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In this paper, we propose a novel planar metamaterial structure for the electromagnetically induced transparency (EIT)-like effect, which consists of a split-ring resonator (SRR) and a pair of metal strips. The simulated results indicate that a single transparency window can be realized in the symmetry situation, which originates from the bright–bright mode coupling. Further, a dual-band EIT-like effect can be achieved in the asymmetry situation, which is due to the bright–bright mode coupling and bright–dark mode coupling, respectively. Different EIT-like effect can be simultaneously achieved in the proposed structure with the different situations. It is of certain significance for the study of EIT-like effect. [ABSTRACT FROM AUTHOR]

We proposed a dual coupled-resonator system based on the metal-insulator-metal bus waveguide and numerically investigated the plasmon-induced transparency and slow light effect with the Finite-Difference Time-Domain simulations in this paper. The electromagnetically induced transparency-like spectral response will occur between two adjacent stub resonators with detuned resonant wavelength due to the phase-coupled effect. The transmissivity and group index equations were been deduced, which indicated that the system can achieve the effect of the multiple electromagnetically induced transparency-like and slow light. With the optimization, the single peak transmission can reach to as high as 92%, dual PIT transmission peaks appear, as well as group index can reach over 75. These characteristics indicate multiple applications of our system in integrated optical circuits. [ABSTRACT FROM AUTHOR]

An in-line fiber sensor for simultaneous measurement of refractive index (RI) and temperature is proposed and demonstrated. The sensor head is composed of an asymmetric Mach–Zehnder interferometer (MZI), which is combining the single mode-multimode-single mode (SMS) fiber structure and a peanut-shape structure. The transmission dips of the sensor will shift as the ambient RI or temperature variation due to the phase changing. The different wavelength transmission dips formed by the cladding modes interfering with the core mode have different sensitivity responses, so the simultaneous measurement of the RI and temperature can be achieved by monitoring the wavelength shifts of the two transmission dips. The experimental results show that the sensing sensitivities of RI and temperature are −86.7434 nm/RIU and 0.0590 nm/°C in the RI range from 1.3105 to 1.3517 and temperature range from 25 °C to 85 °C, respectively. The novel sensor processes easy fabrication, low cost, and high sensitivity, making it offers high potential applications in physical, biological and chemical sensing. [ABSTRACT FROM AUTHOR]

In this paper, a novel configuration of reflection L-band erbium-doped fiber amplifier (L-EDFA) via inserting a 980 nm pump laser diode (LD) in the input part was constructed. By selecting appropriate power ratio of the 980 and 1480 nm pump LD, gain and noise figure (NF) of the L-EDFA are greatly improved in different degree in the wavelength region from 1565 to 1615 nm. Compared to the configuration pumped by only 1480 nm pump LD with given power, the noise figure decreases 1.3–9.4 dB and the gain enhances 1.5–9.9 dB. [Copyright &y& Elsevier]

A fiber optic sensor coated with molybdenum disulfide (MoS 2) hydrogel is firstly proposed for the detection of lead ion (Pb2+). By splicing a dispersion-compensating fiber (DCF) between two single-mode fibers (SMFs) to form a Mach-Zehnder interferometer (MZI), and using a fusion splicer to discharge the SMF input and output to form a thick waist cone to act as a coupler. A portion of the DCF cladding is etched to excite higher order cladding patterns and a hydrogel sensing film is applied to the etched area, the sulfur atoms in the sensing film form coordination bonds with Pb2+ and change the refractive index (RI) of the sensing film, which further leads to the wavelength shift of the resonant dip. The production process is simple and environmentally friendly. By monitoring the wavelength shift, the adsorption of Pb2+ is continuously monitored, and the sensor has a sensitivity of 3.25 × 108 nm/(mol/L) in the range of 0–1.1 × 10−8 mol/L Pb2+ in aqueous solution. The theoretical detection limit of Pb2+ concentration is 6.15 × 10−11 mol/L at a spectrometer resolution of 0.02 nm. In addition, the experimental results show that the sensor has good repeatability , selectivity and stability, and has a broad application prospect in the field of Pb2+ detection in industry and agriculture. • A SMF-DCF-SMF structure fiber sensor coated with molybdenum disulfide hydrogel is proposed for the detection of lead ion. • A sensitivity of 3.25×108 nm/(mol/L) is achieved and the theoretical detection limit of lead ion is 6.15×10-11 mol/L. • The characteristics of the sensor show applications in the field of lead ion detection in industry and agriculture. [ABSTRACT FROM AUTHOR]

