Optical waveguides – With optical coupler – Plural
Reexamination Certificate
2000-04-05
2002-07-02
Spyrou, Cassandra (Department: 2872)
Optical waveguides
With optical coupler
Plural
C385S037000, C385S048000
Reexamination Certificate
active
06415071
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an optical wavelength multiplexed transmission module that is used for wavelength multiplexed optical transmissions, etc., and a wavelength multiplexed transmission system using the module.
BACKGROUND OF THE INVENTION
At present, practical use of optical waveguides (or PLC: Planar light wave circuit) having a plurality of optical waveguides disposed on a silicon or quartz (SiO
2
), etc. substrate has prevailed in view of high bit rate integration and a decrease in production costs in the field of optical transmissions. As one of the optical waveguides, there is an optical waveguide element which divides one transmission light into a plurality, and optical splitters that split a light into 8 beams, 16 beams or 32 beams have been achieved.
Recently, as a method to remarkably increase a transmission capacity of optical transmissions, studies and research have been very active in optical wavelength multiplexed transmissions. Some of them have been practically applied.
Optical wavelength multiplexed transmission multiplexes and transmits a plurality of light having differing wavelengths. In such an optical wavelength multiplexed transmission system, a wavelength synthesizing and dividing module is indispensable, which can pick a plurality of transmitting light by wavelengths, or multiplex a plurality of light having differing wavelengths.
An arrayed waveguide diffraction grating (or AWG: Arrayed Waveguide Grading) as shown in
FIG. 4
is available as one example of the wavelength synthesizing and dividing modules. The arrayed waveguide diffraction grating is such that a waveguide pattern is formed on a substrate as in an optical splitter.
In the waveguide pattern of the arrayed waveguide diffraction grating shown in
FIG. 4
, an incident side slab waveguide
12
acting as the first slab waveguide is connected to the emitting side of one or more incident waveguides formed in parallel on a substrate
5
, and an arrayed waveguide
13
consisting of a plurality of waveguides formed in parallel is connected to the emitting side of the incident side slab waveguide. Also, an emitting side slab waveguide
14
acting as the second slab waveguide is connected to the emitting side of the arrayed waveguide
13
, and a plurality of light emitting waveguides
15
formed in parallel are connected to and formed at the emitting side of the emitting side slab waveguide
14
.
The arrayed waveguide
13
propagates light emitted from the incident side slab waveguide
12
, and optical waveguides secured in parallel are formed with differing wavelengths. Waveguides adjacent to the arrayed waveguide portion are arrayed with a certain fixed optical circuit length &Dgr;L.
Also, the incident waveguides
11
and emitting waveguides
15
are provided so as to correspond to the number of signal lights of differing wavelengths, which are divided by, for example, an arrayed waveguide diffraction grating
10
.
A number (for example, 100) of arrayed waveguides
13
are provided. However, in
FIG. 4
, the number of the respective waveguides is reduced for the purpose of simplification of the drawing, and a few arrayed waveguides are illustrated. For example, a transmission side optical fiber
31
is connected to the incident waveguide
11
so that wavelength multiplexed light is introduced. Light introduced into the incident side slab waveguide
12
through the incident waveguide
11
is spread by its diffraction effect, and is made incident on a plurality of respective arrayed waveguides
13
to propagate in the respective waveguides
13
.
Light propagated through the respective arrayed waveguides
13
reaches the emitting side slab waveguides
14
and is further condensed at and emitted from the emitting waveguides
15
. Since, in the respective arrayed waveguides
13
, the lengths are different by &Dgr;L from each other in adjacent waveguides
13
, shifts occur in individual light phase after light propagates through the respective arrayed waveguides
13
, the wave plane of convergent light is inclined in accordance with the amount of shift, whereby the condensing position of light is determined by an angle of the inclination.
When light is made incident from the arrayed waveguides
13
on the emitting side slab waveguide
14
, the relation indicated by the following expression (1) exists between an angle &thgr; (diffraction angle) and the wavelength &lgr; at which the light is condensed:
ns d &thgr;+nc &Dgr;L=m&lgr;
(1)
where ns is a refractive index of the slab waveguide
14
, d is an interval between adjacent arrayed waveguides in the emitting side slab waveguide portion, nc is a refractive index of the arrayed waveguides, and m is a diffraction order. In the expression (1), for example, if the wavelength is assumed to be &lgr;
0
where &lgr;=0 is assumed,
&lgr;0
=nc &Dgr;L/m
(2)
the above expression is established.
As has been made clear from the expressions (1) and (2) the positions where light of differing wavelengths are condensed at the emitting side of the emitting side slab waveguides
14
will become different from each other. By forming an emitting side waveguide
15
at the condensing position, lights of different wavelengths can be emitted from emitting side waveguides, whose wavelengths differs from each other, by wavelength.
A transmission characteristic of the respective emitting side waveguides
15
is that they have certain transmission bandwidths centering around the respective wavelengths as shown in FIG.
5
A. In
FIG. 5A
, the abscissa indicates a wavelength while the ordinate indicates a transmission characteristic of an optional port of an arrayed waveguide diffraction grating.
In
FIG. 5A
, although there is a spectrum that will become maximum at the center wavelength, the spectrum does not necessarily have only one maximum value, it may be of such a type which will have two maximum values as in FIG.
5
B.
The wavelength (peak wavelength) showing a peak of the transmission characteristic having such a center wavelength is not one per port, and that can be established for the respective wavelengths with respect to differing positive integral values m of the expression (1).
A description is given of functions of the arrayed waveguide diffraction grating when it is used for optical transmissions. When wavelength multiplexed lights having wavelengths &lgr;
1
, &lgr;
2
, &lgr;
3
. . . &lgr;n (n: an integral number) are inputted from a certain single incident waveguide
11
, the lights are widened by the incident side slag waveguide
12
, and reach the arrayed waveguide
13
. Thereafter, the lights are condensed at differing positions by wavelengths via the emitting side slab waveguide
14
and are, respectively, emitted from differing emitting waveguides
15
.
Subsequently, lights of the respective wavelengths can be picked up via optical fibers
32
for optical emission, which are connected to the emitting ends of the respective emitting waveguides
15
. At this time, the wavelength characteristics of the transmission light intensity of the arrayed waveguide diffraction grating
10
shown in
FIG. 4
, respectively, become transmission spectra centering around the respective wavelengths (&lgr;
1
, &lgr;
2
, &lgr;
3
. . . &lgr;n) as shown in FIG.
6
.
Also, in
FIG. 6
, a pattern of wavelength characteristics of lights emitted from differing ports is caused to overlap as illustrated.
The example shown above shows actions of the arrayed waveguide diffraction grating
10
when dividing lights having multiplexed wavelengths.
Also, as shown in
FIG. 7
, the same arrayed waveguide diffraction grating can function as a wavelength synthesizing element
10
A by which light is emitted into the above incident waveguide
11
as wavelength-multiplexed light, where the above emitting waveguides
15
are made the incident waveguides corresponding to the lights of the respective wavelengths, and lights of the respective wavelengths are inputted into the above emitting waveguides
15
, the lights pass
Ota Toshihiko
Saito Tsunetoshi
Assaf Fayez
Lacasse & Associates LLC
Spyrou Cassandra
The Furukawa Electric Co. Ltd.
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