Demonstration of fluorescence enhancement via Bloch surface waves in all-polymer multilayer structures

Dynamics of surface-plasmon lasing in planar metal gratings on semiconductor

We investigate the dynamics of surface plasmon (SP) lasing in Au gratings fabricated on InGaAs with a period of around 400 nm, which locates the SP resonance near the semiconductor energy gap and facilitates efficient energy transfer. By optically pumping the InGaAs to reach the population inversion required for the amplification and the lasing, we observe SP lasing at specific wavelengths that satisfy the SPR condition depending on the grating period. The carrier dynamics in semiconductor and the photon density in the SP cavity was investigated from the time-resolved pump-probe measurement and the time resolved photoluminescence spectroscopy, respectively. Our results reveal that the photon dynamics is strongly correlated with the carrier dynamics and the lasing build-up is accelerated as the initial gain proportional to the pumping power increases, and this trend is satisfactorily explained using the rate equation model.

Refractive Index Dependence of Fluorescence Enhancement in a Nanostructured Plasmonic Grating

Plasmonic gratings are attracting huge interest in the context of realizing sensors based on surface-enhanced fluorescence. The grating features control the plasmonic modes and consequently have a strong effect on the fluorescence response. Within this framework, we focused on the use of a buffer solution flowing across the grating active surface to mimic a real measurement. The refractive index of the surrounding medium is therefore altered, with a consequent modification of the resonance conditions. The result is a shift in the spectral features of the fluorescence emission accompanied by a reshaping of the fluorescence emission in terms of spectral weight and direction.

Plasmonic Modes and Fluorescence Enhancement Coupling Mechanism: A Case with a Nanostructured Grating

The recent development and technological improvement in dealing with plasmonic metasurfaces has triggered a series of interesting applications related to sensing challenges. Fluorescence has been one of the most studied tools within such a context. With this in mind, we used some well characterized structures supporting plasmonic resonances to study their influence on the emission efficiency of a fluorophore. An extended optical analysis and a complementary investigation through finite-difference time-domain (FDTD) simulations have been combined to understand the coupling mechanism between the excitation of plasmonic modes and the fluorescence absorption and emission processes. The results provide evidence of the spectral shape dependence of fluorescence on the plasmonic field distribution together with a further relationship connected with the enhancement of its signal. It has made evident that the spectral region characterized by the largest relative enhancement closely corresponds to the strongest signatures of the plasmonic modes, as described by both the optical measurements and the FDTD findings.

Particle swarm optimization of GaAs-AlGaAS nanowire photonic crystals as two-dimensional diffraction gratings for light trapping

Semiconductor nanowire ordered arrays represent a class of bi-dimensional photonic crystals that can be engineered to obtain functional metamaterials. Here is proposed a novel approach, based on a particle swarm optimization algorithm, for using such a photonic crystal concept to design a semiconductor nanowire-based two-dimensional diffraction grating able to guarantee an in-plane coupling for light trapping. The method takes into account the experimental constraints associated to the bottom-up growth of nanowire arrays, by processing as input dataset all relevant geometrical and morphological features of the array, and returns as output the optimised set of parameters according to the desired electromagnetic functionality of the metamaterial. A case of study based on an array of tapered GaAs-AlGaAs core-shell nanowire heterostructures is discussed.

The Design and Research of a New Hybrid Surface Plasmonic Waveguide Nanolaser

Using the hybrid plasmonic waveguide (HPW) principle as a basis, a new planar symmetric Ag-dielectric-SiO₂ hybrid waveguide structure is designed and applied to nanolasers. First, the effects on the electric field distribution and the characteristic parameters of the waveguide structure of changes in the material, the nanometer radius, and the dielectric layer thickness were studied in detail using the finite element method with COMSOL Multiphysics software. The effects of two different dielectric materials on the HPW were studied. It was found that the waveguide performance could be improved effectively and the mode propagation loss was reduced when graphene was used as the dielectric, with the minimum effective propagation loss reaching 0.025. Second, the gain threshold and the quality factor of a nanolaser based on the proposed hybrid waveguide structure were analyzed. The results showed that the nanolaser has a lasing threshold of 1.76 μm^-1 and a quality factor of 109 when using the graphene dielectric. A low-loss, low-threshold laser was realized, and the mode field was constrained by deep sub-wavelength light confinement. This structure has broad future application prospects in the integrated optics field and provides ideas for the development of subminiature photonic devices and high-density integrated circuits.

