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Abstract: This work proposes a full-duplex 60-GHz Radio-over-Fiber Orthogonal-Frequency-Division-Multiplexing (ROF-OFDM) system employing a frequency quintupling optical up-conversion scheme. To avoid the subcarrier signal beat interference (SSBI) due to dispersion-induced fading, a modified single sideband modulation scheme is proposed for the 10-Gbps QPSK-OFDM down-link signal. The power penalty of less than 2-dB was observed after a 50-km single mode fiber (SMF) and 4m wireless transmission. Wavelength reuse with a 1.25-Gbps OOK for up-link transmission is also demonstrated with a receiver penalty of less than 0.5-dB following 50-km SMF transmission. [Copyright &y& Elsevier]

Abstract: A novel surface plasmon-polaritons (SPPs) refractive index sensor based on tooth-shaped metal–insulator–metal structure is proposed and numerically simulated by using the finite difference time domain method with perfectly matched layer absorbing boundary condition. Both analytic and simulated results show that the transmission minima wavelengths in the transmitted spectrum of the sensor have a linear relationship with the refractive index of material under sensing. Based on the relationship, the refractive index of the material can be obtained from the detection of one of the transmission minima wavelengths in the transmitted spectrum. The resolution of refractive index of the nanometeric sensor can reach as high as 10−6, given the wavelength resolution of 0.01nm. It could be applied to high-resolution biological sensing. [Copyright &y& Elsevier]

Abstract: A full-duplex radio-over-fiber system using frequency-decupling optical millimeter-wave based on external modulation via a Mach–Zehnder modulator is proposed and analyzed theoretically. The simulation results show that the power penalties for both the downstream and upstream signals are less than 0.5dB. In this scheme, the configuration of a base station is simplified due to no laser at a base station, and the frequency of local oscillator signal is largely reduced due to the frequency-decupling millimeter-wave technique. The costs of central office and base station are largely reduced. [Copyright &y& Elsevier]

Abstract: We proposed and simulatedly demonstrated a novel full-duplex radio-over-fiber system using an external modulator and an optical interleaver to generate dual quadrupling-frequency optical millimeter waves for carrying two base station downstream data and wavelength reuse for uplink connection. The simulation results reveal that the power penalties for the downstream and upstream signals of both base stations are less than 0.8dB. In this new scheme, the configuration of the both base stations is simplified further because there is no additional laser at two base stations. The frequency of local oscillator signal is reduced due to frequency quadrupling. The cost of the new system is largely reduced. [Copyright &y& Elsevier]

Abstract: All-optical broadband variable optical attenuators (VOAs) and switches based on plasmonic teeth shaped waveguides have been proposed and numerically investigated. The Finite Difference Time Domain (FDTD) simulation results reveal that VOAs based on three teeth structure filled with CdSe-doped PMMA can continuously attenuate the power of a light beam from 3.7dB to 39dB within a broad forbidden band by an external control light. For wavelengths within the forbidden band, the structure can also operate as a switch with presence or absence of pumping light corresponding to on or off state. For a modulation depth of 27dB, a relatively small variation in the absorption coefficient of CdSe QD-PMMA in side cavity (from κ= 0 to κ= 0.15) is enough. [Copyright &y& Elsevier]

Abstract: A simple fiber-optic sensor based on Fabry–Perot interference for small displacement measurement is investigated both theoretically and experimentally. A broadband light source is coupled into a Fabry–Perot cavity formed by the surfaces of a sensing fiber end and the measured object. The interference signals from the cavity are reflected back into the same fiber. A small displacement via changes in cavity length can be obtained by measuring the wavenumber spacing of the interference fringes. The experimental data meet with the theoretical values very well. Given the light source bandwidth of 40nm and the initial distance of 30μm, the proposed displacement sensing system could achieve high resolution measurement of 16nm. [Copyright &y& Elsevier]

Abstract: We propose a novel radio-over-fiber system based on double-sideband (DSB) modulation and frequency quadrupling to reduce the system cost both at central office (CO) and base station (BS). In this system, by properly biasing the intensity modulator, the repetitive frequency of the optical millimeter-wave (mm-wave) is four times frequency of the local oscillator (LO) signal. Additionally, due to the single-sideband of the mm-wave carrying base data signal, our theoretical simulation shows that the generated mm-wave can be immunized the fading effect and the walk-off of signals. [Copyright &y& Elsevier]

