Dalin Liu

Efficiently Unidirectional Coupling of Surface Plasmons Based on Asymmetric Cascaded Nanoslits

A compact unidirectional plasmonic coupler based on asymmetric cascaded nanoslits is proposed and theoretically analyzed. The incident photons illuminated on the structure are unidirectionally coupled into the metal-insulator-metal waveguide. The operation principle is clarified and a universal theoretical model based on coupled-mode equations is developed to facilitate structure design. Proof-of-principle demonstrations show that an ultrahigh extinction ratio ER = 43.8 dB at a specific wavelength and broadband of 160 nm covering a wide angular range from -20° to 15° with ER ≥ 10 dB are achieved.

Compact Plasmonic Unidirectional Coupler With High Performance Based on an Asymmetric Slit-Groove Structure

A new scheme for unidirectional coupling of surface plasmon polaritons (SPPs) from freely propagating light into a metal-insulator-metal waveguide is proposed, which is composed of an asymmetric double-slit of different widths sandwiched by symmetric grooves. A theoretical model based on coupled-mode equations is developed to facilitate structure design and elucidate the underlying physical mechanism. With the model, the asymmetric double-slit with different widths is designed for unidirectional launching of SPPs with an ultrahigh extinction ratio of 44.8 dB at the wavelength 800 nm. A method of stepwise design is proposed for simplicity of design and convenience of analysis. Proof-of-principle demonstrations show that an ultrahigh extinction ratio of 37.1 dB and significant field enhancement for the proposed whole structure are obtained. In addition, an ultracompact plasmonic dichroic splitter based on the asymmetric double-slit with high extinction ratios of 24.2 and 21.8 dB at splitting wavelengths of 800 and 900 nm is achieved, and the lateral dimension of the plasmonic dichroic splitter is only 760 nm.

Efficient Unidirectional Optical Coupling for Hybrid Plasmonic Waveguide

A new type of efficient and unidirectional optical coupler composed of periodic nanoslits milled in the metallic surface is proposed for the hybrid plasmonic waveguides. The operation principle is clarified and theoretically illustrated by using the coupled-mode model and the fully vectorial aperiodic Fourier modal method. The coupling efficiency of more than 50% and splitting ratios better than 18 dB at the incident angle θ= 12° could be achieved over the C-band ranging from 1530 to 1570 nm.

Unidirectional Coupling of Surface Plasmons Over a Broad-Angle Range Based on Joint Effects of Asymmetric Mode Excitation and Grating Resonance

A new coupling scheme for unidirectional coupling of surface plasmons from free-space light over a broad-angle range is proposed and theoretically investigated. Firstly, the property of strong asymmetric excitation is found in the single wide defect, especially the single dielectric ridge, which is due to the excitation of asymmetric mode in the wide defect under oblique incidence. Then we show that the strong asymmetric excitation by single ridge still exists in the periodic dielectric ridge grating. By cascading the asymmetric mode excitation peak and the grating resonance angle peak, the angular-full-width-half-maximum (AFWHM) is broadened to 39°. Finally, the AFWHM is further broadened to 52° by utilizing the chirped ridge grating and a remarkable property of wide flat-top angular response is achieved.

Compact Ultrabroadband Plasmonic Antenna: Potential Applications in Logic Binary Encoding

A compact ultrabroadband coupling and binary encoding structure based on an array of aperiodic nanoslits cascaded by two different pairs of grooves in a metallic-dielectric-air waveguide is proposed and theoretically analyzed. The nanoslits array function as a broadband antenna to couple the incident lights into surface plasmon polaritons (SPPs) over an ultrawide wavelength range (spectral full-width-half-maximum >430 nm). The two ports composed of different grooves exhibit different transmission for the coupled multiwavelength SPPs. After traveling through different ports, the incident lights dropping in different wavelength ranges are differentiated and endowed with different logic state encodings. The operation principle is clarified and a coupled-mode model is developed for facilitating design.

A novel polarization and dichroic dual-functional splitter with ultra-high splitting ratios

A novel polarization and dichroic dual-functional splitter is proposed, with ultra-high polarization splitting ratios >33dB and >36dB for TE- and TM-polarized modes, respectively; and with high wavelength splitting ratios >26dB and >33dB for 650nm and 850nm, respectively.

Unidirectional optical coupling for plasmonic waveguide based on metallic-dielectric high-contrast gratings

Based on the metallic-dielectric high contrast gratings, we proposed two new different schemes to achieve the unidirectional coupling of incident free-space light into the plasmonic waveguides. Using the cascaded metal-air subgratings (structure 1) or metallic-dielectric subwavelength periodic gratings (structure 2), the ultra-broadband and wideangular SPPs excitation could be both achieved. The operation principle and performance of the structures are analyzed and discussed, respectively.

Efficient Unidirectional Optical Coupling for Hybird Plasmonic Waveguide

A new type of efficient and unidirectional optical coupler composed of periodic nanoslits is proposed for hybrid plasmonic waveguide. The operation principle and performance were analyzed and discussed. The coupling efficiency more than 50%, extinction ratio better than 18dB with incidence angle θ=12° was achieved at λ= 1550nm.

A new plasmonic coupler for MDM waveguide based on the metallic voids

We proposed a new type of plasmonic coupler for the metal-dielectric-metal (MDM) plasmonic waveguide using the periodic metallic voids. The resonance modes in the voids and the performance of the coupler were analyzed and discussed