Fluorescence Coupling to Internal Modes of 1D Photonic Crystals Characterized by Back Focal Plane Imaging

The coupling of fluorescence with surface electromagnetic modes, such as surface plasmons on thin metal films or Bloch surface waves (BSW) on truncated one-dimensional photonic crystals (1DPC), are presently utilized for many fluorescence-based applications. In addition to the surface wave, 1DPCs also support other electromagnetic modes that are confined within the 1DPC structure. These internal modes (IMs) have not received much attention for fluorescence coupling due to lack of spatial overlap of their electric fields with the surface bound fluorophores. However, our recent studies have indicated that the fluorescence coupling with IMs occurs quite efficiently. This observed internal mode-coupled emission (IMCE) is (similar to BSW-coupled emission) indeed wavelength dependent, directional and S-polarized. In this paper, we have carried out back-focal plane (BFP) imaging to reveal that the IMs of 1DPCs can couple with surface bound excited dye molecules, with or without a BSW mode presence. Depending on the emission wavelength, the coupling is observed with BSW and IMs or only IMs of the 1DPC structure. The experimental results are well matching with numerical simulations. The occurrence of IMCE regardless of the availability of BSWs removes the dependence on just the surface mode for obtaining coupled emission from 1DPCs. The observation of IMCE is expected to widen the scope of 1DPCs for surface-based fluorescence sensing and assays.

Characterization and application of nonlinear plastic materials for post-CPA pulse compression

We demonstrate the three-fold post-chirped-pulse-amplification (post-CPA) pulse compression of a high peak power laser pulse using allyl diglycol carbonate (CR39), which was selected as the optimal material for near-field self-phase modulation out of a set of various nonlinear plastic materials, each characterized with respect to its nonlinear refractive index and optical transmission. The investigated materials could be applied for further pulse compression at high peak powers, as well as for gain narrowing compensation within millijoule-class amplifiers. The post-CPA pulse compression technique was tested directly after the first CPA stage within the POLARIS laser system, with the compact setup containing a single 1 mm thick plastic sample and a chirped mirror pair, which enabled a substantial shortening of the compressed pulse duration and, hence, a significant increase in the laser peak power without any additional modifications to the existing CPA chain.

Strategies for Dielectric Contrast Enhancement in 1D Planar Polymeric Photonic Crystals

Historically, photonic crystals have been made of inorganic high refractive index materials coupled to air voids to maximize the dielectric contrast and in turn the light confinement. However, these systems are complex, costly, and time-demanding, and the fabrication processes are difficult to scale. Polymer structures promise to tackle this issue thanks to their easy solution and melt processing. Unfortunately, their low dielectric contrast limits their performance. In this work, we propose a concise but exhaustive review of the common polymers employed in the fabrication of planar 1D photonic crystals and new approaches to the enhancement of their dielectric contrast. Transfer matrix method modeling will be employed to quantify the effect of this parameter in standardized structures and to propose a new polymer structure for applications dealing with light management.

Reshaping Hybrid Perovskites Emission with Flexible Polymer Microcavities

Thanks to versatile optoelectronic properties solution processable perovskites have attracted increasing interest as active materials in photovoltaic and light emitting devices. However, the deposition of perovskite thin films necessitates wide range solvents that are incompatible with many other solution-processable media, including polymers that are usually dissolved by the perovskite solvents. In this work, we demonstrate that hybrid perovskite thin films can be coupled with all polymer planar photonic crystals with different approaches to achieve emission intensity enhancement and reshaping using different approaches. The possibility to control and modify the emission spectrum of a solution processable perovskite via a simple spun-cast polymer structure is indeed of great interest in optoelectronic applications requiring high color purity or emission directionality. Furthermore, thanks to the ease of fabrication and scalability of solution-processed photonic crystals, this approach could enable industrial scale production of low-cost, large area, lightweight and flexible polymer-perovskite lighting devices, which may be tuned without resorting to compositional engineering.

