Slow light enabled wavelength demultiplexing

Photonic crystal waveguides supporting band gap guided modes hold great potential to tailor the group velocity of propagating light. We propose and explore different wavelength demultiplexer design approaches that utilize slow light concept. By altering the dielectric filling factors of each waveguide segment, one can show that different frequencies can be separated and extracted at different locations along the cascaded waveguide. Furthermore, to eliminate the inherent reflection loss of such a design, a composite structure involving a tapered waveguide with a side-coupled resonator is also presented. Such a structure features not only a forward propagating wave but also a backward propagating wave acting as a feedback mechanism for the drop channels. We show that by careful design of the waveguide and the resonator, the destructive and instructive interference of these waves can effectively eliminate the reflection loss and increase the coupling efficiency, respectively. Numerical and experimental verification of the proposed structures show that the targeted frequencies can be coupled out with low cross-talks and moderate quality factors, while maintaining a compact size. © 2016 IEEE.Peer ReviewedPostprint (published version

Nonlinear self-collimated sound beams in sonic crystals

We report the propagation of high-intensity sound beams in a sonic crystal, under self-collimation or reduced-divergence conditions. The medium is a fluid with elastic quadratic nonlinearity, where the dominating nonlinear effect is harmonic generation. The conditions for the efficient generation of narrow, non-diverging beam of second harmonic are discussed. Numerical simulations are in agreement with the analytical predictions made, based on the linear dispersion characteristics in modulated media and the nonlinear interaction in a quadratic medium under phase matching conditions.Comment: Sent to PR

An Aerodynamic Analysis of a Mixed Flow Turbine

The aerodynamic performance of a high-work Mixed Flow Turbine (MFT) is computed and compared with experimental data. A three dimensional (3-D) viscous analysis is applied to the single stage MFT geometry with a relatively long upstream transition duct. Predicted vane surface static pressures and circumferentially averaged spanwise quantities at stator and rotor exits agree favorably with data. Compared to the results of axisymmetric flow analysis from design intent, the 3-D computation agrees much better especially in the endwall regions where throughflow prediction fails to assess the loss mechanism properly. Potential sources of performance loss such as tip leakage and secondary flows are also properly captured by the analysis

Amplification through losses in nonlinear fiber optics

We present the most recent results about a novel modulation instability of a continuous light wave in a normal dispersion nonlinear optical fiber, induced by spectrally asymmetric losses for signal and idler waves. The presence of such spectrally asymmetric losses profile causes energy transfer from the pump to both signal and idler. A variety of applications concerning both amplification of signals and generation of pulses is discussed

Nondiffractive sonic crystals

We predict theoretically the nondiffractive propagation of sonic waves in periodic acoustic media (sonic crystals), by expansion into a set of plane waves (Bloch mode expansion), and by finite difference time domain calculations of finite beams. We also give analytical evaluations of the parameters for nondiffractive propagation, as well as the minimum size of the nondiffractively propagating acoustic beams.Comment: 7 figures, submitted to J. Acoust. Soc. A

High repetition rate multi-similariton laser

We present the numerical demonstration of an harmonically mode-locked multi-similariton laser supporting a low jitter, stable train of self similar high repetition rate pulses exploiting, as mode-locking mechanism, the principle of dissipative Faraday instability (DFI) induced by zigzag modulation of spectral losses [1, 2]. At variance with the theoretical and experimental studies on the DFI [1, 2], where the amplification was distributed along the fiber, we propose here a lumped amplification scheme suitable for a more flexible design of mode-locked lasers pumped by rare-earth gain medium (Erbium, Ytterbium). We have considered an unidirectional all normal dispersion ring resonator with two lumped amplifying sections separated by two passive nonlinear dispersive fibers. Just before each amplifying section is located a spectral filter. The two filters differ by having the transmittance profile respectively blue- and red-detuned relatively to the amplifiers central frequency. The detuned spectral filters provide the necessary periodic zigzag modulation of the spectral losses needed to trigger the DFI. The CW operation of the laser is unstable and the growth of spectral sidebands results in a temporal modulation of the field temporal profile leading to the formation of a pulse train with repetition rate corresponding to the instability frequency around 0.1 THz and pulse duration of about 3 ps. Propagation in the fibers has been modeled using the generalized nonlinear Schrödinger equation and the lumped amplification by a saturable gain term with spectral bandwidth typical of rare-earth amplifiers

