Article
Engineering, Electrical & Electronic
Partha Mondal, Shailendra K. Varshney
Summary: In this study, Kerr beam self-cleaning was experimentally demonstrated in a 90 m long standard graded-index multimode fiber. The nonlinear coupling among the guided modes reshapes the output speckle pattern into a bell shape or higher-order spatially clean beam profile at low input pump powers. The threshold power for the self-cleaning process effectively increases for higher-order modes.
OPTICAL FIBER TECHNOLOGY
(2021)
Article
Optics
Kewei Liu, Xiaosheng Xiao, Changxi Yang
Summary: The experimental observation of multimode Q-switching and spatiotemporal mode locking in a multimode fiber laser was reported. It was found that weak spatial filtering is essential for stable Q-switched pulses, while stronger spatial filtering is needed for spatiotemporal mode locking. Additionally, a reversible transition process between multimode Q-switching and spatiotemporal mode locking was achieved with specific spatial coupling and waveplates sets. The results contribute to understanding nonlinear dynamics in multimode fiber-based platforms and the development of high-pulse energy lasers.
PHOTONICS RESEARCH
(2021)
Article
Optics
Weitao He, Ruihuan Wu, Weiyi Hong, Aiping Luo
Summary: The study investigates the influences of high-order modes on energy flow, revealing that their random distribution evolves to a stationary state over time. The HOMs-attractor acts as a valve in the energy flow.
Article
Optics
Chenghao Liu, Mariusz Klimczak, Ryszard Buczynski, Xiahui Tang, Ming Tang, Haiyong Zhu, Luming Zhao
Summary: Experimental observation of mode-locked dissipative-soliton-resonance (DSR) pulses, including single-mode DSR pulses and multimode DSR pulses, in a Yb-doped fiber laser is reported. DSR pulses in single-mode state and multi-mode state can exist at the same time and can be output stably. The multi-mode DSR pulses exhibit same linearly broadening characteristics and bell-shaped spectral shape as single-mode DSR pulses. The results would be beneficial for expanding the knowledge of nonlinear dynamics to multimode fiber lasers and provide new insights for DSR pulse output with a fully multimode structure to get larger pulse energy.
OPTICS COMMUNICATIONS
(2023)
Article
Mathematics, Interdisciplinary Applications
Gang Wang, Haoye Qin, Jiayao Liu, Hao Ouyang, Xiaogang Wang, Bo Fu
Summary: This paper enriches the study of spatiotemporal mode-locking in multimode fiber lasers by combining it with dissipative soliton resonances, which are characterized by large pulse energy in single mode fiber lasers and generated by the reverse saturable absorption effect from real saturable absorbers. The locking of dissipative soliton resonances in different transverse modes is expected to raise the energy limit further, reaching about twice the maximum single-mode energy in the results. The properties of spatiotemporal dissipative soliton resonances, including evolution and transformation, are investigated by tuning parameters of the multimode fiber laser. These findings may open up new possibilities for high-power and spatiotemporally engineered coherent light fields in laser dynamics and nonlinear optics.
CHAOS SOLITONS & FRACTALS
(2023)
Article
Computer Science, Information Systems
Jianan Dai, Weitao He, Qichang Ma, Ai-Ping Luo, Weiyi Hong
Summary: The proposed scheme utilizes a PeG wave packet to manipulate inner-mode interactions in GRIN-MMF, enabling the cooperation of linear and nonlinear effects to control the nonlinear energy transfer from higher modes to the fundamental mode, resulting in triggering a Stokes soliton in the fundamental mode and negligible Raman red-shifts in higher modes. A nearly perfect Raman self-cleaning with 97.2% energy in the fundamental mode is observed after proper spectral filtering.
Article
Optics
Xuebin Zhang, Zhaokun Wang, Changyu Shen, Tiegang Guo
Summary: In this study, spatiotemporal self-mode-locked operation at 1.55 um was investigated. A compact partial multimode fiber laser system was used to achieve this operation at a low pump threshold. The results showed that stable multimode conventional solitons and complex multimode soliton molecule complexes could be obtained through the application of spatial filtering and saturable absorbers.
