Optical waveguides – Polarization without modulation
Reexamination Certificate
1999-06-16
2001-03-27
Kim, Robert (Department: 2877)
Optical waveguides
Polarization without modulation
C385S012000, C385S014000, C385S016000, C349S196000
Reexamination Certificate
active
06208774
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to light guides, and more particularly, to programmable light guides based on liquid crystals.
BACKGROUND OF THE INVENTION
Data communication systems based on fiber optics provide substantially higher bandwidth than systems based on electrical systems. Unfortunately, switching devices for switching optical signals between an input fiber and a plurality of output fibers have not kept pace. As a result, optical signals are typically converted back to electrical signals prior to switching. The electrical signals are then switched using conventional packet switching techniques and reconverted to optical signals prior to entering the output fibers. The limitations of electrical switching systems prevent the realization of the full data bandwidth of the fibers. Accordingly, a significant amount of research has gone into developing optical switches that avoid the conversion of the light signals back to electrical signals.
One promising method for switching optical signals between optical paths relies on a waveguide whose location is electrically controlled. A waveguide may be generated by altering the index of refraction of a medium along the path over which the light is to travel such that the desired path has a higher index of refraction than the surrounding medium. Devices based on liquid crystals are particularly attractive because of the large changes in index of refraction that can be induced in a liquid crystal layer by applying a low frequency AC electrical field across the layer. A simple switching device can be constructed by energizing one set of electrodes on the surface of the liquid crystal layer while leaving an alternative set in a non-energized state. The region between the energized electrodes then becomes the waveguide that specifies the direction in which the light signal will propagate in the liquid crystal layer.
Unfortunately, liquid crystal based light guides only guide light of one linear polarization. Light of the orthogonal polarization experiences a different index of refraction and is not guided. Since optical signals in such systems typically have randomly changing polarization states, unpredictable transmission can occur.
Broadly, it is the object of the present invention to provide an improved optical switching element.
It is a further object of the present invention to provide an optical switching element that operates on a light signal independent of the polarization state of that light signal without introducing the light losses inherent in polarization dependent waveguides.
These and other objects of the present invention will become apparent to those skilled in the art from the following detailed description of the invention and the accompanying drawings.
SUMMARY OF THE INVENTION
The present invention is a light guiding element for routing a light signal between an input port and an output port or for blocking the propagation of the light signal between the input and output ports depending on the state of the light guiding element. The light guiding element utilizes a polarizing beam splitter for separating the input light signal into physically separated first and second polarized light signals, the first light signal having a polarization that is orthogonal to that of the second light signal. A first polarization rotator rotates the polarization of the first light signal such that the polarization of the first light signal is parallel to that of the second light signal. A first waveguide having first and second states operates on the first light signal such that the first waveguide guides the first light signal along a predetermined path in the first state while not guiding the first light signal in the second state. A second waveguide having first and second states operates on the second light signal such that the second waveguide guides the second light signal along a predetermined path in the first state while not guiding the second light in the second state. A second polarization rotator rotates the polarization of the second light signal such that the polarization of the second light signal is orthogonal to that of the first light signal. A polarizing beam combiner then combines the first and second light signals and couples the same to the output light port. The first and second waveguides are preferably constructed from a guide layer of a guide material having a first index of refraction in the absence of an electric field and a second index of refraction in the presence of an electric field. First and second electrodes apply the electric field to a portion of the layer. The electrodes define a guide region in the layer having an index of refraction that is greater than that of the guide layer in regions adjacent to the guide region. The guide material is preferably a liquid crystal medium.
Baney Douglas M.
Sorin Wayne V.
Agilent Technologie,s Inc.
Kim Robert
LandOfFree
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