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Axial Micro-Strain Sensor Based on Resonance Demodulation Technology Via Dual-Mode CMECF
摘要： This paper firstly and experimentally demonstrates an in-fiber axial micro-strain sensing head, combined with a Mach-Zehnder interferometer (MZI) based on the concentric multilayer elliptical-core fiber (CMECF). This MZI with a high extinction ratio (about 15 dB) is successfully achieved with a CMECF-single mode fiber-CMECF (CSC) structure. The MZI sensor theory and the resonance demodulation technology are systematically described in this paper. In this CSC structure, two sections of the CMECF have a role as the mode generator and coupler, respectively. LP01 and LP11 even, which have similar excitation coefficients, are two dominated propagating mode groups supported in the CMECF. On account of the distinct dual-mode property, a good stability of this sensor is realized. The detected resonance in the MZI shifts as the axial micro-strain variated due to the strong interaction between higher order modes. High sensitivity of ~1.78 pm/με is experimentally achieved within the range of 0 με ? 1250 με, meanwhile, the intensity fluctuation is below 0.38 dB.
关键词： MZI,fiber sensor,Few-mode fiber,axial micro-strain
更新于2025-11-28 14:23:57
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Nonlinear Performance of Few-Mode Fiber Links with Intermediate Coupling
摘要： This paper reviews and extends the study of nonlinear performance of few-mode fiber links operating in all different linear coupling regimes for different mode delay maps. Nonlinear performance was estimated using the four-wave-mixing theory and the split-step Fourier method including semi-analytical solutions for linear mode coupling of arbitrary strength. The optimum link configurations minimizing the nonlinear penalty at practical levels of training sequence length are presented, including: the required coupling strength to give nonlinear distortion below that of the single-mode propagation without mode coupling, and the impact of mode delay maps. Finally, different approximate solution methods of the multimode nonlinear Schr?dinger equation are compared, highlighting the accuracy of a stochastic solution method including distributed linear mode coupling.
关键词： Mode-division multiplexing,few-mode fiber,linear mode coupling,fiber nonlinearity
更新于2025-09-19 17:15:36
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Numerical Investigation of the Equalization Enhanced Phase Noise Penalty for M-Quadrature Amplitude Modulation Formats in Short-Haul Few-Mode Fiber Transmission Systems with Time-Domain Equalization
摘要： The equalization enhanced phase noise (EEPN), caused by the interaction of the chromatic dispersion (CD) with the phase noise of the local oscillator (LO), has been extensively studied for single-mode optical communication systems. Few-mode fiber (FMF) transmission systems introduce a new channel impairment, the differential mode delay (DMD), which also creates EEPN and hence limits the maximum transmission distance of those systems. In this work, we numerically investigate the optical signal to noise ratio (OSNR) penalties caused by the EEPN in a 3-mode FMF transmission system at 25 GBd for quadrature phase-shift keying (QPSK), 16-quadrature amplitude modulation (QAM), 32-QAM and 64-QAM modulation formats when using the blind phase search (BPS) carrier phase recovery (CPR) algorithm, which has been demonstrated to be both robust and suitable for optical communication systems. Our numerical study assumes a short-span of FMF, modeled in the weakly-coupled regime, and includes two cases; the use of ideal mode-selective de/multiplexers at both ends of the FMF span (model A), and the use of ideal non-mode-selective de/multiplexers (model B). The results show that the EEPN has almost no effect in model A. However, EEPN produces a severe penalty in model B with the onset of the OSNR degradation starting for a DMD spread of the impulse response of about 100 symbols for all modulation formats investigated. The distribution ratio of the amount of phase noise between the transmitter and receiver lasers is also assessed for model B and we confirm that the degradation is mainly due to the phase noise of the LO.