A simple and cost-efficient fiber sensor based on multi-mode interference and core diameter mismatch technologies is proposed to detect the refractive index (RI) in this paper. The refractometer is fabricated by embedding a section of no-core fiber between a section of multimode fiber and dispersion-compensating fiber. Since the power distribution in the fiber will change with the effective refractive index of the cladding, the extinction ratio can be used to characterize the RI sensitivity. The experimental results show that a linear response is obtained with a RI sensitivity of 392.585 dB/RIU in the range of 1.333–1.374. Featured with high sensitivity, simple construction, easy fabrication, low cost and good repeatability, the novel refractometer has potential applications in practical chemical detecting and portable biological sensing. • A refractometer based on multi-mode interference and core diameter mismatch technologies is proposed. • The sensor head merely includes a MMF, NCF, and DCF orderly through automatic splicing without any special processing. • Utilizing extinction ratio demodulation, a RI sensitivity of 392.585 dB/RIU is achieved from 1.3330 to 1.3740, 5-7 times higher than untreated sensors. • Featured with high sensitivity, simple construction, easy fabrication, low cost and good repeatability, it holds potential for practical detection. [ABSTRACT FROM AUTHOR]

In this paper, an efficient L-band multi-wavelength erbium-doped fiber ring laser is demonstrated by recycling backward 1550 nm band amplified spontaneous emission as secondary pump source for the unpumped EDF section. The lasing threshold is reduced and the slope efficiency is improved. A piece of multimode fiber is used as a spatial mode-beating filter. By adjusting the polarization state of the light, the number of lasing wavelength and their spaces are controlled. In dual-wavelength laser, the power of each channel is 4 mW with 40 dB side-mode-suppression-ratio. [Copyright &y& Elsevier]

This paper proposes an optical fiber sensor based on multimode interference (MMI) with a lateral offset structure to measure tensile strain. The coupling ratio of each higher-order mode in the coreless fiber (NCF) can be controlled by the dislocation distance. The experimental results show that the best interference fringes are obtained when the dislocation is 10 μ m and the sensitivity in the range of 0–500 μ ɛ is 28 pm/ μ ɛ. To improve the sensitivity of the sensor further, the measured data were filtered by fast Fourier transform (FFT) and inverse fast Fourier transform (IFFT) to obtain a sinusoidal component, superimposed with a simulated signal to form a vernier effect. With the method of virtual vernier effect, the sensitivity is increased to 452.64 pm/ μ ɛ , which is 15.6 times the original sensitivity. Compared with the traditional vernier effect, the virtual vernier effect method does not require cascade or series method, the reference part is not affected by the environment, and the method can be widely used in many types of interferometric fiber optic sensor devices, especially to overcome the problem that MMI is not suitable for vernier effect. • An optical fiber sensor with a lateral-offset structure is proposed in this paper. • We improve the traditional method of vernier effect and propose the method of virtual vernier effect. The original sensitivity of the sensor has been increased by 15.6 times. • The method can be widely used in many types of interferometric fiber optic sensor devices, especially to overcome the problem that MMI is not suitable for vernier effect. [ABSTRACT FROM AUTHOR]

