Browsing by Subject "Multimode fibers"

Now showing 1 - 7 of 7

Open Access
Engineering particle trajectories in microfluidic flows using speckle light fields
(SPIE, 2014) Volpe, G.; Volpe, Giovanni; Gigan, S.
Optical tweezers have been widely used in physics, chemistry and biology to manipulate and trap microscopic and nanoscopic objects. Current optical trapping techniques rely on carefully engineered setups to manipulate nanoscopic and microscopic objects at the focus of a laser beam. Since the quality of the trapping is strongly dependent on the focus quality, these systems have to be very carefully aligned and optimized, thus limiting their practical applicability in complex environments. One major challenge for current optical manipulation techniques is the light scattering occurring in optically complex media, such as biological tissues, turbid liquids and rough surfaces, which give rise to apparently random light fields known as speckles. Here, we discuss an experimental implementation to perform optical manipulation based on speckles. In particular, we show how to take advantage of the statistical properties of speckle patterns in order to realize a setup based on a multimode optical fiber to perform basic optical manipulation tasks such as trapping, guiding and sorting. We anticipate that the simplicity of these "speckle optical tweezers" will greatly broaden the perspectives of optical manipulation for real-life applications. © 2014 SPIE.
Open Access
Geometric parametric instability of femtosecond pulses in graded-index multimode fiber
(Optical Society of America, 2017) Teğin, Ugur; Ortaç, Bülend
We numerically and experimentally study the spatio-temporal femtosecond pulse evolution in graded-index multimode fiber at normal dispersion regime. We report the first demonstration of geometric parametric instability sidebands generation with ultrashort pulses in the literature.
Open Access
Roadmap on wavefront shaping and deep imaging in complex media
(Institute of Physics, 2022-10) Gigan, Sylvain; Katz, Ori; De Aguiar, Hilton B.; Andresen, Esben Ravn; Aubry, Alexandre; Bertolotti, Jacopo; Bossy, Emmanuel; Bouchet, Dorian; Brake, Joshua; Brasselet, Sophie; Bromberg, Yaron; Cao, Hui; Chaigne, Thomas; Cheng, Zhongtao; Choi, Wonshik; Čižmár, Tomáš; Cui, Meng; Curtis, Vincent R.; Defienne, Hugo; Hofer, Matthias; Horisaki, Ryoichi; Horstmeyer, Roarke; Ji, Na; LaViolette, Aaron K.; Mertz, Jerome; Moser, Christophe; Mosk, Allard P; Pégard, Nicolas C; Piestun, Rafael; Popoff, Sebastien; Phillips, David B.; Psaltis, Demetri; Rahmani, Babak; Rigneault, Hervé; Rotter, Stefan; Tian, Lei; Vellekoop, Ivo M.; Waller, Laura; Wang, Lihong; Weber, Timothy; Xiao, Sheng; Xu, Chris; Yamilov, Alexey; Yang, Changhuei; Yılmaz, Hasan
The last decade has seen the development of a wide set of tools, such as wavefront shaping, computational or fundamental methods, that allow us to understand and control light propagation in a complex medium, such as biological tissues or multimode fibers. A vibrant and diverse community is now working in this field, which has revolutionized the prospect of diffraction-limited imaging at depth in tissues. This roadmap highlights several key aspects of this fast developing field, and some of the challenges and opportunities ahead. © 2022 The Author(s). Published by IOP Publishing Ltd.
Open Access
Spatial beam self-cleaning accompanied by self-similar propagation in few-mode graded-index fiber
(Optica Publishing Group (formerly OSA), 2023-07-20) Graini, Leila; Ortaç, Bülend
We numerically investigated a nonlinear Kerr beam self-cleaning (KBSC) dynamics accompanied by self-similar propagation regimes, which leads to single-mode parabolic pulse reshaping and simultaneously high beam quality based on KBSC, for special distributions of initially excited modes in graded-index multimode fiber (GRIN-MMF). We coupled a Gaussian pulse at 1060 nm, with 100 fs duration, into GRIN-MMF supporting 10 modes that fall into four discrete mode groups. As a result, by using initial powers below the KBSC threshold reported in the literature, the output spatial beam evolves from a speckled pattern into a bell-shaped beam; hence, the generated parabolic pulse is mainly carried by the fundamental mode, which is boosted by the KBSC process. We also provide promising indications for KBSC on different higher-order modes.
Open Access
Spatiotemporal dynamics of self-similar parabolic pulse evolution in multimode fibers
(Springer New York LLC, 2022-06-05) Graini, L.; Ortaç, Bülend
In this paper, we have investigated for the first time, the spatiotemporal dynamics of self-similar parabolic pulse evolution in multimode fibers. Two types of fiber are considered, graded-index and step-index MMFs. For the quality of the generated parabolic pulse, the mismatch parameter is used. A thorough study of the evolution of the pulse parameters as a function of the initial parameters has been carried out. As a result, the initial pulse evolved into a linearly chirped pulse with a parabolic intensity shape in both fibers, under the predominantly excitation of the fundamental mode. It has been shown, in particular, that the pulse can be compressed to a temporal duration of about 40 fs. Moreover, a spatiotemporal nonlinear dynamic, beam auto-selection, of one specific mode, is investigated through graded-index MMF, under the different initial modes excitation. The parabolic pulse formation process plays a critical role in this nonlinear dynamic. This approach provides another framework to understand the complex nonlinear dynamics in MMFs.
Open Access
Spatiotemporal evolutions of similariton pulses in multimode fibers with Raman amplification
(MDPI AG, 2021-09) Graini, Leila; Ortaç, Bülend
This paper aims to pave the way towards the demonstration of spatiotemporal similariton pulses’ evolution in passive multimode fibers with Raman amplification. We numerically present this issue in graded-index and step-index multimode fibers and provide a first look at the complex spatiotemporal dynamics of similariton pulses. The results showed that the similariton pulses could be generated in both multimode fibers. The temporal and spectral evolution of the pulses can be characterized as parabolic shapes with linear chirp and kW peak power. By compressing these, high-energy femtoseconds pulses can be obtained, starting initial picosecond pulses. A spatial beam profile could be preserved in both multimode fibers with the most energy coupled to the fundamental mode. Specifically, the similariton pulses’ generation with Raman amplification in a graded-index multimode fiber improves the spatial beam self-cleaning process under the different initial modes’ excitation. The observation of a new beam self-cleaning process is another attractor feature of propagation in graded-index multimode fibers.
Open Access
Spatiotemporal instability of femtosecond pulses in graded-index multimode fibers
(Institute of Electrical and Electronics Engineers Inc., 2017) Teǧin, U.; Ortaç, B.
We study the spatiotemporal instability generated by a universal unstable attractor in normal dispersion graded-index multimode fiber for femtosecond pulses for the first time. Experimentally observed spatiotemporal instability sidebands are 91-THz detuned from the pump wavelength of 800 nm. Detailed analysis carried out numerically by employing coupled-mode pulse propagation model. Numerically obtained results are well-aligned with experimental observations. Spatial evolution of the total field and spatiotemporal instability sidebands is calculated numerically, and for the input pulses of 200-fs duration, formation and evolution of spatiotemporal instability are shown in both spatial and temporal domains. Our results present the unique features of spatiotemporal instability, such as remarkable frequency shift with inherited beam shape of instability sidebands.