Arrays of nanoantennas consisting of plasmonic dipole pairs have been widely used in surface-enhanced Raman spectroscopy (SERS). Fine-tuned structures that can efficiently convert incident electromagnetic energy to excite molecules and provide enhanced detection. However, this tuning mechanism also has its disadvantages. In order to prevent the cross coupling, the distance between each individual element must be increased. This leads to low packing density values which in turn results in a reduction of the overall enhanced Raman signal when these structures are compared to broadly tuned aggregates of particles such as those obtained through metal sputtering or colloidal deposition. In this work we demonstrate through simulations and experimental work that it is possible to increase the reflected signal of an array of nanoantennas by reducing the distance between them in the direction both perpendicular and parallel to the orientation of the incident electric field. It is shown the resonant wavelength shifts in two different spectral directions depending in how the intercell distance was reduced. These resultant shifts can reduce the tuning capabilities of the structures but also can increase the SERS intensity due to close coupling of the dipole pairs. We believe that these results will enable the design and fabrication of structures possessing a greater degree of tunability together with an overall enhanced Raman signal that can rival aggregated SERS substrates.
The deposition of organic molecules on gold nanoantennas is reported through chemisorption for sensing in the midinfrared (mid-IR) spectral range. The specific nanostructures are gold asymmetric-split ring resonators (A-SRRs) based on circular-geometry with two different ‘arc’ lengths. The plasmonic resonant coupling technique was used to match the vibrational responses of the targeted molecules for their enhanced detection. Gold nanostructures are functionalised through chemisorption of octadecanethiol (ODT) in ethanol solution. The molecular vibrational responses were measured using a microscope coupled Fourier Transform Infrared (FTIR) spectroscopy. The experimental findings are closely supported using FDTD simulation. The modified nanoantennas surfaces are capable of supporting wide range of organic-sensing applications.
An asymmetrical H-shaped resonator (ASH) has been designed using gold on a fused silica substrate. The aim is to
obtain a high - quality factor at the reflectance resonance peaks in the mid - infrared wavelength of 2 μm to 8 μm. The
structures were modelled using the Finite Difference Time Domain (FDTD) Lumerical Solution simulation software by
adjusting the parameter of periodic boundary condition on the X and Y-axis and perfectly matched layer (PML) on the
Z- axis. The asymmetric structures give double resonance peaks that depend on the arm-length of the structure. The
periodicity along the X and Y-axis was varied to tune the width of the resonant peaks in order to obtain the maximum Qfactor.
Experimental results broadly confirm the simulations.
In this paper, gold asymmetric-split ring resonators (A-SRRs) are used for proteins sensing in the mid-infrared
(IR) spectral region. Self-assembled monolayers (SAMs) of octadecanethiol (ODT) in ethanolic solution were
deposited on the resonator surfaces to immobilise protein molecules for their detection. Different diameters ASRRs
were fabricated on zinc selenide (ZnSe) substrates using electron-beam lithography technique. Their
plasmonic responses appear in the mid-IR spectral region and match with the vibrational responses of many
organic molecules. After the formation of SAMs layer, one sample was immersed in bovine serum albumin
(BSA) solution for proteins adsorption while other sample was immersed in hydroxyl terminated hexa-ethylene
glycol (EG6-OH) solution to modify SAMs surfaces to resist immobilisation of proteins. The vibrational
responses of these organic molecules, all samples were excited using an incident broadband mid-IR light
source and their reflectance spectra were measured at normal incidence using a microscope coupled Fourier
Transform Infrared (FTIR) spectrometer. This study highlights the capability of plasmonic structures (A-SRRs)
fabricated on transparent and high refractive index ZnSe substrates allows the detection of BSA proteins with
enhanced detection in the mid-IR spectral range, demonstrating their potential for a wide range of sensing
applications, e.g. in biomedical engineering and food industries.
