Investigations of frequency combs in χ optical microresonators are burgeoning nowadays. Changeover to χ resonators promises further advances and brings new challenges. Here, the comb generation entails not only coupled first and second harmonics (FHs and SHs) and two dispersion coefficients but also a substantial difference in the group velocities - the temporal walk-off. We predict walk-off controlled highly stable comb generation, which is drastically different from that known in the χ case. This includes the general notion of antiperiodic states; formation of localized coherent antiperiodic steady states (solitons), where the FH and SH envelopes move with a common velocity without shape changes; characterization of a new vast family of antiperiodic solitons; and the dependence of comb spectra on the pump power and the group velocity difference.
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Investigations of frequency combs in χ optical microresonators are burgeoning nowadays. Changeover to χ resonators promises further advances and brings new challenges. Here, the comb generation entails not only coupled first and second harmonics (FHs and SHs) and two dispersion coefficients but also a substantial difference in the group velocities - the temporal walk-off.
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Department of Electrical and Electronic Engineering, Imperial College London, London, SW7 2AZ, UK.
A sub-pixel image shifter is presented, for use in enhancing the spatial resolution of digital image sensors by combining multiple displaced sub-images using a super-resolution (SR) algorithm. The device uses the walk-off phenomenon in birefringent crystals to separate images with opposite polarizations by a sub-pixel displacement. A liquid crystal (LC) waveplate plus a polarizer can then select the specific image to be exposed, with fast, non-mechanical control.
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Opt Lett
September 2005
Nonlinear Optics and OptoElectronics Lab, Istituto Nazionale per la Fisica della Materia and Department of Electronic Engineering, University Roma Tre, Rome, Italy.
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Opt Lett
June 2005
Nonlinear Optics and Optoelectronics Laboratory, National Institute for the Physics of Matter and Department of Electronic Engineering, University "Roma Tre," Via della Vasca Navale, 84-00146 Rome, Italy.
We demonstrate that, in suitably designed cells with undoped nematic liquid crystals, extraordinary-wave spatial solitons can be excited at every applied voltage without adjustments in the input polarization. Their walk-off, hence direction of propagation, is externally controlled over angles as large as 7 degrees. The results pave the way not only to polarization-forgiving generation but also to voltage readdressing of these extraordinary-wave nematicons.
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Nature
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NooEL (Nonlinear Optics and Optoelectronics Laboratory), National Institute for the Physics of Matter (INFM) and Department of Electronic Engineering, University Roma Tre, Via della Vasca Navale, 84, 00146 Rome, Italy.
In certain materials, the spontaneous spreading of a laser beam (owing to diffraction) can be compensated for by the interplay of optical intensity and material nonlinearity. The resulting non-diffracting beams are called 'spatial solitons' (refs 1-3), and they have been observed in various bulk media. In nematic liquid crystals, solitons can be produced at milliwatt power levels and have been investigated for both practical applications and as a means of exploring fundamental aspects of light interactions with soft matter.
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