Jinsong Zhu

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.

Switchable, dual-wavelength passively mode-locked ultrafast fiber laser based on a single-wall carbon nanotube modelocker and intracavity loss tuning

We demonstrate a dual-wavelength passively mode-locked soliton fiber laser based on the single-wall carbon nanotube saturable absorber. By using a simple scheme of adjusting the intracavity loss, the gain profile of the erbium-doped fiber laser is effectively controlled. Besides operating at a single wavelength, the laser is able to simultaneously generate sub-picosecond pulses at both ~1532 and 1557 nm wavelength. The mode-locking wavelength can also be quickly switched from one wavelength to the other by changing the intracavity loss with a tunable attenuator.

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.

Stable and Sensitive Silver Surface Plasmon Resonance Imaging Sensor Using Trilayered Metallic Structures

The silver surface plasmon resonance (SPR) sensor has long been explored due to its intrinsic sensitivity enhancement over the conventional single-layered gold SPR sensor. However, the silver SPR sensor has not been exploited for practical applications because of pronounced instability problems. We propose a novel gold-silver-gold trilayered SPR sensor chip, in which an extra buffer layer of gold is added between the silver and substrate adhesion layer (i.e., chromium) compared to the previously reported silver-gold bilayered SPR sensors. Subjected to prolonged agitation in phosphate-buffered saline (PBS) solution, the new chip exhibited high integrity according to both optical and atomic force microscopy (AFM) analysis. Having undergone repeated cycles of calibration, binding, and regeneration in various chemical solutions, 25 regions of interest (ROIs) over a 14 mm ×14 mm area were chosen and monitored by large detection area SPR microscopy; the new sensor chip exhibited stability comparable to the single gold layered SPR chip. In terms of sensing performances, over 50% increases in sensitivity and signal-to-noise ratio (S/N) than those of the single gold layered SPR chip were determined by SPR microscopy at 660 nm. Protein arrays of protein A and bovine serum albumin (BSA) on both the new chip and single-layered gold SPR chip were fabricated and underwent biomolecular interactions with human IgG, for the purpose of consistency, comparison on kinetics parameters, values from the microarray trilayered chip showed reasonable consistency with those from the single gold layered SPR chip. This study suggests that the new chip is a viable alternative to the conventional single gold layered SPR chip with improved sensing performances.

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.

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.

Spectral interferometric measurement of wavelength-dependent phase response for surface plasmon resonance sensors

Here we experimentally demonstrate measurements of the wavelength-dependent phase response of a surface plasmon resonance sensor using a spectral interferometric technique. By using a broadband incoherent fiber light source and a polarimetry configuration with a high-birefringence component, the spectral phase response of a surface plasmon resonance sensor can be retrieved. A combination of wavelength interrogation and phase detection is enabled by our proposed scheme. In contrast to the previously demonstrated heterodyne or spatial fringe detection schemes, this in-line optical configuration is much simpler and can be very compact when implemented with advanced fiber optic and integrated components.

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.

Plain silver surface plasmon resonance for microarray application.

The application scope of surface plasmon resonance (SPR) and SPR imaging (SPRi) is rapidly growing, and tools such as high-performance and low-cost slides could enable more rapid growth of the field. We describe herein a novel silver slide, addressing the inherent instability of plain silver structure by improving adhesion between the glass substrate and the silver layer with a thin buffer layer of gold. Covered by a self-assembled monolayer (SAM) only, SPR characteristics of the slide remain steady for more than 3 months under regular storage. In a bioassay, the slide substantiates the predicted nearly 100% sensitivity improvement over gold slides and exhibits exceptional performance stability as determined by sensitivity and resolution measurements during the extended 40,000 s multicycle experiment. We demonstrate the suitability of this new slide for large-area SPRi, describing analysis results from a 1 296-ligand protein microarray. We predict this slide structure will provide a stable, high-sensitivity solution for high-throughput SPRi applications and other surface analysis platforms.