We delineate the four principal surface plasmon polariton coupling and interaction mechanisms in subwavelength gratings, and demonstrate their significant roles in shaping the optical response of plasmonic gratings. Within the framework of width-graded metal-insulator-metal nano-gratings, mode confinement and wave guiding result in multiwavelength light localization provided conditions of adiabatic mode transformation are satisfied. The field is enhanced further through fine tuning of the groove-width (w), groove-depth (L) and groove-to-groove-separation (d). By juxtaposing the resonance modes of width-graded and non-graded gratings and defining the adiabaticity condition, we demonstrate the criticality of w and d in achieving adiabatic mode transformation among the grooves. We observe that the resonant wavelength of a graded grating corresponds to the properties of a single groove when the grooves are adiabatically coupled. We show that L plays an important function in defining the span of localized wavelengths. We show that multiwavelength resonant modes with intensity enhancement exceeding 3 orders of magnitude are possible with w < 30nm and 300nm < d < 900nm for a range of fixed values of L. This study presents a novel paradigm of deep-subwavelength adiabatically-coupled width-graded gratings - illustrating its versatility in design, hence its viability for applications ranging from surface enhanced Raman spectroscopy to multispectral imaging.
We study nanofibers with Bragg gratings from equidistant holes. We calculate analytically and numerically the reflection and transmission coefficients for a single grating and also for a cavity formed by two gratings. We show that the reflection and transmission coefficients of the gratings substantially depend on the number of holes, the hole length, the hole depth, the grating period, and the light wavelength. We find that the reflection and transmission coefficients of the gratings depend on the orientation of the polarization vector of light with respect to the holes. Such a dependence is …
We present an electron interferometer based on near-field diffraction from two nanostructure gratings. Lau fringes are observed with an imaging detector, and revivals in the fringe visibility occur as the separation between gratings is increased from 0 to 3 mm. This verifies that electron beams diffracted by nanostructures remain coherent after propagating farther than the Talbot length $z_T = 2d^2/λ$ = 1.2 mm, and hence is a proof of principle for the function of a Talbot-Lau interferometer for electrons. Distorted fringes due to a phase object demonstrates an application for this new type of…
We demonstrate the use of nanodiamond in constructing holographic nanoparticle-polymer composite transmission gratings with large saturated refractive index modulation amplitudes at both optical and slow-neutron wavelengths, resulting in efficient control of light and slow-neutron beams. Nanodiamond possesses a high refractive index at optical wavelengths and large coherent and small incoherent scattering cross sections with low absorption at slow-neutron wavelengths. We describe the synthesis of nanodiamond, the preparation of photopolymerizable nanodiamond-polymer composite films, the constr…
The preparation of neutron-optical phase gratings with light-optical holography is reviewed. We compare the relevant concepts of i) Kogelnik's theory for Bragg diffraction of light by thick volume gratings, which can be used to analyze holographic gratings with both light and neutrons, and ii) the dynamical theory of neutron diffraction. Without going into mathematical detail, we intend to illuminate their correspondence. The findings are illustrated by analyzing data obtained from reconstruction of nanoparticle holographic gratings with both light and neutrons.
We report the possibility to generate tremendous light-field enhancements within shallow nano-trenches made in a high index dielectric material, because of resonant behaviours reminiscent of what we get with sub-wavelength plasmonic cavities. The high quality factors are explained through a modal analysis and can be tuned with appropriate design rules. The thin dielectric void gratings here simulated could be a relevant alternative to plasmon-based devices for chemical sensing, or could be used as efficient wavelength-selective photo-absorbers by taking weakly absorbing materials.