Sharp acoustic vortex focusing by Fresnel-spiral zone plates

[EN] We report the optimal focusing of acoustic vortex beams by using flat lenses based on a Fresnelspiral diffraction grating. The flat lenses are designed by spiral-shaped Fresnel zone plates composed of one or several arms. The constructive and destructive interferences of the diffracted waves by the spiral grating result in sharp acoustic vortex beams, following the focal laws obtained in analogy with the Fresnel zone plate lenses. In addition, we show that the number of arms determines the topological charge of the vortex, allowing the precise manipulation of the acoustic wave field by flat lenses. The experimental results in the ultrasonic regime show excellent agreement with the theory and full-wave numerical simulations. A comparison with beam focusing by Archimedean spirals also showing vortex focusing is given. The results of this work may have potential applications for particle trapping, ultrasound therapy, imaging, or underwater acoustic transmitters.This work was supported by the Spanish Ministry of Economy and Innovation (MINECO) and European Union FEDER through Project Nos. FIS2015-65998-C2-1 and FIS2015-65998-C2-2. N.J. acknowledges financial support from Generalitat Valenciana through Grant No. APOSTD-2017-042.Jimenez, N.; Romero García, V.; García-Raffi, LM.; Camarena Femenia, F.; Staliunas, K. (2018). Sharp acoustic vortex focusing by Fresnel-spiral zone plates. Applied Physics Letters. 112(20):204101-1-204101-5. https://doi.org/10.1063/1.5029424S204101-1204101-511220J. Nye and M. Berry ,Proceedings of the Royal Society of London A: Mathematical, Physical and Engineering Sciences(The Royal Society, 1974), Vol.336, pp. 165–190.Grier, D. G. (2003). A revolution in optical manipulation. Nature, 424(6950), 810-816. doi:10.1038/nature01935Volke-Sepúlveda, K., Santillán, A. O., & Boullosa, R. R. (2008). Transfer of Angular Momentum to Matter from Acoustical Vortices in Free Space. Physical Review Letters, 100(2). doi:10.1103/physrevlett.100.024302Anhäuser, A., Wunenburger, R., & Brasselet, E. (2012). Acoustic Rotational Manipulation Using Orbital Angular Momentum Transfer. Physical Review Letters, 109(3). doi:10.1103/physrevlett.109.034301Demore, C. E. M., Yang, Z., Volovick, A., Cochran, S., MacDonald, M. P., & Spalding, G. C. (2012). Mechanical Evidence of the Orbital Angular Momentum to Energy Ratio of Vortex Beams. Physical Review Letters, 108(19). doi:10.1103/physrevlett.108.194301Hong, Z., Zhang, J., & Drinkwater, B. W. (2015). Observation of Orbital Angular Momentum Transfer from Bessel-Shaped Acoustic Vortices to Diphasic Liquid-Microparticle Mixtures. Physical Review Letters, 114(21). doi:10.1103/physrevlett.114.214301Wu, J. (1991). Acoustical tweezers. The Journal of the Acoustical Society of America, 89(5), 2140-2143. doi:10.1121/1.400907Marzo, A., Ghobrial, A., Cox, L., Caleap, M., Croxford, A., & Drinkwater, B. W. (2017). Realization of compact tractor beams using acoustic delay-lines. Applied Physics Letters, 110(1), 014102. doi:10.1063/1.4972407Marzo, A., Caleap, M., & Drinkwater, B. W. (2018). Acoustic Virtual Vortices with Tunable Orbital Angular Momentum for Trapping of Mie Particles. Physical Review Letters, 120(4). doi:10.1103/physrevlett.120.044301Shi, C., Dubois, M., Wang, Y., & Zhang, X. (2017). High-speed acoustic communication by multiplexing orbital angular momentum. Proceedings of the National Academy of Sciences, 114(28), 7250-7253. doi:10.1073/pnas.1704450114Thomas, J.-L., & Marchiano, R. (2003). Pseudo Angular Momentum and Topological Charge Conservation for Nonlinear Acoustical Vortices. Physical Review Letters, 91(24). doi:10.1103/physrevlett.91.244302Marchiano, R., & Thomas, J.