In the recently published finite periodic approach to study the optical response of periodic structures, successfully applied to study the optical properties of blue-emitting InGaN/GaN superlattices, the spontaneous charge polarization was neglected. To search the effect of this quantum confined Stark phenomenon, we study here the optical response, assuming parabolic band edge modulations in the conduction and valence bands. We discuss the consequences on the eigenfunction symmetries and the ensuing optical transition selection rules. Using the finite periodic approach in the Wentzel-Kramers-Brillouin approximation, we determine the energy eigenvalues, their corresponding eigenfunctions, and the subband structures in the conduction and valence bands. We calculate the photoluminescence as a function of the charge localization strength and compare it with the experimental result. We show that, for subbands close to the barrier edge, the optical response and the surface states are sensitive to charge polarization strength.

We demonstrate the compact all-optical logic XOR and OR gates in subwavelength plasmonic metal–insulator–metal waveguides with slot cavity resonators, especially for telecommunication wavelengths, with an extinction ratio of 25 dB, which can provide nanoscale logic integrated circuits. The gates behavior is based on suppression or enhancement of resonant modes in a slot cavity resonator induced by a change in position of input ports. The performance of the gates is discussed analytically and verified by the numerical method of finite-difference time-domain (FDTD).

We propose a four-channel plasmonic demultiplexer based on gold–air–gold structure. To do so, an add-drop filter is first proposed consisting of an H-shaped resonant cavity, which is designed to drop a distinct wavelength to other waveguides. Since the selected wavelength depends on the structural parameters of the resonant cavity, two- and four-channel demultiplexers are presented by adding H-shape cavities with different sizes. The results of numerical simulations show that for the total structure, spacing about 50 nm and an average transmission more than 95% for channels are obtained. The proposed device exhibits high-transmission efficiency along with the low channel spacing. The average calculated cross talk is calculated about −18.6  dB.

We show a possibility for soliton formation and superluminality phenomenon at a femtosecond pulse propagation in a medium with noble nanorods. These effects take place if a positive phase grating is induced by laser radiation. We take into account the dependence of two- or one-photon absorption [single-photon absorption (SPA)] on the nanorod aspect ratio and time-dependent nanorod aspect ratio changing due to nanorods reshaping (or melting) because of laser energy absorption. We demonstrate that a fast light propagation mode occurs for various detuning between wave packet carrier frequency and nanorod resonance frequency, which is a key parameter for practical observation of fast or slow light in a physical experiment. We also developed analytical approaches for explanation of laser pulse propagation peculiarities in a medium with nanorods. In particular, in the framework of nonlinear geometric optics approximation, we derived the laws for the pulse intensity and instantaneous frequency evolution if a phase grating is induced by laser radiation in a medium with SPA. We also developed an approximate analytical soliton and derived the chirped soliton amplitude, duration and homogeneous shift evolution, carrier frequency changing, and pulse chirp evolution. The results of analytical consideration are confirmed by computer simulation results.

Conditions of fabrication of first-order distributed-feedback surface gratings designed for single-mode Al0.45Ga0.55As/GaAs quantum cascades lasers with the emission wavelength of about 10  μm are presented. The 1-μm-deep rectangular-shaped gratings with the period of about 1.55  μm and duty cycle in the range of 65% to 71% made by the standard photolithography are demonstrated. The wavenumber difference of about 7  cm−1 at 77 K is observed for the radiation emitted by lasers fabricated from the same epitaxial structure with ridge widths in the range of 15 to 25  μm. Moreover, the emission wavelength of the lasers could be tuned with temperature at a rate of 1  nm/K in the temperature range of 77 to 120 K. The full width at half maximum of the emitted spectra is ∼0.4  cm−1.

We calculate the luminescence of the dilute quaternary InAs(N,Sb). The incorporation of N leads to a reduction of the energy gap of the host InAs and Sb acts as a surfactant, improves the N incorporation, and further reduces the bandgap. This is thus extremely relevant for devices operating in the mid-infrared (MIR) spectral range from 3 to 5  μm. In order to describe this system, the theory starts with the band anticrossing model applied to both conduction and the valence band to generate inputs for analytical approximations that lead to luminescence spectra, including plasma screening, bandgap renormalization, and excitonic enhancements. Direct application of the equations leads to good agreement with some recent experimental data.

