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Femtosecond laser direct written off-axis fiber Bragg gratings for sensing applications
摘要： First order off-axis fiber Bragg gratings (FBGs) were fabricated in a standard single mode fiber (SMF-28e) through femtosecond laser direct writing. A minimum offset distance between the grating and core center of 2.5 μm was found to create a multimode section, which supports two separate fiber modes (LP0,1 and LP1,1), each split into two degenerate polarization modes. The resulting structure breaks the cylindrical symmetry of the fiber, introducing birefringence (≈10?4) resulting in a polarization dependent Bragg wavelength for each mode. Based on the modal and birefringence behavior, three off-axis FBGs were fabricated with 3.0, 4.5 and 6.0 μm offsets from the core center, and then characterized in strain, temperature, and curvature. The tested off-axis FBGs exhibited a similar strain sensitivity of ~1.14 pm/μ? and a temperature sensitivity of ~12 pm/C. The curvature and orientation angle were simultaneously monitored by analyzing the intensity fluctuation and the wavelength shift of the LP1,1 Bragg resonance. A maximum curvature sensitivity of 0.53 dB/m?1 was obtained for the off-axis FBG with a 3.0 μm offset.
关键词： optical fiber sensors,femtosecond laser direct writing,single mode fiber,off-axis fiber Bragg gratings,Birefringence
更新于2025-09-23 15:19:57
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Methanol-Filled Hybrid Photonic Crystal Fiber with High Birefringent and Negative Dispersion
摘要： A unique hexagonal lattice structure of silica-based solid core photonic crystal fiber (PCF) surrounded by array of air holes is proposed. The cladding portion of the structure consists of five rings where core is made up of 11 small rings filled with methanol. Three different-shaped structures are used to analyze the effect on PCF parameters where the first structure uses circular air holes in cladding and core, the second structure consists of circular air holes in cladding and elliptical air holes in core, and the last structure was designed by using elliptical air holes in both cladding and core. Optical properties birefringence, confinement loss, and negative dispersion have been found theoretically and compared. A novel and relatively simple approach depicts the results that attain high birefringence, low confinement loss, and negative dispersion. It is found that the presence of elliptic air holes instead of circular air holes in the core region and the cladding brings higher birefringence, low confinement loss, and highly negative dispersion.
关键词： Photonic crystal fiber,Effective refractive index,Dispersion,Birefringence,Confinement loss
更新于2025-09-23 15:19:57
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Dark, singular and straddled optical solitons in birefringent fibers with generalized antia??cubic nonlinearity
摘要： This paper enumerates optical soliton solutions in birefringent fibers having generalized form of anti–cubic law of refractive index. The unified Riccati equation expansion yields dark, singular as well as solitons that are straddled between dark and singular ones. A few additional solutions emerge from the integration scheme as a byproduct.
关键词： Birefringence,Solitons,Generalized anti–cubic
更新于2025-09-23 15:19:57
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Prediction of MCO [M = S, (Cl <sub/>2</sub> B) <sub/>3</sub> B] Systems with Giant Optical Birefringence and Nonlinearity in the Deep-Ultraviolet Region
摘要： Deep-ultraviolet (DUV) materials with giant optical birefringence and nonlinearity are scarce, and their discovery is very challenging. In this Communication, we predict that the MCO [M = S, (Cl2B)3B] compounds containing the polar C?O motif, which have been synthesized in the experiments, could be the ?rst material systems to achieve this rare capability. First-principles calculations demonstrate that (Cl2B)3BCO and SCO exhibit the largest second-harmonic-generation e?ect (～4.4 pm/V) and the largest birefringence (～0.6) in all known DUV nonlinear-optical (NLO) crystals. In addition, SCO might be a DUV NLO material for the practical 193.7 nm laser output. Our discovery could enrich the structural chemistry of NLO crystals and advance the development of functional DUV optical materials.
