Transmission Characteristics Of Modes Research Articles

Design of photonic crystal fiber to excite surface plasmon resonance for highly sensitive magnetic field sensing.

To improve the sensing performance of optical fiber magnetic field sensor based on magneto-refractive effect, a D-shaped photonic crystal fiber-surface plasmon resonance (PCF-SPR) sensor based on magneto-refractive effect is proposed and its magnetic field sensing characteristics are investigated. The designed D-shaped PCF has a core-analyte-gold structure. Within the D-shaped PCF, the side polishing surface is coated with the gold film and the special hole is sandwiched between the core and the gold film. To realize the high magnetic field sensitivity for the fiber SPR magnetic field sensor, the special hole is filled with magnetic fluid (MF). In this paper, we analyze the mode transmission characteristics and magnetic field sensing characteristics of this fiber sensor by finite element method. We also obtain a general rule for the optimization of PCF-SPR sensors by analyzing the dispersion curves, the energy of the surface plasmon polariton mode and the core mode on the sensing performance of the designed fiber sensor. The maximum refractive index sensitivity and magnetic field sensitivity of the optimized fiber are 59714.3 nm/RIU and 21750 pm/mT (50-130 Oe), respectively. Compared with optical fiber magnetic field sensors based on magneto-refractive effect reported previously, the magnetic field sensitivity in this paper is nearly two orders of magnitude higher and it can initially achieve nT magnitude magnetic field resolution and testing capability. The proposed fiber sensor has the advantages of simple structure, easy production, high sensitivity, and strong environmental adaptability. It not only improves the sensing performance of optical fiber magnetic field sensors, but also provides an ideal alternative platform for biosensors like microfluidics because of its high refractive index sensitivity and the special structure.

Ultra-broadband mid-infrared TE01 vector mode selector based on ring-core few-mode photonic crystal fiber

A mid-infrared TE01 vector mode selector based on chalcogenide ring-core few-mode fiber is proposed and investigated numerically by the finite element method (FEM). By embedding metal composite nanowire in the PCF core to generate surface plasmon resonance, TE01 vector mode could propagate due to low loss transmission, whereas the fundamental mode, TM01 and HE21 modes could hardly be maintained due to high loss. The effects of structural parameters on mode transmission characteristics and mode loss in photonic crystal fibers in the mid-infrared wavelength range are investigated. Under the optimal structural parameters, the loss ratios of each mode to TE01 mode are more than 50 in the waveband range from 2 to 3 μm, which means the TE01 single-mode transmission can be maintained in ultra-wide mid-infrared band. The designed fiber can be connected with the mid-infrared laser as a vector mode selection device to efficiently output pure TE01 mode cylindrical vector beam, which makes preferable application in mid-infrared optical communication, optical capture, super-resolution imaging, biochemical sensing and other fields.

Mode Transmission Characteristics of Heterogeneous Helical Cladding Large Mode Area Fiber

Mode Transmission Characteristics of Heterogeneous Helical Cladding Large Mode Area Fiber

Numerical investigation for the mode transmission characteristics of a large mode area optical fiber with heterogeneous helical claddings designed for 2.0 µm.

Large mode area (LMA) fibers are widely used in high-power fiber lasers to solve the nonlinear problems. In this Letter, a novel LMA fiber with heterogeneous helical claddings (HHCs) is proposed. A coordinate transformation simulation technique is adopted to analyze the fiber mode transmission characteristics. The effects of the fiber parameters such as θ,Λ,r,n0,n1,n2,n3, and λ on the mode transmission characteristics include loss coefficient L and effective mode area Aeff. When θ=14∘, Λ=22mm, n0=n2=1.439, and n1=n3=1.438 are adopted. The loss coefficients are L01=0.093dB/m, L11=9.47dB/m, and L21=23.36dB/m; the single-mode fiber diameter 2r is at least 60 µm; and the corresponding effective mode field area Aeff is 2025µm2. As the helix pitch is a centimeter order of magnitude and the fiber is all solid state, the HHC fiber is relatively easy to fabricate and convenient for cutting, splicing, etc., and will be well applied in the field of high-power fiber lasers.

Design and analysis of trench-assisted dual-mode multi-core fiber with large-mode-field-area.

A novel trench-assisted dual-mode multi-core fiber with large-mode-field-area is proposed. The structure consists of 17 conventional cores and two air holes according to a regular hexagon, which can realize strict dual-mode transmission. The structural parameters' effect on mode transmission characteristics, mode-field-area, and bending loss are analyzed systematically. By optimizing the structural parameters, the mode-field-area of the fundamental mode can reach ${2100.619}\;{{\unicode{x00B5}{\rm m}}^2}$. The introduction of the trench with a lower refractive index than cladding can reduce the bending loss to ${9.88} \times {{10}^{- 4}}\;{\rm dB}/{\rm m}$ when the bending radius is 2.3 cm. Besides, the structural design is flexible, and the manufacturing process is simple, which has broad application prospects.

Mode transmission analysis method for photonic lantern based on FEM and local coupled mode theory.