We designed two kinds of hybrid plasmonic annular resonators with different cross-sectional shapes, i.e., a square and circle called “square ring” and “circle ring” resonators, respectively. Both resonators feature an ultracompact mode volume of ∼10−4  μm3 and a relatively high-quality factor of ∼102 at a submicron footprint within our studied wavelength range from 400 to 900 nm. Their performance as defined by the Q/V ratio (quality factor over mode volume) is enhanced considerably with a reduction in their physical dimensions. There exists critical annular radii, which increase from 400 to 600 nm with an increase in the azimuthal numbers from m=7 to m=10, if the two types of rings are compared with the same mode numbers and same ring thickness of 120 nm. Below the critical radii, the circle ring resonator outperforms the square ring resonator in terms of the Q/V ratio, and the difference in Q/V of the two types of rings increases rapidly with the decrease of the radii. On the other hand, they have critical annular radii of ∼250  nm, below which the square ring resonator outperforms the circle ring resonator at the wavelengths of 490 and 595 nm; however, the difference in Q/V of

An optical waveguide cantilever sensor is introduced, which is determined by monitoring the coupling efficiency between a waveguide cantilever and a waveguide receptor through the cantilever bending. A straightforward model is developed for an optical waveguide cantilever sensor, in which the coupling efficiency between the cantilever and receptor is calculated using the overlap integral. An effective index is introduced to analyze the thickness of input/output waveguides and cantilever for a maximum coupling with a fiber keeping the single-mode operation. The relationship of the optical waveguide sensor (cantilever, gap, and output waveguide) and the sensitivity is presented. As a consequence, we take an optical waveguide cantilever sensor structure of Si3N4/SiO2/Si as an example, and an optimized design is reported. Moreover, the analysis model is compared with a finite-difference beam propagation method. The result means that our model has a similar accuracy but is more simple, intuitive, and time-saving.

We report, for the first time to our knowledge, the usage of platinum silver bimetallic alloy forms on the synthesized N-Gns (PtAg/N-G) as a saturable absorber (SA) for the mode-locking of a thulium-doped fluoride fiber laser. The experimental results have demonstrated that PtAg/N-G exhibits saturable absorption in the 1.5-μm wavelength range and supports ultrashort pulse generation. Mode-locking occurred when the pump power rose to 340 mW, and the output spectrum had a peak at 1506 nm with the 3-dB bandwidth of ∼0.76  nm. The mode-locked pulse train against a cavity roundtrip time of 146 ns that corresponds to a pulse repetition rate around 6.85 MHz. The autocorrelation trace 7.43 ps with a full width at half maximum pulse width of 4.8 ps, and experimental data were closely fit with a sech2 pulse shape and it indicates the generation of soliton pulse. The output power of this fiber laser is 3.24 mW; hence, the pulse energy is 0.31 nJ and peak power is about 56.9 mW as well. We demonstrate graphene-polymer nanocomposites could be an appropriate SA for high-power fiber laser mode-locking.

Graphene nanosheets anchored with SnO2 nanoparticles with super-high surface area were synthesized via the hydrothermal self-assembly method. Investigations found that the SnO2 nanoparticles are uniformly decorated on the surface of graphene nanosheets and the heterocomposites successfully shift the absorption edge from the UV range for pure SnO2 nanoparticles to a visible range. Photocatalytic investigations show that the SnO2/graphene heterostructures possessing enhanced photocatalytic ability for the Rhodamine B degradation under visible light irradiation. The visible light photocatalytic performance can be attributed to the synergetic effect of graphene and dye molecules. The superior photocatalytic efficiency is ascribed to the large specific surface area of the heterocomposites and the superior electronic characteristics of graphene, which greatly restrain the self-radiative recombination of photogenerated electron–hole pairs.

