Optical waveguides – Having nonlinear property
Reexamination Certificate
1999-08-05
2002-12-24
Font, Frank G. (Department: 2877)
Optical waveguides
Having nonlinear property
C385S126000
Reexamination Certificate
active
06498885
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a semiconductor nonlinear waveguide and an optical switch comprising a semiconductor nonlinear waveguide, and especially to a semiconductor nonlinear waveguide and an optical switch used in a field of an optical fiber communication and an optical information process.
BACKGROUND OF THE INVENTION
In an all-optical switch comprising a semiconductor nonlinear waveguide, if a period of repetition of the control light pulses is shorter than the lifetime of the carriers generated in a core of the semiconductor nonlinear waveguide, the all-optical switch operates in a condition that the carriers accumulate in the core of the semiconductor nonlinear waveguide. The accumulation of the carriers degrades the nonlinear property of the semiconductor nonlinear waveguide, and obstructs the realization of the all-optical switch with excellent performances. Accordingly, it can be admitted that a method proposed in Japanese Patent Kokai 4-3125, in which an electrostatic field is applied to the semiconductor nonlinear waveguide to shorten the lifetime of the carrier, is an effective one for deducing the accumulation of the carriers, but the structure of the all-optical switch becomes complicated.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the invention to provide a semiconductor nonlinear waveguide, in which an electrostatic field can be applied to a core layer of the semiconductor nonlinear waveguide without using an external constant-voltage power supply.
It is a further object of the invention to provide a semiconductor nonlinear waveguide, in which an electrostatic field can be applied to an InGaAsP core layer of the semiconductor nonlinear waveguide without using an external constant-voltage power supply.
It is a still further object of the invention to provide an optical switch according to a Mach-Zehnder interferometer having a pair of semiconductor nonlinear waveguides, in each of which an electrostatic field can be applied to a core layer of the semiconductor nonlinear waveguide without using an external constant-voltage power supply.
It is a yet further object of the invention to provide an optical switch according to a Mach-Zehnder interferometer having a pair of semiconductor nonlinear waveguides, in each of which an electrostatic field can be applied to an InGaAsP core layer of the semiconductor nonlinear waveguide without using an external constant-voltage power supply.
It is a yet still further object of the invention to provide an optical switch having a single semiconductor nonlinear waveguide, in which an electrostatic field can be applied to a core layer of the semiconductor nonlinear waveguide without using an external constant-voltage power supply.
It is an additional object of the invention to provide an optical switch having a signal semiconductor nonlinear waveguide, in which an electrostatic field can be applied to an InGaAsP core layer of the semiconductor nonlinear waveguide without using an external constant-voltage power supply.
According to the first feature of the invention, a semiconductor nonlinear waveguide comprises:
a nondoped core layer formed of a medium showing a nonlinear refractive index caused by absorption of a control light,
an under cladding layer of a first conductivity type formed under the nondoped core layer,
an upper cladding layer of a second conductivity type formed on the nondoped core layer, and
means for electrically shortcircuiting the under and upper cladding layers.
According to the second feature of the invention, a semiconductor nonlinear waveguide comprises:
a n-type InP substrate,
a nondoped InGaAsP optical waveguide of a strip structure formed on the n-type InP substrate,
nondoped InP layers formed on both sides of the nondoped InGaAsP optical waveguide,
a p-type InP layer formed on the nondoped InGaAsP optical waveguide and the nondoped InP layers,
a p-type InGaAs cap layer formed on the p-type InP layer,
electrodes respectively formed on an obverse surface of the InGaAs cap layer and a reverse surface of the n-type InP substrate, and
means for electrically shortcircuiting the electrodes formed on the obverse and reverse surfaces.
According to the third feature of the invention, an optical switch comprises:
a Mach-Zehnder interferometer provided with a pair of semiconductor nonlinear waveguides on both arms thereof,
wherein a refractive index of each of the semiconductor nonlinear waveguides changes by absorption of a control light, and
means for supplying the semiconductor nonlinear waveguides with the control light pulses in turn at a predetermined difference in time, which is shorter than a relaxation time of the change of the refractive index of each of the semiconductor nonlinear waveguides,
wherein each of the semiconductor nonlinear waveguides comprises:
a nondoped core layer formed of a medium showing a nonlinear refractive index,
an under cladding layer of a first conductivity type formed under the nondoped core layer,
an upper cladding layer of a second conductivity type formed on the nondoped core layer, and
means for electrically shortcircuiting the under and upper cladding layers.
According to the fourth feature of the invention, an optical switch comprises:
a Mach-Zehnder interferometer provided with a pair of semiconductor nonlinear waveguides on both arms thereof,
wherein a refractive index of each of the semiconductor nonlinear waveguides changes by absorption of a control light, and
means for supplying the semiconductor nonlinear waveguides with the control light pulses in turn at a predetermined difference in time, which is shorter than a relaxation time of the change of the refractive index of each of the semiconductor nonlinear waveguides,
wherein each of the semiconductor nonlinear waveguides comprises:
a n-type InP substrate,
a nondoped InGaAsP optical waveguide of a strip structure formed on the n-type InP substrate,
nondoped InP layers formed on both sides of the nondoped InGaAsP optical waveguide,
a p-type InP layer formed on the nondoped InGaAsP optical waveguide and the nondoped InP layers,
a p-type InGaAs cap layer formed on the p-type InP layer,
electrodes respectively formed on an obverse surface of the InGaAs cap layer and a reverse surface of the n-type InP substrate, and
means for electrically shortcircuiting the electrodes formed on the obverse and reverse surfaces.
According to the fifth feature of the invention, an optical switch comprises:
a semiconductor nonlinear waveguide, which shows a change in a refractive index by absorption of a control light,
means for separating a signal light into two linearly polarized signal lights perpendicular to each other,
means for generating a difference in a propagation time between the two linearly polarized signal lights perpendicular to each other,
means for propagating the two linearly polarized signal lights perpendicular to each other through the semiconductor nonlinear waveguide,
means for supplying a control light to the semiconductor nonlinear waveguide at a predetermined time, and
means for canceling the difference in the propagation time between the two linearly polarized signal lights perpendicular to each other,
wherein the nonlinear waveguide comprises:
a nondoped core layer formed of a medium showing a nonlinear refractive index,
an under cladding layer of a first conductivity type formed under the nondoped core layer,
an upper cladding layer of a second conductivity type formed on the nondoped core layer, and
means for electrically short circuiting the under and upper cladding layers.
According to the sixth feature of the invention, an optical switch comprises:
a semiconductor nonlinear waveguide, which shows a change in a refractive index by absorption of a control light,
means for separating a signal light into two linearly polarized signal lights perpendicular to each other,
means for generating a difference in a propagation time between the two linearly polarized signal lights perpendicular to each other,
means for propagating the two linearly polarized signal lights perpendicul
Nakamura Shigeru
Tajima Kazuhito
Font Frank G.
NEC Corporation
Valentin Juan D.
Young & Thompson
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