Articles de revista
http://hdl.handle.net/2117/3271
20180324T22:05:54Z

Cavity solitons in a microring dimer with gain and loss
http://hdl.handle.net/2117/115529
Cavity solitons in a microring dimer with gain and loss
Milián, Carles; Kartashov, Yaroslav V.; Skryabin, Dmitry V.; Torner Sabata, Lluís
We address a pair of vertically coupled microring resonators with gain and loss pumped by a singlefrequency field. Coupling between microrings results in a twofold splitting of the single microring resonance that increases when gain and losses decrease, giving rise to two cavity soliton (CS) families. We show that the existence regions of CSs are tunable and that both CS families can be stable in the presence of an imbalance between gain and losses in the two microrings. These findings enable experimental realization of frequency combs in configurations with active microrings and contribute toward the realization of compact multisoliton comb sources.
© 2018 Optical Society of America]. Users may use, reuse, and build upon the article, or use the article for text or data mining, so long as such uses are for noncommercial purposes and appropriate attribution is maintained. All other rights are reserved.
20180321T17:02:39Z
Milián, Carles
Kartashov, Yaroslav V.
Skryabin, Dmitry V.
Torner Sabata, Lluís
We address a pair of vertically coupled microring resonators with gain and loss pumped by a singlefrequency field. Coupling between microrings results in a twofold splitting of the single microring resonance that increases when gain and losses decrease, giving rise to two cavity soliton (CS) families. We show that the existence regions of CSs are tunable and that both CS families can be stable in the presence of an imbalance between gain and losses in the two microrings. These findings enable experimental realization of frequency combs in configurations with active microrings and contribute toward the realization of compact multisoliton comb sources.

Lieb polariton topological insulators
http://hdl.handle.net/2117/114509
Lieb polariton topological insulators
Li, Chunyan; Ye, Fangwei; Chen, Xianfeng; Kartashov, Yaroslav V.; Ferrando, Albert; Torner Sabata, Lluís; Skryabin, Dmitry V.
We predict that the interplay between the spinorbit coupling, stemming from the transverse electric–transverse magnetic energy splitting, and the Zeeman effect in semiconductor microcavities supporting excitonpolariton quasiparticles, results in the appearance of unidirectional linear topological edge states when the top microcavity mirror is patterned to form a truncated dislocated Lieb lattice of cylindrical pillars. Periodic nonlinear edge states are found to emerge from the linear ones. They are strongly localized across the interface and they are remarkably robust in comparison to their counterparts in honeycomb lattices. Such robustness makes possible the existence of nested unidirectional dark solitons that move steadily along the lattice edge.
20180226T15:31:17Z
Li, Chunyan
Ye, Fangwei
Chen, Xianfeng
Kartashov, Yaroslav V.
Ferrando, Albert
Torner Sabata, Lluís
Skryabin, Dmitry V.
We predict that the interplay between the spinorbit coupling, stemming from the transverse electric–transverse magnetic energy splitting, and the Zeeman effect in semiconductor microcavities supporting excitonpolariton quasiparticles, results in the appearance of unidirectional linear topological edge states when the top microcavity mirror is patterned to form a truncated dislocated Lieb lattice of cylindrical pillars. Periodic nonlinear edge states are found to emerge from the linear ones. They are strongly localized across the interface and they are remarkably robust in comparison to their counterparts in honeycomb lattices. Such robustness makes possible the existence of nested unidirectional dark solitons that move steadily along the lattice edge.

