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Although abundant research on the anisotropy of van der Waals (vdW) materials has been published, we undertake an in-depth study of their optical properties as they have an important guiding role for light control in two-dimensional (2D) nanospace. As an example, we study the reflectance of few-layered black phosphorus (BP) in the total internal reflection (TIR) mode in detail. We demonstrate that its optical anisotropy can be changed on a large scale by varying the incident angles, polarization states, and the in-plane rotation angles of the BP samples. Theoretical analysis indicates that the phenomena observed are common to all the atom-thick biaxial crystals, so these conclusions can be widely applied to other anisotropic 2D materials. This research furthers the current understanding of the properties of BP more comprehensively, and provides guidance for developing new optoelectronic applications, especially when BP and other atom-thick biaxial crystals are integrated with TIR devices. Keywords: Black phosphorus, Optical anisotropy, Total internal reflection, Biaxial crystal

It has been a great challenge to achieve the direct light manipulation of matter on a bulk scale. In this work the direct light propulsion of matter is observed on a macroscopic scale using a bulk graphene-based material. The unique structure and properties of graphene, and the novel morphology of the bulk three-dimensional linked graphene material make it capable not only of absorbing light at various wavelengths but also of emitting energetic electrons efficiently enough to drive the bulk material, following Newtonian mechanics. Thus, the unique photonic and electronic properties of individual graphene sheets are manifested in the response of the bulk state. These results offer an exciting opportunity to bring about bulkscale light manipulation with the potential to realize long-sought applications in areas such as the solar sail and space transportation driven directly by sunlight.

Large area monolayer of self-assembled polystyrene sphere (PS) arrays were formed by an interface self-assembly method and the gap of PS was adjusted by O2 plasma treatment (OPT). After different duration of OPT, the spacing between the PSs varied from 5 to 88 nm. Then, 20 nm Au film was deposited on the PS arrays by electron beam deposition. The absorption peaks of Au-coated PS array red-shifted obviously by changing the gap of PS. The new absorption peaks emerged when the gap of the PS decreased to about 20 nm. The surface plasmon resonance (SPR) was employed to explain the absorption proportion of this Au-PS structure. These micro-nano structures exhibit tunable SPR bands, which may be useful to the applications in some research fields, such as biosensing, single molecule detection, and novel optoelectronic devices.

Nanosphere lithography is an efficient way to fabricate metallic nanostructures with large area. This paper presents the fabrication of metallic hexagonal nano-pyramid arrays by two dimensional nanospheres lithography assisted with O2 plasma treatment. By O2 plasma treatment, the gap and diameter of nanospheres can be modulated. After electron beam deposition, we can fabricate similar nanostructures with different pyramid gap distances. This method may be an easy way to modulate the geometric parameters of nanostructures.

We fabricated inclined Au nanocup arrays by using the nanosphere lithography method combined with dichloromethane etching and investigated their optical properties. The transmittance spectra of these Au nanocup arrays under different polarizations and incident angles were detected and discussed. Surface plasmon resonance was employed to explain the peaks in the spectra. These inclined Au nanocup arrays may be useful for the potential applications in plasmonic devices.

The transmitted and reflected Z-scan characteristics for light-tunneling heterostructures composed of one-dimensional photonic bandgap material and metallic film are theoretically investigated. An apparent Z-scan signal will appear around the light-tunneling even if the incident peak intensity is very low. Both of the transmitted and reflected Z-scan signals from left incidence are much larger than those from right incidence, demonstrating the nonreciprocal for two incident directions. The variation of the reflected Z-scan curve shape is opposite to that of transmitted Z-scan curve shape as light wavelength increases. Moreover, the reflected Z-scan signals from left incidence will show a very sharp peak around the light-tunneling.

Enhanced transmission through sub-wavelength hole arrays and a single sub-wavelength aperture with periodic corrugations surrounded have been investigated extensively. We report the similar phenomenon through a funnel-type aperture with a sub-wavelength outlet in a thick silver film, which was obtained numerically by using finite-difference time-domain method. Properties of the transmission spectrum can be modulated by geometric parameters of the funnel-type aperture. With periodic grooves or dielectric gratings on the output surface of the structure, beaming light emission can be obtained.

Graphene is an emerging class of two-dimensional (2D) material with unique electrical properties and a wide range of potential practical applications. In addition, graphene hybrid structures combined with other 2D materials, metal microstructures, silicon photonic crystal cavities, and waveguides have more extensive applications in van der Waals heterostructures, hybrid graphene plasmonics, hybrid optoelectronic devices, and optical modulators. Based on well-developed transfer methods, graphene grown by chemical vapor deposition (CVD) is currently used in most of the graphene hybrid applications. Although mechanical exfoliation of highly oriented pyrolytic graphite provides the highest-quality graphene, the transfer of the desired microcleaving graphene (MG) to the structure at a specific position is a critical challenge, that limits the combination of MG with other structures. Herein, we report a new technique for the selective transfer of MG patterns and devices onto chosen targets using a bilayer-polymer structure and femtosecond laser microfabrication. This selective transfer technique, which exactly transfers the patterned graphene onto a chosen target, leaving the other flakes on the original substrate, provides an efficient route for the fabrication of MG-based microdevices. This method will facilitate the preparation of van der Waals heterostructures and enable the optimization of the performance of graphene hybrid devices., 22 pages, 5 figures,Letter

A metal-insulator-metal (MIM) waveguide can support two plasmonic modes. Efficient conversion between the two modes can be achieved by reshaping of both phase and power density distributions of the guided mode. The converters are designed with the assistance of transformation optics. We propose two practical configurations for mode conversion, which only consist of homogeneous materials yielded from linear coordinate transformations. The functionalities of the converters are demonstrated by full wave simulations. Without consideration of transmission loss, conversion efficiency of as high as 95% can be realized.

