Optical: systems and elements – Optical modulator – Light wave directional modulation
Reexamination Certificate
2002-04-30
2004-06-29
Spector, David N. (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave directional modulation
C359S302000, C359S321000
Reexamination Certificate
active
06757095
ABSTRACT:
FIELD OF THE INVENTION
The invention relates generally to semiconductor structures, and more particularly to a semiconductor structure that can transmit optical signals.
BACKGROUND OF THE INVENTION
The use of silicon to manufacture integrated circuits (ICs) is a well-developed technology. Since early years of IC development, silicon has dominated the field of electronics to become the most widely used material to fabricate and integrate various electronic devices, in particular transistors such as bipolar and metal oxide semiconductor (MOS) transistors. Consequently, silicon technology has significantly advanced in comparison to other alternative technologies. As a result, silicon-based ICs have a number of advantages over other technologies. For example, silicon-based ICs can be manufactured with relative ease using established semiconductor processes. In addition, an extremely high density of electronic devices can be fabricated on silicon-based ICs. Therefore, silicon-based ICs are currently the preferred embodiment for large-scale high-volume signal processing electronics.
The preference of silicon-based ICs makes silicon the material of choice for fabrication of light emitting devices so that optical functions can be added to signal processing ICs. Unfortunately, silicon is not well-suited for fabrication of light emitting devices. Due to the indirect bandgap of silicon, any light emitting device fabricated using silicon will not emit radiation with significant quantum efficiency. Nevertheless, there has been much effort to incorporate conventional light emitting devices such as GaAs lasers onto silicon-based signal processing ICs to provide optical interconnectivity.
A concern with incorporating conventional light emitting devices onto silicon-based signal processing ICs is that the manufacturing process of such ICs is significantly more complex than convention IC manufacturing process. The complexity of the manufacturing process translates into increase in the manufacturing cost of the ICs with light emitting devices.
In view of these concerns, there is a need for a semiconductor structure and method for transmitting optical signals that can be readily integrated into a silicon-based IC without significantly increasing manufacturing complexity and cost.
SUMMARY OF THE INVENTION
A semiconductor structure and method for transmitting optical signals modulates an optical property of the semiconductor structure to selectively transmit portions of an externally supplied light beam as optical signals. The use of the externally supplied light beam eliminates the need to fabricate a light emitting device onto the semiconductor structure. Thus, the semiconductor structure can be based on an indirect bandgap material such as silicon. Consequently, the semiconductor structure can be readily integrated into a conventional silicon-based integrated circuit using conventional semiconductor manufacturing processes.
A semiconductor structure in accordance with the invention includes a semiconductor substrate, a port positioned over the semiconductor substrate and an optically active region positioned between the port and the substrate. The optically active region has a controllable optical property to manipulate an externally supplied light beam, which is received through the port, such that portions of the light beam can be selectively transmitted through the port as optical signals. The semiconductor substrate may include an indirect bandgap material.
The optically active region includes a controllable layer having the controllable optical property, which is responsive to an electric field, to selectively retard polarization components of the externally supplied light beam, and a reflective element positioned below the controllable layer to reflect the polarization components. The controllable layer may be configured to substantially operate as a quarter-wave plate.
In an embodiment, the optically active region further includes a walk-off layer configured to displace a polarization component of the externally supplied light beam. The walk-off layer and the controllable layer may each include a birefringent material.
In an embodiment, the semiconductor structure includes a polarizing beamsplitter configured to selectively reflect a polarization component of the externally supplied light beam.
In an embodiment, the port includes a single aperture in an opaque layer positioned above the optically active region. In another embodiment, the port includes an input aperture and an output aperture in the opaque layer.
A method of transmitting optical signals in accordance with the invention includes receiving an externally supplied light beam at a port of a semiconductor structure, and modulating an optical property of the semiconductor structure to manipulate the externally supplied light beam so that portions of the light beam are selectively transmitted though the port as optical signals.
In an embodiment, the externally supplied light beam may be received at an input aperture of the port, while the portions of the externally supplied light beam may be transmitted through an output aperture of the port.
In an embodiment, the method further includes separating first and second polarization components of the externally supplied light beam, reflecting the first and second polarization components toward the port, and displacing one of the first and second polarization components depending on polarized orientations of the first and second polarization components. The separating of the first and second polarization components and the displacing of one of the first and second polarization components may be performed by a walk-off birefringent layer of the semiconductor structure.
In another embodiment, the method further includes transmitting a particular polarization component of the externally supplied light beam, reflecting the particular polarization component toward the port, and selectively reflecting the particular polarization component depending on polarized orientation of the particular polarization component. The transmitting of the particular polarization component and selectively reflecting the particular polarization component may be performed by a polarizing beamsplitter.
In an embodiment, the modulating of the optical property of the semiconductor structure includes controlling an electric field within the controllable layer of the semiconductor to change the optical property of the semiconductor structure to a first state. The controllable layer is configured to substantially function as a quarter-wave plate when the semiconductor structure is changed to the first state.
Other aspects and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrated by way of example of the principles of the invention.
REFERENCES:
patent: 5621564 (1997-04-01), Kageyama et al.
patent: 5920078 (1999-07-01), Frey
Agilent Technologie,s Inc.
Spector David N.
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