Metamaterials are being increasingly used as highly sensitive detection devices. The design of these structures and the
ability to effect changes in response through small changes in the geometry of their constituent elements allow for the
enhancement of known analysis techniques such as infrared or Raman spectroscopy. High electromagnetic fields have
been shown to occur in features such as small gaps and sharp tips and these so called “hot-spots” are the main focus of
recent work in Surface Enhanced Raman Spectroscopy (SERS). Previous work has shown dipole pairs with small gaps
between them to be suitable for the SERS detection of very small amounts of organic compounds. The main difficulties
lie in the small dimensions (≤100 nm) necessary to attain a significant response at the typical Raman pump wavelengths.
Also the small size of the gaps is a challenge when it comes to prevent “bridging” between the structures during the
fabrication process. In this work we show, through simulations, that carefully controlling the length of dipolar structures
as well as the gap between these dipoles a resonant response can be achieved close to the pump Raman wavelengths.
Also, we see that increasing the width of the dipole pair shifts the resonant peaks to longer wavelengths. By optimizing
their geometry, more efficient and easier to fabricate structures can be used as environmental organic sensors.
The effects of two different type of asymmetric nano-antenna that produce distinct resonance peaks were experimentally and numerically observed. At mid-infrared wavelengths broad resonances based upon various metamaterials structures have been previously reported. Here we show that introducing a crossbar on vertical asymmetric dipole nano-antenna can produce narrower resonance peaks than the dipole alone. Our approach to investigating different asymmetric nanoantenna structures yielded quality factor values more than twice the existing values reported within this region of the electromagnetic spectrum.
Acousto-Optic Tunable Filters with large acceptance angle (parallel tangent configuration) are the component of choice for imaging application in visible and NIR region wavelength. AOTF in the wavelength range above 2μm could be impractical due to the λ2 and interaction length dependencies on acoustic field intensity to achieve peak diffraction efficiency. A potential solution to reduce the RF power requirement for full diffraction efficiency is to realize a resonant acoustic cavity, and "recycle" the phonons. This configuration could give a theoretical advantage factor between 4 and 10. A prototype device with an operational wavelength range between 1μm and 2μm has been designed and tested and an optimized design to operate between 2μm - 4μm has been prepared and under construction. Due to the presence of standing wave, when the device is not in resonance a feedback signal from the device is affecting the electrical matching and the power delivered to the device is mostly reflected back (VSWR > 25), therefore a special RF driver is required in order to maintain in resonance the device. The resonance frequencies are also affected by the temperature of the device, thus a temperature control mechanism with high accuracy is required. We present the preliminary results of the first prototype, which are in good agreement with the mathematical model and an advantage factor of about 4 has been measured. Further investigation are planned in order to improve the device performance and develop the RF driver for the resonant configuration.
We tune nanoantennas to resonate within mid-infrared wavelengths to match the vibrational resonances of C=C and C-H of the hormone estradiol. Modelling and fabrication of the nanoantennas produce plasmon resonances between 2 μm to 7 μm. The hormone estradiol was dissolved in ethanol and evaporated, leaving thickness of a few hundreds of nanometres on top of gold asymmetric split H-like shaped on a fused silica substrate. The reflectance was measured and a red-shift is recorded from the resonators plasmonic peaks. Fourier transform infrared spectroscopy is use to observe enhanced spectra of the stretching modes for the analyte which belongs to alkenyl biochemical group.
This presentation is concerned with nanophotonic structures, especially with arrays of asymmetric split-ring resonator (ASRR) structures, that may be exploited in a variety of sensing applications. These applications include bio-medical sensing, organic material sensing more generally - and environmental sensing. Specific attention has been paid to the identification of molecules of interest via their bond-resonance spectral signatures.
Recent advances have seen asymmetric split ring resonators (A-SRRs) developed as sensing elements to record a shift in their peaks when there is a corresponding change in the surrounding environment. These studies have led to the investigation of Fano resonances associated with the coupling of the resonances of the A-SRRs with the molecular resonances of the analyte. The hormone estradiol (E2) was dissolved in ethanol and evaporated, leaving thickness of a few hundreds of nanometres on top of gold A-SRRs on a silica substrate. The reflectance was measured and a red shift is recorded from the resonators plasmonic peaks. The geometric sizes of the ASRRs are calculated to tune the plasmonic resonances near the molecular resonance of the C-H stretch at nominally 3.33 microns. Corresponding Lumerical modelling of the experimental data is performed using only the intensity and wavelength to match the Fano resonance at modified wavelengths of 3.42 and 3.49 microns.