The transmission from a single subwavelength slit in a metal film with periodic dielectric bars on its surfaces has been analyzed numerically by the finite-difference time-domain method. Results show that the role of the periodic dielectric bars is just the same as that of the periodic grooves directly on the surfaces. With the modulations of dielectric bars on the input and output surfaces of the metal film, light transmission through the subwavelength slit is enhanced extraordinarily and confined to directional emission. The CDEW model is employed to explain the mechanism of the transmission enhancement and directional emission caused by the periodic dielectric bars.

The light transmission through a single subwavelength aperture surrounded by periodic grooves in layered films consisting of Ag and transparent dielectric is analyzed numerically by finite difference time domain (FDTD) method. Results show that the transmission through the aperture in the composite films is strongly enhanced by the modulation of grooves on the transparent dielectric. Two models are employed to explain the mechanisms of transmission enhancement.

In this paper, gain and noise characteristics of gain-clamped Fabry-Perot lasing erbium-doped fiber amplifier(EDFA) is investigated in detail when reflective wavelength and reflectivity of the fiber Bragg gratings (FBG) areselected different values. The relationships between gain and noise performance of the gain-clamped EDFA and theselection ofFBG parameters such as reflectivity and reflective wavelength are investigated and analyzed. It is found vianumerical simulation that the selection of FBG parameters has important influence on the performance of the EDFA.The results obtained in this paper can provide significant datum and reference for optimizing and improving the performance of all-optical gain-clamped EDFA. Key words: EJJFA; WDM; all-optical gain clamp; Fabry-Perot cavity 1. Introduction Gain-clamped fiber amplifier is indispensable to overcome the gain fluctuations as the requirements in applications of wavelength-division multiplexing communication system. Generally, there are two main methods torealize gain clamping ofEDFA: electrical gain control 41or all-optical gain control5'21. In the former method, drivingcurrent of pumping laser is modulated in real time according to the feedback signal ofthe output power change detectedby controlling circuit to maintain the constant power level. Its main drawback is that many additional electrical devicesare needed and output signals are obtained with high electrical delay. In the latter method, loop or linear lasing cavity isformed by optical components such as fiber grating, variable attenuators and circulators to constitute stable lasing inamplifier, by which the gain fluctuation of EDFA is under control. This scheme has advantages of real time gainclamped and all-optical integration. The gain clamp in an Erbium-doped fiber amplifier (EDFA) achieved by aFabry-Perot lasing with fiber Bragg reflectors has the advantages of having no additional signal loss, lower cost andsimpler configuration comparing with all-optical gain-clamped EDFA obtained by a fiber-ring lasing cavity. In thispaper, The relationships between gain and noise performance of the gain-clamped EDFA and the selection of FBGparameters such as reflectivity and reflective wavelength are investigated and analyzed in detail. It is found vianumerical simulation that the selection of FBG parameters has important influence on the performance of the EDFA.The results obtained in this paper can provide significant datum and reference for optimizing and improving the

We theoretically study the plasmonic modes in metal-multi-insulator-metal (MMIM) waveguides. Two types of symmetric MMIM structures consisting of three insulators are investigated thoroughly. The effective refractive index, energy confinement, propagation length, and figure of merit are given in terms of geometric parameters. Due to the step index modulation, these properties of MMIM structures differ from the metal-insulator-metal (MIM) structure. Compared with the corresponding MIM structures, MMIM structures can possess either better energy confinement or larger propagation length, which depends on the geometric parameters and the index distribution. Propagation length of up to 10(3) µm and a figure of merit of up to 10(4) are observed for MMIM structure with core thickness of several hundred nanometers.

The enhanced transmission through a single subwavelength slit surrounded with periodic grooves has been simulated by a numerical finite-difference time-domain method. We simulated the transmission as functions of slit depth (film thickness) and groove depth, and also the field distributions in the slit and grooves. The transmission varies periodically as functions of slit depth or groove depth, just like the field distribution in the slit or in the groove. These results imply that the resonance mechanisms in the slit and the grooves are the same and we employ a Fabry–Perot like resonance effect to explain it.

By setting periodic dielectric bars above the incident surface of the metal film instead of grooves directly on it, we study the enhanced transmission through a single subwavelength slit. The surface plasmon excited by the bars is resonant with the incident light, which leads to transmission enhancement. With dielectric bars on or above the film surface, the behaviors of the surface waves excited by the bars are different, which leads to transmission peaks at different incident wavelengths. The similarities and differences of the enhancement of these two cases are discussed. The effects of the height and the refractive index of the dielectric bars on the enhancement are discussed and compared with the results of dielectric bars contacted on the surface. In addition, we change the dielectric bars to silver and a similar enhanced transmission is obtained.

Transmission through a single subwavelength slit surrounded by nonperiodic or approximately periodic grooves in perfect conductive film has been analyzed numerically by the finite-difference time-domain method. Results show that the periodicity of the grooves is not the necessary condition to enhance the transmission, but is sufficient to obtain high enhancement. A spectrum with low enhancement and multiple peaks is obtained through a slit with nonperiodic grooves that is due to the resonances at different wavelengths caused by nonperiodicity. The spectrum of a slit with approximately periodic grooves is almost similar to that of a slit with absolutely periodic grooves regardless of whether the grooves are symmetric with respect to the slit, especially when the deflection of the grooves is very small compared to the grooves' period.