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Enhanced optical Kerr nonlinearity of graphene/Si hybrid waveguide
摘要： In this work, we experimentally study the optical Kerr nonlinearities of graphene/Si hybrid waveguides with enhanced self-phase modulation. In the case of CMOS compatible materials for nonlinear optical signal processing, Si and silicon nitride waveguides have been extensively investigated over the past decade. However, Si waveguides exhibit strong two-photon absorption (TPA) at telecommunication wavelengths, which leads to a signi?cant reduction of the nonlinear ?gure-of-merit (FOM). In contrast, a silicon nitride based material system usually suppresses the TPA but simultaneously leads to the reduction of Kerr nonlinearity by one order of magnitude. Here, we introduce a graphene/Si hybrid waveguide, which maintains the optical properties and CMOS compatibility of Si waveguides, while enhancing the Kerr nonlinearity, by transferring over to the top of the waveguides. The graphene/Si waveguides are measured to have an enhanced nonlinear parameter of 510 W(cid:2)1 m(cid:2)1, compared with that of the Si waveguide of 150 W(cid:2)1 m(cid:2)1. An enhanced nonlinear FOM of 2.48 6 0.25 has been achieved, which is four times larger than that of the Si waveguide of 0.6 6 0.1. This work reveals the potential application of graphene/Si hybrid waveguides with high Kerr nonlinearity and FOM for nonlinear all-optical signal processing.
关键词： nonlinear all-optical signal processing,graphene/Si hybrid waveguide,optical Kerr nonlinearity,CMOS compatible,self-phase modulation
更新于2025-11-28 14:23:57
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Analogue Wireless Beamforming Exploiting the Fiber-Nonlinearity of Radio Over Fiber Based C-RANs
摘要： As a key technique of supporting the fixed backbone network, radio over fiber (RoF) systems transmit the radio frequency signals over optical fiber in order to take advantage of their large available bandwidth. In this context, optical fiber aided phased antenna array (PAA) based beamforming techniques have attracted substantial research interest with the goal of improving the cell-edge coverage of cellular base stations. In this paper, we conceive a novel optical fiber aided beamforming technique based on the fiber's nonlinearity to be applied in cloud radio access network (C-RAN). In our proposed technique, the PAA elements are fed by the phase-shifted signals introduced by our highly nonlinear fiber (HNLF) aided phase-shifting solution, which results in an angular beamsteering range of around 90°. This can be exploited by sectorization in cellular networks to reduce the cochannel interference imposed. Furthermore, we exploit the proposed RoF-aided phase shifting technique in C-RAN, where our proposed system takes advantage of the centralized signal processing capability of the RoF system to conceive an all-optical processing based tunable beamforming system. While our flexible HNLF-aided phase-shifting process is confined to the central office of the C-RAN, the end users in the C-RAN cellular networks are capable of flexibly choosing the serving remote radio heads (RRHs) and employing diverse wireless transmission techniques. Through integrating our HNLF-aided phase-shifting design into the proposed C-RAN, we impose as little as 0.1 dB signal-to-noise Ratio (SNR) degradation compared to its traditional electronic counterpart, which requires extra phase-shifters.
关键词： phase-shifter,self-phase modulation,phased array antenna beamforming,C-RAN,cross-phase modulation,highly nonlinear fiber,Optical fiber,optical nonlinearity
更新于2025-09-23 15:22:29
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[IEEE 2018 International Conference on Wireless Communications, Signal Processing and Networking (WiSPNET) - Chennai (2018.3.22-2018.3.24)] 2018 International Conference on Wireless Communications, Signal Processing and Networking (WiSPNET) - An Efficient Photonic-based Millimeter Wavelength Switching Techniques Towards 5G
摘要： Millimeter Waves (MMWs) operating at 30–300 GHz band, is very encouraging to the next-generation 5G wireless communication systems, supporting data rates of multiple Gbps per user. By using the Four Wave Mixing (FWM), Self-Phase Modulation (SPM) and Cross Phase Modulation (XPM) effects in the Semiconductor Optical Amplifier (SOA) and Erbium Doped Fiber Amplifier (EDFA), the photonic millimeter switching is realized. These effects can reduce the switching crosstalk since the Optical Single Sideband (OSSB) signal occupies the least optical bandwidth. The best operating conditions improve the Sideband Suppression Ratio (SSR) and at the same time reduce the intensity of unintended sideband signal. This leads to a dispersion-free transmission in the optical fiber and improves the data rate as required in 5G communication. In this paper, the wavelength switching of a 9 Gbps QPSK signal carried on the 30 GHz over a spacing of 1.6 nm as a function of probe wavelength of 1548.515 nm and pump wavelength of 1550.115 nm is achieved.