Tailoring the emission of plasmonic nanowire-based lasers represents one of the major challenges in the field of nanoplasmonics, given the envisaged integration of such devices into on-chip all-optical circuits. In this study, we proposed a mode selection scheme based on distributed feedback, achieved via the external coupling of single zinc oxide nanowires to an aluminum grating, which enabled a quasi-single mode lasing action. The nano-manipulation of a single nanowire allowed for a reliable comparison of the lasing emission characteristics in both planar (i.e. nanowire on the metallic subst…
We report a new gateway to enhance the sponatnesous emission rate of single quantum emitters by introducing a cavity in tilted nanofiber Bragg grating (TNFBG). We found that light emitter's coupling efficiency into the tilted grating structure's guided mode is 65%, with 70 grating periods. This novel tilted structure has a high Q factor ~ 1408.71 and low mode volume ~ 0.66 microm3- an important requirement. Further, the Purcell factor of a quantum light emitter inside the nanofiber is nine times more than that of an emitter on the cavity's surface. The further optimized system with enhanced pe…
Modern nonlinear optical materials allow light of one wavelength be efficiently converted into light at another wavelength. However, designing nonlinear optical materials to operate with ultrashort pulses is difficult, because it is necessary to match both the phase velocities and group velocities of the light. Here we show that self-organized nonlinear gratings can be formed with femtosecond pulses propagating through nanophotonic waveguides, providing simultaneous group-velocity matching and quasi-phase-matching for second harmonic generation. We record the first direct microscopy images of …
We experimentally observed the surface plasmon resonance mode splitting in a super-period metal nanohole grating under the transverse magnetic polarization excitation. The mode splitting was observed in the zeroth order transmission and also in the first order diffracted transmission. However, the mode splitting phenomenon is more evident in the first order transmission than in the zeroth order transmission. It is explained that the mode splitting is due to the coupling between the surface plasmon resonance mode in the subwavelength period metal nanohole arrays and the resonance mode of the me…
The emergence of optical micro/nano-fiber (MNF) with a subwavelength diameter, which has ultra-light mass and an intense light field, brings an opportunity for develop fiber based optomechanical systems. In this study, we theoretically show an optomechanical effect in silica MNF Bragg gratings (MNFBGs). The light-induced mechanical effect results in continuously distributed strain along the grating. It is shown that the power-related strain introduces an optically reconfigurable chirp in the grating period. We develop new optomechanical coupled-mode equations and theoretically analyze the infl…
We present a technique capable of producing subwavelength focal spots in the far-field of the source in planar non-resonant structures. The approach combines the diffraction gratings that generate the high-wavevector-number modes and planar slabs of homogeneous anisotropic metamaterials that propagate these waves and combine them at the subwavelength focal spots. In a sense, the technique combines the benefits of Fresnel lens, near-field zone plates, hyperlens, and superlens, and at the same time resolves their fundamental limitations. Several realizations of the proposed technique for visible…
In this work, we design a new tunable nanofocusing lens by the linear-variant depths and nonlinear-variant widths of circular grating for far field practical applications. The constructively interference of cylindrical surface plasmon launched by the subwavelength metallic structure can form a subdiffraction-limited focus, and the focal length of the this structures can be adjusted if the each groove depth and width of circular grating are arranged in traced profile. According to the numerical calculation, the range of focusing points shift is much more than other plasmonic lens, and the relat…
Understanding of material behaviour at nanoscale under intense laser excitation is becoming critical for future application of nanotechnologies. Nanograting formation by linearly polarised ultra-short laser pulses has been studied systematically in fused silica for various pulse energies at 3D laser printing/writing conditions, typically used for the industrial fabrication of optical elements. The period of the nanogratings revealed a dependence on the orientation of the scanning direction. A tilt of the nanograting wave vector at a fixed laser polarisation was also observed. The mechanism res…
Utilizing continues-wave or pulsed laser to induce nano-structures on various material surfaces is one significant method in nano-fabrication technology. In this report, we investigate the formation of high spatial frequency periodic structures on Polyvinyl Pyrrolidone (PVP) film by a linearly polarized femtosecond laser. Ferric (Fe) ions are introduced into the film to improve the photosensitivity. Regular nano-gratings with spatial periods at the range of 60-100nm, which are about one tenth of the irradiating wavelength, can be induced. The period direction of the nano-gratings is perpendicu…