Article
Nanoscience & Nanotechnology
Michal Horak, Andrea Konecna, Tomas Sikola, Vlastimil Krapek
Summary: Electron energy loss spectroscopy (EELS) is commonly used to study localized surface plasmon modes of plasmonic antennas, but it has limited spectral resolution and difficulty in resolving closely spaced modes. In this study, we address this issue by analyzing the plasmon modes of a dimer plasmonic antenna composed of two gold discs. We propose metrics based on spectral and spatial sensitivity to resolve the modes and validate them through electrodynamic simulations. Experimental data demonstrate the capability of these metrics to resolve and identify the modes, except for the transverse bonding and antibonding modes. Overall, the spatio-spectral metrics enhance the information extracted from EELS for plasmonic antennas.
Article
Computer Science, Interdisciplinary Applications
Yaoju Zhang, Chaofei Qin, Qiong Yu, Xinyi Chen, Bo Zhang, Bingnan Pei
Summary: This paper investigates the issue of intermodal dispersion in multimode fibers and derives an analytical expression for calculating pulse widening. It also finds that the Goos-Hanchen shift has an important effect on intermodal dispersion, with positive shift reducing pulse widening and greatly increasing the maximum transmission distance of multimode fibers.
INTERNATIONAL JOURNAL OF MODERN PHYSICS C
(2023)
Article
Optics
Shuo Chang, Zhaokun Wang, D. N. Wang, Tianyu Zhu, Kuo Hua, Feng Gao
Summary: By using the SMF-GIMF-SMF device as the saturable absorber, we demonstrated wavelength-tunable and dual-wavelength operations in ytterbium-doped fiber lasers. The experimental results indicate that the device has a large modulation depth and small saturation fluence, suitable for tunable mode-locking generation.
OPTICS AND LASER TECHNOLOGY
(2021)
Article
Engineering, Electrical & Electronic
Yong Wei, Tianci Jiang, Chunlan Liu, Xingkai Wang, Chunbiao Liu, Chen Shi, Zhuo Ren, Ze Ran, Rui Wang, Yu Zhang, Zhihai Liu
Summary: In this article, a fiber intermode interference sensor with asymmetric structure is proposed for directional bending sensing and reduced temperature and strain crosstalk. The sensor utilizes a D-core multimode fiber with cladding and air on both sides of the fiber core to achieve bending direction recognition. The sensor has low sensitivity to temperature and strain, making it suitable for simultaneous water level and water flow direction detection in water flow applications.
IEEE SENSORS JOURNAL
(2023)
Article
Chemistry, Analytical
Andrei Fotiadi, Edik Rafailov, Dmitry Korobko, Patrice Megret, Alexander Bykov, Igor Meglinski
Summary: A multimode optical fiber can support the excitation and propagation of a single optical mode, and it can interact with other optical modes through stimulated Brillouin scattering (SBS). In this paper, we present a theoretical framework describing the SBS interaction between two selectively excited optical modes in an acoustically isotropic multimode optical fiber. By using a weakly guiding step-index fiber model, we derive an analytical expression for the spatial distribution of the sound field amplitude and investigate the characteristics of the SBS gain spectra, which describe the interaction between modes of different orders. This research provides insights into the sound propagation effects accompanying SBS in multimode optical fibers and demonstrates their specific contributions to the SBS gain spectrum.
Article
Optics
Jian Cui, Yuyang Gao, Shuailuo Huang, Jinyi Yu, Lei Shen, Lei Zhang, Changkun Yan, Liubo Yang, Ruichun Wang, Yongqi He, Zhangyuan Chen, Juhao Li
Summary: This paper proposes an all-fiber low-modal-crosstalk orthogonal combine reception scheme for degenerate linearly-polarized modes, and fabricates a pair of 4-LP-mode mode multiplexers/demultiplexers (MMUX/MDEMUX) with low crosstalk and insertion loss. The scheme is scalable and capable of supporting more modes, paving the way for practical implementation of intensity modulation and direct detection mode division multiplexing (MDM) transmission applications.
Article
Multidisciplinary Sciences
Chun-Wei Chen, Kabish Wisal, Yaniv Eliezer, A. Douglas Stone, Hui Cao
Summary: High-power fiber laser amplifiers have become widely used in industry, science, and defense. However, the power scaling of these amplifiers is limited by transverse mode instability. We propose a theoretical method using a highly multimode fiber amplifier to efficiently suppress thermal and optical instability. By exciting multiple modes, the threshold power for transverse mode instability increases linearly. Additionally, when the frequency bandwidth of the seed laser is narrower than the spectral correlation width of the multimode fiber, the amplified light maintains high spatial coherence and can be transformed to any target pattern or focused to a diffraction-limited spot.