By breaking the symmetry of the structure, we obtain bound states in the continuum (BIC) in terahertz (THz) using metasurfaces which were prepared with Si and/or Si-compatible materials. With the help of the quasi-BIC with an ultra-high Q factor, the enhanced Goos–Hanchen (GH) shift can reach 5812 times of wavelength. At the same time, the high reflectance is maintained, which makes up for the defect of low reflectance when the GH shift is enhanced by the Brewster angle effect and transmission-type resonances and is convenient for experimental measurement. In addition, the metasurface can be used as an environmental refractive index sensor, and its maximum sensitivity can reach 1.27 × 107mm/RIU, which promotes the development of THz high-resolution sensors. The results could boost the development of silicon-photonics to provide low-cost, highly efficient integrated devices benefited from the same fabrication process as that of large-scale integrated circuit production. • The Goos–Hanchen shift is enhanced by quasi-bound states in the continuum. • High reflectance can be maintained while greatly enhancing the Goos–Hanchen shift. • A high sensitivity refractive index sensor is designed. [ABSTRACT FROM AUTHOR]

A graphene-based metamaterial structure with tunable plasmon induced transparency (PIT) effect is numerically and theoretically researched in this paper. Both the collinear and parallel graphene strips serve as bright mode and a PIT window emerges due to the weak hybridization between them. The transparency window can be tuned by not only adjusting the geometry parameter of the structure but also changing the chemical potential of the graphene strips. Different from the reported tunable PIT system, the spectra width and resonance strength can be tuned with the PIT peak at a fixed frequency in this research. Moreover, the Q factor can be affected by the distance between two bright modes and a figure of merit (FOM) as high as 15.20 can be achieved in this research. These properties expand the application for PIT phenomenon in mid-infrared metamaterial devices, such as filter, modulator and sensor. [ABSTRACT FROM AUTHOR]

Graphene metasurface has attracted a lot of attentions due to the unique tunability for exotic electromagnetic properties. In this work, we propose and numerically investigate a tunable metasurface with two non-coplanar and inter-perpendicular graphene nanoribbon arrays. The variation of transmission at different substrate thickness and the coupled mode are analyzed. It is shown that the Rabi-like splitting can be achieved by the coupling between localized and delocalized graphene surface plasmon polaritons. Tunable coupling strength and positions with different gate-voltages have been discussed. The effect of relaxation time and oblique incidences to resonant responses are also investigated. Additionally, we find an optical analogue of a spring, where the spectral dip vibrates around its equilibrium position at a certain wavelength. Our study suggests that the proposed structure is potentially attractive for realization of tunable double-channel filter, optical switch, and variable optical attenuator based on the graphene metasurface. [ABSTRACT FROM AUTHOR]

Dynamically tunable plasmonic multi-functional is particularly desirable for various nanotechnological applications. In this paper, graphene nano-sheet pair arrays separated by a substrate, which can act as a dynamically tunable plasmonic band stop filter with transmission at resonance wavelength lower than 1%, a high sensitivity refractive index sensor with sensitivity up to 4879 nm/RIU, figure of merit of 40.66 and a two circuit optical switch with the modulation depth up to 0.998, are proposed and numerically investigated. These excellent optical performances are calculated by using FDTD numerical modeling and theoretical deduction. Simulation results show that a slight variation of chemical potential of the graphene nano-sheet can achieve significant resonance wavelength shifts. In additional, the resonance wavelength and transmission of this plasmonic device can be tuned easily by two voltages owing to the simple patterned graphene. These studies may have great potential in fabrication of multi-functional and dynamically tunable optoelectronic integrated devices. [ABSTRACT FROM AUTHOR]

We firstly investigate plasmon induced transparency (PIT) effect in a metal–dielectric–metal (MDM) waveguide coupled to a single loop stub resonator by finite difference time domain method (FDTD). Compared with previous PIT sup based on MDM waveguide, PIT phenomena can be realized in a single plasmonic composite nanocavity without employment of additional optical elements. Plasmon induced transparency windows can be controlled by adjusting the geometrical parameters of the vertical branches or the horizontal branch in the plasmonic structure. The red-shift of PIT peak is almost linearly proportional to the refractive index of the horizontal branch. This plasmonic system takes the advantages of easy fabrication and compactness. The results may pave a way for the dynamic control of light in highly integrated optical circuits, which can realize ultrafast switching, light storage and nanosensor devices. [ABSTRACT FROM AUTHOR]