Recently artificial inhomogeneous broadening was proposed to expand the bandwidth of slow light. The point is to independently slow down all harmonic components of the input pulse via inhomogeneous broadening. An input pulse or sequence of pulses can be split into independent spectral channels by a dispersive element such as a prism or grating. These sub-pulses are then slowed by bandwidth-matched slow-light array elements, and then recombined with another dispersive element to produce the output pulse. The proof of principle experiment was done with a photorefractive crystal Ce:BaTiO3 where the crystal function as both dispersive elements and slow lights devices.
Ultrasound-modulated optical tomography (UOT) is a new technique that combines laser light and ultrasound to provide images with good optical contrast and good ultrasound resolution in soft biological tissue. We improve the method proposed by Murray et al to obtain UOT images in thick biological tissues with the use of photorefractive crystal based interferometers. It is found that a long ultrasound burst (on the order of a millisecond) can improve the signal-to-noise ratio dramatically. Also with a long ultrasound burst, the response of the acoustic radiation force impulses can be clearly observed in the UOT signal, which will help to acquire images that record both the optical and mechanical properties of biological soft tissues.
Associative memories that recognize a pattern based on partial input have numerous applications such as homeland security. Optical implementations of associative memories, for example using computer-generated holograms, have the inherent parallelism as an advantage over software realizations. The nonlinear thresholding operation is a key step in the optical associative memories. A major source error in these memories is the thresholding uncertainties caused by fluctuation, for example in the input illumination or varying degrees of partial obscuration. Here, we show a proof-of-principle demonstration of a new scheme to suppress such errors using real time thresholding and a modified Hopfield associative memory model.
A critical limitation of slow light schemes is the limited time-bandwidth product. Recently we showed that this limitation can be overcome by making use of inhomogeneities. Here we analyze the effects of crosstalk noise that can be induced by these inhomogeneities in certain situations, and how to minimize such noise. The proof of principle experiment was done using three-wave mixing in a photorefractive crystal Ce:BaTiO3 where Bragg selection is used to provide the inhomogeneity.
For many applications of slow or stopped light, the delay-time-bandwidth product is a fundamental issue. However, existing slow light demonstrations do not give a satisfactory delay-time bandwidth product, especially in room temperature solids. Here we demonstrate that the use of artificial inhomogeneous broadening has the potential to solve this problem by simultaneously slow down all the frequency components of the input pulse. The proof of principle experiment was done using three-wave mixing in a photorefractive crystal Ce:BaTiO3 where Bragg selection is used to provide the inhomogeneity.
To investigate the dependence of the sensitivity of optical waveguide sensors on the polarization of guided modes, we have analyzed their absorption coefficients for both TE and TM modes by group index method [D.-K. Qing, X-. M. Chen, K. Itoh, M. Murabayashi: J. Lightwave Technol. 14, pp. 1907-1917, 1996]. As field distributions of TE and TM modes are different, the absorption coefficient for TE and TM modes are different. For open clad type evanescent wave sensors, whose mode is more favorable depends on whether the refractive index of the measurand is lower or higher than that of the substrate; for buffered clad type evanescent wave sensors, This depends on the role of the buffer layer; for sensing layer type evanescent wave sensors, TE mode has larger sensitivity than TM mode; for guided wave sensors, both TE and TM mode are suitable for highly sensitive sensors.
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