This invention relates generally to optical modulators and more particularly to ZnO optical modulators capable of operation in the ultraviolet range.
Electrical and optical control of optical anisotropy in semiconductor heterostructures have become effective methods of producing both high contrast and high speed modulation of normal incident light. See H. Shen, J. Pamulapati, M. Wraback, M. Taysing-Lara, M. Dutta, H. C. Kuo, and Y. Lu, IEEE Phot. Tech. Lett. 6, 700 (1994); H. Shen, M. Wraback, J. Pamulapati, M. Dutta, P. G. Newman, A. Ballato, and Y. Lu, Appl. Phys. Lett. 62, 2908 (1993); M. J. Snelling, D. R. Harken, A. L. Smirl, and E. Towe, IEEE J. Quant. Elect. 33, 1114 (1997); D. S. McCallum, X. R. Huang, A. L. Smirl, D. Sun, and E. Towe, Appl. Phys. Lett. 66, 2885 (1995), incorporated herein by reference as if fully set forth. These techniques rely upon the manipulation of the polarization rotation and phase retardation of linearly polarized light associated with a processing- or growth-induced lowering of symmetry. See H. Shen, M. Wraback, J. Pamulapati, P. G. Newman, M. Dutta, Y. Lu, and H. C. Kuo, Phys. Rev. B47, 13933 (1993); R. Binder, Phys. Rev. Lett. 78, 4466 (1997); R. H. Henderson and E. Towe, J. Appl. Phys. 79, 2029 (1995), incorporated herein by reference as if fully set forth. An infrared optical modulator has been demonstrated which exploits the optical anisotropy created by an internal thermally induced, in-plane anisotropic strain in a GaAs/AlGaAs multiple quantum well (MQW) to achieve a contrast ratio of 5000:1 for electrical addressing and 300:1 for optical addressing. Time-resolved measurements (see M. Wraback, H. Shen, J. Pamulapati, M. Dutta, P. G. Newman, M. Taysing-Lara, and Y. Lu, Surf Sci. 305, 238 (1994); M. Wraback, H. Shen, J. Pamulapati, P. G. Newman, and M. Dutta, Phys. Rev. Lett. 74, 1466 (1995), incorporated herein by reference as if fully set forth) indicate that the device possesses a sub-100 fs turn-on time driven by ultrafast large-angle polarization rotation, and a turn-off time governed primarily by carrier sweepout. Electrically and optically addressed InGaAs/GaAs MQW modulators with xcx9c25:1 contrast which employ an optical anisotropy associated with growth on a (110) GaAs substrate have also been realized. Nevertheless, despite the success of these techniques in the fabrication of high contrast high speed infrared modulators, high contrast, ultra-fast modulators operating in the visible and ultraviolet range have not yet been realized. Of course, a vastly greater amount of information could be conveyed by a high contrast optical modulator capable of operating in the ultraviolet range.
Accordingly, it is an object of the present invention to provide a high contrast, ultrahigh speed optical modulator capable of operating in the ultraviolet range. Still other objects of the present invention will become readily apparent to those skilled in this art from the following description herein, where there is shown and described a preferred embodiment of this invention, simply by way of illustration one of the modes to best carry out the invention. Pursuant to the invention the limitations of the existing art are overcome and additional advantages provided by a high contrast, ultrafast optically-addressed ultraviolet light modulator based upon optical anisotropy. The invention in one embodiment encompasses a high contrast, high speed ultraviolet light modulator including a light source, a semiconductor having a bandgap in the ultraviolet range grown on a substrate surface of low rotation symmetry whereby the semiconductor exhibits optical anisotropy, a pulse generator for delivering a pulsed modulating beam for the optical control of the optical anisotropy whereby the light source is modulated. In another embodiment of the invention, the lower rotation symmetry surface is R-plane sapphire. In another embodiment of the invention the semiconductor comprises a single crystal ZnO film epitaxially grown on an R-plane sapphire substrate.
Yet another embodiment of the invention is a high contrast, high speed ultraviolet light modulator including a light source, a bulk crystal having a bandgap in the ultraviolet range cut such that the surface of the crystal is a surface of low rotation symmetry whereby the crystal exhibits optical anisotropy, and a pulse generator for delivering a pulsed modulating beam for the optical control of an optical anisotropy in the bulk crystal whereby the light source is modulated. In another embodiment of the invention the bulk crystal is ZnO. As will be realized, the invention is capable of other different embodiments and its several details are capable of modification in various, obvious aspects all without departing from the invention. Accordingly, the drawings and descriptions will be regarded as illustrative in nature and not restrictive.
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