Arrayed waveguide grating

Details Arrayed waveguide grating Arrayed waveguide grating

2001-03-27

2003-05-13

Healy, Brian (Department: 2874)

Optical waveguides

With optical coupler

Input/output coupler

C385S014000, C385S031000, C385S129000, C385S130000, C359S199200, C359S199200, C359S199200

Reexamination Certificate

active

06563986

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to an arrayed waveguide grating that is used as at least either of an optical multiplexer, an optical demultiplexer, or an optical multiplexer and demultiplexer in, for example, optical wavelength division multiplexing communications, etc.
BACKGROUND OF THE INVENTION
Recently, in optical communications, research and development have been carried out with respect to optical wavelength division multiplexing communications as a method for remarkably increasing the transmission capacity, and practical use thereof has been increasingly employed. The optical wavelength division multiplexing communications are used, for example, to transmit a plurality of light having wavelengths different from each other. In such a system of optical wavelength division multiplexing communications, in order to pick up light per wavelength at the light receiving side from multiplexed light that has been transmitted, it is indispensable that an optical transmission device that can transmit only light of predetermined wavelengths is provided in the systems.
As one of the examples of optical transmission devices, there is an arrayed waveguide grating (AWG) of a planar lightwave circuit (PLC) as shown in FIG.
6
. The arrayed waveguide grating is such that a waveguide-formed area
10
provided with a waveguide construction as shown in
FIG. 6
is formed of silica-based glass, etc., on a substrate
1
made of silicon or the like.
A waveguide 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 end of the optical input waveguides
2
; an arrayed waveguide
4
consisting of a plurality of channel waveguides
4
a
arranged side by side, 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 connected to the output end of the second slab waveguide.
The above-described arrayed waveguide
4
propagates light introduced from the first slab waveguide
3
. The channel waveguides
4
a
of the arrayed waveguide
4
are formed so as to have lengths different by a set amount from each other, wherein the lengths of channel waveguides
4
a
adjacent to each other differ by &Dgr;L from each other. Further, the optical output waveguides
6
are provided, for example, so as to correspond to the number of signal lights having wavelengths different from each other, which are demultiplexed or multiplexed by an arrayed waveguide grating. The channel waveguides
4
a
are usually provided in a large number, for example, 100 wavegides. However, in
FIG. 6
, in order to simplify the drawing, the number of the respective optical output waveguides
6
, channel waveguides
4
a
and optical input waveguides
2
are simplified for illustration.
For example, a transmission side optical fiber (not shown) is connected to one of optical input waveguides
2
so that the wavelength multiplexed light is introduced thereinto. The light that is introduced into the first slab waveguide
3
through the corresponding optical input waveguide
2
spreads due to its diffraction effect and enters respective channel waveguides
4
a.
Then, it propagates through the arrayed waveguide
4
.
The light that has propagated through the arrayed waveguide
4
reaches the second slab waveguide
5
, and is condensed at the optical output waveguides
6
and is outputted therefrom. At this time, since the lengths of all the channel waveguides
4
a
differ by a set amount from each other, a deviation occurs in individual phases of the light that has propagated through the arrayed waveguide
4
, the phasefront of the lights may be inclined according to the deviation, and the position of light condensation is determined on the basis of the angle of inclination.
Therefore, the light condensing positions of light of different wavelengths differ from each other, wherein, by forming the optical output waveguides
6
at the positions, it is possible to output light of different wavelengths (demultiplexed light) from the optical output waveguides
6
differing per wavelength.
That is, the arrayed waveguide grating has an optically demultiplexing feature by which light of one or more wavelengths is demultiplexed from multiplexed light of a plurality of wavelengths different from each other, which is inputted from one of optical input waveguides
2
, and is outputted from respective optical output waveguides
6
. The center wavelength of demultiplexed light is proportional to a difference (&Dgr;L) in the length between the adjacent of the channel waveguides
4
a
and its effective refractive index n
c.
Since the arrayed waveguide grating has the above-described characteristic, the arrayed waveguide grating can be used as an optical demultiplexer for optical wavelength division multiplexing transmission systems. For example, as shown in
FIG. 6
, if wavelength multiplexed light of wavelengths &lgr;1,&lgr;2,&lgr;3, . . . &lgr;n (n is an integral number not less than 2) is inputted from one of optical input waveguides
2
, the light of the respective wavelengths is spread by the first slab waveguide
3
and reaches the arrayed waveguide
4
. And, the light is condensed at positions differing from each other according to the wavelengths, as described above, passing through the second slab waveguide
5
. Then, the light is made incident into the optical output waveguides
6
different from each other, and is outputted from the output end of the optical output waveguides
6
, passing through the respective optical output waveguides
6
.
And, by connecting optical fibers (not shown) for optical output to the output end of the respective optical output waveguides
6
, the light of the respective wavelengths can be picked up via the optical fibers.
Also, when optical fibers (an optical fiber) are (is) connected to the respective optical output waveguides
6
and the above-described one of the optical input waveguides
2
respectively, an optical fiber arraying tool, in which optical fibers (an optical fiber) are (is) arrayed and fixed in a state of the primary array, is prepared, and the optical fiber array is fixed at the connection end faces of the optical output waveguides
6
and one of the optical input waveguides
2
respectively, wherein the optical fibers (an optical fiber) are (is) connected to the optical output waveguides
6
and one of the optical input waveguides
2
respectively.
In addition, since the arrayed waveguide grating utilizes the principal of light reciprocity (reversibility), it has a function as an optical demultiplexer and a function as an optical multiplexer. That is, contrary to
FIG. 6
, if light of a plurality of wavelengths different from each other is taken in, wavelength by wavelength, from respective optical output waveguides
6
, the light passes through the propagation channel contrary to the above, and is multiplexed by the arrayed waveguide
4
. The light is outputted from one of optical input waveguides
2
as wavelength-multiplexed light.
In such an arrayed waveguide grating, as described above, the wavelength resolution of the arrayed waveguide grating is proportional to a difference (&Dgr;L) in the lengths of the adjacent channel waveguides
4
a
that constitute the arrayed waveguide grating. Therefore, by designing the &Dgr;L to become large, it becomes possible to demultiplex and multiplex wavelength multiplexed light of a narrow wavelength interval that cannot be achieved in the prior art of optical demultiplexer/multiplexer. Therefore, it is necessary to achieve high bit-rate optical wavelength multiplexed communications. The arrayed waveguide grating can have functions for optical demultiplexing/multiplexing of a plurality of signal lights, that is, functions for demultiplexing or multiplexing a plurality of signal lights whose wavelength interval is 1 nm or less.
When producing the above-described arrayed waveguide grating, for

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