In this paper, a novel full vector numerical simulation method based on the finite element method (FEM) and local coupled mode theory (LCMT) for analyzing the mode transmission characteristics of photonic lantern (PL) with arbitrary input mode field is proposed. Compared with the traditional numerical simulation methods for PL, our method can greatly reduce the computational complexity and ensure high precision. Taking a three-core PL as an example, we verify the validity of our method. The advantages and properties of our method are also discussed in detail and found instructive for optimization design of PL. Through specifically optimizing the geometric parameters of the PL according to the properties, mode selectivity of LP01 and LP11 can be respectively improved up to 44.5 dB and 54.7 dB with more than 95% coupling efficiency.

Refractive index sensor based on multimode interference in a twin-hole fiber

We report a simple refractive index (RI) sensor based on a twin-hole fiber (THF). The THF is fused with the single-mode fiber to realize sensing by the multimode interference. The mode transmission characteristics in the THF are numerically investigated. In the sensing experiment, when the surrounding RI changes, the wavelength shift of the transmission spectrum shows approximate linearity in the low RI region and nonlinearity in the high RI region. When a THF with the length of 10 mm is used, the highest sensitivity can be up to 1351 nm / RIU in the RI range from 1.430 to 1.445. Moreover, the effect of the temperature on the transmission spectrum relative to the RI is much smaller when the external temperature changes from 30°C to 80°C.

Whispering gallery modes in a microsphere attached to a side-polished fiber and their application for Magnetic field sensing

This paper proposes a magnetic field sensor based on side-polished fiber and microspheres. We use side-polished fiber and SiO2 microspheres to form fiber microsphere cavity, and then package the fiber microspheres in a capillary filled with magnetic fluid form magnetic field sensor. By adding optical fiber microspheres, light propagates through the near-field coupling to the microspheres and directly arouse the whispering gallery modes. The WGM resonance formed in the microcavity will cause a resonance peak with an ultra-narrow spectral line-width in the transmission spectrum, which will improve the quality factor (Q) and figure of merit (FOM) of the sensor. The paper uses finite element analysis to simulation the mode transmission characteristics of side-polished fiber microspheres and the magnetic field sensing performance. The simulation results show that the magnetic field sensor has a strength sensitivity of up to 0.75 dB/Oe and the quality factor up to 2.5 × 104, which has a refractive index sensitivity of 125 nm/RIU, and a maximum FOM of 2.5 × 103. The paper effectively improves the quality factor of the sensor, by adding a microsphere, which provides an alternative research platform for the development of new magnetic field sensors compatible with high-sensitivity sensing and high-precision detection.

Lossy mode resonance generated by titanium dioxide nanoarray: a comprehensive theoretical research

The lossy mode resonance (LMR)-based optical fiber waveguide based on titanium dioxide nanoarrays was discovered and researched for the first time in this paper. Two kinds of waveguide coating structures, titanium dioxide nanoarrays and nanofilms-nanoarrays systems, were researched using finite element method, where the localized field distribution, the mode transmission characteristics and measurement sensitivities of surrounding refractive index were researched in detail. In the former structure, there exists a localized electromagnetic field that can be generated by both TE and TM polarization modes around nanoarrays. By increasing the diameters of nanoparticles and decreasing the intervals of nanoarrays, the resonance wavelength will redshift and the measurement sensitivity will be enhanced. In the latter structure, the localized electromagnetic field can be obviously enhanced due to the mode coupling between nanofilms and nanoarrays. In addition, the measurement sensitivity of refractive index was 5179 nm/RIU in the range of 1.333–1.343, which is two times higher than that of the structure without TiO2 nanoarrays. This paper opened up a door to study the LMR generated by semiconductor nanoparticles, which is useful in the research of electromagnetic resonance-based sensors in nanoscales.

Experimental study on short-distance free-space transmission characteristics of OAM beam

The short-distance free-space transmission characteristics of the optical orbital angular momentum (OAM) beam were experimentally studied. The transmission distance is 0~50 m indoors. A digital micromirror device (DMD) was used in the experimental setup to generate the OAM beam. At the receiver, a spatial beam analyzer was used to measure the intensity pattern of the OAM beam. The beam broadening effect of the OAM beam at different transmission distances was studied. The phase pattern of the OAM beam was studied by the interferometric method. At the receiver, a single path Sagnac interferometer (SPSI) was used to separate and detect the intensity of modes of the OAM beam. The effects of energy migration from the sending mode to the sideband modes of the OAM beam were studied. A heater was used to generate the strong turbulence to simulate the influence to the OAM beam mode transmission characteristics. The experimental results show that the OAM beam with large mode topological charge has more deterioration of the mode purity after transmission in the strong turbulence.

外径波动下空心布拉格光纤的模式传输特性

外径波动下空心布拉格光纤的模式传输特性

Transmission characteristics of modes in dielectric slab waveguides with finite‐length, uniformly bent sections

A new, rigorous theory is presented for analyzing radiation and transmission of electromagnetic waves in uniformly curved sections of slab waveguides. General fields are expressed, in this theory, in terms of a spectral integral of eigenmodes with continuous eigenvalues. The theory is applied to the investigation of mode transmission characteristics of a circularly bent, finite‐length dielectric slab waveguide, sandwiched between the two straight sections. It is demonstrated that the analysis method is also applicable, though approximately, to the study of radiation and transmission of electromagnetic fields in a uniform bend of a three‐dimensional dielectric waveguide.