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Tailored Index Materials

The Nonlinear Optical Memory Effect

Light propagating in random media produces characteristic speckle patterns, which remain correlated for small perturbations of the parameters of the incoming beam, including e.g. its angle and position. This behaviour is known as memory effect. In a paper published in Optics Letters, fruit of the collaboration of our group with Dr Tom Vettenburg (University of Dundee) and Prof. Claudio Conti (CNR, Italy), we generalise the memory effect to the case of light propagating in random nonlinear media. In particular, in a series of pump-probe experiments, we quantify the nonlinear memory effect produced by the opto-thermal response of silica aerogel. In this work, the memory effect… Read More »The Nonlinear Optical Memory Effect

Perturbation of Transmission Matrices in Nonlinear Random Media

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In this paper, published in Annalen der Physik, we present the direct measurement of the nonlinear transmission matrix of complex materials, exploiting the strong optothermal nonlinearity of scattering silica aerogel. It is shown that the dephasing effects due to nonlinearity are both controllable and reversible, opening the road to applications based on the nonlinear response of random media  

Optical Shock Waves in Silica Aerogel

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In a work published recently in Optics Express we experimentally investigated the occurrence of optical dispersive shock waves (DSWs) in silica aerogel (SA). Here we studied the interplay between disorder and nonlinearity; on the other hand the determination of the conditions for the suppressions of the DSWs, is fundamental for the realization of high power nonlinear optical devices based on SA. The convection-free solid-state structure of SA gives peculiar thermal properties, such as very low heat conductivity and high melting point, making this material robust with respect to very high nonlinear regimes, a topic so far unexplored. This is at variance with most the systems presenting thermal nonlinearity, that being dyed soft-matter, exhibit boiling… Read More »Optical Shock Waves in Silica Aerogel

Random super-prism wavelength meter

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In a recent paper published in Optics Letter we demonstrate that a random medium can be used as a cheap and reliable wavemeter. The system is made of a small drop of alumina particles in water solution casted on a glass slide, placed at the end of a fiber coupler as in figure. When propagating through the drop, light of different wavelengths produce specific speckle patterns that can be stored for future reference. The unknown wavelength of a further beam can then be assessed using principal component analysis with a resolution up to 13 pm.

Transformation Optics in Silicon Photonics

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The Luneburg lens is a gradient index lens that focuses light from all incident directions, thus being free from aberrations that affect conventional lenses. Like the Maxwell fish-eye lens or the Eaton lens, the Luneburg lens can be described via non-Euclidean transformation, where light in a medium is experiencing a curved spatial geometry. The Luneburg lens focuses light on the edge of the lens in the same direction of the incident light. The position of the focus thus indicates the direction of light corresponding to a Fourier transform in terms of light waves. Luneburg lenses are commonly used in microwave technology and have recently been… Read More »Transformation Optics in Silicon Photonics