关键词： Deep-ultraviolet,nonlinearity,polar C?O motif,DUV nonlinear-optical crystals,first-principles calculations,MCO compounds,second-harmonic-generation,optical birefringence
更新于2025-09-23 15:19:57
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Effects of a chiral atomic medium on the manipulation of light birefringence and lateral Goos–H?nchen shifts via Kerr nonlinearity and local field effects
摘要： We present a new scheme to report on the effects of a five-level chiral atomic medium on the lateral Goos–H?nchen (GH) shift in Gaussian probe beams via Kerr nonlinearity (KNL) and local field effects. The physical realization of birefringence in absorption, dispersion, reflection and transmission beams is investigated, with special emphasis on the manipulation of absolute and fractional change in lateral GH shifts in birefringence transmission and reflection beams, via local fields and Kerr nonlinearity. We have employed a semiclassical atomic density-matrix formalism so as to obtain the expression for electric and magnetic susceptibilities of the chiral medium and the corresponding chirality coefficients in conjunction with Kerr and local fields, both separately and in combination. Stationary-phase theory is used to compute GH shift from the calculated birefringent reflection and transmission coefficients of probe beams. A negative and positive GH shift is observed in reflection and transmission beams, respectively, subjected to local field and Kerr effect. In contrast, a positive GH shift is observed in both reflection and transmission beams in the presence of both local field and Kerr effects. The local and Kerr fields also alter the divergence angle between left and right circularly polarized birefringence beams. GH shift depends on incident angle and probe detuning. The anisotropy of medium is lessened by switching ON the Kerr field in the medium. We observed a positive fractional change of ±30% in the GH shift in the birefringence reflection beam in the presence of a local field without KNL, while a 20% fractional GH shift was observed in the presence of both local field and KNL effects. Our results suggest promising applications in nonlinear optical, plasmonic and biophotonic devices for the manipulation of light propagation and optical signal processing.
关键词： stationary-phase theory,Kerr nonlinearity,birefringence chiral medium,Goos–H?nchen shift,density-matrix formalism,Doppler broadening medium
更新于2025-09-23 15:19:57
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Terahertz Polarization Imaging and Its Applications
摘要： This review focuses on several recent research activities regarding precise and fast polarization-sensitive terahertz time-domain spectroscopy systems for imaging purposes, and explains three interesting application examples. Owing to modulation techniques that have recently been developed for the evaluation of the instantaneous terahertz electric-field (E-field) vector, fast and precise terahertz polarization imaging becomes feasible. This terahertz technology enables high-resolution surface topography, precise understanding of the spatial E-field vector distribution of the focused terahertz pulse, and examination of strain-induced birefringence in polymeric materials. These examples constitute a new application area of terahertz photonics with emphasis on both fundamental optics and industrial applications.
关键词： topography,birefringence,polarization,parabolic mirror,terahertz spectroscopy
更新于2025-09-19 17:15:36
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Broadband Dispersion Compensation of Single Mode Fiber by using Modified Decagonal Photonic Crystal Fiber having High Birefringence
摘要： This paper presents a highly birefringent dispersion compensating microstructure modified decagonal photonic crystal fiber for broadband transmission communication system. According to simulation, negative dispersion coefficient of ?610 ps/(nm.km) and a relative dispersion slope (RDS) close to that of single mode fiber of about 0.0036 nm-1 with birefringence of the order 2.1×10-2 was obtained at 1550 nm. The variation of structural parameters is also studied to evaluate the tolerance of the fabrication. Moreover, effective area, residual dispersion, effective dispersion, confinement loss, and nonlinear coefficient of the proposed modified decagonal photonic crystal fiber (M-DPCF) are also mentioned and discussed.