关键词： equalization enhanced phase noise,mode-division multiplexing,few-mode fiber optical communication systems,time-domain MIMO equalization
更新于2025-09-19 17:15:36
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402.7-Tb/s MDM-WDM transmission over weakly coupled 10-mode fiber using rate-adaptive PS-16QAM signals
摘要： The mode-division-multiplexing (MDM) transmission technique using a few-mode fiber (FMF) has been investigated to overcome the theoretical limitation of the transmission capacity of a single-mode fiber. In MDM transmission, multiple-input multiple-output (MIMO) digital signal processing (DSP) is generally required on the receiver side to compensate for the modal crosstalk (XT) between the spatial modes. However, the computational cost is high, especially for high-order MDM systems that use many spatial modes. To reduce the MIMO matrix size, MDM transmission with partial MIMO-based DSP has been proposed using weakly coupled FMFs. The modal XT in such fibers can be suppressed by a special fiber design; however, the modal XT still remains and strongly limits the signal-to-noise-ratio (SNR) and capacity. To further increase the capacity for a given SNR, an optimization of the modulation format is significant. Recently, probabilistic shaping (PS) has received attention since it can gradually change the entropy of a modulation format and maximize the capacity for a given SNR. In this work, we demonstrate weakly coupled 10-mode-multiplexed transmission with four 4×4 MIMOs and two 2×2 MIMOs using rate-adaptive PS-16QAM signals over 48-km FMF, achieving a record transmission capacity of 402.7 Tb/s in 125-μm cladding single-core fiber transmission experiments. Furthermore, we also show the possibility of a further capacity increase by adjusting the entropies of the PS-16QAM signals depending on the spatial mode.
关键词： high-capacity transmission,probabilistic shaping,mode-division multiplexing (MDM),Few-mode-fiber (FMF),rate optimization,coded modulation
更新于2025-09-19 17:13:59
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All few-mode fiber passively mode-locked figure-8 cavity laser
摘要： We propose and demonstrate an all few-mode fiber (FMF) passively mode-locked figure-8 cavity laser, for the first time to the best of our knowledge. In this laser, all the components including the used gain medium of few-mode erbium-doped fiber (FM-EDF) are based on and connected with FMF. A homemade wavelength division multiplexing-mode selective coupler (WDM-MSC) makes it possible for 976 nm pump light source to be simultaneously converted to LP11 mode and multiplexed into the FM-EDF. The obtained cylindrical vector beams (CVBs) pulses exhibit a signal-to-noise ratio 78 dB with fundamental repetition rate of 3.51 MHz. Furthermore, CVBs with the purity of over 94% have been obtained by simply adjusting the polarization controllers. The all-FMF mode-locked fiber laser could not only have the potential applications for MDM telecommunication and high-power fiber laser seed sources, but also is a perfect platform for nonlinear science.
关键词： mode-locking,cylindrical vector beam,few-mode fiber
更新于2025-09-16 10:30:52
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Optimal coupling condition analysis of free-space optical communication receiver based on few-mode fiber
摘要： Effective coupling between space light and optical fiber is one of the key technologies in free space optical communication. Few-mode fiber coupling is becoming a promising method to improve the performance of free space optical communication receiver. The dependence of the few-mode fiber coupling efficiency on the focal ratio, the central occlusion ratio and the numerical aperture are analyzed in this paper. The research results may be beneficial for the design of the receiver based on FMF coupling in the FSOC system.
关键词： Coupling condition,Free-space optical communication,Few-mode fiber
更新于2025-09-16 10:30:52
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[IEEE 2019 18th International Conference on Optical Communications and Networks (ICOCN) - Huangshan, China (2019.8.5-2019.8.8)] 2019 18th International Conference on Optical Communications and Networks (ICOCN) - Sensing Characteristics of Helical Long-Period Grating Inscribed in Graded Index Few Mode Fiber
摘要： Helical long-period grating fabricated in graded-index few-mode fiber was experimentally demonstrated. The high sensitivities corresponding to torque, curvature, temperature and surrounding refractive index are up to 0.293 nm/rad/m, 2.486nm/m-1, 0.095 nm/(cid:31) and 1242 nm/RIU, respectively.
