The arbitrary control of electromagnetic waves is a key aim of photonic research. Although, for example, the control of freely propagating waves (PWs) and surface waves (SWs) has separately become possible using transformation optics and metamaterials, a bridge linking both propagation types has not yet been found. Such a device has particular relevance given the many schemes of controlling electromagnetic waves at surfaces and interfaces, leading to trapped rainbows, lensing, beam bending, deflection, and even anomalous reflection/refraction. Here, we demonstrate theoretically and experimentally that a specific gradient-index meta-surface can convert a PW to a SW with nearly 100% efficiency. Distinct from conventional devices such as prism or grating couplers, the momentum mismatch between PW and SW is compensated by the reflection-phase gradient of the meta-surface, and a nearly perfect PW-SW conversion can happen for any incidence angle larger than a critical value. Experiments in the microwave region, including both far-field and near-field characterizations, are in excellent agreement with full-wave simulations. Our findings may pave the way for many applications, including high-efficiency surface plasmon couplers, anti-reflection surfaces, light absorbers, and so on.

http://www.physics.fudan.edu.cn/tps/people/lzhou/papers/84-NM%2011,426.pdf

Gradient-index meta-surfaces as a bridge linking propagating waves and surface waves

Researchers used an inverse design algorithm and experimentally demonstrated an integrated polarization beamsplitter with a footprint of 2.4 × 2.4 μm2.

An integrated-nanophotonics polarization beamsplitter with 2.4 × 2.4 μm2 footprint

The conversion from spatial propagating waves to surface plasmon polaritons (SPPs) has been well studied, and shown to be very efficient by using gradient-index metasurfaces. However, feeding energies into and extracting signals from functional plasmonic devices or circuits through transmission lines require the efficient conversion between SPPs and guided waves, which has not been reported, to the best of our knowledge. In this paper, a smooth bridge between the conventional coplanar waveguide (CPW) with 50 Ω impedance and plasmonic waveguide (e.g., an ultrathin corrugated metallic strip) has been proposed in the microwave frequency, which converts the guided waves to spoof SPPs with high efficiency in broadband. A matching transition has been proposed and designed, which is constructed by gradient corrugations and flaring ground, to match both the momentum and impedance of CPW and the plasmonic waveguide. Simulated and measured results on the transmission coefficients and near-filed distributions show excellent transmission efficiency from CPW to a plasmonic waveguide to CPW in a wide frequency band. The high-efficiency and broadband conversion between SPPs and guided waves opens up a new avenue for advanced conventional plasmonic integrated functional devices and circuits.

Broadband and high-efficiency conversion from guided waves to spoof surface plasmon polaritons

A hybrid plasmonic waveguide with a metal cap on a silicon-on-insulator rib (or slab) is presented. There is a low-index material nano-layer between the Si layer and the metal layer. The field enhancement in the nano-layer provides a nano-scale confinement of the optical field (e.g., 50nm × 5nm) when operates at the optical wavelength λ = 1550nm. The theoretical investigation also shows that the present hybrid plasmonic waveguide has a low loss and consequently a relatively long propagation distance (on the order of several tens of λ).

A silicon-based hybrid plasmonic waveguide with a metal cap for a nano-scale light confinement.

The application of portable, easy-to-use and highly sensitive lab-on-a-chip biosensing devices for real-time diagnosis could offer significant advantages over current analytical methods. Integrated optics-based biosensors have become the most suitable technology for lab-on-chip integration due to their ability for miniaturization, their extreme sensitivity, robustness, reliability, and their potential for multiplexing and mass production at low cost. This review provides an extended overview of the state-of-the-art in integrated photonic biosensors technology including interferometers, grating couplers, microring resonators, photonic crystals and other novel nanophotonic transducers. Particular emphasis has been placed on describing their real biosensing applications and wherever possible a comparison of the sensing performances between each type of device is included. The way towards achieving operative lab-on-a-chip platform incorporating the photonic biosensors is also reviewed. Concluding remarks regarding the future prospects and potential impact of this technology are also provided.

/pdf/integrated-optical-devices-for-lab-on-a-chip-biosensing-4dvxngj3uf.pdf

Integrated optical devices for lab-on-a-chip biosensing applications

We present design, fabrication, and characterization of a silicon-on-insulator grating coupler of high efficiency for coupling between a silicon nanophotonic waveguide and a single mode fiber. By utilizing the lag effect of the dry etching process, a grating coupler consisting of nonuniform grooves with different widths and depths is designed and fabricated to maximize the overlapping between the upward wave and the fiber mode. The measured waveguide-to-fiber coupling efficiency of 64% (-1.9 dB) for the transverse electric polarization is achieved by the present nonuniform grating coupler directly defined on a regular silicon-on-insulator wafer.

Highly efficient nonuniform grating coupler for silicon-on-insulator nanophotonic circuits

Negatively and positively refractive behaviors are achieved in a two-dimensional photonic crystal of pillar type for TE and TM polarizations, respectively, at the same frequency. The photonic cry ...

Polarization beam splitter based on a two-dimensional photonic crystal of pillar type

An ultracompact polarization beam splitter (PBS) is proposed based on an asymmetrical directional coupler consisting of a silicon hybrid plasmonic waveguide (HPW) and a silicon nanowire. The widths ...

Ultracompact and broadband polarization beam splitter utilizing the evanescent coupling between a hybrid plasmonic waveguide and a silicon nanowire.

We present both theoretical and experimental results of an ultracompact waveguide coupler that is capable of highly efficient coupling of light from strip waveguides to slot waveguides, and vice versa. By optimizing the geometrical parameters, it is possible to achieve extremely low-loss coupling. A coupling efficiency of 97% has been obtained experimentally while keeping the overall size down to the range below 10 μm. Further analysis shows that the proposed coupler has relatively high tolerance to fabrication errors and is wavelength insensitive.

Ultracompact low-loss coupler between strip and slot waveguides

An ultracompact polarization beam splitter (PBS) based on a dielectric-hybrid plasmonic-dielectric coupler is proposed. The device utilizes the polarization-dependent nature of hybrid plasmonic wav ...

Lech Wosinski

Papers

Highly efficient nonuniform grating coupler for silicon-on-insulator nanophotonic circuits

Polarization beam splitter based on a two-dimensional photonic crystal of pillar type

Ultracompact and broadband polarization beam splitter utilizing the evanescent coupling between a hybrid plasmonic waveguide and a silicon nanowire.

Ultracompact low-loss coupler between strip and slot waveguides

Ultracompact polarization beam splitter based on a dielectric–hybrid plasmonic–dielectric coupler