Embedding strong photonic stopbands into traditional optical fibre that can directly access and sense the outside environment is challenging, relying on tedious nanoprocessing steps that result in fragile thinned fibre. Ultrashort pulsed laser filaments have recently provided a non contact means of opening high aspect ratio nanoholes inside of bulk transparent glasses. This method has been extended here to optical fibre, resulting in high density arrays of laser filamented holes penetrating transversely through the silica cladding and guiding core to provide high refractive index contrast Brag…
We experimentally demonstrate graphene-plasmon polariton excitation in a continuous graphene monolayer resting on a two-dimensional subwavelength silicon grating. The subwavelength silicon grating is fabricated by a nanosphere lithography technique with a self-assembled nanosphere array as a template. Measured transmission spectra illustrate the excitation of graphene-plasmon polaritons, which is further supported by numerical simulations and theoretical prediction of plasmonband diagrams. Our grating-assisted coupling to graphene-plasmon polaritons forms an important platform for graphene-bas…
We report a refractive index sensor comprising of unique T grating on top of periodic nano-cavities. The sensor has two resonant modes sensitive to different regions of the structure with low inter-region interference, hence allows simultaneous detection of two different analytes or more accurate detection of a single analyte. The sensor also provides a self-referencing feature for a broad range of refractive index, from 1.3 to 1.5. Using the FDTD method, the sensitivities of 801.7 nm/RIU and 1386.8 nm/RIU have been recorded for the two modes respectively. The versatility of the structure make…
We show a large enhancement of two-photon absorption processes in nanocrystal quantum dots and of light upconversion efficiency from the IR to the near-IR spectral regime, using a hybrid optical device in which near-IR emitting InAs quantum dots were embedded on top a metallic nanoslit array. The resonant enhancement of these nonlinear optical processes is due to the strong local electromagnetic field enhancements inside the nanoslit array structure at the extraordinary transmission resonances. A maximal two-photon absorption enhancement of more than 20 was inferred. Different high field regio…
Recent experiments have shown that spatial dispersion may have a conspicuous impact on the response of plasmonic structures. This suggests that in some cases the Drude model should be replaced by more advanced descriptions that take spatial dispersion into account, like the hydrodynamic model. Here we show that nonlocality in the metallic response affects surface plasmons propagating at the interface between a metal and a dielectric with high permittivity. As a direct consequence, any nanoparticle with a radius larger than 20 nm can be expected to be sensitive to spatial dispersion whatever it…
Fibre Bragg grating sensors have emerged as a simple, inexpensive, accurate, sensitive and reliable platform, a viable alternative to the traditional bulkier optical sensor platforms. In this work we present an extensive theoretical analysis of the tilted fibre Bragg grating sensor (TFBG) with a particular focus on its polarization-dependent properties. We have developed a highly efficient computer model capable of providing the full characterization of the TFBG device in less then $3$~minutes for a given state of incident light polarization. As a result, the polarization-dependent spectral re…
We demonstrate that plasmonic helical gratings consisting of metallic nanowires imprinted with helical grooves or ridges can be used efficiently to generate plasmonic vortices with radius much smaller than the operating wavelength. In our proposed approach, these helical surface gratings are designed so that plasmon modes with different azimuthal quantum numbers (topological charge) are phase-matched, thus allowing one to generate optical plasmonic vortices with arbitrary topological charge. The general principles for designing plasmonic helical gratings that facilitate efficient generation of…
We report on the detection of diffraction gratings buried below a stack of tens of 18 nm thick $\mathrm{SiO_2}$ and $\mathrm{Si_3N_4}$ layers and an optically opaque metal layer, using laser-induced, extremely-high frequency ultrasound. In our experiments, the shape and amplitude of a buried metal grating is encoded on the spatial phase of the reflected acoustic wave. This grating-shaped acoustic echo from the buried grating is detected by diffraction of a delayed probe pulse. The shape and strength of the time-dependent diffraction signal can be accurately predicted using a 2D numerical model…
We demonstrate theoretically a large transverse magneto-optical Kerr effect (TMOKE) in subwavelength gratings consisting of alternating magneto-insulating and nonmagnetic dielectric nanostripes. The reflectivity of the grating reaches $96\%$ at the frequencies corresponding to the maximum of the TMOKE response. The combination of a large TMOKE response and high reflectivity is important for applications in $3$D imaging, magneto-optical data storage, and magnonics.