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
(2023)
Article
Optics
Kinga Zolnacz, Waclaw Urbanczyk
Summary: We propose an effective method for selectively exciting different combinations of LP01 and LP11 polarization modes in a birefringent optical fiber using a Wollaston prism, rotatable polarizer, and achromatic half-wave plate. The method is minimally wavelength-dependent and can be used for high-power sources. The relative coupling efficiencies of different modes can be continuously tuned, with a suppression rate of unwanted modes exceeding 20 dB.
Article
Optics
Suchita, Balaji Srinivasan, Govind P. Agrawal, Deepa Venkitesh
Summary: Stimulated Brillouin scattering was studied in a few-mode graded-index fiber, revealing the impact of higher-order acoustic modes and pump beam modal composition on the multi-peak Brillouin gain spectrum. Numerical simulations matched well with experimental observations, showing significantly different linewidths of BGS peaks for different pump beam modal compositions.
OPTICS COMMUNICATIONS
(2021)
Article
Optics
S. A. Wadood, K. Liang, G. P. Agrawal, T. D. Visser, C. R. Stroud, A. N. Vamivakas
Summary: This study investigates the evolution of partially coherent beams in longitudinally modulated graded-index media, focusing on the cases of Gaussian Schell-model beams and parametric modulation with a half fiber self-imaging period. It is shown that in parametrically modulated parabolic graded-index media, the widths of intensity and coherence of Gaussian Schell-model beams undergo amplification. This process is analogous to quantum mechanical parametric amplification and generation of squeezed states, and may have applications in spatial and temporal imaging of partially coherent beams in fiber-based imaging systems.
Article
Optics
Surajit Bose, Oliver Melchert, Stephanie Willms, Ihar Babushkin, Uwe Morgner, Ayhan Demircan, Govind P. Agrawal
Summary: The frequency dependence of the nonlinear parameter plays a crucial role in the evolution of femtosecond solitons inside photonic crystal fibers. The conventional approach based on the self-steepening effect is not appropriate for fibers with two zero-dispersion wavelengths, and higher-order nonlinear terms are necessary for realistic modeling of nonlinear phenomena in PCFs. These terms not only affect the Raman-induced wavelength shift of a soliton but also impact its shedding of dispersive radiation.
Article
Optics
Junchi Zhang, W. R. Donaldson, Govind P. Agrawal
Summary: This study investigates the impact of the finite rise time of a spatiotemporal boundary inside a dispersive medium on the reflection and refraction of optical pulses. It is found that the frequency range over which reflection can occur decreases as the rise time increases. Additionally, total internal reflection can occur even for boundaries with long rise times, suggesting the possibility of realizing spatiotemporal waveguides through cross-phase modulation with pump pulses of relatively long rise and fall times.
Review
Optics
Aneesh Sobhanan, Aravind Anthur, Sean O'duill, Mark Pelusi, Shu Namiki, Liam Barry, Deepa Venkitesh, Govind P. Agrawal
Summary: This review article focuses on the fundamentals, broad applications, and importance of semiconductor optical amplifiers (SOAs) in optical communication, especially in optical channels with advanced modulation formats and optical signal processing.
ADVANCES IN OPTICS AND PHOTONICS
(2022)
Article
Optics
Junchi Zhang, William Donaldson, Govind P. Agrawal
Summary: This article investigates the temporal reflection of an optical pulse from a refractive-index barrier created by a short pump soliton in a nonlinear dispersive medium such as an optical fiber. One notable feature is that the soliton's speed continuously changes due to intrapulse Raman scattering, resulting in significant effects on the shape and spectrum of the reflected pulse. Under certain conditions, the reflected pulse can become considerably narrower, exhibiting a phenomenon similar to temporal focusing.
JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS
(2022)
Article
Optics
Xiaotong He, Luis Cortes-Herrera, Kwadwo Opong-Mensah, Yi Zhang, Meiting Song, Govind P. Agrawal, Jaime Cardenas
Summary: In this work, the authors demonstrate continuous on-chip optical frequency conversion using an electrically tunable lithium niobate ring resonator. Frequency shifts of up to 14.3 GHz are achieved by adjusting the voltage, allowing dynamic control of light behavior within the cavity.
