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Longitudinal wave propagation in a one-dimensional quasi-periodic waveguide
摘要： The paper deals with the analysis of wave propagation in a general one-dimensional (1D) non-uniform waveguide featuring multiple modulations of parameters with different, arbitrarily related, spatial periods. The considered quasi-periodic waveguide, in particular, can be viewed as a model of pure periodic structures with imperfections. Effects of such imperfections on the waveguide frequency bandgaps are revealed and described by means of the method of varying amplitudes and the method of direct separation of motions. It is shown that imperfections cannot considerably degrade wave attenuation properties of 1D periodic structures, e.g. reduce widths of their frequency bandgaps. Attenuation levels and frequency bandgaps featured by the quasi-periodic waveguide are studied without imposing any restrictions on the periods of the modulations, e.g. for their ratio to be rational. For the waveguide featuring relatively small modulations with periods that are not close to each other, each of the frequency bandgaps, to the leading order of smallness, is controlled only by one of the modulations. It is shown that introducing additional spatial modulations to a pure periodic structure can enhance its wave attenuation properties, e.g. a relatively low-frequency bandgap can be induced providing vibration attenuation in frequency ranges where damping is less effective.
关键词： frequency bandgaps,quasi-periodic structures,elastic wave propagation,imperfections,dispersion relation,method of varying amplitudes
更新于2025-09-12 10:27:22
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Experimental study of the effects of thermally induced optical turbulence on underwater wireless optical communication link parameters
摘要： In this experimental research, the effects of refractive index fluctuations resulting from temperature fluctuations on some of the most important underwater communication link parameters such as the average received power, Signal to Noise Ratio (SNR) and normalized power variance (aperture averaged scintillation) has been experimentally investigated. Moreover, by introducing a new probability density function which is fitted more appropriately to the experimental data obtained from our simulator tank, the Bit Error Rate (BER) behavior of an Underwater Wireless Optical Communication (UWOC) link is also studied. These investigations are essential due to the optical turbulence limiting effects on the performance of UWOC systems. The experimental results indicate that reduction of the aperture averaged scintillation effects by using of optical components in the transmitter and receiver of UWOC links can enhance their performance. In general, increasing the strength of the optical turbulence (by increasing the temperature gradient induced by the rod heater) or the distance of the localized turbulence screen generated by temperature gradient from the transmitter plane, the aperture averaged scintillation decreases and consequently the SNR raises whilst the BER declines. Also, expanding the aperture diameter of the receiver optics reduces the normalized power variance which leads to decrease and increase in the BER and the SNR amounts respectively. The results are presented as experimental simulation graphs.
关键词： Laser beam propagation through turbulence,aperture averaged scintillation,Probability density function,BER,SNR,Underwater optical communication link
更新于2025-09-12 10:27:22
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-point dependent electromagnetic beam propagation in a graphenelike triangular metallic photonic structure
摘要： We study the electromagnetic wave propagation in a graphenelike triangular metallic photonic structure and show that, associated to trigonally warped Dirac cones, the transport properties resulting from an incident beam at the armchair edge display drastically different behaviors as compared to the results obtained for other analogous systems. Namely, at K point, only the center beam associated to the lower Dirac cone and the side beams to the upper cone and, at K (cid:2) point, only the center beam associated to the lower cone display signi?cant intensities. The other expected beams are all strongly inhibited. This can be related to the metallic nature of the structure, where the low frequency electromagnetic bands are formed by local resonance modes con?ned inside the structural units. A propagating wave should follow the structure local patterns that govern its ?eld distribution, whose symmetry properties determine its excitation by an incident wave.
关键词： graphenelike triangular metallic photonic structure,trigonal warping,armchair edge,electromagnetic wave propagation,Dirac cones
更新于2025-09-12 10:27:22
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Scintillation of laser beams carrying orbital angular momentum propagating in a near-maritime environment
摘要： Laser beams carrying orbital angular momentum (OAM) were propagated in a near-maritime environment along an 890 meter link across the Severn River at the United States Naval Academy. The OAM beams were generated using green light ( ?? = 532 nm) and etched spiral phase plates with different topological charges. The light intensity fluctuations of Gaussian and beams carrying OAM with topological charges of 1, 6, and 8 were measured and the scintillation indices of each beam were compared. Additionally, atmospheric turbulence was measured using a co-aligned scintillometer along the 890 meter propagation path. During testing, a wide range of atmospheric conditions occurred and the refractive index structure parameter measurements ranged from 5 × 10?14 down to 5 × 10?15 m ???∕??. Our measurements of transmitted voltage in the radial intensity across the maritime link, and calculated scintillation index, for the Gaussian beam and laser beams carrying OAM indicate a weak reduction in scintillation index for increasing topological charge. To reduce the measurement uncertainty and improve upon statistical significance of our findings, additional testing is needed.
