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To improve the selectivity of carbon nanotubes for gas sensors, we design a surface plasmon polarization waveguide based on graphene that can sense trace gases. In addition, a gas concentration measurement system was designed for a sensor based on optical cavity ring-down spectroscopy. The gas concentration measurement system was composed of two loops, which were combined with the minimum mean square error algorithm to achieve an amplified spontaneous emission noise filter. The experimental results show that the gas concentration measurement error was significantly improved after CO filtering. The slope of the logarithmic ring-down curve and the ring-down time decreased with the increasing gas concentration. The gas concentration and ring-down time showed an improved linear relationship. The design system can detect trace gases as a single gas or a variety of toxic gases in special environments. The device provided a wide range of sensors and measurements. Moreover, the proposed device is relatively simple and easy to implement, with high detection sensitivity.

In this paper, a novel image watermarking method is proposed which is based on discrete wave transformation (DWT), Hessenberg decomposition (HD), and singular value decomposition (SVD). First, in the embedding process, the host image is decomposed into a number of sub-bands through multi-level DWT, and the resulting coefficients of which are then used as the input for HD. The watermark is operated on the SVD at the same time. The watermark is finally embedded into the host image by the scaling factor. Fruit fly optimization algorithm, one of the natural-inspired optimization algorithms is devoted to find the scaling factor through the proposed objective evaluation function. The proposed method is compared to other research works under various spoof attacks, such as the filter, noise, JPEG compression, JPEG2000 compression, and sharpening attacks. The experimental results show that the proposed image watermarking method has a good trade-off between robustness and invisibility even for the watermarks with multiple sizes.

With the superiority of capacity space in storage and transmission, multiple-image encryption has become the new focus of information security technology. In this paper, we introduce a multiple-image encryption scheme by using robust chaotic map in wavelet domain, based on the architecture of unified permutation and separate diffusion. Firstly, the original images are decomposed using discrete wavelet transform (DWT) and the low-frequency components are reassembled as the plain image (approximate image). Then, the plain image is entirely scrambled by using Arnold cat map. Thirdly, the scrambled image is further decomposed and the resulted block images are separately employed to combine with the amplitude parameter of robust chaotic map (RCM) to generate key stream in each diffusion process. Since the keys in every diffusion process depend on the plain image and each encrypted block image contains aliased information of multiple images, it is difficult for the intruder to decipher the intercepted encrypted information. Numerical simulations are made to further demonstrate the reliability of the encryption scheme.

The two-dimensional material, represented by graphene, is an immediate research focus of interdisciplinary fields, such as nanophotonics and life sciences. The unique advantages of surface plasmon polaritons, such as enhanced transmission and sub-wavelength structure, bring opportunities for achieving all optical circuits. In this paper, based on graphene, silicon dioxide, air cavity, and so on, a novel channel surface plasma waveguide was developed. By contrasting the waveguide characteristics of graphene and gold, it is found that the mode field could be restricted in air cavity region using graphene, and the deep sub-wavelength of light field was restrained. Besides, through finite element simulation, it is investigated that propagation losses could be as low as 0.019 dB/μm, the area of normalized mode field could be as low as 0.014 λ2, and the limiting factor is 0.5. Compared with the current waveguide, the above result shows that the propagation losses is an order of magnitude lower; 20.52% of limiting factor is promoted, besides; better waveguide characteristics could be obtained with realization of sub-wavelength optical field limit. Meanwhile, the production process of waveguide structure is simple, and it is an important way to solve the high speed and miniaturization and integration of optoelectronic integrated technology in the future.

