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- 2019
- higher- order modes
- few-mode regime
- on-board cable systems
- mode coupling
- laser-based multi-Gigabit data transmission
- large core multimode optical fiber
- industrial networks
- differential mode delay
- Optoelectronic Information Science and Engineering
- Povolzhskiy State University of Telecommunications and Informatics (PSUTI)
- Malaviya National Institute of Technology Jaipur
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Method for Quantum Key Establishment through a Multimode Fiber
摘要： Secure communication became extremely important in the Information Age. Quantum communication protocols have been developed to provide absolutely secure transmission of information. Historically, quantum key distribution (QKD) uses the two-dimensional polarization basis to encode information and the key element of long-distance communication is single-mode optical fiber. However, it intrinsically limits the information content to 1 bit per photon. Nowadays, significant effort is devoted to increase the data carrying capacity of a single quantum secure optical line. Large-core multimode fibers support a multitude of transverse optical modes and can potentially transfer information at much higher density. Here we propose a fundamentally new concept for secure high-dimensional remote key establishment. Our method uses a quantum-secure wavefront shaping procedure to transmit information through a light-scrambling large-core multimode fiber. It naturally works with a high-dimensional alphabet. The main idea is illustrated in Fig. 1. To send a symbol, Alice prepares a wavefront that leads to a focus at a particular point on the fiber output facet. Throughout the fiber, the photon will be present as a disordered superposition of all fiber modes. If an eavesdropper (Eve) intercepts, the photon collapses at a nearly random position on Eve’s detector, which varies even between identical copies of the same symbol. Only at Bob’s end, the photon will be spatially localized and Bob can unambiguously identify the symbol. In contrast to popular QKD protocols, our method allows to detect eavesdropper attacks without using two randomly switched mutually unbiased bases. Moreover, information is sent in a deterministic way, allowing direct decoding at the receiver end without classical postprocessing. Since it is optical fiber based, our method allows to naturally extend secure communication to larger distances. We argue that our method is quantum secure if symbols are encoded into single photons. Moreover, we show that our method does not require the light to be in an entangled (or otherwise special) quantum state; a weak coherent state (even when several photons per symbol are used) still guarantees the security of the protocol. We experimentally characterise the setup for this new type of key exchange method by encoding information into a few-photon light pulse decomposed over guided modes of an easily available step-index multimode fiber.
关键词： multimode fiber,wavefront shaping,high-dimensional alphabet,secure communication,Quantum key distribution
更新于2025-09-11 14:15:04
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[IEEE 2018 IEEE CPMT Symposium Japan (ICSJ) - Kyoto (2018.11.19-2018.11.21)] 2018 IEEE CPMT Symposium Japan (ICSJ) - Fabrication and Evaluation for Polymer Waveguide Coupler Devices Using the Imprint Method
摘要： For further increase of data rate in multimode fiber (MMF) links widely deployed in datacenters, wavelength division multiplexing (WDM) transmission technology is expected to be introduced. In this paper, we propose a Y-branched polymer waveguide with graded-index core for optical coupler in the MMF WDM links. The low loss structure of the Y-branched polymer waveguide is designed applying BPM simulation, and designed waveguide structures are actually fabricated using an imprint method to confirm their applicability to a low-loss optical coupler in MMF WDM links.
关键词： Y branched polymer optical waveguide,optical coupler,Imprint Method,multimode fiber link,Beam propagation method
更新于2025-09-11 14:15:04
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Suppressing Dark Counts of Multimode-Fiber-Coupled Superconducting Nanowire Single-Photon Detector
摘要： Large active-area superconducting nanowire single-photon detectors (SNSPDs) coupled with multimode fibers (MMFs) can provide high light-gathering capacity, which is essential for free-space detection applications in photon-starved regimes. However, MMF-coupled SNSPDs often suffer from large system dark count rates (DCRsys) over kHz due to blackbody radiation of the MMF at room temperature. Such large DCRsys would significantly degrade signal-to-noise ratio (SNR) of the receiving system. This paper reports an MMF-coupled large-active-area SNSPD system with low DCRsys by using a homemade cryogenic MMF filter bench. The filter bench, which consists of lenses and optical filters, can provide a high transmittance of about 80% at the central wavelength of the passband (1550 ± 12.5 nm) and a wide blocking range from 500 nm to over 6000 nm at 40 K. With using the filter bench, the DCRsys of an MMF-coupled 9-pixel SNSPD array with an active area of 50 μm in diameter is greatly suppressed by 23 dB with 1 dB loss of system detection efficiency (SDE). The detector demonstrates an SDE of 51% at a DCRsys of 100 Hz for 1550 nm photons. Thus, SNR of the detector is enhanced by about 160 times and the noise equivalent power is improved to 3×10?19 W/Hz1/2.