Using a hydrodynamic approach we examine bulk- and surface-induced second and third harmonic generation from semiconductor nanowire gratings having a resonant nonlinearity in the absorption region. We demonstrate resonant, broadband and highly efficient optical frequency conversion: contrary to conventional wisdom, we show that harmonic generation can take full advantage of resonant nonlinearities in a spectral range where nonlinear optical coefficients are boosted well beyond what is achievable in the transparent, long-wavelength, non-resonant regime. Using femtosecond pulses with approximate…
On-chip nanophotonics serves as the foundation for the new generation of information technology, but it is challenged by the diffraction limit of light. With the capabilities of confining light into (deep) subwavelength volumes, plasmonics makes it possible to dramatically miniaturize optical devices so as to integrate them into silicon chips. Here we demonstrate that by cascading nano-corrugation gratings with different periodicities on silver nanowires atop silicon, different colors can be spatially separated and chronologically released at different grating junctions. The released light fre…
Spoof surface modes on nanostructured metallic surfaces are known to have tailorable dispersion dependent on the geometric characteristics of the periodic pattern. Here we examine the spoof plasmon dispersion on an isolated grating and a grating-planar mirror cavity configuration. The spoof polariton dispersion in the cavity is obtained using the scattering matrix approach, and the related differential modal density of states is introduced to obtain the mode dispersion and classify the cavity polariton modes. The grating-mirror cavity geometry is an example of periodically nanostructured metal…
We configure and analyze a nanostructured device that hybridizes grating modes and surface plasmon resonances. The model uses an effective index of refraction that considers the volume fraction of the involved materials, and the propagation depth of the plasmon through the structure. Our geometry is an extruded low-order diffraction grating made of dielectric nano-triangles. Surface plasmon resonances are excited at a metal/dielectric interface, which is separated from the analyte by a high-index dielectric layer. The optical performance of the refractometric sensor is highly competitive in se…
We present two-dimensional plasmonic Doppler grating (PDG) for broadband azimuthal angle-resolved nanophotonic applications. The PDG consists of a set of non-concentric circular rings mimicking the wavefronts of a moving point source that exhibits Doppler Effect and thereby offers continuous azimuthal angle-dependent lattice momentum for photon-plasmon coupling. The center and span of the working frequency window are fully designable for optimal performance in specific applications. We detail the design, fabrication and optical characterization of the PDG. The design of Doppler grating provide…
We experimentally measure and analytically describe the fluorescence enhancement obtained by depositing CdSe/CdS nanocrystals onto a gold plasmonic crystal, a two-dimensional grating of macroscopic size obtained by gold deposition on a self-assembled opal. We show evidences of nanocrystals near-field coupling to the gold Surface Plasmons Polaritons (SPP) followed by grating-induced SPP re-emission to far-field. We develop a theoretical framework and an original method in order to evaluate, from photoluminescence experiments, the SPP extraction efficiency of a grating.
Metasurfaces are nano-structured devices composed of arrays of subwavelength scatterers (or meta-atoms) that manipulate the wavefront, polarization, or intensity of light. Like other diffractive optical devices, metasurfaces suffer from significant chromatic aberrations that limit their bandwidth. Here, we present a method for designing multiwavelength metasurfaces using unit cells with multiple meta-atoms, or meta-molecules. Transmissive lenses with efficiencies as high as 72% and numerical apertures as high as 0.46 simultaneously operating at 915 nm and 1550 nm are demonstrated. With proper …
Surface Plasmon Polaritons (SPP) are exploited due to their intriguing properties for photonic circuits fabrication and miniaturization, for surface enhanced spectroscopies and imaging beyond the diffraction limit. However, the excitation of these plasmonic modes by direct illumination is forbidden by energy/momentum conservation rules. One strategy to overcome this limitation relies on diffraction gratings to match the wavevector of the incoming photons with that of propagating SPP excitations. The main limit of the approaches so far reported in literature is that they rely on highly ordered …
Optical nanosensors are promising for hydrogen sensing because they are small, free from spark generation, and feasible for remote optical readout. Conventional optical nanosensors require broadband excitation and spectrometers, rendering the devices bulky and complex. An alternative is spatial intensity-based optical sensing, which only requires an imaging system and a smartly designed platform to report the spatial distribution of analytical optical signals. Here, we present a spatial intensity-based hydrogen sensing platform based on Fano-like spatial distribution of the transmission in a P…
All-reflective interferometry based on nano-structured diffraction gratings offers new possibilities for gravitational wave detection. We investigate an all-reflective Fabry-Perot interferometer concept in 2nd order Littrow mount. The input-output relations for such a resonator are derived treating the grating coupler by means of a scattering matrix formalism. A low loss dielectric reflection grating has been designed and manufactured to test the properties of such a grating cavity.