关键词： Photonic crystal fiber,Birefringence,Dispersion compensating fiber,Effective mode area,Residual dispersion,Full-vector Finite Element Method
更新于2025-09-19 17:15:36
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Magnetic linear birefringence of light in Tb3Ga5O12
摘要： The spectra of the magnetic linear birefringence (MLB) in the terbium-gallium garnet TbGG (Tb3Ga5O12) have been studied within the visible spectral range for temperature T = 90 K. Analysis of the temperature and spectral dependences of MLB has made it possible to determine the “e?ective” frequencies of the allowed →f d electric dipolar transitions in rare-earth (RE) ions of Tb3+ ions responsible for the formation of quadratic magneto-optical e?ect in this garnet. The results of the performed magneto-optical experiments in TbGG have con?rmed the Akulov's relations (for the quadratic magnetic e?ects) arising from the phenomenological consideration of MLB for the values of Δn measured at the orientation of the external ?eld in the plane (110) along the main crystallographic directions of the garnet crystal. From analysis of the experimental data on MLB was obtained that for the TbGG MLB changes quadratically with the ?eld within the temperature range 90–300 K. At the same time with a decrease in temperature, its value grows inversely proportional to the square of temperature. A certain di?erence was also found in the “e?ective" frequencies of the allowed transitions in Tb3+ ions of the garnet, which is determined from the optical absorption spectra of TbGG on the one hand, and from the analysis of the spectral dependence of MLD on the other one. It has been assumed that this di?erence can be due to signi?cant distortions of the TbGG crystal lattice caused by this signi?cant magnetostriction at low temperatures, leading to the "mixing" of the 9D term states with the "optically resolved" states of the 7D term.
关键词： Terbium-gallium garnet,Akulov's relation,Magnetic linear birefringence
更新于2025-09-19 17:15:36
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Selective Angular Momentum Generator Based on a Graphene Hybrid Plasmonic Waveguide
摘要： Manipulation of the angular momentum (AM) of photons are of great importance in many fields such as optical communications, holographic, particle manipulation. Although there are many demonstrations focusing on dynamic manipulation of AM in free space, the active tuning of AM in nanophotonic waveguides is mainly exclusive, especially in the Terahertz regime. Here we proposed a selected AM generation scheme based on graphene hybrid waveguide, which can convert a quasi-linear mode into a quasi-circular mode with dynamic tuning manner. Also, we show that the proposed waveguide structure can serve as a distinguisher between left- and right-handed quasi-circular modes. These results allow for the dynamic control of AM of light in nanophotonic waveguides, which are crucial for various devices with compact footprint, such as on-chip bio-sensing and integrated quantum information processing.
关键词： hybrid waveguide,graphene surface plasmons,birefringence effect,Angular momentum
更新于2025-09-19 17:13:59
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Nonlinear Optics - Novel Results in Theory and Applications || Polarization Properties of the Solitons Generated in the Process of Pulse Breakup in Twisted Fiber Pumped by ns Pulses
摘要： Common optical fibers are randomly birefringent, and solitons formatting and traveling in them are randomly polarized. However, it is desirable to have solitons with a well-defined polarization. With pump relatively long pulses, the nonlinear effects of modulation instability (MI) and stimulated Raman scattering (SRS) are dominant at the initial stage of the process of supercontinuum (SC) generation; modulation instability results in pulse breakup and formation of short pulses that evolve finally to a bunch of solitons and dispersive waves. We do the research of the polarization of solitons formed by the pulse breakup process by the effect of modulation instability with pump pulses of nanoseconds in standard fiber (SMF-28) with circular birefringence introduced by fiber twist, and the twisted fiber mitigates the random linear birefringence. In this work, we found that polarization ellipticity of solitons is distributed randomly; nevertheless, the average polarization ellipticity is closer to the circular than the polarization ellipticity of the input pulse. In the experimental setup. 200 m of SMF-28 fiber twisted by 6 turns/m was used. We used 1 ns pulse to pump the fiber. The results showed that at circular polarization of the input pulse solitons at the fiber output have polarizations close to the circular, while in the fiber without twist, the soliton polarization was random.
关键词： pulse propagation and temporal solitons,birefringence and polarization,fiber optic,stimulated Raman scattering,nonlinear optics
更新于2025-09-19 17:13:59