Bound states in the continuum in a twodimensional PT  symmetric system
http://hdl.handle.net/2117/114423
Bound states in the continuum in a twodimensional PT  symmetric system
Kartashov, Yaroslav V.; Milian, Carles; Konotop, Vladimir V; Torner Sabata, Lluís
We address a 2D paritytime (¿¿)symmetric structure built as a chain of waveguides, where all waveguides except for the central one are conservative, while the central one is divided into two halves with gain and losses. We show that such a system admits bound states in the continuum (BICs) whose properties vary drastically with the orientation of the line separating amplifying and absorbing domains, which sets the direction of internal energy flow. When the flow is perpendicular to the chain of the waveguides, narrow BICs emerge when the standard defect mode, which is initially located in the finite gap, collides with another mode in a standard symmetry breaking scenario, and its propagation constant enters the continuous spectrum upon increase of the strength of gain/losses. In contrast, when the energy flow is parallel to the chain of the waveguides, the symmetry gets broken even for a small strength of the gain/losses. In that case, the most rapidly growing mode emerges inside the continuous spectrum and realizes a weakly localized BIC. All BICs found here are the most rapidly growing modes; therefore, they can be excited from noisy inputs and, importantly, should dominate the beam dynamics in experiments.
© 2018 Optical Society of America. Users may use, reuse, and build upon the article, or use the article for text or data mining, so long as such uses are for noncommercial purposes and appropriate attribution is maintained. All other rights are reserved.
20180223T18:31:55Z
Kartashov, Yaroslav V.
Milian, Carles
Konotop, Vladimir V
Torner Sabata, Lluís
We address a 2D paritytime (¿¿)symmetric structure built as a chain of waveguides, where all waveguides except for the central one are conservative, while the central one is divided into two halves with gain and losses. We show that such a system admits bound states in the continuum (BICs) whose properties vary drastically with the orientation of the line separating amplifying and absorbing domains, which sets the direction of internal energy flow. When the flow is perpendicular to the chain of the waveguides, narrow BICs emerge when the standard defect mode, which is initially located in the finite gap, collides with another mode in a standard symmetry breaking scenario, and its propagation constant enters the continuous spectrum upon increase of the strength of gain/losses. In contrast, when the energy flow is parallel to the chain of the waveguides, the symmetry gets broken even for a small strength of the gain/losses. In that case, the most rapidly growing mode emerges inside the continuous spectrum and realizes a weakly localized BIC. All BICs found here are the most rapidly growing modes; therefore, they can be excited from noisy inputs and, importantly, should dominate the beam dynamics in experiments.

STED imaging performance estimation by means of Fourier transform analysis
http://hdl.handle.net/2117/113009
STED imaging performance estimation by means of Fourier transform analysis
Merino, David; Mallabiabarrena, Arrate; Andilla, Jordi; Artigas García, David; Zimmermann, Timo; Loza Alvarez, Pablo
Due to relatively high powers used in STED, biological samples may be affected by the illumination in the process of image acquisition. Similarly, the performance of the system may be limited by the sample itself. Optimization of the STED parameters taking into account the sample itself is therefore a complex task as there is no clear methodology that can determine the image improvement in an objective and quantitative manner. In this work, a method based on Fourier transform formalism is presented to analyze the performance of a STED system. The spatial frequency distribution of pairs of confocal and STED images are compared to obtain an objective parameter, the Azimuth Averaged Spectral Content Spread (AASCS), that is related to the performance of the system in which the sample is also considered. The method has been first tested on samples of beads, and then applied to cell samples labeled with multiple fluorescent dyes. The results show that a single parameter, the AASCS, can be used to determine the optimal settings for STED image acquisition in an objective way, only by using the information provided by the images from the sample themselves. The AASCS also helps minimize the depletion power, for better preservation of the samples.
20180119T15:34:23Z
Merino, David
Mallabiabarrena, Arrate
Andilla, Jordi
Artigas García, David
Zimmermann, Timo
Loza Alvarez, Pablo
Due to relatively high powers used in STED, biological samples may be affected by the illumination in the process of image acquisition. Similarly, the performance of the system may be limited by the sample itself. Optimization of the STED parameters taking into account the sample itself is therefore a complex task as there is no clear methodology that can determine the image improvement in an objective and quantitative manner. In this work, a method based on Fourier transform formalism is presented to analyze the performance of a STED system. The spatial frequency distribution of pairs of confocal and STED images are compared to obtain an objective parameter, the Azimuth Averaged Spectral Content Spread (AASCS), that is related to the performance of the system in which the sample is also considered. The method has been first tested on samples of beads, and then applied to cell samples labeled with multiple fluorescent dyes. The results show that a single parameter, the AASCS, can be used to determine the optimal settings for STED image acquisition in an objective way, only by using the information provided by the images from the sample themselves. The AASCS also helps minimize the depletion power, for better preservation of the samples.