关键词： Millimeter Waves,Four Wave Mixing,Self Phase Modulation,Cross Phase Modulation,Erbium Doped Fiber Amplifier
更新于2025-09-23 15:22:29
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Effect of quintic nonlinearity on self-phase modulation and modulation instability in multiple coupled quantum wells under electromagnetically induced transparency
摘要： The self-phase modulation and modulation instability of an optical probe electromagnetic field in multiple quantum well systems under electromagnetically induced transparency has been investigated. The probe field experiences large Kerr and quintic nonlinearities that can be controlled by two controlling laser beams. The probe beam experiences self-phase modulation which is suppressed by the quintic nonlinearity. The probe field is modulationally unstable due to the existence of large nonlinearities. The bandwidth of unstable frequencies and growth of the instability could be controlled by the probe beam power, the Rabi frequency and detunings of two control fields. The presence of the higher order nonlinearity and dispersion significantly reduce the instability growth and bandwidth of unstable frequency.
关键词： Self-phase modulation,Coupled quantum well,Modulation instability,electromagnetically induced transparency
更新于2025-09-23 15:21:01
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A perturbative approach to self-phase modulation and self-steepening of short laser pulses propagating in nonlinear media
摘要： The solution of the wave equation in the envelope approximation with temporal corrections for a laser pulse propagating in a medium where the Kerr effect, field ionization, and associated absorption take place, is obtained through a first order perturbative approach. Dispersion is, however, neglected to decouple the equations for the amplitude and the phase. The closed-form expressions so obtained clarify the influence of the various terms of the equation on the laser amplitude and on the frequency generation as a function of the retarded time. Furthermore, they allow extracting scaling parameters which size the nonlinear effects. The results are illustrated quantitatively in the case of a femtosecond pulse focused in the air with typical parameters.
关键词： perturbative approach,self-phase modulation,self-steepening,short laser pulse propagation
更新于2025-09-23 15:21:01
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[IEEE 2019 IEEE 8th International Conference on Advanced Optoelectronics and Lasers (CAOL) - Sozopol, Bulgaria (2019.9.6-2019.9.8)] 2019 IEEE 8th International Conference on Advanced Optoelectronics and Lasers (CAOL) - Nonlinear compression of ultra-high-power laser pulses
摘要： Nowadays the peak power of PW lasers is limited by the damage threshold of optical compressor diffraction gratings. A promising way to overcome the difficulty and increase peak power is to use an additional pulse shortening after optical compressor without significant energy loses. The discussed method is called CafCA – Compression after Compressor Approach. CafCA possesses three undisputed merits: simplicity and low cost, negligible pulse energy loss, and applicability to any high-power lasers without changing their optical schemes. The key idea of the approach is to broaden spectrum of powerful laser pulses exactly after grating compressor and correct spectral phase with help of reflected dispersion devices (chirped mirrors in particular). The idea has been known since the end of 1960s but its application to lasers with a peak power higher 1 TW has been restricted by a number of physical reasons. The reasons and ways of its overcoming are discussed in the paper. We analyze the recent experimental results that demonstrate the CafCA efficiency in the range up to 200 TW.
关键词： temporal compression,self-phase modulation,PW-level femtosecond laser pulses
更新于2025-09-19 17:13:59
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Optical and Thermal Properties of Laser-Ablated Platinum Nanoparticles Graphene Oxide Composite
摘要： Platinum nanoparticles were synthesized in graphene oxide aqueous solution using a laser ablation technique to investigate the effect of optical linear, nonlinear and thermal properties of platinum-graphene oxide nanocomposite solution. The samples were prepared with different ablation times. The platinum nanoparticles that formed a spherical shape on the surface of graphene oxide solution were authenticated using UV-visible spectrum and transmission electron microscopy patterns. The particle size decreased with increasing ablation time, and the concentration and volume fraction of samples were increased. To obtain the optical linear, nonlinear and thermal properties of platinum-graphene oxide nanocomposite solution, UV-visible spectroscopy, Z-scan, thermal lens and photoacoustic techniques were used. Consequently, the linear and nonlinear refractive indices increased with an increase in the volume fraction of platinum nanoparticles. It was observed from the spatial self-phase modulation patterns that, the optical nonlinear property of the graphene oxide was enhanced in the presence of platinum nanoparticles, and the nonlinearity increased with an increase in the volume fraction of platinum nanoparticles inside the graphene oxide solution. The thermal diffusivity and thermal effusivity of platinum nanoparticles graphene oxide were measured using a thermal lens and photoacoustic methods, respectively. The thermal diffusivity and thermal effusivity of samples were in the range of 0.0341 × 10?5 m2/s to 0.1223 × 10?5 m2/s and 0.163 W s1/2 cm?2 K?1 to 0.3192 W s1/2 cm?2 K?1, respectively. Consequently, the platinum enhanced the optical and thermal properties of graphene oxide.
