wavelength division multiplexing. The light transmissive device only transmits light of certain given wavelengths.
Examples of the light transmissive device include an arrayed waveguide grating (AWG) including a planar lightwave circuit (PLC) such as shown in FIG.
15
. The arrayed waveguide grating has a waveguide forming region
10
formed from quartz-based glass on a substrate
1
made of silicon or the like. The waveguide forming region
10
has a waveguide structure as illustrated in FIG.
15
and formed from a core.
The waveguide structure of the arrayed waveguide grating includes one or more optical input waveguides
2
arranged side by side, a first slab waveguide
3
connected to the output ends of the optical input waveguides
2
, an arrayed waveguide
4
connected to the output end of the first slab waveguide
3
, a second slab waveguide
5
connected to the output end of the arrayed waveguide
3
, and a plurality of optical output waveguides
6
arranged side by side and connected to the output end of the second slab waveguide
5
. The size of the arrayed waveguide grating can be set, for example, such that A=B=40 mm.
The arrayed waveguide
4
propagates light output from the first slab waveguide
3
, and includes a plurality of channel waveguides
4
a
arranged side by side. Lengths of adjacent channel waveguides
4
a
are different from each other with the differences (&Dgr;L) preset. The number of optical output waveguides
6
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 or multiplexing of signal light by the arrayed waveguide grating. The channel waveguides
4
a
constituting the arrayed waveguide
4
are usually provided in a large number, for example 100. However,
FIG. 15
is simplified and the number of the channel waveguides
4
a
, the optical output waveguides
6
, and the optical input waveguides
2
in
FIG. 15
does not reflect the actual number thereof.
The optical input waveguides
2
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
2
. The light output from the optical input waveguides
2
is introduced to the first slab waveguide
3
, is diffracted by the diffraction effect thereof, and enters the arrayed waveguide
4
to travel along the arrayed waveguide
4
.
After traveling through the arrayed waveguide
4
, the light reaches the second slab waveguide
5
and then is condensed in the optical output waveguides
6
to be output therefrom. Because of the preset differences in lengths between adjacent channel waveguides
4
a
of the arrayed waveguides
4
, light beams after traveling through the arrayed waveguides
4
have different phases from one another. The phase front of many light beams from the arrayed waveguide
4
is tilted in accordance with the differences and the position where the light is condensed is determined by the angle of this tilt.
Therefore, light beams having different wavelengths are condensed at different positions from one another. By forming the optical output waveguides
6
at these positions, light beams &lgr;
1
, &lgr;
2
, . . . &lgr;
n
having different wavelengths can be output from the respective optical output waveguides
6
provided for the respective wavelengths.
In other words, the arrayed waveguide grating has an optical multiplexing/demultiplexing function. With this function, the arrayed waveguide grating can demultiplex light input from the optical input waveguides
2
, which has previously undergone the division multiplexing and possesses different wavelengths from one another, into light beams of one or more wavelengths, and then output the light beams from their respective optical output waveguides
6
. The central wavelength of light to be demultiplexed is in proportion to the differences (&Dgr;L) in lengths of adjacent channel waveguides
4
a
constituting the arrayed waveguide
4
and to the effective refractive index n
e
of the channel waveguides
4
a.
Having the characteristics as above, the arrayed waveguide grating can be used as a light transmissive device for optical multiplexing/demultiplexing applied to a wavelength division multiplexing transmission system. For instance, as shown in
FIG. 15
, light beams which have undergone 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), respectively, are input to one of the optical input waveguides
2
. The light beams are diffracted in the first slab waveguides
3
, reach the arrayed waveguides
4
, and travel through the arrayed waveguides
4
and the second slab waveguides
5
. Then, as described above, the light beams are respectively condensed at different positions determined by their wavelengths, enter different optical output waveguides
6
, travel along their respective optical output waveguides
6
, and are output from the output ends of the optical output waveguides
6
.
The light beams having different wavelengths can then be further taken out through optical fibers for outputting light (not shown) that are connected to the output ends of the optical output waveguides
6
. When connecting the optical fibers to the optical output waveguides
6
and to the optical input waveguides
2
, an optical fiber array is prepared for each. In the optical fiber array, connection terminal faces of the optical fibers are arranged and fixed into a one-dimensional array. The optical fiber array is fixed to the connection terminal faces of the optical output waveguides
6
or to the optical input waveguides
2
to thereby connect the optical fibers to the optical output waveguides
6
or to the optical input waveguides
2
.
The above arrayed waveguide grating has such light transmission characteristics (wavelength characteristics of transmission light intensity in the arrayed waveguide grating) of light beams output from the optical output waveguides
6
such that with the respective light transmission central wavelengths (e.g., &lgr;
1
, &lgr;
2
, &lgr;
3
, . . . &lgr;n) as the center, the light transmittance of the output light beams becomes smaller as the wavelength deviates from their respective light transmission central wavelength.
Every light transmission central wavelength &lgr;
o
is determined by the effective refractive index n
e
of the arrayed waveguide
4
, the difference (&Dgr;L) in length of adjacent channel waveguides
4
a
of the arrayed waveguide
4
, and diffraction order m, and is expressed by the following nu
Kashihara Kazuhisa
Nara Kazutaka
Nekado Yoshinobu
Healy Brian
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Rahll Jerry T
The Furukawa Electric Co. Ltd.
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