Optical waveguides – With optical coupler – Plural
Reexamination Certificate
1998-12-18
2001-11-13
Font, Frank G. (Department: 2877)
Optical waveguides
With optical coupler
Plural
C385S037000
Reexamination Certificate
active
06317534
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to an optical wavelength routing device, and more particularly to an optical wavelength routing device having a wavelength routing function used for a WDM (Wavelength Division Multiplexing) transmission for the optical communication system, in which a maximum central wavelength deviation (defined “wavelength difference” hereinafter in some cases) is reduced to minimum.
BACKGROUND OF THE INVENTION
In recent years, as a communication system providing an information service with high speed and large capacity, a WDM (Wavelength Division Multiplexing) optical communication system has been developed. In particular, as an interconnection device for an optical communication system, an optical wavelength routing device using an arrayed waveguide diffraction grating as an optical wavelength multiplexer/demultiplexer has been researched intensively.
For example, U.S. Pat. No. 5,412,744 discloses a frequency routing device having a spatially filtered optical grating for providing an increased passband width, which has a spectral efficiency maximized by providing a relatively wide passband and a relatively narrow channel spacing for a given cross talk level.
As a structure of an optical wavelength routing device using an arrayed waveguide, a structure comprising an arrayed waveguide provided between an input slab waveguide and an output slab waveguide has been known.
FIGS. 1A
to
1
C show a structure of a conventional optical wavelength routing device composed of an arrayed waveguide diffraction grating type optical multiplexer/demultiplexer, wherein
FIG. 1A
is a schematic view of the conventional optical wavelength routing device.
As shown in
FIG. 1A
, the optical wavelength routing device comprises a substrate
3
, input waveguides
1
having input ports
7
with a total number M, an input slab waveguide
4
coupled to the input waveguides
1
, which radiates a light supplied from the input waveguides
1
with predetermined angles by diffraction, a diffraction grating type arrayed waveguide
5
composed of a plurality of waveguides
8
and coupled to an output side of the input slab waveguide
4
, which transmits lights supplied from the input slab waveguide
4
through the waveguides
8
, an output slab waveguide
6
coupled to an output side of the arrayed waveguide
5
, which focuses the radiated lights supplied from the arrayed waveguide
5
with predetermined angles, and output waveguides
2
having output ports
9
with a total number N and being coupled to an output side of the output slab waveguide
6
.
Herein, the input and output waveguides land
2
, the input and output slab waveguides
4
and
6
, and the arrayed waveguide
5
are formed on the substrate
3
. The light (optical signal) supplied to the input waveguides
1
is firstly radiated with the predetermined angles at the input slab waveguide
4
by diffraction, then transmitted through a plurality of the waveguides
8
of the arrayed waveguide
5
. The radiated lights are focused at the output slab waveguide
6
and finally emitted from the output waveguides
2
.
FIGS. 1B and 1C
show a light input side and a light output side of the optical wavelength routing device, respectively. In
FIG. 1B
, the input ports
7
with the total number M of the input waveguides
1
are numbered (
1
_
1
) to (
1
_M), respectively, and an emitting angle of a light emitted from one of the input waveguides
1
is expressed as &PHgr;. In
FIG. 1C
, the output ports
9
with the total number N of the output waveguides
2
are numbered (
2
_
1
) to (
2
_N), respectively, and a focusing angle of the light output from respective waveguides
8
of the arrayed waveguide
5
is expressed as &thgr;. Both of the emitting angle &PHgr; and the focusing angle &thgr; are angles formed by respective optical axes of the lights relative to a central line O.
FIG. 2
shows an example of a wavelength routing function in an ideal optical wavelength routing device, wherein the total number of the input ports is M and the total number of the output ports is N.