The evaluation of electromagnetic material parameters from metamaterial structures has received much attention in the literature. Among others, one method is to retrieve the material parameters from the reflection and transmission measurements of the sample material. It has been found that the electromagnetic material parameters depend on the angle of incidence. Although based on the Nicholson-Ross-Weir technique, the proposed extraction technique has no limitations on the angle of incidence. The proposed extension of the NRW extraction technique is used to study a fishnet structure fabricated by nanoimprint lithography. Silver (Ag)- Magnesium Fluoride (MgF2) - silver (Ag) was deposited on the thick PMMA layer before directly imprinted by a stamp. The effective material parameters have been found to characterise the imprinted fishnet structure.
Since their inception, metamaterial fishnet structures have frequently been used to exhibit a negative refractive index. Their shape and structure make it possible to independently produce both a negative permeability (μ) and a negative permittivity (ε). Fishnets that display this characteristic can be referred to as a double negative metamaterial. Although other techniques have been demonstrated, fishnets are commonly fabricated using electron-beam lithography (EBL) or focused ion-beam (FIB) milling. In this paper we demonstrate the fabrication of fishnets using nano-imprint lithography (NIL). Advantages associated with NIL include a shorter fabrication time, a larger feasible pattern area and reduced costs. In addition to these advantages, the quality of the fabricated structures is excellent. We imprint a stamp directly into a metal-dielectric-metal stack which creates the fishnet and, as an artifact of the technique, a periodic array of nanopillars. Two different designs of the fishnet and nanopillar structure have been fabricated and optical measurements have been taken from both. In addition to the experimental measurements the structures have also been extensively simulated, suggesting a negative refractive index with a real part as large in magnitude as five can be achieved.
We report on the fabrication and characterisation of fishnet structures of various dimensions on a polymer layer. The fabrication process causes metal-dielectric-metal rectangular pillars to be compressed to the bottom of fishnet structures. The metamaterial structures are fabricated using nanoimprint lithography, allowing large areas to be patterned quickly and good reproducibility through multiple use of the nanoimprint stamp. A tri-layer comprising of silver (Ag) and magnesium fluoride (MgF2) was deposited on a thick polymer layer, in this instance PMMA, before being directly imprinted by a stamp. When the metal-dielectric layered pillars are imprinted to a sufficient depth in the PMMA below the fishnet, distinct resonance peaks can be measured at both visible and near-infrared frequencies. The precise wavelength of the resonant peak at near-infrared and its Q-factor can be changed by altering the physical dimensions and number of metal and dielectric layers of the fishnet respectively. The response viewed at visible frequencies is due to the pillars that sit in the PMMA, below the fishnet. Silver and magnesium fluoride layers that comprise the suppressed pillars are crushed during the imprinting process but still allow for light to be transmitted. Despite imprinting directly into multiple metal and dielectric layers, high quality structures are observed with a minimum feature size as low as 200 nm. Resonance peaks are measured experimentally in reflectance using an FTIR spectrometer with a calcium fluoride (CaF2) beam-splitter and a visible wavelength range spectrometer with a silicon (Si) detector.
Optical metamaterials are able to achieve optical properties that do not exist in nature. Approaches to the homogenization of optical metamaterials are becoming more and more complex in the desire to achieve accurate representation. Here we propose to modify an existing retrieval approach for metamaterials to characterize their properties. To extract the effective refractive index and material parameters from reflection and transmission coefficients for double negative metamaterial in the optical regime, the modified Nicholson-Ross-Weir (NRW) method is used. In order to obtain a true picture of these metamaterials, as a function of angle of incidence of the illumination, it is important to present not only the effective parameters of permittivity and permeability but also some other important parameters such as coupling coefficients, that represent the inherent anisotropy.
