Optical waveguides – With optical coupler – Particular coupling structure
Reexamination Certificate
2000-03-21
2002-04-16
Palmer, Phan T. H. (Department: 2874)
Optical waveguides
With optical coupler
Particular coupling structure
C385S016000
Reexamination Certificate
active
06374018
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to an optical switch, and in particular, to an optical switch which electrically controls the direction in which an optical signal proceeds, and to a method of operating the optical switch, and a method of designing the optical switch.
Conventionally, in the field of optical communications, optical switches which electrically control the direction in which the optical signal proceeds have been used. One example of such an optical switch is a reversed &Dgr;&bgr; direction coupler optical switch.
The structure of a reversed &Dgr;&bgr; direction coupler optical switch will be discussed hereinafter with reference to FIG.
7
.
FIG. 7
is a plan view which illustrates the main structural portions, i.e., only the waveguide portions and electrode portions, of a reversed &Dgr;&bgr; direction coupler optical switch
100
(hereinafter “switch
100
”).
The optical switch
100
comprises a linear first waveguide
102
, a linear second waveguide
104
which is disposed parallel to the waveguide
102
, a linear first electrode
106
and a linear second electrode
108
which are disposed on the first waveguide
102
so as to be spaced apart from each other, and a linear third electrode
110
and linear fourth electrode
112
which are disposed on the second waveguide
104
so as to be spaced apart from each other. The first electrode
106
and the third electrode
110
oppose one another, whereas the second electrode
108
and the fourth electrode
112
oppose one another.
A coupling arises between the respective propagation modes of the first waveguide
102
and the second waveguide
104
. While the polarity (e.g., positive) of the voltage with respect to a given reference potential, which voltage is applied to the first electrode
106
and the fourth electrode
112
, and the polarity (e.g., negative) of the voltage with respect to a given reference potential, which voltage is applied to the second electrode
108
and the third electrode
110
are reversed, by controlling the magnitudes of these voltages, for example, an optical signal inputted from an input port P
101
is outputted from either an output port P
103
(a so-called “bar state”) or an output port P
104
(a so-called “cross state”).
The range of values of the voltages which are applied to the electrodes and which are needed in order to bring the optical switch
100
into the cross state is broad. (Hereinafter, these values are referred to as “cross voltage values”.) Namely, the operational range of the cross state is broad. Therefore, the applied voltages can be easily set to cross voltages, and as a result, switching to the cross state can be carried out stably.
However, the range of values of the voltages which are applied to the electrodes and which are needed in order to bring the optical switch
100
into the bar state is narrow. (Hereinafter, these values are referred to as “bar voltage values”.) Namely, the operational range of the bar state is narrow. Therefore, it is difficult to set the applied voltages to bar voltages. As a result, even if attempts are made to switch the optical switch
100
to the bar state, a problem arises in that the optical signal leaks in the cross direction.
An example of another optical switch is disclosed in Applied Physics Letters, Vol. 35, No. 10, November 1979, pp. 748-750. In accordance with the structure of this optical switch (which is referred to hereinafter as “the second optical switch”), a first waveguide is a linear waveguide, whereas a second waveguide is a gently curved waveguide which is convex toward the first waveguide. Electrodes are provided for the first waveguide and the second waveguide. Switching is carried out by independently controlling the voltages which are applied to these electrodes.
The range of bar voltage values for the second optical switch is broad. Namely, the operational range of the bar state is broad. Accordingly, it is easy to set the applied voltages to bar voltages. As a result, switching to the bar state can be carried out stably.
However, the range of cross voltage values in the second optical switch is narrow. Namely, the operational range of the cross state is narrow. As a result, it is difficult to set the applied voltages to cross voltages. As a result, even if attempts are made to switch to the cross state, a problem arises in that the optical signal leaks in the bar direction.
SUMMARY OF THE INVENTION
Thus, an optical switch in which the operational range of the bar state is broad and the operational range of the cross state is broad is desired. Further, a method of operation of such an optical switch and a method of designing such an optical switch is desired.
In order to achieve the above objects, the present invention provides an optical switch for outputting an optical signal in different states, comprising: (a) first and second waveguides each including a propagation mode, the waveguides having a plurality of mode coupling regions permitting coupling between propagation modes and a plurality of non mode coupling regions where substantially no coupling arises between propagation modes of the waveguides, the mode coupling regions being opposing portions of the waveguides, and the non mode coupling regions also being opposing portions of the waveguides, wherein the opposing portions of the mode coupling regions are nearer to one another relative to the opposing portions of the non mode coupling regions; and (b) a plurality of electrodes spaced apart from one another, wherein the electrodes are disposed along at least the first waveguide.
In accordance with this structure, as will be explained later, operational ranges of the bar state and the cross state are made wide by appropriately adjusting the voltages of the respective electrodes. Accordingly, switching to the bar state or to the cross state is stable.
In this invention, preferably, the electrodes are disposed along the first waveguide and the second waveguide, with the electrodes disposed along the first waveguide opposing, in a one-to-one relationship, the electrodes disposed along the second waveguide. Or, an electrode is provided at mode coupling regions, and no electrode is provided at non mode coupling regions.
When operating the above optical switch, preferably, when the electrodes are disposed along only one of the first and second waveguides, voltages are applied independently to the respective electrodes, and the polarities of the voltages are successively reversed, with respect to a given reference potential, in the order in which the electrodes are arranged. Or, when electrodes are disposed along the first and second waveguides, voltages are applied independently to the respective electrodes, and the polarities of the voltages are successively reversed, with respect to a given reference potential, in the order in which the electrodes are disposed in a line. Further, absolute values of differences between the reference potential and a potential of each of the electrodes disposed so as to oppose one another along the first and second waveguides are equal.
In accordance with such methods, the operational ranges of the bar state and the cross state are both broad. Accordingly, switching to the bar state or to the cross state is stable.
In the present invention, preferably, at least one of the waveguides includes a periphery having at least one curve. Or, the first and second waveguides each include a periphery having at least one curve with a convex section, with the convex section of the curve of each waveguide opposing the convex section of the curve of the other waveguide.
The structures of the first and second waveguides are substantially the same as the structure of a waveguide of a conventionally known optical wavelength filter. Accordingly, it is easy to design the waveguide. Further, the unit curve may be, for example, a substantially cycloid curve, or may be a substantial sine curve.
Further, in the present invention, preferably, the waveguides substantially mirror one another.
In order to
Burdett James R.
Oki Electric Industry Co. Ltd.
Venable
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