Optical waveguides – With optical coupler – Input/output coupler
Reexamination Certificate
2001-06-27
2004-01-27
Glick, Edward J. (Department: 2882)
Optical waveguides
With optical coupler
Input/output coupler
C385S129000
Reexamination Certificate
active
06684009
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an AWG (arrayed waveguide grating) that is applied to an optical communication device and used in multiplexing/demultiplexing communication lights of different wavelength, and the present invention relates to an optical multiplex/demultiplex system and an optical multiplexer/demultiplexer using the AWG.
DESCRIPTION OF THE RELATED ART
The AWG is a waveguide diffraction grating which utilizes the phase difference made by the difference of optical path length between arrayed waveguides. In the following, the principle of the AWG will be explained in comparison with a prior art.
In the conventional diffraction grating type demultiplexer, incident lights of different wavelength inputted to a diffraction grating from an input optical fiber are separated into the respective wavelength by the angles. Then, the angles of the wavelengths are converted into variations of positions by an optical lens and converged to an output optical fiber. In this way, in the prior art diffraction grating, a wavelength dispersion has been realized by an interference effect created by the phase difference owing to the periodic structure of the grating.
On the other hand, in the AWG of the present invention, a plurality of channel waveguides are provided with a fixed deviation of the optical path length, and an interference effect created at the output ends realizes segmentation of the lights according to the angle of the respective wavelengths. As the optical element which is equivalent to the optical lens of the prior art diffraction grating type demultiplexer, in the AWG of the present invention, a fan-shape slab waveguide is used, in which a plurality of channel waveguides are positioned in an arc shape.
In the above-mentioned fan-shape slab waveguide, arrayed input/output waveguide groups and an arrayed waveguide group are positioned in an arc shape, keeping a fixed distance from each other. The curvature center of the fan-shape slab waveguide is positioned at an arrayed input/output waveguide group, and an arrayed waveguide is positioned in a radial pattern so that the optical axis goes through the curvature center. Since there is no horizontal optical confinement in a slab waveguide, lights outputted from one input waveguide are spread out in a radial pattern by diffraction, and an arrayed waveguide group of the AWG is driven at the same phase. The arrayed waveguide group of the AWG is composed of a plurality of channel waveguides which are separated from each other having a difference (&Dgr;L) in length. The difference (&Dgr;L) in length causes a constant amount of phase shift at the output ends of the arrayed waveguides, and the interference effect created by the phase shift brings about a dispersion of the wavelength.
FIG. 1
is a plane view showing a construction of a prior art AWG. Referring to
FIG. 1
, the principle of the AWG will be explained taking a demultiplexing operation as an example. In
FIG. 1
, the conventional AWG comprises an input waveguide
121
, an input-side slab waveguide
122
, an arrayed waveguide group
123
, an output-side slab waveguide
124
, an output waveguide
125
on a waveguide substrate
120
. An input fiber array
126
is connected to the input waveguide
121
, and an output fiber array
127
to the output waveguide
125
.
Multiplexed lights &lgr;
1
to &lgr;n go through a single fiber
128
and the input fiber array
126
, and are made incident into the input waveguide
121
. The multiplexed lights &lgr;
1
to &lgr;n are spread in a radial pattern by the input-side slab waveguide
122
and segmented to the arrayed waveguide group
123
at the same phase at almost the same photon quantities. The arrayed waveguide group
123
is composed of a plurality of waveguides, and each of them has a difference (&Dgr;L) in length. When the multiplexed lights &lgr;
1
to &lgr;n propagate through the arrayed waveguide group
123
, the optical phase difference is created. Undergoing a multiple beam diffraction interference at the output-side slab waveguide
124
, the multiplexed lights &lgr;
1
to &lgr;n are converged at the output waveguide
125
corresponding to each wavelength, and thus demultiplex is realized. The demultiplexed lights &lgr;
1
to &lgr;n outputted to each of the output waveguides
125
go through the output fiber array
127
and are outputted to a tape fiber
129
. The demultiplexed lights &lgr;
1
to &lgr;n have a wavelength profile with a center wavelength which causes loss at a minimum level.
One of the prominent characters of the AWG is to be able to design the specific character freely by such as making appropriate selection of the length of arrayed waveguides or the space between them. Up to this point, a variety of multiplexers/demultiplexers with the AWG have been realized by utilizing such materials as a siliceous material, a semiconductor and a polymer.
FIG. 2
is a sectional view of a module structure provided with the conventional AWG. In
FIG. 2
, a module
130
includes at the lower layer within a case
131
, a temperature controlling device (i.e., a peltier device)
132
, an AWG element
133
, a temperature detecting device (i.e., a thermistor device)
134
, an input fiber array
135
, an output fiber array
136
(fiber arrays
135
and
136
are positioned at both ends of the AWG element), a single fiber
137
and a tape fiber
138
, and at the upper part a cover
139
. According to the module structure shown in
FIG. 2
, the single fiber
137
and the tape fiber
138
are extended from the both ends of the module comprising the case
131
and the cover
139
.
Recently, in optical communication network, an optical communication device has come into use for network nodes which perform not only simple point-to-point transmission, but also circuit switching and input/output of signals. Thus, the optical communication device for structuring a network with larger capacity, higher flexibility and reliability has become essential.
In particular, a demand for the AWG as an optical communication device of the sort is rapidly increased in accordance with multiplexing and increase in the number of wavelength in the optical communication system. Consequently, it is urgently required to have a miniaturized AWG with the lower price.
However, the above-mentioned conventional AWG has some problems as follows. First of all, since an element is enlarged due to increase in the number of wavelengths, quantity of elements which can be obtained from one wafer is decreased. Secondly, since characteristic dispersion occurs due to increase in the number of wavelengths, non-defective ratio is lowered, that is a yielding percentage (non-defective products/gross product) is deteriorated. Thirdly, since an optical communication system has become highly efficient and the AWG has been required to have high specifications, it is hard to secure a non-defective AWG. Furthermore, as is apparent from the above-mentioned structure of a module, since a single fiber and a tape fiber are extended from the both ends of the module, there are increase in the mounting area and a limitation in the mounting position.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide an AWG, an optical multiplex/demultiplex system and an optical multiplexer/demultiplexer with the AWG, which realize miniaturization and lowering the price, as well as, have less limitation in the mounting space and position.
In other words, the present invention provides an AWG, an optical multiplex/demultiplex system and an optical multiplexer/demultiplexer with the AWG, which realize miniaturization and lowering the price, by composing a plurality of selective circuits within one element, and converging input/output waveguides of both multiplex side and demultiplex side at given one side of the element.
In order to achieve the above object, an AWG in accordance with the first aspect of the present invention is structured by forming multiple waveguides on a substrate, and has a plurality of selective circuits.
In accordan
Glick Edward J.
NEC Corporation
Suchecki Krystyna
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