An approach is proposed for deriving effective layer parameters of a metafilm, based on a combination of the Maxwell–Garnet and generalized sheet transition conditions methods, which can be employed to an arbitrarily shaped particle array. For patch particles, it is revealed that both width and thickness of the particles have a critical role in effective layer parameters. To this end, this paper conceptualizes that with the engineering of width and thickness of the arrayed semiconductor patch particles, near unity absorption can be achieved in the optical frequency range. Our final absorption device contains an array of a specific shape particle, which is a combination of two particles with different widths and thicknesses. The simulation result of the proposed structure is also proved by translation matrix (T-matrix) method.

A midinfrared band-tunable graphene-based plasmonic waveguide is analytically and numerically investigated to realize electromagnetically induced-transparency-like transmission and to slow rainbow trapping light. By applying different Fermi energy levels to the top and bottom graphene nanoribbons, a dynamic control of resonant wavelengths is thus obtained at the desired working regions. Plus, the structural size parameters play a significant role in modulating the resonant spectra and resonant depth. Combining the manipulation of the two sets of influential factors, the transparency window is therefore under control. Detailed investigations of the analytic mechanism of the device are made as well. Furthermore, the light signal that travels in the waveguide can be successfully slowed down to over 340 times the speed in a vacuum. If the nanoribbon width is gradiently distributed, the so-called rainbow trapping can be achieved. Hence, the device has potential applications in nanoimaging, sensing, integrated circuits, and light energy storage domains.

We have proposed and analyzed the plasmonically induced reflection (PIR) effect in a graphene plasmonic device numerically using the two-dimensional finite-difference time-domain method. The obtained PIR window is due to the destructive interference between the bright and the dark modes of the resonators. As an application, a channel add–drop filter based on this PIR window has been proposed and analyzed. The proposed filter and its effect are useful in photonic-integrated circuits and nanoplasmonic devices.

Ion-exchange process is one of the most common techniques used in glass waveguide fabrication. This has many advantages, such as low cost, ease of implementation, and simple equipment requirements. The technology is based on the substitution of some of the host ions in the glass (typically Na+) with other ions that possess different characteristics in terms of size and polarizability. The newly diffused ions produce a region with a relatively higher refractive index in which the light could be guided. A critical issue arises when it comes to designing such waveguides, which is carefully and precisely determining the resultant index profile. This task has been proven to be hideous as the process is generally governed by a nonlinear diffusion model with no direct general analytical solution. Furthermore, numerical solutions become unreliable—in terms of stability and mean squared error—in some cases, especially the K+−Na+ ion-exchanged waveguide, which is the best candidate to produce waveguides with refractive index differences compatible with those of the commercially available optical fibers. Linearized finite-element method formulations were used to provide a reliable tool that could solve the nonlinear diffusion model of the ion-exchange in both one- and two-dimensional spaces. Additionally, the annealed channel waveguide case has been studied. In all cases, unprecedented stability and minimum mean squared error could be achieved.

A design of split-nanotube-based negative index metamaterial for the infrared spectrum has been proposed. The proposed design and its operation are similar to that of a split-ring resonator (SRR) without inheriting the fabrication difficulties associated with conventional SRR. A negative refractive index has been achieved using a split-nanotube in combination with a periodic array of metallic wires between 1.5 and 3.3  μm.

We report on the study and characterization of nanoclusters-related recombination centers within quantum-disks-in-nanowires heterostructure by utilizing microphotoluminescence (μ-PL) and cathodoluminescence scanning transmission electron microscopy (CL-STEM). μ-PL measurement shows that the nanoclusters-related recombination center exhibits different temperature-dependent characteristics compared with the surrounding InGaN quantum-disks-related recombination center. CL-STEM measurements reveal that these recombination centers mainly arise from irregularities within the quantum disks, with a strong, spatially localized emission when measured at low temperature. The spectra obtained from both CL-STEM and μ-PL correlate well with each other. Our work sheds light on the optical and structural properties of simultaneously coexisting recombination centers within nanowires heterostructures.