Solution Processed Polymer-ABX4 Perovskite-Like Microcavities

Thanks to solution processability and broad emission in the visible spectral range, 2D hybrid perovskite-like materials are interesting for the realization of large area and flexible lighting devices. However, the deposition of these materials requires broad-spectrum solvents that can easily dissolve most of the commercial polymers and make perovskites incompatible with flexible photonics. Here, we demonstrated the integration of broadband-emitting (EDBE)PbCl4 (where EDBE = 2,2-(ethylenedioxy)bis(ethylammonium)) thin films with a solution-processed polymer planar microcavities, employing a sacrificial polymer multilayer. This approach allowed for spectral and angular redistribution of the perovskite-like material, photoluminescence, that can pave the way to all-solution-processed and flexible lightning devices that do not require complex and costly fabrication techniques.

All-polymer methylammonium lead iodide perovskite microcavities

Thanks to a high photoluminescence quantum yield, large charge carrier diffusion, and ease of processing from solution, perovskite materials are becoming increasingly interesting for flexible optoelectronic devices. However, their deposition requires wide range solvents that are incompatible with many other flexible and solution-processable materials, including polymers. Here, we show that methylammonium lead iodide (MAPbI3) films can be directly synthesized on all-polymer microcavities via simple addition of a perfluorinated layer which protects the polymer photonic structure from the perovskite processing solvents. The new processing provides microcavities with a quality factor Q = 155, that is in agreement with calculations and the largest value reported so far for fully solution processed perovskite microcavities. Furthermore, the obtained microcavity shows strong spectral and angular redistribution of the the MAPbI3 photoluminescence spectrum, which shows a 3.5 fold enhanced intensity with respect to the detuned reference. The opportunity to control and modify the emission of a MAPbI3 film via a simple spun-cast polymer structure is of great interest in advanced optoelectronic applications requiring high colour purity or emission directionality.

Surface Plasmon Nanolaser: Principle, Structure, Characteristics and Applications

Photonic devices are becoming more and more miniaturized and highly integrated with the advancement of micro-nano technology and the rapid development of integrated optics. Traditional semiconductor lasers have diffraction limit due to the feedback from the optical system, and their cavity length is more than half of the emission wavelength, so it is difficult to achieve miniaturization. Nanolasers based on surface plasmons can break through the diffraction limit and achieve deep sub-wavelength or even nano-scale laser emission. The improvement of modern nanomaterial preparation processes and the gradual maturity of micro-nano machining technology have also provided technical conditions for the development of sub-wavelength and nano-scale lasers. This paper describes the basic principles of surface plasmons and nano-resonators. The structure and characteristics of several kinds of plasmonic nanolasers are discussed. Finally, the paper looks forward to the application and development trend of nanolasers.

Low Threshold Plasmonic Nanolaser Based on Graphene

A hybrid plasmonic nanolaser based on nanowire/air slot/semicircular graphene and metal wire structure was designed. In this structure, the waveguides in the nanowires and the graphene-metal interface are coupled to form a hybrid plasma mode, which effectively reduces the metal loss. The mode and strong coupling of the laser are analyzed by using the finite-element method. Its electric field distribution, propagation loss, normalized mode area, quality factor, and lasing threshold are studied with the different geometric model. Simulation results reveal that the performance of the laser using this structure can be optimized by adjusting the model parameters. Under the optimal parameters, the effective propagation loss is only 0.0096, and the lasing threshold can be as low as 0.14 μm−1. This structure can achieve deep sub-wavelength confinement and low-loss transmission, and provides technical support for the miniaturization and integration of nano-devices.

Design of Surface Plasmon Nanolaser Based on MoS2

The paper has proposed a new structure based on MoS2. The electric field distribution, the locality and the loss of the mode, and the threshold under different geometric shapes and parameters are investigated using COMSOL Multiphysics software, based on the finite element method. The different influenced degree of each component is also analyzed. Simulation results reveal that this kind of nanolaser has a low loss and high field confinement ability, the radius of CdS and Ag make a major contribution to the low loss and low threshold, and field confinement ability is mainly affected by the height of air gap. Under optimal parameters, effective propagation loss is only 0.00013, and the lasing threshold can be as low as 0.11 μm−1. The results provide theory and technique support to the field of new nanolaser design.