-L. (2005). Synthesis and analysis of linear and nonlinear acoustical vortices. Physical Review E, 71(6). doi:10.1103/physreve.71.066616Ealo, J. L., Prieto, J. C., & Seco, F. (2011). Airborne ultrasonic vortex generation using flexible ferroelectrets. IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, 58(8), 1651-1657. doi:10.1109/tuffc.2011.1992Gspan, S., Meyer, A., Bernet, S., & Ritsch-Marte, M. (2004). Optoacoustic generation of a helicoidal ultrasonic beam. The Journal of the Acoustical Society of America, 115(3), 1142-1146. doi:10.1121/1.1643367Hefner, B. T., & Marston, P. L. (1999). An acoustical helicoidal wave transducer with applications for the alignment of ultrasonic and underwater systems. The Journal of the Acoustical Society of America, 106(6), 3313-3316. doi:10.1121/1.428184Jiang, X., Li, Y., Liang, B., Cheng, J., & Zhang, L. (2016). Convert Acoustic Resonances to Orbital Angular Momentum. Physical Review Letters, 117(3). doi:10.1103/physrevlett.117.034301Ye, L., Qiu, C., Lu, J., Tang, K., Jia, H., Ke, M., … Liu, Z. (2016). Making sound vortices by metasurfaces. AIP Advances, 6(8), 085007. doi:10.1063/1.4961062Naify, C. J., Rohde, C. A., Martin, T. P., Nicholas, M., Guild, M. D., & Orris, G. J. (2016). Generation of topologically diverse acoustic vortex beams using a compact metamaterial aperture. Applied Physics Letters, 108(22), 223503. doi:10.1063/1.4953075Esfahlani, H., Lissek, H., & Mosig, J. R. (2017). Generation of acoustic helical wavefronts using metasurfaces. Physical Review B, 95(2). doi:10.1103/physrevb.95.024312Jiménez, N., Picó, R., Sánchez-Morcillo, V., Romero-García, V., García-Raffi, L. M., & Staliunas, K. (2016). Formation of high-order acoustic Bessel beams by spiral diffraction gratings. Physical Review E, 94(5). doi:10.1103/physreve.94.053004Wang, T., Ke, M., Li, W., Yang, Q., Qiu, C., & Liu, Z. (2016). Particle manipulation with acoustic vortex beam induced by a brass plate with spiral shape structure. Applied Physics Letters, 109(12), 123506. doi:10.1063/1.4963185Muelas-Hurtado, R. D., Ealo, J. L., Pazos-Ospina, J. F., & Volke-Sepúlveda, K. (2018). Generation of multiple vortex beam by means of active diffraction gratings. Applied Physics Letters, 112(8), 084101. doi:10.1063/1.5016864Jiang, X., Zhao, J., Liu, S., Liang, B., Zou, X., Yang, J., … Cheng, J. (2016). Broadband and stable acoustic vortex emitter with multi-arm coiling slits. Applied Physics Letters, 108(20), 203501. doi:10.1063/1.4949337Jiménez, N., Romero-García, V., Picó, R., Cebrecos, A., Sánchez-Morcillo, V. J., Garcia-Raffi, L. M., … Staliunas, K. (2014). Acoustic Bessel-like beam formation by an axisymmetric grating. EPL (Europhysics Letters), 106(2), 24005. doi:10.1209/0295-5075/106/24005Sanchis, L., Yánez, A., Galindo, P. L., Pizarro, J., & Pastor, J. M. (2010). Three-dimensional acoustic lenses with axial symmetry. Applied Physics Letters, 97(5), 054103. doi:10.1063/1.3474616Farnow, S. A., & Auld, B. A. (1974). Acoustic Fresnel zone plate transducers. Applied Physics Letters, 25(12), 681-682. doi:10.1063/1.1655359Molerón, M., Serra-Garcia, M., & Daraio, C. (2014). Acoustic Fresnel lenses with extraordinary transmission. Applied Physics Letters, 105(11), 114109. doi:10.1063/1.4896276Jiménez, N., Romero-García, V., Picó, R., Garcia-Raffi, L. M., & Staliunas, K. (2015). Nonlinear focusing of ultrasonic waves by an axisymmetric diffraction grating embedded in water. Applied Physics Letters, 107(20), 204103. doi:10.1063/1.4935917Cox, B. T., Kara, S., Arridge, S. R., & Beard, P. C. (2007). k-space propagation models for acoustically heterogeneous media: Application to biomedical photoacoustics. The Journal of the Acoustical Society of America, 121(6), 3453. doi:10.1121/1.271740

