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Creation of light-controlling-light devices can be achieved at high speed by way of the optical Kerr effect. This nonlinear optical process changes the effective index of refraction based on the intensity of an optical pulse. Using this, two otherwise non-interacting pulses can influence one another's velocity while traveling through a nonlinear medium, thus a single pulse accumulates a different phase shift than two co-propagating pulses of twice the intensity. Coupling this effect with optical interference, it becomes possible to create all optical logic operations.
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Photograph of a nonlinear Sagnac interferometer. |
Diagram of a nonlinear Sagnac interferometer showing the input pulse, the counter-propagating paths, the reflected and transmitted pulses. |
Silica fibers, whose diameters are smaller than the wavelength of light, can be twisted into a loop structure that behaves as a Sagnac interferometer. When ultrashort pulses (~100 fs) are launched into the loop, the nonlinear effects create a device with a power-dependent transmission. By tuning the coupling region and the input pulse power, the Sagnac loop can perform optical switching as well as optical logic.
Miniaturization of these optical devices for signal processing is a key obstacle to overcome in order to achieve the production of so-called photonic chips. A major limiting factor is the accumulation of this nonlinear phase. This requires a balance between the intrinsic nonlinearity of the material, the degree of light confinement and the overall interaction length. Our work with silica nanowires has overcome the relatively small nonlinearity of silica by tightly confining the light over relatively long interaction lengths. As we look to the future, we are investigating novel materials that can be efficiently manufactured and integrated into existing material platforms, possessing both high intrinsic nonlinearities and high indices of refraction to create nanophotonic devices.
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| Plainly Speaking | An optical computer will probably not replace your existing desktop computer for many years. Although the speed of optical computation exceeds that of current silicon based electrical technology, cutting edge silicon technology can get around this by using many processors working together. On the other hand, optical computations will dramatically speed up the internet. Currently, information is sent over the internet through a series of fiber optic cables and redirecting stations. These redirecting stations use slow electrical signals. If these redirecting stations could be replaced by optical redirecting station, the internet could be made 100 times faster than it is today. Our work investigates and develops platforms in which to perform such optical computation.
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