The design, modeling, fabrication, and experimental measurements on optical nanobeam cavities that change resonant frequency in response to changes in the
refractive index of the surrounding environment are presented. Nanobeam cavities based on Silicon-On-Insulator (SOI) that work at telecommunication
wavelengths (1550 nm) provide an ideal platform for label-free sensing, due to their features of high resonance Q-factors, high sensitivity and capability for integration with silicon CMOS.
Domenico Giannone, Fabian Dortu, Damien Bernier, Nigel Johnson, Graham Sharp, Lianping Hou, Ali Khokhar, Péter Fürjes, Sándor Kurunczi, Peter Petrik, Robert Horvath, Timo Aalto, Kai Kolari, Sami Ylinen, Tomi Haatainen, Holger Egger
We present the most recent results of EU funded project P3SENS
(FP7-ICT-2009.3.8) aimed at the development of a
low-cost and medium sensitivity polymer based photonic biosensor for point of care applications in proteomics. The
fabrication of the polymer photonic chip (biosensor) using thermal nanoimprint lithography (NIL) is described. This
technique offers the potential for very large production at reduced cost. However several technical challenges arise due
to the properties of the used materials. We believe that, once the NIL technique has been optimised to the specific
materials, it could be even transferred to a kind of roll-to-roll production for manufacturing a very large number of
photonic devices at reduced cost.
Asymmetric split ring resonators (A-SRRs) are formed when two separate metallic arcs of different lengths
share the same centre-of-curvature. The resonances of the two arcs interact to produce steep slopes in the
reflection spectrum. Due to their size they are also known as nano antennas. By depositing very thin films of
poly-methyl-methacrylate (PMMA), a shift in resonance reflection spectra is obtained. Similarly, it is known
that the spectral position of the A-SRR resonances can be tuned with size. We show that, when PMMA is
used as an organic probe (analyte) on top of an A-SRR array, the phase and amplitude of a characteristic
molecular bond resonance associated with PMMA changes the appearance of the observed Fano resonance,
according to the spectral position of the plasmonic reflection peaks. This effect can be utilized to give
characteristic signatures for the purpose of detection. We also show the effectiveness of localizing different
blocks of PMMA at different places on the A-SRR array to detect very small amounts of non-uniformly
distributed analytes. Finally we show that even though the resonance Q-factor is much smaller when
compared to values achievable in photonic crystal microcavities, the plasmonic nano-antenna arrays can be
used to provide highly sensitive detection of organic compounds.
We present the design modelling and fabrication of Silicon-On-Insulator (SOI) nanobeam cavities that are immersed in
a microfluidic system for refractive index sensing. The device has sensitivity value of greater than 200 nm/RIU with a
Q-factor more than 20 000 in water. It was fabricated on a SOI platform and working at telecom wavelengths. The use
of the SOI platform also offers further possibilities of integration with CMOS technologies.
We report on the fabrication of 70 nm wide, high resolution rectangular U-shaped split ring resonators (SRRs) using
nanoimprint lithography (NIL). The fabrication method for the nanoimprint stamp does not require dry etching. The
stamp is used to pattern SRRs in a thin PMMA layer followed by metal deposition and lift-off. Nanoimprinting in this
way allows high resolution patterns with a minimum feature size of 20 nm. This fabrication technique yields a much
higher throughput than conventional e-beam lithography and each stamp can be used numerous times to imprint patterns.
Reflectance measurements of fabricated aluminium SRRs on silicon substrates show a so-called an LC resonance peak in
the visible spectrum under transverse electric polarisation. Fabricating the SRRs by NIL rather than electron beam
lithography allows them to be scaled to smaller dimensions without any significant loss in resolution, partly because
pattern expansion caused by backscattered electrons and the proximity effect are not present with NIL. This in turn helps
to shift the magnetic response to short wavelengths while still retaining a distinct LC peak.