关键词： cryogenic MMF filter bench,multimode fibers (MMFs),Superconducting nanowire single-photon detectors (SNSPDs),dark count rates (DCRsys),signal-to-noise ratio (SNR)
更新于2025-09-11 14:15:04
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All-Fiber Saturable Absorbers for Ultrafast Fiber Lasers
摘要： The past decade has witnessed tremendous achievements of ultrafast ?ber laser technologies due to rapid developments of saturable absorbers (SAs) based on, in particular, nanomaterials such as 0D quantum dot, 1D carbon nanotubes, 2D layered materials, and 3D nanostructures. However, most of those nanomaterials-based SAs are inevitably absence of the high damage threshold and all-?ber integration, therefore challenging their applications on highly integrated and high-energy pulse generations. Recently, the real all-?ber SAs based on the nonlinear multimodal interference (NLMMI) technique using multimode ?bers are demonstrated to overcome the above limitations. In this review, a detailed summary of the recent advances in NLMMI-based all-?ber SAs is provided, including the fundamental theory, implementation scenarios, and ultrafast ?ber lasers of the all-?ber SAs, covering wide wavelength range of 1, 1.55, and 2 μm. In addition to the state-of-the-art overview, optical rogue waves in the all-?ber SA-based ultrafast ?ber laser are extensively analyzed, which reveals the laser physics behind the dynamics from low-energy to high-energy pulses and directs the design of high-energy ultrafast ?ber lasers. The conclusions and perspectives of the all-?ber SAs are also discussed at the end.
关键词： nonlinear multimode interference effect,high-energy pulse generation,saturable absorber,Ultrafast ?ber laser,optical rogue wave
更新于2025-09-11 14:15:04
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Random Mode Coupling Assists Kerr Beam Self-Cleaning in a Graded-Index Multimode Optical Fiber
摘要： Spatiotemporal light beam dynamics in multimode ?bers (MMF) recently has attracted renewed interest in both fundamental physics and various ?elds of practical application [1,2]. Recent experiments [2,3] have shown that, owing to the Kerr effect, a process of beam self-cleaning can be observed in graded-index (GRIN) MMFs. As a result, one observes a robust nonlinear beam, which has a size that is close to the fundamental mode at the ?ber output, in contrast to a speckled output beam, which is obtained in the case of the linear regime. In this paper, we numerically investigate the process of beam self-cleaning in GRIN MMFs. Unlike previous approaches [3], where the nonlinear propagation of a spatial beam along the multimode ?ber was described by the generalized 3D nonlinear Schrdinger equation, we use the coupled-mode model, which has the following form: 2i dAp,m dζ = D(n + 1)2Ap,m + p ∑ m+m1=m2+m3 ∑ p+p1=p2+p3 f m,m1,m2,m3 p,p1,p2,p3 Ap1,m1Ap2,m2Ap3,m3 + ∑ m1,p1 Cm,m1 p,p1 Ap1,m1 . These equations separately describe the evolution of the amplitude of each mode Ap,m. The coupled mode approach signi?cantly reduces the computation time, due to the use of a large integration step. To account for the various imperfections of the multimode ?ber, caused by fabrication, bending or tilting, we added a random linear coupling term to the equation. Fig. 1 Dynamics of energy distribution by modes and the output ?eld for the model without random linear coupling (a) and with random linear coupling between degenerate modes (b). In this contribution, we describe various models of random linear coupling between spatial modes, including coupling between all modes, or only between degenerate ones, and investigate the effects of random mode coupling on the beam self-cleaning process. Fig. 1a shows the spatial dynamics of energy distribution among the modes, corresponding to a model without any random linear coupling. In this case, in spite of being in a strong nonlinear regime, the power of the fundamental mode oscillates along the ?ber, and we still obtain a speckled beam at the ?ber output. On the other hand, if we consider a model with random linear coupling between spatial modes with equal mode numbers, one readily observes the appearance of a self-cleaning effect, and the fundamental mode power swiftly stabilizes upon the propagation (see Fig. 1b). The output beam in this case has a size that is close to that of the fundamental mode. The results of numerical investigations are in complete agreement with our experimental data.