Nondifractive Propagation of Light in Photonic Crystals

We show that diffraction of electromagnetic radiation (in particular of a visible light) can disappear in propagation through materials with periodically in space modulated refraction index, i.e. photonic crystals. In this way the light beams of arbitrary width can propagate without diffractive broadening and, equivalently, arbitrary light patterns can propagate without diffractive smearing

Slowdown of photoexcited spin dynamics in the non-collinear spin-ordered phases in skyrmion host GaV4S8

Formation of magnetic order alters the character of spin excitations, which then affects transport properties. We investigate the photoexcited ultrafast spin dynamics in different magnetic phases in Néel-type skyrmion host GaV(4)S(8) with time-resolved magneto-optical Kerr effect experiments. The coherent spin precession, whose amplitude is enhanced in the skyrmion-lattice phase, shows a signature of phase coexistence across the magnetic phase transitions. The incoherent spin relaxation dynamics slows down by a factor of two in the skyrmion-lattice/cycloid phases, indicating significant decrease in thermal conductivity triggered by a small change of magnetic field. The slow heat diffusion in the skyrmion-lattice/cycloid phases is attributed to the stronger magnon scattering off the domain walls formed in abundance in the skyrmion-lattice/cycloid phase. These results highlight the impact of spatial spin structure on the ultrafast heat transport in spin systems, providing a useful insight for the step toward ultrafast photocontrol of the magnets with novel spin orders

Acoustic Bessel-like beam formation by an axisymmetric grating

We report Bessel-like beam formation of acoustic waves by means of an axisymmetric grating of rigid tori. The results show that the generated beam pattern is similar to that of Bessel beams, characterized by elongated non-diffracting focal spots. A multiple foci structure is observed, due to the finite size of the lens. The dependence of the focal distance on the frequency is also discussed, on the basis of an extended grating theory. Experimental validation of acoustic Bessel-like beam formation is also reported for sound waves. The results can be generalized to wave beams of different nature, as optical or matter waves.The work was supported by the Spanish Ministry of Science and Innovation and the European Union FEDER through projects FIS2011-29731-C02-01 and -02, also MAT2009-09438, MTM2012-36740-C02-02 and UPV-PAID 2012/253. VR-G acknowledges financial support from the "Pays de la Loire" through the post-doctoral programme.Jimenez, N.; Romero García, V.; Picó Vila, R.; Cebrecos Ruiz, A.; Sánchez Morcillo, VJ.; García-Raffi, LM.; Sánchez Pérez, JV.... (2014). Acoustic Bessel-like beam formation by an axisymmetric grating. EPL. 106(2):240051-240055. doi:10.1209/0295-5075/106/24005240051240055106