Abstract: A fiber Bragg grating (FBG) interrogating technique based on the relative intensity–demodulating and the demultiplexing of an arrayed waveguide grating (AWG) is presented in this paper. The analytical simulation and the experiment validate the feasibility of this setup. Both theoretical and experiment results show that the shift of the Bragg wavelength of the FBG sensors can be precisely interrogated by the relative intensity reading of two-adjacent-channels of the AWG-based demultiplexer. Errors caused by the light source fluctuation and micro-band losses can be reduced with the relative technique. This technique potentially offers a low-cost, compact, and high-performance solution for the interrogation of FBG distributed sensors. [Copyright &y& Elsevier]

Abstract: A novel arrayed waveguide grating (AWG) with asymmetric configuration is proposed. In this configuration, the length of the output slab region, the width and the spacing of the output waveguides are unequal to the corresponding parts of the input ones. Compared to a conventional symmetric AWG, the asymmetric AWG proposed in this paper has a smaller size without degrading its performance The analytic method used in a conventional symmetric AWG is extended to the asymmetric AWG. A design example of an asymmetric AWG with low insertion loss, low channel crosstalk and wide bandwidth is presented. [Copyright &y& Elsevier]

In this work, a terahertz (THz) fiber directional coupler with a symmetric dual-suspended core structure has been proposed for realizing low loss and polarization-insensitive coupling length in the THz frequency region. The fiber core of the directional coupler consists of two round solid dielectric rods supported by two intersecting thin dielectric layers. Numerical simulations performed using the full-vector finite element method show that a short polarization-independent coupling length can be obtained by adjusting the geometric parameters of the fiber. Moreover, a low-loss THz fiber directional coupling performance can also be achieved at a central frequency of 1.00-THz and approximately 0.16 THz of bandwidth. For example, a coupler with a length of 0.421 cm has a transmission loss of 0.30 dB and 0.26 dB for the x- and y-polarization modes, respectively. • The fiber core consists of two dielectric rods supported by dielectric layers. • The length of the coupler can be tuned to shorter lengths. • The coupling length is made polarization-independent. • The loss of the device is reduced effectively. [ABSTRACT FROM AUTHOR]

This paper introduces a novel hollow cylinder array (HCA) two-dimensional (2D) reflective grating for polarization-independent high diffraction efficiency at a condition of Littrow mounting of wavelength of 780 nm. Remarkably, the (−1, 0) order efficiency for transverse electric (TE) and transverse magnetic (TM) polarizations reaches 98.53 % and 98.24 %, respectively, ensuring excellent diffraction efficiency equilibrium (99.70 %) and extinction ratio (E r TE = 46.02 dB, E r TM = 33.39 dB). The grating's diffraction behavior across incident wavelengths and angles is explored, which shows the grating has a wavelength bandwidth of 16 nm and an angular bandwidth of 3.4° when the main orders efficiencies over than 90 %, along with a thorough analysis of manufacturing tolerances. This grating promises significant potential in high-precision displacement measurement applications, offering robust performance and broad operational bandwidths. • A novel hollow cylinder array two-dimensional reflective grating is presented for the polarization-independent property. • The (−1, 0) order efficiency reaches 98.53 % and 98.24 % for TE polarization and TM polarization, respectively. • Excellent efficiency equilibrium is 99.70 % and extinction ratio 46.02 dB/33.39 dB is for TE/TM polarization. [ABSTRACT FROM AUTHOR]

Variable optical attenuation and optical modulation are essential operations in integrated photonic circuits. A new graphene plasmonic gap waveguide structure, which possesses the functions of variable optical attenuator and modulator, is proposed and numerically investigated. The propagation and attenuation modes of the structure can be realized by tuning the gate-voltage. The result shows that it can achieve great modulation depth per micrometer and the working frequency range of 8 THz or more for the variable optical attenuator and the modulator. It also has the advantages of high tolerance, large attenuation range/ modulation depth, wide bandwidth and high integration without crosstalk, which would be promising for high integrated optical circuits. [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]

Stimulated emission depletion (STED) is a very important technique in super-resolution microscopy. Until now, while autofocusing Airy beam (AAB) has been an attractive theme for both theoretical and applied researches, there are almost no report on AABs being used in STED microscopy. In this paper, we propose a novel STED microscopy based on AABs. A radially symmetric 3/2 phase plate is involved to simultaneously generate autofocusing excitation- and depletion-Airy beams. Remarkably, the AAB can auto-focus to a wavelength-scale spot with a long focal depth (several millimeters): on the contrary, the working distance of a conventional high numerical aperture (NA) objective is usually very short (about 200 μ m). Our calculations indicate that the AAB based STED microscopy can achieve a super-resolution spot with FWHM of 58 nm while the focal length is 4.638 mm. Moreover, with properties of non-diffracting and self-healing, the Airy beam could enable a reduction of the scattering distortion induced by the specimens and has a great potential in imaging thick specimens. [ABSTRACT FROM AUTHOR]