Optical waveguides – With optical coupler – Input/output coupler
Reexamination Certificate
2002-03-12
2003-12-23
Healy, Brian (Department: 2874)
Optical waveguides
With optical coupler
Input/output coupler
C385S014000, C385S031000, C385S129000, C385S130000, C398S043000, C398S048000, C398S068000, C398S079000, C398S087000
Reexamination Certificate
active
06668117
ABSTRACT:
BACKGROUND OF THE INVENTION
Recently, in optical communications, as a method capable of rapidly increase transmission capacities, many researches and developments of optical wavelength division multiplexing communications have been positively performed and practically used. An optical wavelength division multiplexing communication corresponds to such an optical communication that, for instance, a plurality of lights having different wavelengths from each other are multiplexed and then the multiplexed light is transferred. In such an optical wavelength division multiplexing communication system, in order to demultiplex lights with the different wavelengths each other from the transmitted multiplexed light, an optical transmission device and the like which may transmit, therethrough only such lights having a predetermined wavelengths is necessary.
As one example of such an optical transmission device, a planar lightwave circuit (PLC) as shown in
FIG. 15
has been proposed. The planar lightwave circuit indicated in
FIG. 15
is called as an arrayed waveguide grating (AWG). This arrayed waveguide grating includes a waveguide forming region
10
made of silica-based glass is formed on a substrate
1
made of, for example, silicon. The waveguide forming region
10
of the arrayed waveguide grating has such a waveguide structure as indicated in FIG.
15
.
In other words, the waveguide structure of the arrayed waveguide grating comprises at least one optical input waveguide
2
, a first slab waveguide
3
, an arrayed waveguide
4
, a second slab waveguide
5
, and a plurality of optical output waveguides
6
. The first slab waveguide
3
is connected to an output side of the at least one optical input waveguide
2
. The arrayed waveguide
4
is connected to an output side of the first slab waveguide
3
. The second slab waveguide
5
is connected to an output side of the arrayed waveguide
4
. The plurality of optical output waveguides
6
are connected to an output side of the second slab waveguide
5
, and arranged side by side.
The arrayed waveguide
4
transmits a light which is outputted from the first slab waveguide
3
. This arrayed waveguide
4
is formed in such a manner that a plurality of channel waveguides
4
a
are arranged side by side. The lengths of adjacent channel waveguides
4
a
are different by a set amount (&Dgr;L) from each other.
The channel waveguides
4
a
which constitute the arrayed waveguide
4
are normally a large number, for example, 100 pieces. Also, a plurality of optical output waveguides
6
are provided in correspondence with a total number of signal lights having different wavelengths. In the drawings, for the sake of simple illustrations, a plurality of channel waveguides
4
a
, optical input waveguides
2
, and optical output waveguides
6
are represented in a simple abbreviated manner.
For instance, while an optical fiber (not shown) on the transmission side is connected to one of the optical input waveguides
2
, multiplexed light may be conducted, to this optical fiber. This multiplexed light is conducted via one of the optical input waveguides
2
to the first slab wavelength
3
, and then, is entered into the arrayed waveguide
4
, while this multiplexed light is widened due to the diffraction effect thereof, and thereafter, the widened light is transferred via the arrayed waveguide
4
.
This multiplexed light which has been transferred via the arrayed waveguide
4
is reached to the second slab waveguide
5
, and furthermore, light beams are condensed to each of the optical output waveguides
6
, and then, the condensed lights are outputted therefrom. In this case, since the lengths of all of these channel waveguides
4
a
of this arrayed waveguide
4
are different from each other, phases of the individual light after being transferred via the arrayed waveguide
4
are shifted. Then, a wavefront of condensed light is tilted in response to this shift amount each other, and a position where the lights are condensed may be determined based upon this tilt angle.
It should also be noted that assuming now that an angle (diffraction angle) of light to be condensed is set as “&phgr;” when this light is inputted from the arrayed waveguide
4
to the second slab waveguide
5
, formula 1 may be substantially satisfied between this diffractive angle “&phgr;” and a center wavelength (center wavelength of light transmission) &lgr; of the light to be condensed:
n
s
×d
×sin&phgr;+
n
c
×&Dgr;L=m×&lgr;
(formula 1)
where symbol “n
s
” shows equivalent index of both the first and second slab waveguide; symbol “d” represents an interval between edge portions of the mutual channel waveguides on the side of the first and second slab waveguide; symbol “&phgr;” denotes a diffraction angle; symbol “n
c
” shows an equivalent index of the arrayed waveguide; symbol “&Dgr;L” shows a difference between lengths of the adjacent channel waveguides; and also, symbol “m” indicates a diffraction order.
In this case, assuming now that a wavelength is set to “&lgr;
0
” at the diffraction angle &phgr;=0, this wavelength “&lgr;
0
” is substantially expressed by the below-mentioned formula (2). Generally speaking, this wavelength “&lgr;
0
” is referred to as a center wavelength of an arrayed waveguide grating.
&lgr;
0
=n
c
×&Dgr;L/m
(formula 2)
Also, as shown in
FIG. 18
, assuming now that a light condensed point of such an arrayed waveguide grating is set to a point “O” at the diffraction angle &phgr;=0, as to a condensed position of such light having another diffraction angle “&phgr;
p
”, this light is condensed at a position “P” which is different from the above-explained point “O.” This position “P” corresponds to such a position which is shifted from the point “O” along an X direction. In this case, assuming now that a distance between these points “O” and “P” along the X direction is set to “x”, the below-mentioned formula (3) be substantially satisfied between the distance “x” and the wavelength “&lgr;”.
ⅆ
χ
ⅆ
λ
=
L
f
·
Δ
L
n
s
·
ⅆ
·
λ
0
n
g
(
formula
3
)
.
where, symbol “L
f
” indicates a focal distance of the second slab waveguide
5
; and symbol “n
g
” represents a group index of the arrayed waveguide
4
. It should also be noted that the group index “n
g
” of this arrayed waveguide
4
may be given by the equivalent index “n
c
” of the arrayed waveguide
4
in accordance with the following formula (4).
n
g
=
n
c
-
λ
0
ⅆ
n
c
ⅆ
λ
(
formula
4
)
.
The above-explained formula (3) implies such a fact that since the input end of the optical output waveguide
6
is arranged/formed at such a position which is separated from the focal point “O” of the second slab waveguide
5
by a distance “dx” along the X direction, such light having a wavelength different by “d&lgr;” can be derived.
Also, the relationship established in the above-explained formula (3) may be similarly established as to the first slab waveguide
3
. That is to say, for example, assuming now that a focal center of the first slab waveguide
3
is set to a point “O” and also, such a point is set to another point “P′” whose location is shifted by a distance “dx′” from this point “O′” along the X direction, when light is entered into this point “P′”, a wavelength of an output may be shifted by “d&lgr;′.” When this relationship is expressed by a formula, the below-mentioned formula (5) may be substantially obtained:
ⅆ
χ
′
ⅆ
λ
′
=
L
f
′
·
Δ
L
n
s
·
ⅆ
·
λ
0
n
g
(
formula
5
)
.
where, symbol “L
f
′” indicates a focal distance of the first slab waveguide
33
.
The above-explained formula (5) implies such a fact that since the
Hasegawa Junichi
Hi Raizumi Atsushi
Nekado Yoshinobu
Saito Tsunetoshi
Healy Brian
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
The Furukawa Electric Co. Ltd.
Wood Kevin S
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