Colorimetric Detection of Perfluorinated Compounds by All-Polymer Photonic Transducers

We report on the highly sensitive optical and colorimetric detection of perfluorinated compounds in the vapor phase achieved by all-polymer dielectric mirrors. High optical quality and uniformly distributed Bragg reflectors were fabricated by alternating thin films of poly(N-vinylcarbazole) and Hyflon AD polymers as high and low refractive index medium, respectively. A new processing procedure has been developed to compatibilize the deposition of poly(N-vinylcarbazole) with the highly solvophobic Hyflon AD polymer layers to achieve mutual processability between the two polymers and fabricate the devices. As a proof of principle, sensing measurements were performed using the Galden HT55 polymer as a prototype of the perfluorinated compound. The Bragg stacks show a strong chromatic response upon exposure to this compound, clearly detectable as both spectral and intensity variations. Conversely, Bragg mirrors fabricated without fluorinated polymers do not show any detectable response, demonstrating that the Hyflon AD polymer acts as the active and selective medium for sensing perfluorinated species. These results demonstrate that organic dielectric mirrors containing perfluorinated polymers can represent an innovative colorimetric monitoring system for fluorinated compounds, suitable to improve both environmental safety and quality of life.

Lasing from dot-in-rod nanocrystals in planar polymer microcavities

Colloidal nanocrystals attract considerable attention in the field of light emitting devices thanks to their high fluorescence quantum yield, low amplified spontaneous emission (ASE) threshold, and spectral tunability via electronic structure engineering and surface functionalization. Combining polymer microcavities with colloidal nanocrystals as gain material promises a solution-based fabrication route to plastic laser cavities as well as applications in the field of smart flexible large area light sources and sensors. Here we demonstrate lasing from polymer microcavities embedding solution processable dot-in-rod (DiR) CdSe/CdS nanocrystals. Two highly reflective polymer dielectric mirrors are prepared by spin-coating of alternated layers of polyacrylic acid and poly(N-vinyl carbazole), with their photonic band gap tailored to the emission of the DiRs. The DiRs are enclosed in the polymer microcavity by drop-cast deposition on one mirror, followed by pressing the mirrors onto each other. We obtain excellent overlap of the ASE band of the DiRs with the photonic band gap of the cavity and observe optically pumped lasing at 640 nm with a threshold of about 50 μJ cm-2.

Re-usable PDMS stamps for non-destructive fluorescence evaluation and imaging of thin film photonic structures

We report on a non-destructive method for evaluating fluorescence emission from fluorophores placed upon engineered photonic structures. Our method utilizes re-usable, fluorescent thin film coated polydimethylsiloxane (PDMS) stamps. We harness the inherent characteristics of PDMS slabs; their ability to form conformal contact through van der Waals interactions in bringing the coated fluorescent layer on PDMS into close proximity of the photonic structure of interest. Fluorescence measurements are performed using the PDMS slab while in conformal contact with the test structure, allowing one to re-use these stamps for reliable evaluation over multiple samples. Transfer of the fluorescent film from the PDMS to the test structures is mitigated by the use of appropriate cross linkers that covalently bond the fluorescent film to the PDMS surface. To demonstrate the application potential of this approach, we report on the evaluation of fluorescence emission modulation from patterned nanoporous thin films, which are particularly challenging to evaluate using traditional approaches, and from plasmonic gratings supporting metal enhanced fluorescence. Comparison with traditional evaluation approaches has been made to showcase the superiority of the reported technique.

Label-Free Vapor Selectivity in Poly(p-Phenylene Oxide) Photonic Crystal Sensors

The lack of sensors for low cost, extensive, and continuous detection of vapor pollutants is a serious concern for health and safety in industrialized urban areas. Colorimetric sensors, such as distributed Bragg reflectors made of polymers, could achieve this task thanks to their low cost and easy signal transduction but are typically affected by low vapor permeability and lack of selectivity without chemical labeling. Here we demonstrate all-polymer Bragg multilayers for label-free selective detection of organic volatile compounds. The system exploits the ability of amorphous poly(p-phenylene oxide), PPO, to uptake large amount of guest molecules and to form cocrystalline phases with distinct optical properties. Bragg stacks embedding PPO active layers show selective colorimetric response to vapors of carbon tetrachloride and aromatic homologues, which can be revealed by the naked eye.