Bound states in the continuum in spinorbitcoupled atomic systems
http://hdl.handle.net/2117/108096
Bound states in the continuum in spinorbitcoupled atomic systems
Kartashov, Yaroslav V.; Konotop, Vladimir V; Torner Sabata, Lluís
We show that the interplay between spinorbit coupling and Zeeman splitting in atomic systems can lead to the existence of bound states in the continuum (BICs) supported by trapping potentials. Such states have energies falling well within the continuum spectrum, but nevertheless they are localized and fully radiationless. We report the existence of BICs, in some cases in exact analytical form, in systems with tunable spinorbit coupling and show that the phenomenon is physically robust. We also found that BIC states may be excited in spinorbitcoupled BoseEinstein condensates, where under suitable conditions they may be metastable with remarkably long lifetimes.
20170928T15:13:59Z
Kartashov, Yaroslav V.
Konotop, Vladimir V
Torner Sabata, Lluís
We show that the interplay between spinorbit coupling and Zeeman splitting in atomic systems can lead to the existence of bound states in the continuum (BICs) supported by trapping potentials. Such states have energies falling well within the continuum spectrum, but nevertheless they are localized and fully radiationless. We report the existence of BICs, in some cases in exact analytical form, in systems with tunable spinorbit coupling and show that the phenomenon is physically robust. We also found that BIC states may be excited in spinorbitcoupled BoseEinstein condensates, where under suitable conditions they may be metastable with remarkably long lifetimes.

Gap solitons on a ring
http://hdl.handle.net/2117/107785
Gap solitons on a ring
Kartashov, Yaroslav V.; Malomed, B A; Vysloukh, Victor A.; Torner Sabata, Lluís
We introduce a new species of gap solitons (GSs) supported by an azimuthally modulated guiding ring in defocusing cubic media. The periodicity in the azimuthal direction strongly modifies properties and existence domains of GSs. In addition to the fundamental solitons, we report even and twisted bound states. The former type is found to be stable, while the twisted states are always unstable in defocusing media.
20170919T15:56:40Z
Kartashov, Yaroslav V.
Malomed, B A
Vysloukh, Victor A.
Torner Sabata, Lluís
We introduce a new species of gap solitons (GSs) supported by an azimuthally modulated guiding ring in defocusing cubic media. The periodicity in the azimuthal direction strongly modifies properties and existence domains of GSs. In addition to the fundamental solitons, we report even and twisted bound states. The former type is found to be stable, while the twisted states are always unstable in defocusing media.

Fourwave mixing of light beams with engineered orbital angular momentum in cold cesium atoms
http://hdl.handle.net/2117/107784
Fourwave mixing of light beams with engineered orbital angular momentum in cold cesium atoms
Barreiro, S; Tabosa, J W R; Pérez Torres, Juan; Deyanova, Y; Torner Sabata, Lluís
We report an experimental demonstration that shows that the spatial structure carried by engineered coherent superpositions of light beams with orbital angular momentum can be mapped into the nonlinear polarization induced in a cloud of cold cesium atoms. The structure of such polarization was revealed by nearly degenerate fourwavemixing processes.
20170919T15:55:34Z
Barreiro, S
Tabosa, J W R
Pérez Torres, Juan
Deyanova, Y
Torner Sabata, Lluís
We report an experimental demonstration that shows that the spatial structure carried by engineered coherent superpositions of light beams with orbital angular momentum can be mapped into the nonlinear polarization induced in a cloud of cold cesium atoms. The structure of such polarization was revealed by nearly degenerate fourwavemixing processes.

