Qiang Ren

Deep-subwavelength light transmission in hybrid nanowire-loaded silicon nano-rib waveguides

Hybrid plasmonic waveguides leveraging the coupling between dielectric modes and plasmon polaritons have emerged as a major focus of research attention during the past decade. A feasible way for constructing practical hybrid plasmonic structures is to integrate metallic configurations with silicon-on-insulator waveguiding platforms. Here we report a transformative high-performance silicon-based hybrid plasmonic waveguide that consists of a silicon nano-rib loaded with a metallic nanowire. A deep-subwavelength mode area (λ2/4.5×105−λ2/7×103), in conjunction with a reasonable propagation distance (2.2–60.2xa0μm), is achievable at a telecommunication wavelength of 1.55xa0μm. Such a nano-rib-based waveguide outperforms its conventional hybrid and plasmonic waveguiding counterparts, demonstrating tighter optical confinement for similar propagation distances and a significantly enhanced figure of merit. The guiding properties of the fundamental mode are also quite robust against possible fabrication imperfections. Due to the strong confinement capability, our proposed hybrid configuration features ultralow waveguide cross talk and enables submicron bends with moderate attenuation as well. The outstanding optical performance renders such waveguides as promising building blocks for ultracompact passive and active silicon-based integrated photonic components.

Leap-Frog Continuous–Discontinuous Galerkin Time Domain Method for Nanoarchitectures With the Drude Model

A continuous–discontinuous Gakerkin time domain method (CDGTD) with vector basis functions is proposed to analyze the wideband response of plasmonic structures with the Drude dispersive model. Compared to the conventional time domain approaches, such as FDTD and PSTD, the unstructured mesh can provide a better geometrical approximation of curved surfaces and fine features. An EB scheme Riemann solver is employed to calculate the flux between adjacent subdomains. The relationship between the electric field and the polarization currents is modeled by a first order auxiliary differential equation (ADE). A leap-frog scheme is proposed to update Maxwells equations, the ADEs of the Drude medium and the perfectly matched layer (PML) in an efficient manner. This new approach is validated by virtue of simulating the ultra-wideband behavior of a gold nanoloop antenna with and without a substrate as well as the reflectivity of a dual-band infrared absorber. Its advantage in computational cost is demonstrated via comparison to a commercial software package. In this light, the CDGTD method represents a more efficient forward modeling tool, which has been successfully employed here to perform a parametric study of a dual-band infrared absorber.

Hybrid vanadate waveguiding configurations for extreme optical confinement and efficient polarization management in the near-infrared

Vanadate materials such as CaVO3 and SrVO3 were recently proposed as promising alternatives to their conventional transparent conducting oxide counterparts owing to the superior capability for simultaneous realization of high optical transparency and high electrical conductivity originating from strong electron-electron interactions. Here we show that, in addition to their remarkable optoelectronic properties as conducting materials, their incorporation into planar waveguiding configurations could enable outstanding optical performance that is otherwise difficult to achieve with conventional material building blocks, especially metals. Starting from the guided wave at a single CaVO3/dielectric interface, the unique dispersion relationship and propagation property of the fundamental mode are revealed and compared to the conventional surface plasmon polariton associated with a silver/dielectric planar configuration. The superior confinement capability and the unique modal attenuation of the CaVO3-based waveguiding platform are further demonstrated via investigating silicon-based hybrid guiding schemes integrated with a CaVO3 nanostructure. By leveraging the pronounced polarization dependent loss in the hybrid configuration, an ultra-compact TE-pass polarizer is numerically demonstrated at telecommunication wavelengths. This transformative design features a reduced footprint and enhanced optical performance when benchmarked against the current state-of-the-art in hybrid silicon polarizers. The combination of these vanadate materials with traditional waveguiding platforms thereby opens new avenues towards miniaturized functional integrated photonic devices, and potentially enables a variety of intriguing applications at the sub-diffraction-limited scale.

Ultra-deep-subwavelength light transport in hybrid nanowire-loaded silicon nano-rib waveguides

We report a high-performance silicon-based hybrid plasmonic waveguide that consists of a silicon nano-rib loaded with a metallic nanowire. An ultra-deep-subwavelength mode area (λ²/4.5×10⁵ ∼ λ²/7×10³), in conjunction with a reasonable propagation distance (2.2 ∼ 60.2 μm), is achievable at a telecommunication wavelength of 1.55 μm, which indicates that this device outperforms its conventional hybrid and nanowire waveguiding counterparts.