Planar devices that can be categorised as having a nanophotonic dimension constitute an increasingly important area of
photonics research. Device structures that come under the headings of photonic crystals, photonic wires and
metamaterials are all of interest - and devices based on combinations of these conceptual approaches may also play an
important role. Planar micro-/nano-photonic devices seem likely to be exploited across a wide spectrum of applications
in optoelectronics and photonics. This spectrum includes the domains of display devices, biomedical sensing and sensing
more generally, advanced fibre-optical communications systems - and even communications down to the local area
network (LAN) level. This article will review both device concepts and the applications possibilities of the various
different devices.
F. Dortu, H. Egger, K. Kolari, T. Haatainen, P. Furjes, Z. Fekete, D. Bernier, G. Sharp, B. Lahiri, S. Kurunczi, J.-C. Sanchez, N. Turck, P. Petrik, D. Patko, R. Horvath, S. Eiden, T. Aalto, S. Watts, N. Johnson, R. De La Rue, D. Giannone
In this work, we report advances in the fabrication and anticipated performance of a polymer biosensor photonic chip
developed in the European Union project P3SENS (FP7-ICT4-248304). Due to the low cost requirements of point-ofcare
applications, the photonic chip is fabricated from nanocomposite polymeric materials, using highly scalable nanoimprint-
lithography (NIL). A suitable microfluidic structure transporting the analyte solutions to the sensor area is also
fabricated in polymer and adequately bonded to the photonic chip.
We first discuss the design and the simulated performance of a high-Q resonant cavity photonic crystal sensor made of a
high refractive index polyimide core waveguide on a low index polymer cladding. We then report the advances in doped
and undoped polymer thin film processing and characterization for fabricating the photonic sensor chip. Finally the
development of the microfluidic chip is presented in details, including the characterisation of the fluidic behaviour, the
technological and material aspects of the 3D polymer structuring and the stable adhesion strategies for bonding the
fluidic and the photonic chips, with regards to the constraints imposed by the bioreceptors supposedly already present on
the sensors.
Double asymmetric split ring resonators (DA-SRRs) are composed of four separate asymmetric metallic arcs that share
the same centre-of-curvature. These four arcs interact to produce very steep slopes in the reflection spectrum and also
increase the number of trapped modes. This combination produces larger resonance quality-factors (Q-factors), making
arrays of such resonators potentially useful for optical sensing.
In this paper we discuss theoretical modelling methods for the design of photonic crystal and photonic quasi-crystal
(PQC) LEDs - and apply them to the analysis of the extraction enhancement performance and shaping of the emitted
beam profile of PQC-LED structures. In particular we investigate the effect of the pitch of the PQC patterning, and
consider the physical mechanisms giving rise to performance improvements. In addition, we examine the relative
contributions to performance improvements from effective index reduction effects that alter the conditions for total
internal reflection at the device air interface, and from photonic crystal scattering effects that give rise to radically
improved extraction performance. Comparisons are made with the performance of recently fabricated devices.
The response of metallic split ring resonators (SRRs) scales linearly with their dimensions. At higher frequencies, metals
do not behave like perfect conductors but display properties characterized by the Drude model. In this paper we compare
the responses of nano-sized gold-based SRRs at near infra-red wavelengths. Deposition of gold SRRs onto dielectric
substrates typically involves the use of an additional adhesion layer. We have employed the commonly used metal
titanium (Ti) to provide an adhesive layer for sticking gold SRRs to silicon substrates - and have investigated the effect
of this adhesion layer on the overall response of these gold SRRs. Both experimental and theoretical results show that
even a two nm thick titanium adhesion layer can shift the overall SRR response by 20 nm.
Metamaterials based on single-layer metallic Split Ring Resonators (SRR) and Wires have been
demonstrated to have a resonant response in the near infra-red wavelength range. The use of
semiconductor substrates gives the potential for control of the resonant properties of split-ring
resonator (SRR) structures by means of active changes in the carrier concentration obtained using
either electrical injection or photo-excitation. We examine the influence of extended wires that are
either parallel or perpendicular to the gap of the SRRs and report on an equivalent circuit model that
provides an accurate method of determining the polarisation dependent resonant response for
incident light perpendicular to the surface. Good agreement is obtained for the substantial shift
observed in the position of the resonances when the planar metalisation is changed from gold to
aluminium.