Polaritons can provide strong optical field enhancement allowing to boost light-matter interaction. Here, we experimentally observe enhancement of mid-infrared second-harmonic generation (SHG) using grating-coupled surface phonon polaritons of the 6H-SiC surface. In our experiment, we measure the SHG along the polariton dispersion by changing the incidence angle of the excitation beam. We observe hybridization between the propagating surface phonon polaritons and localized plasmon resonances in the gold grating, evidenced by the modification of the polariton dispersion as we change the area ra…
2D and 3D micro/nano fabrication based on two-photon polymerization (TPP) has emerged as a strong contender for additive manufacturing for wide variety of applications. In this manuscript we report one step patterning of structurally stable, subwavelength 2D and 3D gold nanostructures using femto-second laser by incorporating single photon photoinitiator only in pure and metal precursor doped polymers. The metal polymer composite nanostructures are written directly by in-situ reduction of gold precursor within the photoresist using femto-second laser irradiation. The photo-initiator triggers t…
We compare the characteristics of two types of patterns obtained with two azopolymer materials: a Gaussian random pattern and a quasi-random grating pattern. The surface structurations have been obtained with a simple bottom-up technique by illuminating azopolymer thin films with a single laser beam. We demonstrate the interesting generated properties of these two surfaces. In particular, the surface with quasi-random gratings can address beam splittings for light coupling in different directions in an ultra-thin film. We use these two surfaces as a mold and replicate them on a transparent ela…
Under white light illumination, gratings produce an angular distribution of wavelengths dependent on the diffraction order and geometric parameters. However, previous studies of gratings are limited to at least one geometric parameter (height, periodicity, orientation, angle of incidence) kept constant. Here, we vary all geometric parameters in the gratings using a versatile nanofabrication technique, two-photon polymerization lithography, to encode hidden color information through 2 design approaches. The first approach hides color information by decoupling the effects of grating height and p…
In this paper, the implementation of optical elements in the form of Pancharatnam-Berry optics is considered. With respect to 3D bulk and diffractive optics, acting on the dynamic phase of light, Pancharatnam-Berry optical elements transfer a phase which is geometric in nature by locally manipulating the polarization state of the incident beam. They can be realized as space-variant sub-wavelengths gratings that behave like inhomogeneous form-birefringent materials. We present a comprehensive work of simulation, realization, and optical characterization at the telecom wavelength of 1310 nm of t…
By using a self-consistent Maxwell-Bloch method, we demonstrate the simultaneously lasing and spasing behavior in a simple metal grating-film nanostructure, which can be attributed to spatial hole burning and the gain competition of different modes at the band edge and in the plasmonic band gap. We show three modes: one spaser mode in gap with quality factor as high as 248.54, one plasmon lasing mode at band edge which emit vertically from the grating surface, and the other plasmon lasing mode at band edge which is suppressed by the spaser mode. This method may find significant applications in…
In this work, we propose an approach for the design of a waveguide structure that allows for efficient and highly asymmetric coupling of the quantum sources with circularly polarized transition dipole moments to the guided mode of the structure. The approach is based on the mixing of the two quasi-degenerate modes of a periodic waveguide with an auxiliary single-mode waveguide leading to the formation of the dispersion with a stationary inflection point and consequently to the high coupling efficiency of this mode with a dipole source. We show that the distribution of the field polarization in…
The interplay between electronic properties and optical response enables the realization of novel types of materials with tunable responses. Superconductors are well known to exhibit profound changes in the electronic structure related to the formation of Cooper pairs, yet their influence on the electromagnetic response in the optical regime has remained largely unstudied. Photonics metamaterials offer new opportunities to enhance the light-matter interaction, boosting the influence of subtle effects on the optical response. The combination of photonic metamaterials and superconducting quantum…
Plasmonic biosensing chips were prepared by fabricating wavelength-scaled dielectric-metal interfacial gratings on polymer film covered bimetal layers. Lysozyme biomolecules (LYZ) and gold nanoparticle bioconjugates (AuNP-LYZ) with 1:5 mass ratio were seeded onto the biochip surfaces. Comparison of the reflectance curves measured in a modified Kretschmann arrangement and computed numerically proved that monitoring the narrower secondary peaks under optimal rotated-grating coupling condition makes it possible to achieve enhanced sensitivity in biodetection. The enlarged resonance peak shift is …
We report narrow quadrupolar surface lattice resonances (SLRs) under normal incidence, and the observation, for the first time, of the band reversal effect of SLRs supported by a vertical metal-insulator-metal nanograting, which is embedded in a homogeneous dielectric environment. Simulation results show that under normal incidence, quadrupolar SLR with linewidth of 1~nm and high quality factor of 979 can be excited in the near-infrared regime, and that under oblique incidence, out-of-plane dipolar SLRs of relatively large quality factors (>=150) can be launched. By varying the incidence angle…
Light propagation in a Bragg periodic structure containing thin films with metallic nanoparticles is studied. Plasmonic resonance frequency, Bragg frequency, and light carrier frequency are assumed to be close. Exact solutions describing solitary gap-waves are found, and a light arrest phenomenon due to nonlinearity of plasmonic oscillations is studied.