Article
Optics
Govind P. Agrawal
Summary: Doped and optically pumped GRIN fibers are used to amplify optical beams, improving their spatial quality at the output end. We developed a simple model of the amplification process and solved the resulting equations analytically. The solution showed that the amplifying beam's width oscillates and becomes narrower due to the radial dependence of optical gain. Our simplified approach provides an analytic expression for the damping distance of beam-width oscillations, clarifying the role of various physical parameters.
Article
Optics
Govind P. Agrawal
Summary: This study uses coherence theory to investigate the effect of partial coherence on the focusing of an optical beam by a graded-index (GRIN) lens. The Gaussian-Schell model demonstrates that a partially coherent beam exhibits self-imaging and periodic evolution in a GRIN medium with a parabolic index profile. The spatial coherence of the beam affects a parameter governing the compression of the beam at the focal point. Our results indicate that the size of the focal spot depends on the fraction of the beam's diameter over which coherence persists. Focusing ceases to occur, and the beam may even expand at the focal point of a GRIN lens when this fraction is below 10%.
Article
Optics
Govind P. Agrawal
Summary: A semi-analytic model is proposed to describe the amplification process of Raman amplifiers using graded-index multimode fibers. When the pump beam is much stronger than the signal, it evolves in a self-similar manner and periodically recovers its initial width. The width of the amplified signal satisfies an equation similar to a damped harmonic oscillator, which is used to discuss spatial beam narrowing inside a Raman amplifier. Our simplified approach provides an analytic expression for the damping distance of width oscillations, highlighting the role of various physical parameters.
JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS
(2023)
Article
Optics
Junchi Zhang, William R. Donaldson, Govind P. Agrawal
Summary: We investigated the propagation of optical pulses in a temporal waveguide formed by two solitons in a dispersive nonlinear medium like an optical fiber. Due to intrapulse Raman scattering, the solitons, which are short enough, decelerate and their spectra continuously shift towards the red side. It was found that a probe pulse trapped between the two solitons evolves in a periodic fashion with a blueshift in its spectrum. We developed a coupled-mode theory to explain these changes, which are caused by mode coupling induced by the deceleration of the short solitons, resulting in a curved waveguide. A simplified two-mode model was used to introduce a single parameter that governs the modal coupling and find the condition for the probe pulse to blueshift its spectrum without changing its pulse shape.
Article
Optics
Junchi Zhang, William Donaldson, Govind P. Agrawal
Summary: This study demonstrates the formation of a Raman-induced temporal waveguide by launching short pump and probe pulses inside a photonic crystal fiber. The pump pulse creates a fundamental soliton with continuously changing speed due to the Raman-induced red shift of its spectrum. The spectrum of the probe pulse is blue-shifted to ensure that both pulses move at the same speed and trajectory over the entire length of the fiber. The output wavelengths of the pulses depend on the peak power of the input pump pulses and agree with the predictions based on dispersion data.
Article
Optics
Sergey A. Ponomarenko, Junchi Zhang, Govind P. Agrawal
Summary: We discover a significant temporal shift of the peak of an optical pulse when it is totally internally reflected from a sharp temporal boundary in a uniform and isotropic linear medium. The sign of this temporal shift depends on the group-velocity mismatch between the pulse and the temporal boundary, suggesting the possibility of a delay or advancement of the pulse upon reflection. Our analytical results, validated by numerical simulations, provide insights into the fundamental aspects of wave packet interaction with temporal boundaries in material media.
Article
Optics
Luis Cortes-Herrera, Xiaotong He, Jaime Cardenas, Govind P. Agrawal
Summary: This paper presents a comprehensive theoretical study of energy efficiency in adiabatic frequency conversion (AFC) in an all-pass resonator. The study analyzes the upper limit of energy efficiency using the Cauchy-Schwarz inequality and examines its dependence on input pulse shape.
Article
Optics
Luis Cortes-Herrera, Xiaotong He, Jaime Cardenas, Govind P. Agrawal
Summary: The article investigates the polarization evolution problem when using lithium niobate as the core of a microring resonator, analyzing the polarization coupling using quantum mechanics techniques. It specifically describes the evolution of the polarization state of injected light along the circular path in a lithium niobate ring resonator.