This paper describes the design, modeling, fabrication and characterization of single-row photonic crystal multiple micro-cavity structures embedded in 500 nm photonic wire waveguides. The strength of coupling between the resonators and the free spectral range (FSR) between the split resonance frequencies of the coupled-cavity combination were controlled via the use of different numbers of periodic hole structures - and through the use of different aperiodic hole taper arrangements between the two cavities in the middle mirror section of the mirrors. Both 2D and 3D finite-difference time-domain (FDTD) computations have been used to simulate the device structures. Comparisons have been made with the results of measurements and show good agreement.
This paper describes the realization of high quality factor (Q-factor) single row photonic crystal extended cavity
structures embedded in 500 nm wide photonic wire waveguides. Cavities spacer lengths of between 2 µm and 9 µm have
been inserted between two periodic mirrors with aperiodic tapering of the hole diameter and the spacing between holes.
A Q-factor value of approximately 74,000 has been measured for a 5 µm long cavity at a selected resonance frequency.
We have also demonstrated experimentally a tuning capability for the resonance frequency by means of small variations
of the cavity length. A shift of approximately 10 nm in resonance frequency has been obtained for a 250 nm variation of
the cavity length, both in simulation and in measured results. In addition, a free spectral range (FSR) in resonance
frequency of between 20 nm and 30 nm has also been demonstrated for a small variation in the mirror hole diameter of
approximately 20 nm. Tapering within and outside the cavity has produced a substantial increase in both the Q-factor
and the optical transmission at resonance. Both 2D and 3D finite-difference time-domain (FDTD) computations have
been used to simulate the device structures. Comparisons between the simulation and measured results show reasonably
good agreement.
We report a novel method for modeling the resonant frequency response of infra-red light, in the range of 2 to 10
microns, reflected from metallic spilt ring resonators (SRRs) fabricated on a silicon substrate. The calculated positions of
the TM and TE peaks are determined from the plasma frequency associated with the filling fraction of the metal array
and the equivalent LC circuit defined by the SRR elements. The capacitance of the equivalent circuit is calculated using
conformal mapping techniques to determine the co-planar capacitance associated with both the individual and the
neighbouring elements. The inductance of the equivalent circuit is based on the self-inductance of the individual
elements and the mutual inductance of the neighboring elements.
The results obtained from the method are in good agreement with experimental results and simulation results obtained
from a commercial FDTD simulation software package. The method allows the frequency response of a SRR to be
readily calculated without complex computational methods and enables new designs to be optimised for a particular
frequency response by tuning the LC circuit.
Photonic devices that exploit photonic crystal (PhC) principles in a planar environment continue to provide a fertile field of research. 2D PhC based channel waveguides can provide both strong confinement and controlled dispersion behaviour. In conjunction with, for instance, various electro-optic, thermo-optic and other effects, a range of device functionality is accessible in very compact PhC channel-guide devices that offer the potential for high-density integration. Low enough propagation losses are now being obtained with photonic crystal channel-guide structures that their use in real applications has become plausible. Photonic wires (PhWs) can also provide strong confinement and low propagation losses. Bragg-gratings imposed on photonic wires can provide dispersion and frequency selection in device structures that are intrinsically simpler than 2D PhC channel guides--and can compete with them under realistic conditions.
Gold Split Ring Resonators (SRRs) were fabricated on silicon substrates by electron beam lithography and lift-off, with overall dimensions of approximately 200 nm. Reflectance spectra from the SRRs are similar to those published elsewhere. New devices are proposed based on the additional functionality afforded by the use of a silicon substrate.
We describe a simple technique for the selective area modification of the bandgap in planar 3-D photonic crystals (PhC). The PhCs are grown by controlled drying of monosized polystyrene spheres. Uniaxial pressure of 41 MPa can produce a shift in the bandgap of ~90 nm from 230 nm spheres. An unexpected broadening of the bandgap is attributed to the change in topology associated with large necks formed between spheres at pressures greater than 10 MPa.
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