关键词： helical long-period grating,sensing,graded-index few-mode fiber
更新于2025-09-16 10:30:52
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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) - Investigation of Grating Assisted Mode-Selective Few-Mode Fused Fiber Couplers
摘要： Spatial division multiplexing (SDM) in form of mode division multiplexing (MDM) is one solution to keep up with the increasing data traffic demand [1]. MDM is based on using individual modes of a few-mode or multi-mode fiber as individual transmission channels and requires the addressing of individual modes at the input and output of the multimode fiber link. Here, among others, mode-selective fused fiber couplers based on evanescent coupling can be applied for addressing individual modes of fiber optic transmission links. In this case, light coupling occurs when the mode propagation constants are equal and this can be achieved e.g. by applying grating structures and, thus, compensate for the mismatch of the propagation constants of the modes to be coupled [2]. In this work, we will present our latest efforts towards the development of grating assisted mode-selective fused fiber couplers. In order to realize these, the fabrication process is divided into two steps. First, the asymmetric fused fiber couplers are fabricated by using an etching, fusing and tapering process of a step index single-mode (sm) fiber from Fibercore SM1500 (4.2/125) and a four mode step index few-mode (fm) fiber from OFS. The cross-section of a fabricated asymmetric fused fiber coupler with a parabolic shape at the taper waist is shown in Fig. 1a. Following this step the grating structure is inscribed into the core of the sm fiber using the amplitude mask method. The grating structure is applied in order to obtain mode-selective light coupling between the sm and fm fibers. The amplitude mask method for inscribing the grating structure is realized by using a bronze foil mask (Optofab) and a KrF-excimer laser (Atlex FBG, ATL Lasertechnik). Moreover, the process parameters (repetition rate, pulse energy and exposure time) are taken from previous investigations of inscribing LPGs into the highly germanium doped sm fiber [3]. In order to determine the required grating period for mode selective light coupling a CAD model was designed in RSOFT. The model takes the fiber parameters as well as the heating zone, the fiber extension and the degree of fusion (DOF) of the coupler fabrication process into account. In Fig. 1b an illustration of the CAD model of the fabricated asymmetric fused fiber coupler is shown. To determine the required grating period for mode-selective light coupling and to simulate the performance of the grating assisted mode-selective fiber coupler the beam propagation method was applied (BeamPROP-toolbox in RSOFT). As illustrated in Fig. 1c, mode-selective light coupling can be obtained between the LP11 mode of the fm fiber and the LP01 mode of the sm fiber for a grating period of 500 μm.
关键词： fused fiber couplers,mode division multiplexing,few-mode fiber,grating structures,spatial division multiplexing
更新于2025-09-12 10:27:22
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[IEEE 2019 18th International Conference on Optical Communications and Networks (ICOCN) - Huangshan, China (2019.8.5-2019.8.8)] 2019 18th International Conference on Optical Communications and Networks (ICOCN) - Mode manipulation based on few-mode fiber devices
摘要： In this paper, several kinds of few-mode fiber (FMF) based devices has been designed. Then an all-FMF mode-locked ring laser with carbon nanotubes was demonstrated with the generation of high purity cylindrical vector beams (CVBs).
关键词： few-mode fiber,cylindrical vector beams,Mode manipulation
更新于2025-09-12 10:27:22
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A temperature sensor based on tapered few mode fiber long-period grating induced by CO2 laser and fusion tapering
摘要： A temperature sensor based on tapered few mode fiber long-period grating is proposed, which is induced by CO2 laser and fusion tapering. Based on the coupling of LP01 and LP11 modes in few mode fiber, the influence of the grating period on resonant wavelength is discussed, and the relationship between the ambient temperature and resonant wavelength shift is analyzed. The temperature measurement experiments of this sensor is performed. The experimental results shows that the temperature sensitivity can reach ?0.0393 nm/°C in the range of 30–90 °C. Therefore, the sensor can be applied to temperature measurement in different environments due to its compact structure, small size and easy fabrication.
关键词： Few mode fiber,Temperature sensor,Long-period grating,Tapered fiber
更新于2025-09-12 10:27:22