关键词： graphene oxide,z-scan,spatial self-phase modulation,Pt-NPs,platinum nanoparticles/graphene oxide composite,laser ablation,photoacoustic,thermal lens
更新于2025-09-16 10:30:52
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Synthesis of bilayer graphene nanosheets by pulsed laser ablation in liquid and observation of its tunable nonlinearity
摘要： Bilayer graphene nanosheets (B-GNSs) have been synthesized from dry-cell graphite electrode by using facile laser ablation in liquid technique in ambient condition. The plasma plume generated on incidence of ns pulsed Nd:YAG laser fundamental radiation of 1064 nm has facilitated the transformation of bulk graphite (BG) into B-GNSs via liquid carbon phase within 30 min of laser irradiation, and the layer number is are found to be increased with further increase in laser ablation time. The thickness dependent coherent nonlinear optical (NLO) response of the synthesized materials in aqueous dispersion has been determined by spatial self-phase modulation technique. The oxygen-containing surface defects in multilayer GNSs (M-GNSs) have led to scarcity in amount of e-h pairs in compared to that in B-GNSs. Therefore, a better NLO polarization has been observed in B-GNSs in compared to that of M-GNSs. Moreover, the thickness dependent thermal conductivity and hydrodynamic performance of GNSs-water dispersion has led to the observation of tunable NLO response with change in temperature as well as with the intensity of pump laser. The experimental findings obtained in this work may be considered as a key step towards fabrication of graphene from graphitic waste materials for development of future nonlinear photonics devices.
关键词： Waste material,Nonlinear optical properties,Optical properties,Spatial self-phase modulation,Laser ablation,Graphene nanosheets
更新于2025-09-16 10:30:52
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Use of heavily doped germanosilicate fibres with a small core diameter in stretchers of ultrashort laser pulses at a wavelength of 1.03 μm
摘要： The use of a heavily doped germanosilicate fibre with a W-profile refractive index and small core diameter in stretchers of ultrashort laser pulses with their subsequent amplification and compression in all-fibre laser systems is considered. The application of fibres of this type makes it possible to stretch, amplify, and then compress a laser pulse with minimum distortions of its initial shape and width. Due to the dispersion properties of these fibres, which allow the pulse duration to be increased significantly at a small fibre length and the third-order positive dispersion of the diffraction-grating-based output compressor to be compensated for, amplified pulses with an energy of 2 mJ and width of 250 fs, free of a picosecond pedestal, are obtained. Several types of fibres intended for the use in stretchers of ultrashort laser pulses are comparatively analysed from the point of view of their dispersion compatibility with a diffraction-grating-based output compressor.
关键词： nonlinear self-phase modulation,fibre lasers,heavily doped germanosilicate fibre,group-velocity dispersion,femtosecond lasers,amplification of ultrashort laser pulses
更新于2025-09-16 10:30:52
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Spectral broadening of a KrF laser via propagation through Xe in the negative nonlinear index regime
摘要： In inertial con?nement (ICF) experiments at the NIKE laser facility, the high-power krypton ?uoride (KrF) laser output beams propagate through long (～75 m) air paths to achieve angular multiplexing, which is required because the KrF medium does not store energy for a suf?ciently long time. Recent experiments and simulations have shown that, via stimulated rotational Raman scattering, this propagation can spectrally broaden the laser beam well beyond the ～1 THz laser linewidth normally achieved by the induced spatial incoherence (ISI) technique used in NIKE. These enhanced bandwidths may be enough to suppress the laser-plasma instabilities which limit the maximum intensity that can be incident on the ICF target. In this paper we investigate an alternative technique that achieves spectral broadening by self-phase modulation in Xe gas, which has a large, negative nonlinear refractive index ～248 nm, and thus completely avoids transverse ?lamentation issues. The collective, nonlinear atomic response to the chaotic, nonsteady state ISI light is modeled using a two-photon vector model, and the effect of near-resonant behavior on the spectral broadening is studied.
关键词： self-phase modulation,laser-plasma instabilities,negative nonlinear index,KrF laser,spectral broadening,Xe gas
更新于2025-09-16 10:30:52