Optical waveguides – With optical coupler – Input/output coupler
Reexamination Certificate
2001-07-16
2003-12-23
Nguyen, Khiem (Department: 2874)
Optical waveguides
With optical coupler
Input/output coupler
C385S046000
Reexamination Certificate
active
06668116
ABSTRACT:
BACKGROUND OF THE INVENTION
Recently, in optical communications, research and development of the optical wavelength division multiplexing (WDM) transmission systems have been conducted actively for the way to dramatically increase the transmission capacity thereof, and practical applications have been proceeding. The optical wavelength division multiplexing transmission systems are that a plurality of lights having a wavelength different from each other is wavelength-multiplexed and is transmitted, for example. In such optical wavelength division multiplexing transmission systems, lights need to be demultiplexed at every wavelength from the transmitted multiplexed lights on the light receiving side. On this account, the optical wavelength division multiplexing transmission systems are provided with optical devices that only transmit predetermined optical wavelengths.
One example of the optical devices is an arrayed waveguide grating (AWG) of a planar lightwave circuit (PLC), as shown in FIG.
4
. The arrayed waveguide grating is that a waveguide forming area
10
made of silica-based glass is formed on a silicon substrate
1
, for example. On the waveguide forming area
10
of the arrayed waveguide grating, the waveguide configuration as shown in the same drawing is formed of cores.
The waveguide configuration of the arrayed waveguide grating is formed to have one or more of 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
made of a plurality of channel waveguides
4
a
arranged side by side, the channel waveguides 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
4
; and a plurality of optical output waveguides
6
arranged side by side, the optical output waveguides connected to the output end of the second slab waveguide
5
.
The channel waveguides
4
a
are a set for propagating lights that have been lead through the first slab waveguide
3
and are formed to have a different set length each other. The length of adjacent channel waveguides
4
a
are different from each other with &Dgr;L. The channel waveguides
4
a
that constitute the arrayed waveguide
4
are generally disposed in multiple such as a hundred. However, in the same drawing, the number of the channel waveguides
4
a
is schematically depicted to simplify the drawing.
Additionally, optical output waveguides
6
are disposed corresponding to the number of signal light(s) having a different wavelength each other, the signal light(s) is (are) demultiplexed or multiplexed by the arrayed waveguide grating, for example. However, in the same drawing, the number of the optical input waveguides
2
and the optical output waveguides
6
is schematically depicted to simplify the drawing.
To the optical input waveguides
2
, optical fiber(s) (not shown) on the transmitting side, for example, is (are) connected to lead wavelength multiplexed light. The light that have been lead to the first slab waveguide
3
through the optical input waveguides
2
spread by the diffraction effect thereof to enter each of the plurality of channel waveguides
4
a
, propagating through the arrayed waveguide
4
.
The light that have propagated through the arrayed waveguide
4
reach the second slab waveguide
5
and are condensed at the optical output waveguides
6
to be outputted. The length of the entire channel waveguides
4
a
that constitute the arrayed waveguide
4
are different from each other. Thus, a shift is generated in the phase of the respective lights after propagating through the channel waveguides
4
a
, a phasefront of the lights is tilted according to this shifted amount and the positions at which the lights are condensed are determined by this tilted angle.
Therefore, the positions at which the lights having a different wavelength are condensed differ from each other, the optical output waveguides
6
are formed on each of the position at which the lights are condensed and thereby the lights having a different wavelength can be outputted from the different optical output waveguides
6
at every wavelength.
That is, the arrayed waveguide grating has the function of light demultiplexing where plurality of lights having different wavelengths are demultiplexed from the multiplexed light that is inputted from the optical input waveguides
2
and have a plurality of wavelengths different from each other.
Since the arrayed waveguide grating has the characteristic as described above, the arrayed waveguide grating can be used as an optical demultiplexer for the wavelength division multiplexing transmission. For example, as shown in
FIG. 4
, when wavelength multiplexed light having wavelengths &lgr;
1
, &lgr;
2
, &lgr;
3
, . . . and &lgr;n (n is an integer equal to or larger than 2 are inputted from one optical input waveguide
2
, these lights spread at the first slab waveguide
3
. Then, they reach the arrayed waveguide
4
, pass through the second slab waveguide
5
, are condensed at different positions according to wavelengths and enter the optical output waveguides
6
different from each other, as set forth. The lights entered to the respective optical output waveguides
6
pass through the respective optical output waveguides
6
and are outputted from the output end of the optical output waveguides
6
.
An optical fiber (not shown) for outputting light is connected to the output end of each of the optical output waveguides
6
and thereby each of the lights having different wavelength is outputted. Furthermore, when the optical fiber is connected to each of the optical output waveguides
6
or optical input waveguides
2
mentioned above, an optical fiber array, for example, is prepared in which the connecting ends of optical fibers are arranged and fixed in a linear array. Then, this optical fiber array is fixed on the connecting end side of the optical output waveguides
6
or optical input waveguides
2
and the optical fiber is connected to the optical output waveguides
6
and the optical input waveguides
2
.
The arrayed waveguide grating utilizes the principle of reciprocity (reversibility) of optical circuits and thereby it has the function of an optical multiplexer as well as the function of an optical demultiplexer. That is, as reverse to the
FIG. 4
, when a plurality of lights having different wavelength from each other is entered from each of the optical output waveguides
6
, these lights pass through the propagation path inverse to that described above, are multiplexed by the arrayed waveguide
4
and are emitted from the optical input waveguide
2
.
In such an arrayed waveguide grating, the wavelength resolution is in proportion to a difference in length (&Dgr;L) of the adjacent channel waveguides
4
a
that constitute the arrayed waveguide
4
, as set forth. Therefore, in the arrayed waveguide grating, the &Dgr;L is designed large and thereby the optical multiplexing/demultiplexing of wavelength-multiplexed lights having a narrow wavelength spacing is made possible, which could not be realized by a conventional optical multiplexer/demultiplexer. For example the &Dgr;L is made greater, a designed wavelength spacing for multiplexing/demultiplexing is designed 1 nm or less and thereby the function of multiplexing or demultiplexing a plurality of light signals having a wavelength spacing of 1 nm or less can be served. Thus, the function of multiplexing or demultiplexing a plurality of signal lights can be served, which is needed to realize the high-density optical wavelength division multiplexing transmission.
When the arrayed waveguide grating as described above is fabricated, for example, the flame hydrolysis deposition method (FHD) is first used, and an under cladding layer and a core layer are formed on a silicon substrate one by one. Then, photolithography is applied through a photomask depicted with the waveguide configuration of the arrayed waveguide grating. Subsequently, the reactive ion
Kashihara Kazuhisa
Nara Kazutaka
Nekado Yoshinobu
Saito Tunetoshi
Nguyen Khiem
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
The Furukawa Electric Co. Ltd.
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