Surface-relief gratings fabricated through nanoimprint lithography (NIL) are prone to topographic distortion induced by resist shrinkage. Characterizing the impact of this effect on blazed diffraction efficiency is particularly important for applications in astrophysical spectroscopy at soft x-ray wavelengths ($λ\approx 0.5 - 5$~nm) that call for the mass-production of large-area grating replicas with sub-micron, sawtooth surface-relief profiles. A variant of NIL that lends itself well for this task is substrate-conformal imprint lithography (SCIL), which uses a flexible, composite stamp forme…
A one-dimensional dielectric grating, based on a simple geometry, is proposed and investigated to enhance light absorption in a monolayer graphene exploiting guided mode resonances. Numerical findings reveal that the optimized configuration is able to absorb up to 60% of the impinging light at normal incidence for both TE and TM polarizations resulting in a theoretical enhancement factor of about 26 with respect to the monolayer graphene absorption (about 2.3%). Experimental results confirm this behaviour showing CVD graphene absorbance peaks up to about 40% over narrow bands of few nanometers…
Diffusion of heat in metals is a fundamental process which is crucial for a variety of applications of metal nanostructures. Surprisingly, however, {\em ultrafast} heat diffusion received only limited attention so far. Here, we show that heat diffusion can be made faster than $e-ph$ energy transfer rate, in which case, it dominates the spatio-temporal dynamics of the temperature. This enables the metals to overcome the conventional limitations of the nonlinear optical response of materials - it can be simultaneously fast and strong. As a specific example, we identify the underlying (femtosecon…
We propose a graphene-on-grating nanostructure to enable second-order spatial differentiation computation in terahertz (THz) region. The differentiation operation is based on the interference between the direct reflected field and the leakage of two excited surface plasmon polaritons counter-propagating along the graphene sheet. With the spatial coupled-mode theory, we derive out that the requirement for the second-order spatial differentiation is the critical coupling condition. We numerically demonstrate such an analog computation with Gaussian beams. It shows that the spatial bandwidth of t…
It is shown here that rendering the width of nano-grooves into a tunable parameter presents a new means of light trapping in subwavelength gratings. Particularly, in gratings with groove-widths below 150 nm, the plasmon coupling between the perimeter walls of the groove becomes dominant and thus turns groove width into the principle geometric parameter in determining light trapping. Using this parameter, we investigate the prospect of tunable optical functionalities. An analytical formula is derived by treating each nano-groove as a plasmonic waveguide resonator. The resulting change in the ca…
Plasmonic gratings and nano-particle arrays in a metal-insulator-metal structures are fabricated on an erbium doped silicon nitride layer. This material system enables simple fabrication of the structure, since the active nitride layer can be directly grown on metal. Enhancement of collected emission of up to 12 is observed on resonance, while broad off-resonant enhancement is also present. The output polarization behavior of the gratings and nano-particle arrays is investigated and matched to plasmonic resonances, and the behavior of coupled modes as a function of inter-particle distance is a…
