Two-Dimensional Nonlinear Fabry-Perot Interferometer: An Unconventional Computing Substrate for Maze Exploration and Logic Gate Operation

This study examined a possibility to use a two-dimensional nonlinear Fabry-Perot interferometer (2DNFP) as a novel information processing device. Optical bistability was realized through positive or negative feedback between heat generated by absorption of light and change in resonance condition induced by temperaturedependent refractive index. Due to heat conduction in lateral direction, “turn-on” wave propagates twodimensionally in this device. A novel feature of this device is that the ON-state region can degenerate at suitably weak light intensity. The authors examined the function of 2DNFP as a maze solver utilizing the extension and degeneration modes, as well as its function as logic gates. “AND”, “OR”, and “NOT” gates were realized, thus the logical universality of the 2DNFP was demonstrated. (Sharfin, 1986), and so on. Especially optical bistability in nonlinear Fabry-Perot interferometer has been studied both experimentally and theoretically as a basis to control light by light (Migus, 1985; Marino, 2007; Ono, 2001; Khoo, 1983; Kreuzer, 1994; Cheung, 1983; Wang, 2001; Quintero-Torres, 1995; Sharfin, 1986). Fabry-Perot interferometer is an optical DOI: 10.4018/jnmc.2011010102 14 International Journal of Nanotechnology and Molecular Computation, 3(1), 13-23, January-March 2011 Copyright © 2011, IGI Global. Copying or distributing in print or electronic forms without written permission of IGI Global is prohibited. device consisting of two parallel mirrors with high reflectivity (Figure 1a) in which the injected light is reflected many times between the mirrors. When the round-trip optical length equals to an integral multiple of the light wavelength, the multiply reflected lights interferes constructively and transmittance of the interferometer becomes high because of interference. If the wavelength does not satisfy the condition above, transmittance is low. Therefore, the transmission presents a resonance property as a function of wavelength (Figure 1b). A nonlinear FabryPerot interferometer utilizes refractive index change of the medium between the mirrors. This change can be induced by light through third-order nonlinear optical process or heat through temperature dependence of refractive index. Assume that a Fabry-Perot interferometer is off-resonant at the wavelength of incident laser light as shown by the dashed thick line in Figure 1b. When the incident light intensity is increased from zero, small fraction of the incident light enters in the interferometer and the intensity in the interferometer increases almost proportional to the incident light intensity. At certain intensity of incident light, positive feedback starts: increase of light intensity in the interferometer causes change in refractive index and resonance shift, resulting in further increase of intensity in the interferometer. This turns the device to a resonant state or “ON” state with high transmission. When decreasing the incident light intensity, the “ON” state is kept down to a considerably weak light intensity, since large fraction of light enters to the interferometer. Thus hysteresis and bistability is realized. Comparing refractive index change induced by light through the third-order nonlinear optical process and by heat through temperature change, the former is advantageous in its rapid response, but much higher light intensity is necessary. The latter requires much lower light intensity, but the response is much slower. We selected thermal effect as the origin of nonlinearity, since it requires lower intensity of light and thus is suitable to a wide-area device for two-dimensional (2-D) operation. Moreover, slow response due to heat conduction is convenient to observe the device operation. Most of the studies on nonlinear FabryPerot interferometer are concentrated in the behavior at one point (zero-dimension), and there are only a few examples that investigated application to 2-D systems (Khoo, 1983; Cheung, 1983; Wang, 2001). In this study, we examined two-dimensional nonlinear FabryPerot interferometer (2DNFP) to utilize propagation of ON-state wavefront. In a 2DNFP, when Figure 1. Schematic illustration of 2DNFP. (a) structure of a 2DNFP, illustrated with incident light, multiple reflection of light in the interferometer, heated area at ON state, and heat conduction to neighboring area. (b) Optical transmission as a function of wavelength. Resonance peak shifts when the refractive index of the medium in the interferometer decreases with heating, as shown by the arrow. If the incident laser wavelength is at the tail of the initial resonance curve (dashed vertical red line), the transmission increases with the peak shift, which induces positive feedback resulting in optical bistability. 9 more pages are available in the full version of this document, which may be purchased using the "Add to Cart" button on the publisher's webpage: www.igi-global.com/article/two-dimensional-nonlinear-fabryperot/54341