In this optical wavelength routing device, when wavelength division multiplexed optical signals having different wavelengths &lgr;
1
, &lgr;
2
- - - &lgr;
N
are input into the first input port, optical signals each having one of wavelengths &lgr;
1
, &lgr;
2
- - - &lgr;
N
are output from the first to Nth output ports, respectively. Further, when the wavelength division multiplexed optical signals having different wavelengths &lgr;
1
, &lgr;
2
, - - - &lgr;
N
are input into the second input port, the optical signals each having one of wavelengths &lgr;
2
, &lgr;
3
, - - - &lgr;
N
, &lgr;
1
are output from the first to Nth output ports, respectively. Still further, when the wavelength division multiplexed optical signals having different wavelengths &lgr;
1
, &lgr;
2
, - - - &lgr;
N
are input into the third input port, the optical signals each having one of wavelengths &lgr;
3
, &lgr;
4
, - - - &lgr;
N
, &lgr;
1
, &lgr;
2
are output in order from the first to Nth output ports, respectively. As described above, the ideal optical wavelength routing device has a routing function in which the wavelengths of the optical signals output from the output ports are circulated in accordance with the selection of an input port from the input ports.
Next, a wavelength routing function of the above explained conventional optical wavelength routing device composed of the arrayed waveguide diffraction grating type optical multiplexer/demultiplexer will be explained.
When a light having a wavelength &lgr; is input to each of input ports
7
of input waveguides
1
, a relation of the wavelength &lgr; of the light, an emitting angle &PHgr; at an input slab waveguide
4
and a focusing angle &thgr; at an output slab waveguide
6
is given by a following formula (1):
&lgr;={n
s
(&lgr;)d/m}·(sin&PHgr;+sin&thgr;)+n
eff
(&lgr;)&Dgr;L/m (1)
wherein &Dgr;L is a waveguide length difference of two adjacent waveguides
8
of an arrayed waveguide
5
, d is an interval between central axes of the two adjacent waveguides
8
at coupling portions with the input slab waveguide
4
and the output slab waveguides
6
, n
eff
(&lgr;) is an equivalent refractive index of the arrayed waveguide
5
for a propagated light having a wavelength &lgr;, n
s
(&lgr;) is an equivalent refractive index of the input slab waveguide
4
and the output slab waveguide
6
for a propagated light having a wavelength &lgr;, and m is a diffraction order number.
Accordingly, by aligning each of the input ports
7
of the input waveguides
1
and each of the output ports
9
of the output waveguides
2
with the emitting angle &PHgr; and the focusing angle &thgr;, respectively, a light having a central wavelength &lgr; given by the formula (1) is output from each of the output port
9
of the output waveguides
2
. Namely, the emitting angle &PHgr; is a locating angle for locating the input waveguides
1
and the focusing angle &thgr; is a locating angle for locating the output waveguides
2
.
In this structure, when a wavelength range of the transmitting light is sufficiently narrow and respective ranges of the locating angles for locating the input waveguides
1
and the output waveguides
2
are sufficiently narrow, it is possible to approximate n
eff
(&lgr;), n
s
(&lgr;), sin&PHgr;, and sin&thgr; to n
eff
, n
s
, &PHgr;, and &thgr;, respectively. Accordingly, the relation between the wavelength &lgr; of the transmitting light and the locating angles &PHgr; and &thgr; can be linear functions.
FIG. 3
shows a relation between the wavelength &lgr; of the transmitting light and the focusing angle &thgr; , when the emitting angle &PHgr; is kept to be constant, wherein a range (
3
-a) of light wavelengths &lgr;
1
to &lgr;
N
indicates the wavelength range of the transmitting light, a curve (
3
-b) indicates a curve of a diffraction order number m, and a curve (
3
-c) indicates a curve of a diffraction order number m+1. As shown in
FIG. 3
, when a transmitting light (a
Maru Koichi
Miyazaki Tetsuya
Uetsuka Hisato
Yamamoto Shu
Font Frank G.
Kokusai Denshin Denwa Co. Ltd.
McDermott & Will & Emery
Natividad Phil
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