Extraordinary Light Transmission Research Articles

Extraordinary transmission of light enhanced by exciting hybrid states of Tamm and surface plasmon polaritions in a single nano-slit

Extraordinary optical transmission (EOT) through a metallic nano-slit or nano-slit arrays has become an efficient method to manipulate the light on a subwavelength scale. While a variety of nano-devices based on surface plasmon polaritons (SPPs) could be an ideal candidate for the next-generation ultra-compact integrated photonic circuits, this EOT phenomenon is also generally attributed to the excitation of SPPs in the nano-slit. Thus, due to its being compact in structure and amenable to integrate with other nano-devices, single nano-slit can be implemented to construct an optical source in the nano-device based on SPPs. However, the transmission through an isolated nano-slit is too low to be practically used. The main reason is that the excitation efficiency of SPPs in the nano-slit is not high enough. In fact, one of the key issues is how to enhance the excitation efficiency in a nano-slit. In this paper, a novel method and the related structure are proposed to effectively enhance the EOT in a single nano-slit by improving the excitation efficiency of SPPs. This structure is made up of a silver film on a distributed Bragg reflector (DBR), where a single nano-slit is imbedded in the silver film. Under the illumination of a TM polarized light from the DBR side of this structure, the Tamm plasmon polaritons (TPPs) at the interface between the silver film and the DBR and the SPPs in the nano-slit can be excited simultaneously. The TPP is another surface mode, which describes how an electromagnetic field is localized at the boundary of silver film and the DBR. In this structure, coupling between the TPPs and the SPPs leads to the appearance of a TPP-SPP hybrid state. When the wave-vectors between the TPP and the SPP modes are matched, due to the local field enhancement of the TPP mode, the excitation efficiency of SPPs can be improved significantly. Furthermore, utilizing the quasi Fabry-Pérot (F-P) resonance in the nano-slit, where a single nano-slit can be regarded as an F-P cavity with two open ends, a high light transmission through the single nano-slit can be achieved. In the present paper, the transmission properties of the “DBR-silver nano-slit” structure are analyzed with the finite element method and the transfer matrix method. After optimizing the structure parameters, with a thickness of the silver film of 100 nm and a width of the nano-slit of 11 nm, the light transmission through the single nano-slit in this structure can be increased by about 16 times, in comparison with the light transmission through a single nano-slit in a silver film on the TiO2 substrate (without DBR). This method of enhancing the light transmission through a single nano-slit by exciting TPPs mode and utilizing its local field enhancement property, has potential applications in the polariton lasers, the nano-scale photonic integration, the near-field imaging and sensing, and other relevant areas.

Three-Dimensional Superlocalization Imaging of Gliding Mycoplasma mobile by Extraordinary Light Transmission through Arrayed Nanoholes.

In this paper, we describe super-resolved sampling of live bacteria based on extraordinary optical transmission (EOT) of light. EOT is produced by surface plasmon confinement and coupling with nanostructures. Bacterial fluorescence is excited by the localized fields for subdiffraction-limited sampling. The concept was applied to elucidating bacterial dynamics of gliding Mycoplasma mobile (M. mobile). The results analyzed with multiple M. mobile bacteria show individual characters and reveal that M. mobile undergoes a significant axial variation at 94 nm. The sampling error of the method is estimated to be much smaller than 1/10 of the diffraction limit both in the lateral and depth axis. The method provides a powerful tool for investigation of biomolecular dynamics at subwavelength precision.

Extraordinary transmission in optical Helmholtz resonators.

Optical Helmholtz resonators (OHRs) have been adapted from acoustics designs for light absorbing structures, exhibiting extreme light confinement. Here, extraordinary transmission of light is theoretically demonstrated through symmetric OHRs, comprising a cavity with two λ/500 narrow slits on either side. This device has appealing features to act as a spectral bandpass filter in the context of multispectral imaging, in particular its high angular tolerance because of the localized nature of the resonance. Besides, the cavity can be modeled as an inductor and the two slits can be modeled as capacitors, the whole design acting as a LC circuit thus preventing any harmonic features.