Surface plasmon polariton lasers are the basis for photonic circuits, but their losses, thresholds, and some other problems remain thorny issues. In this study, we put forward a novel ridge-type gold film surface plasmon polariton laser. The device adopts a multi-layer hybrid waveguide structure, where the bottom layer is a gold film, and a gold ridge is formed over the center of the gold film. We symmetrically place the two SiO2layers on both sides of the gold ridge as buffer layers and deposit a gold nanoribbon on the top of gold ridge. Two air gaps are formed between the gold ridge and SiO2buffer layers. We numerically study the structure, and the results show that at the operating wavelength of 1550 nm, the effective mode area reaches 1.375 × 10−5λ2 , and the confinement factor reaches 0.75. When the width of the SiO2layer is 2 nm, the height of the ridge is 10 nm, and the angle of the ridge is 80°, the waveguide can effectively enhance the light field confinement so as to limit the energy to a very small range and exhibits the minimum gain threshold. The waveguide can provide a solution for the optical source device of the surface plasma excitation circuits and has great application potential in the ultra-small and high-density optical chips.

Graphene has potential to replace germanium as compound semiconductor for high-performance devices because of its unique optoelectronic properties and availability of existing integrated circuit manufacturing technology. This study investigates surface plasmon polariton (SPP) waveguide-based interaction between CdS nanowires and graphene nanobelts to determine shortcomings of the existing technology. The structure uses MgF2 as cladding, which symmetrically covers CdS nanowires and graphene nanobelts. An air gap of same width is etched in middle of CdS nanowires and graphene nanobelts. SPP is optically excited. Gain compensation is obtained through coupling effect of nanowires, capacitance-enhanced effect of air gap and GaAs semiconductor material, and low refractive index of buffer layer to reduce transmission loss. The structure can achieve strong photon localization and easily implement low threshold for nanometer laser. Experiments on characteristics of SPP show that increasing air gap width of structure reduces transmission loss and increases limiting factors. Limiting factor of waveguide structure is less than 0.15, which indicates ultra-deep subwavelength constraints. SPP waveguide can be integrated with various nanophotonic and electronic devices and has broad application prospects in optical sensing, optical communication, and other fields.

Hyperbolic-type equilibrium requires that all the real parts of the corresponding eigenvalues are nonzero. In this paper, a three-dimensional autonomous chaotic system is introduced, and interestingly we find that one non-hyperbolic equilibrium point and two hyperbolic equilibrium points coexist in this system, which, according to the information we know, has not been previously reported. We first reveal the basic dynamics of the system through analyzing phase portrait, frequency spectrum, Poincare map, bifurcation diagram and Lyapunov exponent. Then, based on the idea of the improved modular technology, we build an analog circuit to realize the chaotic system, which further verifies the theoretical results. Finally, we design a simple feedback controller on account of Lyapunov asymptotic stability theory, to globally suppress the system to its equilibrium points.

Semiconductor surface plasmon polariton (SPP) waveguide has unique optical properties and compatibility with existing integrated circuit manufacturing technology; thus, SPP devices of semiconductor materials have wide application potential. In this study, a new integrated graphene SPP waveguide is designed using the bottom and top roles of graphene. Moreover, a T waveguide structure is designed by InGaAs of semiconductor gain, with rectangular GaAs material on both sides. The structure adopts light to stimulate the SPP, where its local area is enhanced by the interaction between two interface layers and a semiconductor gain and where its frequency can be adjusted by the thickness of the graphene. Characteristic analysis reveals the coupling between the T semiconductor gain and the SPP mode. The propagation distance of the waveguide can reach 75 cm, the effective mode field is approximately 0.0951λ 2, the minimum of gain threshold is approximately 2992.7 cm−1, and the quality factor (FOM) can reach 180. The waveguide structure which provides stronger localization can be compatible with several optical and electronic nanoscale components. That means, it can provide light for surface plasmon circuit and also can provide a great development in the low-threshold nanolaser.

In recent years, surface plasma resonance (SPR) technology for the preparation of multifunctional detection chips has drawn considerable research attention. This study designs a multilayered SPR waveguide sensing device based on a metal medium that features moderate temperature and humidity. The surface plasma is stimulated using a Kretschmann-type structure and a single temperature and humidity chip of SPR technology to achieve multifunctional detection. The sensing principle of the proposed device is based on SPR angle and the environmental relationship between relative humidity and temperature. Characteristic analysis also verifies that SPR with an incident wavelength of 632 nm can be accomplished by the basic linear relationship between the resonance angle and SiO 2 refractive inde. The accuracy of dual-channel sensors is higher than that of single-channel sensors. The metal layer for gold channel sensitivity can reach 7000 nm/RIU. The dual-channel sensor designed in this study exhibits low refractive index, temperature, and humidity and can thus achieve improved sensitivity.

