Yusheng Bian

Symmetric hybrid surface plasmon polariton waveguides for 3D photonic integration

A two-dimensional symmetric hybrid plasmonic waveguide that integrates two high-refractive-index dielectric slabs with a finite-width insulator-metal-insulator (IMI) structure is proposed, and the characteristics of its long-range propagation mode are numerically analyzed at 1550 nm wavelength. In contrast to the previously studied structures, the gap between the slabs and the metal stripe and the associated field enhancement effect result in the dramatically modified modal behavior. It is shown that, under optimized configurations, the transmission loss can be reduced significantly with little change in the mode confinement capability compared to similar dielectric-loaded surface plasmon polariton waveguides. Studies on the crosstalk between adjacent such hybrid waveguides reveal the ability to increase the integration density by approximately 60 times compared with the traditional IMI structures when used in 3D photonic circuits. The studied waveguide could be an interesting alternative to realize high density photonic circuits.

Hybrid wedge plasmon polariton waveguide with good fabrication-error-tolerance for ultra-deep-subwavelength mode confinement

A novel hybrid plasmonic waveguide consisting of a high-index dielectric nanowire placed above a triangular metal wedge substrate is proposed and analyzed theoretically. The strong coupling between the wedge plasmon polariton and the dielectric nanowire mode results in both the ultra-tight confinement and low propagation loss. Compared to the previous studied hybrid surface plasmon polariton structures without the metal wedge substrate, stronger field enhancement in the low-index gap region as well as improved figure of merit (FOM) could be realized simultaneously. Results of the modal properties considering certain fabrication imperfections show that the proposed structure is also quite tolerant to these errors.

Dielectric-loaded surface plasmon polariton waveguide with a holey ridge for propagation-loss reduction and subwavelength mode confinement

A novel dielectric-loaded surface plasmon polariton (DLSPP) waveguide with an air nanohole within a high-index dielectric ridge is proposed and analyzed. It is demonstrated by simulations that the introduced air nanohole could strongly modify the modal behavior, and it could alleviate the transmission loss caused by the high-index ridge with rather small sacrifice in the mode area. Under certain geometric parameter ranges, a shallow and wide air nanohole at the metal surface could result in strong local field enhancement while improves the figure of merit (FOM). The proposed structure could enable the realization of the DLSPP waveguide with a high-index ridge to achieve subwavelength mode confinement with relatively low transmission loss.

Coplanar Plasmonic Nanolasers Based on Edge-Coupled Hybrid Plasmonic Waveguides

A novel type of coplanar plasmonic laser based on an edge-coupled hybrid plasmonic waveguide is proposed and analyzed theoretically. This structure enables the realization of an air gap between the nanowire and the metal layer that could facilitate enhanced field confinement. By simulating the modal properties and the lasing threshold under different geometric parameters, it is demonstrated that with smaller gap widths and metal films of a larger rounded-corner radius, the lasing threshold could be reduced significantly. The structure could enable deep-subwavelength lasing with low pump thresholds and be readily integrated with other plasmonic structures for future coplanar active plasmonic circuits.

Nearly three orders of magnitude enhancement of Goos-Hanchen shift by exciting Bloch surface wave

Goos-Hanchen effect is experimentally studied when the Bloch surface wave is excited in the forbidden band of a one-dimensional photonic band-gap structure. By tuning the refractive index of the cladding covering the truncated photonic crystal structure, either a guided or a surface mode can be excited. In the latter case, strong enhancement of the Goos-Hanchen shift induced by the Bloch-surface-wave results in sub-millimeter shifts of the reflected beam position. Such giant Goos-Hanchen shift, ~750 times of the wavelength, could enable many intriguing applications that had been less than feasible to implement before.

Guiding of Long-Range Hybrid Plasmon Polariton in a Coupled Nanowire Array at Deep-Subwavelength Scale

A novel type of hybrid plasmonic waveguiding structure that integrates semiconductor and metallic nanowires has been proposed and investigated at telecommunication wavelengths. Semiconductor nanowires symmetrically placed on both sides of a metallic nanowire provide an additional degree of freedom for tuning the characteristics of the plasmonic nanowire mode. Theoretical analysis reveals that at appropriate geometrical parameters, the symmetric hybrid plasmonic mode of the waveguide could achieve subwavelength mode confinement with ultra-long propagation distance (even exceeding the millimeter range). Such a hybrid plasmonic nanowire structure could facilitate ultra-strong light-matter interaction between semiconductor and metal materials, and enable important applications in nanolasers and nonlinear photonics.

Highly Confined Hybrid Plasmonic Modes Guided by Nanowire-Embedded-Metal Grooves for Low-Loss Propagation at 1550 nm

A waveguiding configuration consisting of a semiconductor nanowire embedded in a dielectric-coated V-shaped metal groove is presented. The modal properties of the fundamental quasi-TE hybrid plasmonic mode are investigated at the wavelength of 1550 nm. Simulation results reveal that by tuning the size of the nanowire, the hybridization between the dielectric mode, and plasmonic mode could be effectively controlled. Through appropriate design, the hybrid mode could be strongly localized in the nanowire and the gap regions on each side, featuring both tight-mode confinement and low propagation loss. Besides, the compromise between confinement and loss could also be balanced by controlling the angle or depth of the metal groove. Moreover, it is found that the hybrid mode could exist for a wide geometrical parameter range, even when the corresponding metal groove by itself does not support a guided channel plasmon polariton mode. The proposed hybrid structure is technologically simple and compatible with planar fabrication methods while avoiding alignment errors.

Design and analysis of a nanostructure grating based on a hybrid plasmonic slot waveguide

A novel nanostructure grating with broadband reflection is proposed and analyzed in this paper. The grating is based on a hybrid plasmonic slot waveguide that consists of a vertical dielectric-slot incorporated at the gap between the upper silicon rib and the metal substrate. The structure could provide an ultra-tight mode confinement in the cross-section while maintaining a relatively low propagation loss. By exploiting the superior modal properties, an ultra-compact and broadband Bragg grating is presented, which shows the capability of efficient wavelength selection near the telecom bandwidths. The waveguide-based Bragg grating could be used as a filter in telecommunication systems and could be a promising candidate for future integrated photonic circuits.

Dielectrics Covered Metal Nanowires and Nanotubes for Low-Loss Guiding of Subwavelength Plasmonic Modes

Two types of surface plasmon polariton waveguides consisting of square metal nanowires or nanotubes covered by low-high index dielectric layers are presented and their guiding characteristics are investigated numerically at the telecom wavelength of 1550 nm. Numerical analysis reveals that depending on the sizes of the covered low-high index dielectric layers, the nanowire based waveguides can be tuned to provide subwavelength confinement of the plasmonic modes with low propagation loss. Even enhanced optical confinement could be achieved by further increasing the nanowire size or replacing the metal nanowires by nanotubes. Consideration of directional coupling between two identical such plasmonic waveguides reveal ultra-low-crosstalk can be realized with relatively small separation distances. These waveguiding structures, compatible with modern fabrication methods, potentially enable the realization of numerous ultra-compact integrated photonic components.

Direct experimental observation of giant Goos–Hänchen shifts from bandgap-enhanced total internal reflection

Giant Goos-Hänchen (GH) shifts are experimentally demonstrated from a prism-coupled multilayer structure incorporating a one-dimensional photonic crystal (PC) through a bandgap-enhanced total internal reflection scheme. By combining the large phase changes near the bandgap of the PC and the low reflection loss of the total internal reflection, 2 orders of magnitude enhancement of the GH shift is realized with rather low extra optical loss, which might help to open the door toward many interesting applications for GH effects.