Plasmonic electrodes for bulk-heterojunction organic photovoltaics: a review

Here, we review recent progress on the integration of plasmonic electrodes into bulk-heterojunction organic photovoltaic devices. Plasmonic electrodes, consisting of thin films of metallic nanostructures, can exhibit a number of optical, electrical, and morphological effects that can be exploited to improve performance parameters of ultrathin photovoltaic active layers. We review the various types of plasmonic electrodes that have been incorporated into organic photovoltaics such as nanohole, nanowire, and nanoparticle arrays and grating electrodes and their impact on various device performance parameters. The use of plasmonic back electrodes can impact device performance in a number of ways because the mechanisms of performance improvements are often a complex combination of optical, electrical, and structural effects. Inverted bulk heterojunction device architectures have been shown to benefit from the multifunctionality of plasmonic back electrodes as they can minimize space-charge effects and reduce hole carrier collection lengths in addition to providing improved light localization in the active layer. The use of semi-transparent plasmonic electrodes can also be beneficial for organic photovoltaics as they can exhibit a variety of optical properties such as light scattering, light localization, extraordinary transmission of light, and absorption-induced transparency, in addition to providing an alternative to metal oxide–based transparent electrodes.

Development of a complete plasmonic grating-based sensor and its application for self-assembled monolayer detection

This work presents an integrated plasmonic biosensing device consisting of a one-dimensional metallic lamellar grating designed to exploit extraordinary transmission of light toward an underlying silicon photodetector. By means of finite element simulations, the grating parameters have been optimized to maximize the light transmission variation induced by the functionalization of the gold nanostructures. An optimized grating was fabricated using an electron beam process and an optoelectronic test bench suitable for sample tests was developed. A clear difference in the grating transmitted light due to surface functionalization was observed in presence of TM polarized illumination.

Getting real: influence of structural disorder on the performance of plasmonic hole array sensors fabricated by a bottom-up approach

Periodic hole arrays in gold films showing extraordinary transmission of light are fabricated using solely chemical methods. The degree of order of the hole arrays has a strong impact on their transmission properties, which can be utilized for a spectral quality control of the produced plasmonic sensors.

Formation of Gold Microparticles by Ablation with Surface Plasmons.

The formation of gold microparticles on a silicon substrate through the use of energetic surface plasmons is reported. A laser-assisted plasmonics system was assembled and tested to synthesize gold particles from gold thin film by electrical field enhancement mechanism. A mask containing an array of 200 nm diameter holes with a periodicity of 400 nm was prepared and placed on a silicon substrate. The mask was composed of 60 µm thick porous alumina membrane sputter-coated with 100 nm thin gold film. A Nd:YAG laser with 1064 nm wavelength and 230 µs pulse width (free-running mode) was then passed through the mask at an energy fluence of 0.35 J/cm2. The extraordinary transmission of laser light through alumina/gold micro-hole optical antenna created both extended and localized surface plasmons that caused the gold film at the bottom of the mask to fragment into microparticles and deposit on the silicon substrate that is in direct contact with the mask. The surface plasmon method is simpler, quicker, more energy efficient, and environmentally safer than existing physical and chemical methods, as well as being contamination-free, and can be extended to all types of materials that will in turn allow for new possibilities in the formation of structured surfaces.

Optical Tamm state and extraordinary light transmission through a nanoaperture

We investigate the light transmission through a nanoaperture in a metal film deposited on a planar metamaterial. An effect of an anomalously high light transmission (up to $800%$) through the nanoaperture is revealed, which we associate with the enhancement of the field at the interface of the planar structure ``metamaterial--metal-film'' due to the appearance of an optical Tamm state. Our numerical results are in qualitative agreement with experimental data.

Free-field characterization via directional transmission through a nanoaperture

We propose a scheme based on extraordinary transmission of light through a single nanoaperture, surrounded by periodic corrugations, for direct characterization of focal-region optical fields with subwavelength-scale structure. We describe the design of the device on the basis of rigorous diffraction theory and fabricate a prototype using a process that involves electron beam lithography, dry etching, and template stripping. First experimental results performed with a transmission-type confocal optical microscope demonstrate the potential of the method.

Optical Curtain Effect: Extraordinary Optical Transmission Enhanced by Antireflection

In this paper, we employ an antireflective coating which comprises inverted π-shaped metallic grooves to manipulate the behaviour of a transverse-magnetic (TM)-polarised plane wave transmitted through a periodic nanoslit array. At normal incidence, such scheme cannot only retain the optical curtain effect in the output region but also generate the extraordinary transmission of light through the nanoslits with the total transmission efficiency as high as 90 %. Besides, we show that the spatially invariant field distribution in the output region as well as the field distribution of resonant modes around the inverted π-shaped grooves can be reproduced immaculately when the system is excited by an array of point sources beneath the inverted π-shaped grooves. Furthermore, we investigate the influence of centre groove and side-corners of the inverted π-shaped grooves on suppressing the reflection of light, respectively. Based on our work, it shows promising potential in applications of enhancing the extraction efficiency as well as controlling the beaming pattern of light emitting diodes.

