Patent Number: 052372332
Section: summary

TECHNICAL FIELD The present invention pertains to the field of optoelectronic devices. In particular, this invention pertains to an optoelectronic element comprised of a light source means, an optical control means and a photocell means intimately coupled together so that the optoelectronic element behaves like an active circuit element, such as a transistor or a diode. BACKGROUND ART It is well known that optical energy can be absorbed in a semiconductor material if the photon energy is greater than the band-gap energy of the semiconductor material. This phenomenon, known as the photovoltaic or photoconductive effect, occurs when the photons absorbed by the semiconductor material generate electron-hole pairs that produce a potential difference or increased conductance across the p-n junction of the semiconductor. The phenomenon has been used in the prior art to create a variety of hybrid optical/electrical devices. For a more detailed explanation of this phenomenon and its application, reference is made to J. Wilson and J. Hawkes, Optoelectronics: An Introduction, pgs. 286-327, Prentice Hall (1983). Most well known among the uses of the photovolatic/photoconductive effect is the use of a photodiode for generating electrical power, e.g., solar cells converting sunlight to electricity. Other variations of the basic photodiode include the avalanche photodiode and the phototransistor, both of which internally amplify the current flow across the p-n junction of the photodiode. The photodiode is also used as a photodetector for detecting the presence or absence of optical energy, e.g. the light beam switch in an elevator door or a photochopper wheel. Optoisolators make use of the photodiode and a photoemmissive device (e.g., a light emitting diode or LED) to convert electrical energy to photon energy and back again for the purpose of decoupling a power source or an electrical signal. For example, U.S. Pat. No. 4,695,120 shows the combined use of optoisolators to electrically isolate all of the signals to an integrated circuit and a photodiode to provide the electrical power for the integrated circuit. A detailed description of the various types of optoelectronic devices that are available in the prior art is provided in Optoelectronics Fiber-Optic Applications Manual, Hewlett Packard (1981), and Optoelectronics: Theory and Practice, Texas Instruments (1978). Another phenomenon that has been put to use in optical and hybrid optical/electrical circuit devices is the atomic level relationship between electrical fields and optical transmisivity, sometimes referred to as photorefractivity. Photorefractive substances exhibit a change in their index of refraction in response to the application of an electrical field. The most well known of photorefractive materials is the liquid crystal display or LCD. For a more detailed explanation of this phenomenon and its application, reference is made to Photorefractive Materials and Their Applications, Topics in Applied Physics, Vols. 61 and 62, Gunter, P. and Huignard, J. (eds.) (1989). For purposes of understanding the wide variety of electrical/optical devices that are available in the prior art with respect to the present invention, it is helpful to categorize present hybrid electrical/optical circuit devices based upon the nature of their inputs and outputs. Primary electrical/optical devices convert photon energy (input) to electrical energy (output) or vice-versa. Examples of primary types of hybrid electrical/optical devices include the photodiode (optical input/electrical output), the light emitting diode (electrical input/optical output) and the semiconductor laser (electrical input/optical output). Intermediary or secondary electrical/optical devices have a common input and output, but use either photon energy or electrical energy as part of an intermediary step internal to the device. Examples of intermediary or secondary types of hybrid electrical/optical devices include solid state image intensifiers and electroluminiscient devices (optical input/output, electrical intermediary) and photoisolators and optocouplers (electrical input/output, optical intermediary). Of interest for purposes of the present invention are those secondary or intermediary hybrid electrical/optical devices that utilize photorefractive materials as part of the intermediary step. Prior art application of photorefractive materials to hybrid electrical/optical devices has been limited to secondary devices having optical inputs and outputs with an electrical intermediary. The most prevalent uses of photorefractive materials include optical amplifiers, waveguides and light valves, such as liquid crystal light valves, which are used as part of an optical computing network. For example, U.S. Pat. No. 4,764,889 describes the use of optically nonlinear self electro-optic effect devices as part of an optical logical arrangement. U.S. Pat. No. 4,818,867 describes the use of an optical shutter on the output of an optical logic element. An overview of the various types of hybrid electrical/optical devices used in connection with prior art optical computing networks is provided in Feitelson, D., Optical Computing (1988). Although the use of photorefractive materials is well known as part of the intermediary step for electrical/optical hybrid devices having optical inputs and outputs with an electrical intermediary, photorefractive materials have not been used in connection with other types of electrical/optical hybrid devices having electrical inputs and outputs with an optical intermediary. The optical intermediaries of photoisolators and optocouplers are designed for the optimum transfer of photon energy between the photoemissive device and the photovoltaic/photoconductive element and, hence, there is no need for intermediary optical control in such devices. Accordingly, it would be desirable to provide an optoelectronic device that makes use of photorefractive materials as part of an optical intermediary for electrical/optical hybrid devices having electrical inputs and outputs that could take advantage of a modulated transfer function of the photon energy in such a device. SUMMARY OF THE INVENTION In accordance with the present invention, an optoelectronic active circuit element is comprised of a light source means, a photocell means and an optical control means. The light source means has at least one light emitting surface for emitting light energy in a specified frequency bandwidth and the photocell means also has at least one light collecting surface for absorbing light energy. The optical control means is intimately interposed between the light emitting surface of the light source means and the light collecting surface of the photocell means for controlling the emitted light energy that may be absorbed by the photocell means in response to an input signal. The light optical means is capable of either frequency or amplitude modulation of the emitted light energy as a result of changes in the indices of refraction and/or polarization of a photorefractive material. In the preferred embodiment, the photorefractive material is a liquid crystal display material or a lead lantium zirconium titinate material capable of fast switching speeds in response to small changes in an electrical input signal. In the preferred embodiment of the present invention, the light source means is self-powered by the use of a light emitting polymer as the light source means. The light emitting polymer is comprised of a tritiated organic polymer to which at least one organic phosphor or scintillant is bonded. Because the electrical energy generated by the preferred embodiment is dependent upon the rate of emission of photons from the light emitting polymer (which is in turn dependent upon the rate of beta-emissions from the radioisotope used to activate the light emitting polymer), the amount of photon energy available is essentially constant and determinable and is isolated from any electrical noise in the system. In addition to providing a unique source of electrical energy, as well as electrical signals, for CMOS, NMOS and other low power types of electronic circuitry, the output stability and isolation of the present invention makes it ideally suited for applications that require a voltage or current sources that have high signal to noise ratios. Accordingly, a primary objective of the present invention is to provide an optoelectronic active circuit element that includes an optical control means for controlling the amount of electrical energy generated by a photovoltaic cell by controlling the amount of light that is received by a photovoltaic cell from a light source. Another objective of the present invention is to provide an optoelectronic device that makes use of photorefractive materials as part of an optical intermediary for electrical/optical hybrid devices having electrical inputs and outputs and takes advantage of a modulated transfer function of the photon energy in such a device. A further objective of the present invention is to provide an optoelectronic active circuit element wherein the light source means is selfpowered by the use of a light emitting polymer as the light source means. Still another objective of the present invention is to provide an optoelectronic active circuit element that includes an optical control means capable of both amplitude and frequency modulation of the photon energy transmitted through the optical control means. A still further objective of the present invention is to provide an optoelectronic active circuit element having an optical control means comprised of an interference filter means and a photorefractive material in combination. These and other objectives of the present invention will become apparent with reference to the drawings, the detailed description of the preferred embodiment and the appended claims.