Metal-insulator-metal (MIM) waveguides with subwavelength apertures exhibit unique properties that are considered breakthroughs in surface plasma technology. In this paper, we established a surface plasmon polariton (SPP) mode of MIM structure as well as a theoretical model of reflectivity and excitation coefficients to clarify the SPP mode structure. During simulation calculations, attenuation of the TM ground state mode with large-thickness dielectrics is over the oscillation mode, which is obviously different from the traditional dielectric waveguide. The TE mode exhibits characteristics of anamorphic dielectric optical waveguides, and its propagation distance is longer than that of the TM 0 mode. With increasing length, the cavity quality factor Q increases, which indicates that the SPP reflection is limited. The quality factor of the cavity and the end-face have a close relationship. MIM waveguides with larger Q values can produce optical waves coupled with the SPP mode. In this paper, we analyzed SPP propagation constants and attenuation coefficients to promote the development of an integrated surface plasmon.

Memristive system and encryption technology are two hot topics in the study of nonlinear dynamics. In this paper, we introduce a memristor-based circuit system and conventionally explore its dynamical behavior by analyzing phase portraits, time series, Lyapunov exponents and bifurcation diagrams. It is found that this system exhibits abundant dynamics such as multi-stability, transient dynamics and antimonotonicity. As it is difficult to reproduce the accurate dynamics because of the extremely sensitive dependence on initial conditions and system parameter, and this system can be recommendable for secure encryption application. Consequently, by virtue of the excellent characteristics of the memristive system, we design a chaotic image encryption algorithm based on dynamic DNA operation and dynamic diffusion (CIEA-4D). The pixel updating, permutation, DNA operation and diffusion of the encryption algorithm are all closely related to the plain image, which strongly enhances the security since a tiny change in plain image will influence the whole encryption process. What’s more, the algorithm has a high operational efficiency for the parallel computing of DNA operation, the pre-acquired chaotic sequence and hash values of plaintext images.

This paper reports a new fractional-order four-dimensional (4D) smooth autonomous system which is special since it can generate a four-wing hyperchaotic attractor but has only one zero equilibrium. The issue of robust control for the fractional-order hyperchaotic system with uncertainties and interference is considered. On the basis of the fractional Lyapunov stability theorem, a linear state feedback controller is derived to guarantee robust Mittag–Leffler stability of the fractional-order hyperchaotic system. The control strength matrix is obtained by solving the linear matrix inequality (LMI). The effectiveness and robustness of the proposed scheme is verified via numerical simulation.

In this paper, the synchronization between spatially distributed power plants and their supported consumers is studied, where the case of Kuramoto-like model power grids connected to an external permanent magnet synchronous motor (PMSM) is taken as an example. We focus on the dependence of the synchronization on the coupling coefficient. To quantitatively study the synchronization degree, we introduce the order parameter and the frequency deviation to measure the synchronization of the coupled system. It is found that as the external coupling coefficient is increased, the distributed power grids and the loading system become more and more synchronized in space, and the complete synchronization appears at a particular value of external coupling coefficient. Our results may provide a useful tip for analyzing the synchronous ability of distributed power grids.

The value of the output capacitance (C) should be carefully considered when designing a photovoltaic (PV) inverter since it can cause distortion in the working state of the circuit, and the circuit produces nonlinear dynamic behavior. According to Kirchhoff's laws and the characteristics of an ideal operational amplifier for a strict piecewise linear state equation, a circuit simulation model is constructed to study the system parameters (time, C) for the current passing through an inductor with an inductance of L and the voltage across the capacitor with a capacitance of C. The developed simulation model uses Runge–Kutta methods to solve the state equations. This study focuses on predicting the fault of the circuit from the two aspects of the harmonic distortion and simulation results. Moreover, the presented model is also used to research the working state of the system in the case of a load capacitance catastrophe. The nonlinear dynamic behaviors in the inverter are simulated and verified.