Nanoporous gold—Application to extraordinary optical transmission of light

The authors present their work in the preparation of nanoporous gold layers and their patterning with an original procedure preserving the porosity, to obtain the phenomenon of extraordinary transmission of light with a porous material. The design, fabrication, and characterization of nanoslit arrays made with bulk gold and nanoporous gold films are presented and their sensing performances are compared after coating with thiolated organic molecules. Thanks to a greatly enhanced surface-to-volume ratio, nanoporous gold reveals benefits for better reaction efficiency and detection sensitivity. Moreover, plasmonic properties in the near-IR range assure employment in plasmonic devices.

FIB lithography of nanoporous gold slits for extraordinary transmission

There is a growing interest in discovering new materials for sensing purposes that provide better sensitivity and efficiency. Thanks to a greatly enhanced surface-to-volume ratio, nanoporous gold reveals benefits for better reaction efficiency and detection sensitivity purposes. Moreover plasmonic properties in the near-IR range assure employment in plasmonic devices. Here we present our work of design, fabrication and characterization of nanoporous gold slit arrays that support the phenomenon of extraordinary transmission of the incident light. The gold surface of fabricated samples has been coated with dodecanethiol and the optical response to functionalization has been analyzed in zero-order transmission.

Elementary processes of light transformation for slit structures in real and perfect metals

Efficiencies of the elementary transformation processes, transmission, diffraction and surface-plasmon excitation, which occur at the interface with 1D nano-perforated metal, are analyzed. The cases of single slits and periodic arrays of slits as well as the cases of real and perfect metals are considered. The dependences of the found efficiencies on the slit width and on the optical metal permittivity show a number of pronounced peculiarities. The transition to the perfect-metal case with increasing the absolute value of the dielectric optical permittivity ɛm is highly nontrivial. The results obtained are relevant to the description of the extraordinary light transmission through nano-holes in metals. They can serve as a reference point for the treatment of numerous problems of nano-optics of metals.

Plasmonic interaction of visible light with gold nanoscale checkerboards

Intersecting corners and checkerboards of negative refractive index materials (NRIM) represent highly singular electromagnetic systems that involve very highly enhanced local fields and the local density of modes. It is well known that plasmonic metallic systems can mimic the behavior of NRIM in the near-field limit at optical frequencies. Opaque gold films have been structured by focused ion-beam technologies at submicrometer scales in a checkerboard fashion and their optical properties measured. Subwavelength square holes in thick gold films placed in checkerboard fashion show a broadband extraordinary transmission of light at visible wavelengths. We find that the smaller the square holes, the larger is the transmission over a band of wavelengths from 650 to 950 nm suggesting that such structured surfaces have very unusual effective medium properties, which is confirmed by the band-structure diagrams computed with finite elements. Theoretical results also confirm the experimental transmission measured to be well over $80%$ from 750 to 950 nm for a checkerboard with $150\phantom{\rule{0.28em}{0ex}}\mathrm{nm}\ifmmode\times\else\texttimes\fi{}150$ nm square holes. This unusual broadband nature of checkerboard structured films is confirmed by the dark-field reflection spectra. Microscopic studies reveal that these structures have enhanced interaction of light at the edges and corners. These checkerboards are also found to give rise to an enhancement of fluorescence by imbedded dye molecules. There is a strong correspondence between the theoretical predictions and the experimental measurements.

Optical transmission through subwavelength hole arrays in ultrathin metal films

Contrary to thick opaque metal films, where an extraordinary high transmission of light is observed through subwavelength hole arrays, in ultrathin metal films perforation can lead to a suppressed or an enhanced transmission. Here we systematically investigate the optical transmission through semitransparent Au films structured with square arrays of subwavelength holes experimentally and theoretically. We measure the transmission at various angles of incidence through hole arrays with different thicknesses, diameters, and periodicities. We compare the data with an empty lattice approximation and with calculations based on a Fourier modal method. The results evidence that for gold the exact dielectric function has to be considered and that not only the periodicity and film thickness influences the transmission, but that also the shape and diameter of the holes play an important role.

Extraordinary light transmission through opaque thin metal film with subwavelength holes blocked by metal disks

We observed that when subwavelength-sized holes in an optically opaque metal film are completely covered by opaque metal disks larger than the holes, the light transmission through the holes is not reduced, but rather enhanced. Particularly we report (i) the observation of light transmission through the holes blocked by the metal disks up to 70% larger than the unblocked holes; (ii) the observation of tuning the light transmission by varying the coupling strength between the blocking disks and the hole array, or by changing the size of the disks and holes; (iii) the observation and simulation that the metal disk blocker can improve light coupling from free space to a subwavelength hole; and (iv) the simulation that shows the light transmission through subwavelength holes can be enhanced, even though the gap between the disk and the metal film is partially connected with a metal. We believe these finding should have broad and significant impacts and applications to optical systems in many fields.

