Optical waveguides – Integrated optical circuit
Reexamination Certificate
2001-07-26
2004-02-03
Ben, Loha (Department: 2873)
Optical waveguides
Integrated optical circuit
C385S129000, C385S130000, C385S132000
Reexamination Certificate
active
06687425
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to optical signal transmission and, more specifically, an improved optical waveguide useful in applications requiring modulation and switching of optical signals.
It is becoming increasingly important to frequently upgrade telecommunication networks to increase their capacity due to the recent rapid increase in network traffic caused by multimedia communications. Although optical technologies are replacing most transmission lines, the nodes of optical networks, such as switching and cross-connect nodes, still depend on relatively slow electrical technologies. Specifically, time-division multiplexing (TDM) systems are widely used in existing optical communications systems and are inherently dependent on electrical circuits for multiplexing and demultiplexing. As a result, the electrical nodes in these types of optical networks limit throughput.
Accordingly, there is a need in the art for advances in telecommunication network design. More specifically, there is a need for innovation in the areas of switching, modulation, multiplexing and demultiplexing via optical technologies.
BRIEF SUMMARY OF THE INVENTION
This need is met by the present invention wherein waveguides and integrated optical devices incorporating optically functional cladding regions are provided. A significant advantage of many embodiments of the present invention lies in the use of two or more electrooptic cladding regions that are, through appropriate poling and/or deposition procedures, oriented with their polar axes in different directions. This type of orientation and variations thereof, as described herein, allow for production of waveguides and integrated optical devices exhibiting unique functionality and allowing for optimum flexibility in device design. The waveguides and integrated optical devices described herein may be exploited in various ways, many of which are described herein.
In accordance with one embodiment of the present invention, an electrooptic clad waveguide is provided comprising an optical waveguide core and first and second cladding regions. The optical waveguide core defines a primary axis of propagation z. The first cladding region is offset from the z axis in a first direction along an x axis perpendicular to the z axis. The second cladding region is offset from the z axis in a second direction along the x axis. The optical waveguide core comprises a substantially non-electrooptic material defining a refractive index n
1
and the first and second cladding regions comprises an electrooptic polymer defining a refractive index that is less than n
1
. The first and second cladding regions may be poled in opposite or perpendicular directions.
In accordance with another embodiment of the present invention, an electrooptic clad waveguide is provided where first and second control electrodes are arranged to enable electrooptic modification of the refractive indices of the first and second cladding regions by creating a contoured electric field in the first and second cladding regions. The contoured electric field and the respective directions of polarization in the first and second cladding regions define a polarization-independent waveguide structure along the primary axis of propagation of the electrooptic clad waveguide. Preferably, the first and second cladding regions are poled along substantially the same contour of the electric field.
In accordance with yet another embodiment of the present invention, an integrated optical device is provided comprising an optical input, an optical output, an electrooptic clad waveguide, and first and second control electrodes. The electrooptic clad waveguide is arranged along an optical path defined between the optical input and the optical output. The electrooptic clad waveguide is characterized by an optical phase delay &phgr;=2&pgr;Ln
eff
/&lgr;, where n
eff
is the effective index of refraction of the waveguide, L is the length over which the phase delay occurs, and &lgr; is the wavelength of light propagating along the optical path. The electrooptic clad waveguide comprises an optical waveguide core defining a primary axis of propagation z, a first cladding region offset from the z axis in a first direction along an x axis perpendicular to the z axis, and a second cladding region offset from the z axis in a second direction along the x axis. The optical waveguide core comprises a substantially non-electrooptic material defining a refractive index n
1
. The first and second cladding regions comprise an electrooptic polymer defining a refractive index that is less than n
1
. The waveguide core defines a cross-sectional x axis width that decreases from a region outside of the first and second cladding regions to a region bounded by the first and second cladding regions. The first and second control electrodes are arranged to create an electric field in the first and second cladding regions capable of changing the refractive indices of the first and second electrooptic cladding regions without a corresponding change in the refractive index n
1
of the waveguide core so as to induce a core-independent change in n
eff
and a corresponding change in the optical phase delay &phgr; of the waveguide.
In accordance with yet another embodiment of the present invention, an integrated optical device is provided where first and second waveguides are arranged to define a Mach-Zehnder interferometer. The interferometer includes first and second directional coupling regions, an intermediate coupling region disposed between the first and second directional coupling regions, a set of control electrodes, an optical input, and at least one optical output. One or both of the first and second waveguides comprise an electrooptic clad waveguide comprising a substantially non-electrooptic optical waveguide core defining a refractive index n
1
. The waveguide core of the electrooptic clad waveguide is disposed between first and second cladding regions in the intermediate coupling region. The first and second cladding regions comprise a poled electrooptic polymer defining a refractive index that is less than n
1
. The control electrodes are arranged to create an electric field in the first and second cladding regions capable of changing the refractive indices of the first and second electrooptic cladding regions so as to induce a change in an effective index of refraction n
eff
of the electrooptic clad waveguide. The control electrodes are further arranged so that a quantitative combination of the electric field and the poling in the first cladding region is substantially equivalent to a quantitative combination of the electric field and the poling in the second cladding region. In this manner an output intensity I
out
at one of the optical outputs is related to an input intensity I
in
according to one of the following equations
&LeftBracketingBar;
I
ou
t
&RightBracketingBar;
2
=
&LeftBracketingBar;
I
i
n
&RightBracketingBar;
2
sin
2
(
φ
2
)
&LeftBracketingBar;
I
out
&RightBracketingBar;
2
=
&LeftBracketingBar;
I
i
n
&RightBracketingBar;
2
cos
2
(
φ
2
)
where &phgr; represents optical phase delay resulting from the change in the effective index of refraction n
eff
of the electrooptic clad waveguide.
In accordance with yet another embodiment of the present invention, an integrated optical device is provided comprising first and second electrooptic clad waveguides arranged to define a Mach-Zehnder interferometer. The interferometer includes first and second directional coupling regions, an intermediate coupling region disposed between the first and second directional coupling regions, a set of control electrodes, first and second optical inputs, and first and second optical outputs. The waveguide core of the first waveguide is disposed between first and second cladding regions of the first waveguide in the intermediate coupling region. The waveguide core of the second waveguide is disposed between first and second cladding regi
Nippa David William
Ridgway Richard William
Wood Van Earl
Battelle (Memorial Institute)
Ben Loha
Choi William
Killworth, Gottman Hagan & Schaeff LLP
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