关键词： Kerr effect,graded-index multimode optical fiber,beam self-cleaning,random mode coupling
更新于2025-09-11 14:15:04
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Disorder-Induced Acceleration of Condensation in Multimode Fibers
摘要： Recent studies on wave turbulence revealed that a purely classical system of random waves can exhibit a process of condensation, whose thermodynamic properties are analogous to those of Bose-Einstein condensation [1-3]. Classical wave condensation finds its origin in the natural thermalization toward the Rayleigh-Jeans equilibrium distribution, whose divergence is responsible for the macroscopic occupation of the fundamental mode of the system. The experimental study of condensation in a conservative (cavity-less) configuration constitutes a major challenge, because of the prohibitive large propagation lengths required to achieve thermalization. In contrast with this commonly accepted opinion, a remarkable phenomenon of spatial beam self-cleaning has been recently discovered in graded-index multimode optical fibers (MMFs) [4-7]. This phenomenon is due to a purely conservative Kerr nonlinearity [7] and its underlying mechanism still remains debated. Light propagation in MMFs is known to be affected by a structural disorder of the material due to inherent imperfections and external perturbations. On the basis of the wave turbulence theory, we formulate a nonequilibrium kinetic description of the random waves that accounts for the impact of disorder. The theory reveals that a structural disorder is responsible for a dramatic acceleration of the process of condensation by several orders of magnitudes. This counterintuitive mechanism of condensation acceleration provides a natural explanation for the effect of spatial beam self-cleaning: As a consequence of the fast condensation process, the beam power rapidly flows toward the fundamental mode of the MMF, which becomes macroscopically populated to the detriment of the other modes that exhibit energy equipartition, as predicted by the Rayleigh-Jeans distribution [1]. The simulations of the nonlinear Schrodinger equation (NLSE) are in quantitative agreement with those of the derived kinetic equation, and thus confirm the validity of the theory and the effect of acceleration of condensation mediated by disorder (see Fig. 1). Furthermore, the derived kinetic equation also explains why spatial beam self-cleaning has not been observed in step-index MMFs. We performed experiments in a MMF to evidence the transition to light condensation by varying the coherence of the input beam (as described in Fig. 1c). When a large number of modes are excited, the output intensity distribution tends to relax toward the thermal Rayleigh-Jeans distribution, i.e., the 'temperature' is above the critical value for condensation (E > Ecrit in Fig. 1c) and spatial beam self-cleaning is not observed. By reducing the excitation of modes (E < Ecrit in Fig. 1c), the power gradually condenses into the fundamental mode of the MMF, leading to a cleaned beam with a measured condensate fraction as large as ～60%.
关键词： multimode fibers,spatial beam self-cleaning,condensation,wave turbulence,disorder
更新于2025-09-11 14:15:04
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Wavelength Independent Image Classification through a Multimode Fiber using Deep Neural Networks
摘要： Deep Neural Networks (DNNs) have been increasingly implemented in different research fields or industrial applications. Large amounts of data are processed daily in order to extract useful information using machine learning techniques. Many research groups have shown impressive results on improving resolution in microscopy and quantitative phase retrieval by training DNNs on real datasets. Recently, recovery and reconstruction of images after they have propagated through multimode optical fibers (MMFs) have also been achieved using DNNs. When images propagate through MMFs they suffer severe scrambling because the information gets distributed among the different spatial modes that the fiber supports. Furthermore, since the fiber modes propagate with different velocities, the local information of the input decorrelates after a few millimeters along the MMF, thus resulting in the formation of a speckle pattern at the output. Recovery of information from such speckle patterns is of practical interest for integrating the MMFs for endoscopic applications in medicine or for signal recovery in telecommunications.