Seeing protein monolayers with naked eye through plasmonic Fano resonances

We introduce an ultrasensitive label-free detection technique based on asymmetric Fano resonances in plasmonic nanoholes with far reaching implications for point-of-care diagnostics. By exploiting extraordinary light transmission phenomena through high-quality factor (Q(solution) ∼ 200) subradiant dark modes, we experimentally demonstrate record high figures of merits (FOMs as high as 162) for intrinsic detection limits surpassing that of the gold standard prism coupled surface-plasmon sensors (Kretschmann configuration). Our experimental record high sensitivities are attributed to the nearly complete suppression of the radiative losses that are made possible by the high structural quality of the fabricated devices as well as the subradiant nature of the resonances. Steep dispersion of the plasmonic Fano resonance profiles in high-quality plasmonic sensors exhibit dramatic light intensity changes to the slightest perturbations within their local environment. As a spectacular demonstration of the extraordinary sensitivity and the quality of the fabricated biosensors, we show direct detection of a single monolayer of biomolecules with naked eye using these Fano resonances and the associated Wood's anomalies. To fabricate high optical-quality sensors, we introduce a high-throughput lift-off free evaporation fabrication technique with extremely uniform and precisely controlled nanofeatures over large areas, leading to resonance line-widths comparable to that of the ideally uniform structures as confirmed by our time-domain simulations. The demonstrated label-free sensing platform offers unique opportunities for point-of-care diagnostics in resource poor settings by eliminating the need for fluorescent labeling and optical detection instrumentation (camera, spectrometer, etc.) as well as mechanical and light isolation.

Transmission and scattering properties of subwavelength slits in metals

Using an advanced eigenmode-expansion method, we analyze the basic transmission and scattering properties of subwavelength slits in real metals characterized by the complex optical permittivity ${\ensuremath{\varepsilon}}_{m}$. This includes the slit-width, wavelength, and ${\ensuremath{\varepsilon}}_{m}$ dependences of the efficiencies and cross sections of the main transformation processes: (i) transformation of the incident plane wave into the propagating mode, into the surface plasmons, and into diffracted waves in air and (ii) internal reflection of the propagating mode and its transformation to the surface plasmons and diffracted waves. In conjunction with the known perfect-metal-related efficiencies, the established dependences exhibit a wealth of important subwavelength features, including the nontrivial transmission peculiarities. Transition from the case of the periodic array of slits to the single-slit case when increasing the metal-wall width is considered as well. The established characteristics of a single interface between air and perforated metal are sufficient to describe the extraordinary light transmission through subwavelength slits in metal films.

An optofluidic nanoplasmonic biosensor for direct detection of live viruses from biological media.

Fast and sensitive virus detection techniques, which can be rapidly deployed at multiple sites, are essential to prevent and control future epidemics and bioterrorism threats. In this Letter, we demonstrate a label-free optofluidic nanoplasmonic sensor that can directly detect intact viruses from biological media at clinically relevant concentrations with little to no sample preparation. Our sensing platform is based on an extraordinary light transmission effect in plasmonic nanoholes and utilizes group-specific antibodies for highly divergent strains of rapidly evolving viruses. So far, the questions remain for the possible limitations of this technique for virus detection, as the penetration depths of the surface plasmon polaritons are comparable to the dimensions of the pathogens. Here, we demonstrate detection and recognition of small enveloped RNA viruses (vesicular stomatitis virus and pseudotyped Ebola) as well as large enveloped DNA viruses (vaccinia virus) within a dynamic range spanning 3 orders of magnitude. Our platform, by enabling high signal to noise measurements without any mechanical or optical isolation, opens up opportunities for detection of a broad range of pathogens in typical biology laboratory settings.

Tuning the optical transmission through a homogeneous doped semiconductor film by applying an external magnetic field

We theoretically and numerically studied the transmission of light through a homogeneous doped semiconductor film with a Drude tensor in the presence of an external magnetic field. The magneto-induced homogeneous metal films are found to exhibit a magneto-induced light transparency due to cyclotron resonance. In particular, the surface plasmon (SP) resonance mode of the magneto-induced metal film move to higher frequencies with increasing magnetic field, bringing about large changes in the extraordinary light transmission peaks predicted to occur in such a magneto-induced semiconductor film.