Orbital angular momentum of entangled counterpropagating photons
http://hdl.handle.net/2117/107783
Orbital angular momentum of entangled counterpropagating photons
Pérez Torres, Juan; Osorio Tamayo, Clara Inés; Torner Sabata, Lluís
We elucidate the paraxial orbital angular momentum of entangled photon pairs generated by spontaneous parametric downconversion in different noncollinear geometries in which the entangled photons counterpropagate. We find, in particular, the orbital angular momentum of entangled pairs generated in transverseemitting configurations, in which none of the known rules for selecting orbital angular momentum holds.
20170919T15:54:33Z
Pérez Torres, Juan
Osorio Tamayo, Clara Inés
Torner Sabata, Lluís
We elucidate the paraxial orbital angular momentum of entangled photon pairs generated by spontaneous parametric downconversion in different noncollinear geometries in which the entangled photons counterpropagate. We find, in particular, the orbital angular momentum of entangled pairs generated in transverseemitting configurations, in which none of the known rules for selecting orbital angular momentum holds.

Soliton eigenvalue control in optical lattices
http://hdl.handle.net/2117/107782
Soliton eigenvalue control in optical lattices
Kartashov, Yaroslav V.; Crasovan, L C; Zelenina, A; Vyslokh, V V; Sanpera, Anna; Lewenstein, Maciej; Torner Sabata, Lluís
We address the dynamics of higherorder solitons in optical lattices, and predict their selfsplitting into the set of their singlesoliton constituents. The splitting is induced by the potential introduced by the lattice, together with the imprinting of a phase tilt onto the initial multisoliton states. The phenomenon allows the controllable generation of several coherent solitons linked via their ZakharovShabat eigenvalues. Application of the scheme to the generation of correlated matter waves in BoseEinstein condensates is discussed.
20170919T15:53:36Z
Kartashov, Yaroslav V.
Crasovan, L C
Zelenina, A
Vyslokh, V V
Sanpera, Anna
Lewenstein, Maciej
Torner Sabata, Lluís
We address the dynamics of higherorder solitons in optical lattices, and predict their selfsplitting into the set of their singlesoliton constituents. The splitting is induced by the potential introduced by the lattice, together with the imprinting of a phase tilt onto the initial multisoliton states. The phenomenon allows the controllable generation of several coherent solitons linked via their ZakharovShabat eigenvalues. Application of the scheme to the generation of correlated matter waves in BoseEinstein condensates is discussed.

Second harmonic generation tuning curves in quasiphasematched potassium titanyl phosphate with narrow, highintensity beams
http://hdl.handle.net/2117/107781
Second harmonic generation tuning curves in quasiphasematched potassium titanyl phosphate with narrow, highintensity beams
Katz, M; Eger, D; Kim, H; Jankovic, L; Stegeman, G; Carrasco Rodríguez, Sílvia; Torner Sabata, Lluís
The second harmonic generation (SHG) tuning curves with temperature and angle of incidence were measured in periodically poled KTiOPO4 for narrow fundamental beams at intensities typical of quadratic soliton generation. Mutual selffocusing of the fundamental and harmonic, cascading, and walkoff for light incidence away from the poling axis drastically distorted the SHG response curves, in good agreement with theory.
20170919T15:34:15Z
Katz, M
Eger, D
Kim, H
Jankovic, L
Stegeman, G
Carrasco Rodríguez, Sílvia
Torner Sabata, Lluís
The second harmonic generation (SHG) tuning curves with temperature and angle of incidence were measured in periodically poled KTiOPO4 for narrow fundamental beams at intensities typical of quadratic soliton generation. Mutual selffocusing of the fundamental and harmonic, cascading, and walkoff for light incidence away from the poling axis drastically distorted the SHG response curves, in good agreement with theory.