Efficient cross-talk reduction of nanophotonic circuits enabled by periodic silicon strip arrays

We develop a simple and efficient crosstalk reduction approach for Si-based nanophotonic circuits by introducing a periodic array of Si strips between adjacent waveguides. Studies indicate that the coupling length can be extended by more than two orders of magnitude for a waveguide pair with an edge-to-edge distance of ∼λ/3. Our approach offers a feasible route toward photonic integrated circuits with an ultra-high packing density.

Ultra-compact broadband TE-pass polarizer based on vanadate-nanowire-integrated SOI waveguides

An ultra-compact TE-pass polarizer is numerically demonstrated at telecommunication wavelengths by integrating a vanadate nanowire with a SOI platform. Results show that a device of 15 μm in length is capable of achieving a high extinction ratio of 22 ∼ 34 dB, in conjunction with a low insertion loss of 0.18 ∼ 0.23 dB in a wavelength range of 1.52 ∼ 1.62 μm.

An efficient wideband numerical simulation technique for nanostructures comprised of DCP media

This work presents an efficient time domain numerical approach to simulate the wideband response of Drude-critical point (DCP) media. Based on previous research and development of the Discontinuous Galerkin Time Domain (DGTD) method, this approach applies the collocated E-J scheme to discretize the electric fields and polarization currents. A hybridization of the Runge-Kutta and Newmark methods is also proposed to solve the associated first-order and second-order temporal auxiliary differential equations. The effectiveness and efficiency of this new approach is validated through comparison with commercial software.

Reconfigurable nanowire assembly enabled field-switchable broadband polarizers

In this paper, a switchable broadband polarizer based on the electric field directed reconfigurable assembly of gold nanowires (NWs) is presented. Taking advantage of the collective optical properties of the two-dimensional gold NW lattices, we have experimentally demonstrated that transmission of linear polarized light can be purposely controlled using a dual electrode design to reversibly rotate the lattice by 90° on-demand. In addition, our experiments reveal that the transmission control is closely related to the geometrical dimensions of the NWs as well as the applied electric field conditions.

A vanadium dioxide integrated hybird metamaterial with electrically driven multifunctional control

An electric current triggered multifunctional vanadium dioxide (VO2) integrated photonic metamaterial is presented. In our metamaterial design, the nanoengineered topologically continuous metallic structure simultaneously supports the optical and electrical functionalities. Moreover, acting as part of the resonating structure, the VO2 thin film enables the tunable nature of the device. By presenting a series of proof-of-concept studies, we demonstrate the proposed hybrid metamaterial as a new platform for multifunction electro-optic control including reflectance switching, a rewritable memory process and manageable localized camouflage. The design methodology introduced here provides a universal approach to creating self-sufficient and highly versatile nanophotonic systems.

Efficient Cross-talk Reduction of Nanophotonic Circuits Enabled by Fabrication Friendly Periodic Silicon Strip Arrays

Reduction of the crosstalk between adjacent photonic components has been regarded as one of the most effective, yet most challenging approaches for increasing the packing density of photonic integrated circuits. Recently, extensive efforts have been devoted to this field, leading to a number of elaborate designs, such as waveguide supperlattice and nanophotonic cloaking, among others. Here we develop a simple and efficient crosstalk reduction approach for silicon-based nanophotonic circuits by introducing a periodic array of silicon strips between adjacent waveguides. Studies indicate that the coupling lengths can be extended by more than two orders of magnitude for a waveguide pair with an edge-to-edge distance of ~λ/3 at the telecommunication wavelength. Further investigations reveal that our method is effective for both strongly and weakly confined silicon photonic modes, and works well over a broad band of operational wavelengths. In addition, the crosstalk reduction technique is shown to be capable of improving the coupling lengths of other elements as well, such as vertical silicon slot waveguides. Our approach offers a promising platform for creating ultra-compact functional components that is fabrication friendly, thereby providing a feasible route toward the realization of photonic integrated circuits with ultra-high packing densities.