关键词： Wavelength Independence,Image Classification,Speckle Patterns,Multimode Optical Fibers,Deep Neural Networks
更新于2025-09-11 14:15:04
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Kerr Beam Self-Cleaning in the Telecom Band
摘要： Multimode graded index (GRIN) fibers received a renewed interest in recent years, in particular for the development of new laser sources [1]. In many cases, the use of GRIN fibers is limited by multimodal propagation, leading to a spatially modulated intensity distribution (speckles) at the fiber output. Recent studies have found that quasi-single mode propagation can be recovered in GRIN fibers by the so-called Kerr self-cleaning effect [2]. It consists in the spontaneous recovery of the spatial beam quality, without any frequency shift [2] (as opposed to, e.g., Raman beam self-cleaning [3]). This nonlinear process was only observed so far at laser wavelengths around 1 μm, for peak power levels above a certain threshold value. In this communication, we show that Kerr beam self-cleaning also occurs in a GRIN fiber pumped with chirped pulses in the telecom band (1562 nm). At these wavelengths, the power threshold of the self-cleaning process is decreased by one order of magnitude with respect to pumping at 1 μm.
关键词： GRIN fiber,multimode fibers,nonlinear optics,Kerr beam self-cleaning,telecom band
更新于2025-09-11 14:15:04
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - High-Power Short-Wavelength Infrared Supercontinuum Generation in a Multimode Fluoride Fiber
摘要： Supercontinuum light (SC) is a broadband source with unique properties generated via cascaded nonlinear processes when intense light propagates in a nonlinear material. Depending on the nonlinear material and pump source used, the spectrum of a SC source can span from the visible to the mid-infrared with up to several Watt-average power. Recently, the generation of broadband SC sources operating in the mid-infrared (MIR) has attracted significant interest due to a wide range of potential applications in spectroscopy, microscopy, molecular fingerprinting, environmental monitoring and LIDAR. Fibers made of non-silica soft glasses such as fluoride, tellurite and chalcogenide are good candidates for SC generation in the MIR due to their high intrinsic nonlinearity and wide transparency window in this wavelength range. To date, most of supercontinuum sources demonstrated in the mid-infrared have been generated in single mode soft glass fibers that cannot sustain high level of average power due to their small core size and low damage threshold. This generally imposes a limit on the maximum output power which can be a limitation for practical applications, especially in long-distance remote sensing for which high power is key. In order to overcome this problem, multimode fibers with large core size and higher damage threshold are a promising alternative. Here, we demonstrate for the first time the generation of an octave-spanning SC by injecting 1 MHz, 350 fs pulses from an optical parametric amplifier in a meter-long multimode step-index InF3 fiber with 100 μm core diameter. We performed a systematic study of the SC spectrum as a function of the pump wavelength and the largest SC spectrum spanning from 1100 nm to 2500 nm with 600 mW output power was generated when injecting the pulses at 1960 nm, in the anomalous dispersion regime of the fundamental mode. The output beam profile of the SC was characterized in different wavelengths bands, illustrating the highly multimode nature of the SC generation process. Numerical simulation results shows that higher-order soliton dynamics and dispersive wave generation in multiple higher-order modes are key contributions to reaching octave-spanning bandwidth in a fiber with large core size. Our results open up a promising route towards ultra-high power broadband sources in the MIR for applications where a single-mode spatial intensity distribution is not essential such as e.g. in remote sensing.
关键词： mid-infrared,high-power,fluoride fibers,multimode fibers,Supercontinuum generation
更新于2025-09-11 14:15:04
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Nonlinear interactions in multimode optical fibers
摘要： The limitations of single-mode fibers incite multimode fibers to meet the technological demands and explore new physics. Multimode fibers support many spatial modes which can interact with each other through various nonlinear processes and give rise to complex spatiotemporal dynamics. In this review paper, we address intermodal coupling based nonlinear phenomena in short and long pulse regimes. Ultrashort femtosecond pulse regime is dominated by four-wave mixing, self and cross-phase modulation, interpulse as well as intrapulse Raman scattering and provides strong platform for the realization of multitude of nonlinear phenomena such as multimode soliton formation, generation of intense combs of dispersive waves from the multimode soliton, beam clean-up, geometric parametric instability, and optical event horizon. On the other hand, long pulse regime exhibits strong stimulated Raman processes and provides natural tool for the investigation of nonlinear phenomena such as, cascaded Raman scattering, intermodal four-wave mixing based wideband frequency generation, transient grating formation and many others. This article reviews the recent developments in intermodal nonlinear interactions in multimode fiber for both the short and long pulse regimes and provides a roadmap for future research directions in the area of multimode nonlinear fiber optics.
关键词： Intermodal interaction,Multimode fiber,Nonlinear optics
更新于2025-09-11 14:15:04