关键词： Orbital angular momentum,OAM,Scintillation,Laser propagation,Near-maritime environment
更新于2025-09-12 10:27:22
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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 Brightness 2.1 μm Direct-Diode Laser Module
摘要： Direct diode lasers at 2 μm provide the opportunity for more compact sources that can perform similar tasks that are currently undertaken by solid state lasers operating in this wavelength. Infrared countermeasure, gas detection and atmospheric sensing are but a few examples. A high brightness mid-infrared direct-diode laser diode module is presented as a compact source for atmospheric propagation. Optomechanical design enables spatial beam combining to produce excellent combined beam quality deteriorating based only on the performance of each emitter and number of emitters used. The following study showcases the optomechanical design and development of six one-tab C-mount GaSb 2.1 μm single emitter diodes in a module featuring a right-angled staircase spatial beam combining technique.
关键词： GaSb,spatial beam combining,atmospheric propagation,2 μm,Direct diode lasers
更新于2025-09-12 10:27:22
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Demonstration of low loss <b> <i>β</i> </b> -Ga <sub/>2</sub> O <sub/>3</sub> optical waveguides in the UV–NIR spectra
摘要： In this paper, we report the fabrication of low loss beta-phase gallium oxide (b-Ga2O3) optical waveguides and the propagation loss analysis of the waveguides in the ultraviolet (UV) to near infrared (NIR) spectral region. The b-Ga2O3 thin films were grown on sapphire substrates using metal organic chemical vapor deposition and were fabricated into various waveguide structures using nanofabrication processes. A low propagation loss of 3.7 dB/cm was obtained on the b-Ga2O3 waveguide at the wavelength of 810 nm, which is comparable to the state of the art. Combined with theoretical simulations, various loss mechanisms from two-photon absorption, sidewall scattering, top surface scattering, and bulk scattering were discussed for b-Ga2O3 waveguides, and their contributions to the total optical loss were estimated. These results show that b-Ga2O3 is a promising optical material for the fabrication of various integrated photonic devices in the UV–NIR spectra region.
关键词： integrated photonic devices,b-Ga2O3,propagation loss,UV–NIR spectra,optical waveguides
更新于2025-09-12 10:27:22
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Enhanced Terahertz Detection Efficiency via Grating-Assisted Noncollinear Electro-Optic Sampling
摘要： Sensitive detection of phase-locked terahertz (THz) pulses is routinely achieved using electro-optic sampling (EOS), a technique that harnesses second-order optical nonlinearities in a crystalline semiconductor. The thickness and electro-optic coefficient of such a crystal set the detection sensitivity in EOS, while its linear optical properties often determine the accessible detection bandwidth through the phase-matching conditions. Here, we demonstrate how a periodically patterned structure on the incident surface of an EOS crystal can be used to overcome bandwidth limitations by enabling noncollinear propagation between the THz waves and a near-infrared (NIR) gating pulse. The concept is demonstrated with phase gratings etched on a 1-mm-thick gallium phosphide (GaP) semiconductor. The use of a diffracted NIR gating pulse to retrieve the THz waveform results in a sensitivity enhancement of a factor of approximately 2 with regard to the spectral maximum at 2 THz and exceeding an order of magnitude at 5 THz. This extends the spectral detection bandwidth up to 5 THz, which is twice as large as that achievable in a similar configuration with collinear THz and NIR pulses, facilitating the broadband detection of weak signals in THz spectroscopy.
关键词： electro-optic sampling,phase grating,gallium phosphide,noncollinear propagation,terahertz
更新于2025-09-12 10:27:22
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Fiber Optic and Atmospheric Optical Communication || Optical Wave Propagation
摘要： Electromagnetic (EM) wave plays a key role in modern communication systems, radio and optical, including optical telecommunication systems. Therefore, fiber optic or laser communications emphasize the EM phenomena described mathematically by Maxwell’s unified theory, which we will consider in detail subsequently. Investigation of optical communications started just after the invention of the laser in 1960. Atmospheric propagation of optical waves was investigated parallelly with improvements in optical lasers and understanding of the problems of optical wave’s generation both in the time and space domains. Thus, problems with weather, line-of-site (LOS) clearance, beam spreading and bending in the real atmosphere consisting of gaseous structures (aerosols, fog, smoke, turbulence, etc.), and hydrometeors (snow, rain, clouds, etc.) eliminated free-space optical communication as a major aspect in wireless communication.
关键词： Optical Wave Propagation,Maxwell’s Equations,Atmospheric Propagation,Electromagnetic Waves,Fiber Optic Communication
更新于2025-09-11 14:15:04
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Broadband Laser Ultrasonic Excitation and Multi-band Sensing for Hierarchical Automatic Damage Visualization
摘要： It is well known that the selection of a frequency for signal generation and data acquisition signi?cantly affects the quality of ultrasonic or laser ultrasonic nondestructive testing (NDT) results, and the analog ?lter is essential to prevent the aliasing effect. This paper presents a systematic approach using a hierarchical inspection scheme for automatic inspection processes. A frequency band divider (FBD) with a single-input–multiple-output (SIMO) system was newly created to examine quickly various frequency ranges at single scanning using laser-based broadband excitation. The FBD was implemented into a pulse-echo ultrasonic propagation imaging (PE UPI) system capable of fully noncontact laser ultrasonic inspection. Only two scans are required to determine the optimal frequency range for unknown specimens. This tremendously reduces the number of scanning trials for the investigation of complete frequency ranges.
关键词： Nondestructive testing,Programmable band-pass ?lter,Pulse-echo ultrasonic propagation imager,Hierarchical approach
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