Jungang Huang

Fresnel diffraction and fractal patterns from polygonal apertures

Two compact analytical descriptions of Fresnel diffraction patterns from polygonal apertures under uniform illumination are detailed. In particular, a simple expression for the diffracted field from constituent edges is derived. These results have fundamental importance as well as specific applications, and they promise new physical insights into diffraction-related phenomena. The usefulness of the formulations is illuminated in the context of a virtual source theory that accounts for two transverse dimensions. This application permits calculation of fractal unstable-resonator modes of arbitrary order and unprecedented accuracy.

Current control of light by nonreciprocal magnetoplasmonics

The ability to actively control light has long been a major scientific and technological goal. We proposed a scheme that allows for active control of light by utilizing the nonreciprocal magnetoplasmonic effect. As a proof of concept, we applied current signal through an ultrathin metallic film in a magneto-plasmonic multilayer and found that dynamic photonic nonreciprocity appears in magnetic-optical material layer due to the magnetic field being induced from current signal and modulates surface plasmon polaritons trapped in the metal surface and the light reflected. The proposed concept provides a possible way for the active control of light and could find potential applications such as ultrafast optoelectronic signal processing for plasmonic nanocircuit technology and ultrafast/large-aperture free-space electro-optic modulation platform for wireless laser communication technology.

Frequency - Selective Nanostructured Plasmonic Absorber by Highly Lossy Interface Mode

We report on an existence of a highly lossy interface mode (HLIM) in a designed plasmonic nanostructure for perfect absorption of the incident optical waves. Interactions between the single thin- metallic-layer (TML) and slits arrays for excitation of the HLIM in the proposed plasmonic absorber are investigated, and eigenfrequency formula for the HLIM is derived. Analytical and numerical results show that the HLIM is frequency-selective, opens a narrow and steep absorption band in photonic stopband of the slits arrays. Due to the HLIM lossy characteristic, surface plasmon polaritons are signiflcantly trapped at the TML interface with absorption close to 100%.

Spontaneous spatial fractal pattern formation in dispersive systems

We report spontaneous spatial optical fractal patterns in a ring cavity containing a thin slice of diffusive Kerr-type material. The Turing threshold instability condition is derived through linear analysis, and static patterns are found to be described by spectra with multiple-minimum characteristics. These theoretical predictions are subsequently verified through numerical simulations with both one and two transverse dimensions. Our findings support that a proposed fractal-generating criterion for nonlinear wave-based systems with thin-slice host media can have independence with respect to both system geometry and nonlinearity. We conclude by detailing further potential research directions and possible applications of fractal light sources.

SPONTANEOUS SPATIAL FRACTAL PATTERN FORMATION IN ABSORPTIVE SYSTEMS

We predict, for the first time to our knowledge, that purely-absorptive nonlinearity can support spontaneous spatial fractal pattern formation. A passive optical ring cavity with a thin slice of saturable absorber is analyzed. Linear stability analysis yields threshold curves for Turing (static) instabilities with features proposed as characteristics of potential fractal pattern formation. Numerical simulations of the fully-nonlinear dynamics, with both one and two transverse dimensions, confirm theoretical predictions.

Unstable resonators with Gosper-island boundary conditions: Virtual-source computation of fractal eigenmodes

The Gosper island is a well-known fractal belonging to a family of self-similar “root 7” curves constructed from a simple iterative algorithm [1]. One begins with a regular hexagon (the initiator, corresponding to iteration n = 0) with sides of reference length l<inf>0</inf>, and then breaks each of these straight-edge elements into three equal segments of length l<inf>n</inf> = l<inf>0</inf> (1/7^1/2)ⁿ where n = 1, 2,3,… (the generator stages). If the total number of length elements after applying the generator n times is given by N<inf>n</inf> = 6 × 3ⁿ, then the Hausdorff-Besicovich dimension of such a curve is calculated to be D = lim<inf>n→∞</inf>-log(N<inf>n</inf>)/log(l<inf>n</inf>) = 2log(3)/log(7) ≈ 1.1292.

A new scheme for novel all-optical wavelength conversion withultrabroad conversion tunability and modulation-transparency

A scheme named “spoof” four wave mixing (SFWM) is proposed, where a dynamic refractive index grating induced by the beating of the co-propagating pump and signal is able to modulate a Bragg grating (BG) to create additional reflective peaks (ARPs) at either side of the unperturbed BG bandgap. When a probe wave located at the wavelength of ARPs is counter-propagating, it is reflected from the induced ARPS while tracking the signal data information but at the new wavelength. In contrast to the well-known FWM, where the induced dynamic refractive index grating modulates photons to create a wave at a new frequency, the SFWM is different in that the dynamic refractive index grating is generated in a nonlinear BG to excite ARPS at either side of the original BG bandgap in reflection spectrum. This fundamental difference enable the SFWM to avoid the intrinsic shortcoming of stringent phase matching required in the conventional FWM, and allows novel all-optical wavelength conversion with modulation format transparency and ultrabroad conversion range, which represents a major advantage for next generation of all-optical networks.

Complexity and Fractality in Kaleidoscope Laser Eigenmodes

Kaleidoscope lasers are investigated using virtual source modelling. We calculate families of eigenmodes for cavities with arbitrary parameters, and consider the implications of non-trivial transverse symmetry for fractal dimension.

All Optical Nanostructed Sensor Based on Metal-Dielectric-Metal Plasmonic Waveguide

Based on a two-dimensional plasmonic metal-dielectric-metal waveguide with a thin metallic layer and dual nanocavites inserted in the core, a novel nanostructured absorber is presented. A transfer matrix model for the proposed structure is established, and the optical spectra are investigated. Design results show that a narrow reflection spectrum occurs at position of the near-unity absorption, and is significantly influenced by the environment. It is able to generate a sensitivity as high as 1000 nm/RIU, which be used as an excellent sensing platform for chemical and biochemically relevant molecules.

Mode hop free tunable blue laser

A mode hop free tunable blue laser at 465 nm based on an external cavity system is investigated. The single longitudinal mode second-harmonic generation (SHG) blue laser was generated using quasi-phase matching (QPM) based MgO: PPLN pumped by infrared diode laser at 930 nm with one lasing longitudinal mode. The wide turning rang in excess of 100 GHz is achieved by using combination the etalon, silica glass plate and narrow band filter into the external cavity, which only allow one longitudinal mode running and operating wavelength tuning. 30 mw blue light was obtained at wavelength of 465 nm with beam quality better then M2 =1.3.