Development of novel plasmonic nanopatterns is of great interest for various applications, including chemical and biological analysis. Systems based on gold nanoelements have been designed and tested in several research works for the study and detection of various kinds of biological analytes, giving appreciable results. Plasmonic properties associated to the nanostructure can be tuned by changing the size and the shape of the nanoparticles or the periodicity or, more in general, the geometry of the nanopattern. These features are key to many applications aiming at signal enhancement and low threshold sensing. In this work we present a study of periodic arrangements of novel plasmonic metamolecular unit cells made of triangular nanoelements. Nanostructures analyzed were fabricated using electron beam lithography technique (EBL) that allows to create patterns with high accuracy and repeatability. Morphological analysis was realized by Scanning Electron Microscopy (SEM) and their plasmonic properties were studied and compared using experimental set-up for Surface Plasmon Resonance (SPR) and Surface Enhanced Raman Spectroscopy (SERS) measurements. We tested the sensing performance of our nanostructures by analyzing the SARS-CoV-2 (COVID-19) Spike Antibody (3525) getting its molecular fingerprint. Our results suggest that these plasmonic patterns are promising to develop highly sensitive nanosensors for the detection of biological analytes.
Plasmonic devices are of great interest for different applications including chemical sensing for food and water contaminants. Their properties to confine high electromagnetic fields strictly depend on the size, shape and, more in general, on the geometry of their basic constituents. In this work we fabricate and characterize two-dimensional periodic arrangements of novel plasmonic supra-molecular cells with different minimum intercell distance and in both nanopillars and nanocavities geometries. For patterns based on nanopillars we evaluate the bulk sensitivity associated to their localized surface plasmon resonance which results to have a value up to 408 nm/RIU while for the patterns based on nanocavities we found a SERS enhancement factor up to 2.1x106. We tested the sensing performance of these nanostructures analyzing different concentrations in water of fipronil pesticide using both LSPR and SERS tools. Our results suggest that these plasmonic patterns are promising to develop nanosensors for a dual-sensing detection of water contaminants with high sensitivity.
Three-dimensional organic microlasers were fabricated and lasing with low threshold was demonstrated. The
cavities were fabricated via UV lithography from SU-8 doped with different laser dyes. The fabrication scheme
relies on commercially available products and is both cheap and rapid. Cubic and stripe-shaped (Fabry-P´erot)
microlasers were investigated. The periodic ray trajectories on which their lasing modes are localized were
identified as a first step towards the exploration of general three-dimensional microlasers.
We report on the linear electro-optical scattering response from individual ferroelectric (KTiOPO4) nano-crystals. The newly developed Pockels Linear Electro-Optical Microscopy (PLEOM)1-3 is used in this context to map the second-order susceptibility χ(2) of non-centrosymmetric materials with a high sensitivity due to a stabilized interferometric homodyne detection. The random spatial orientation of single nano-crystals (with an average size of 150 nm), together with the orientation of the electric dipole moment of ferroelectric domains can be jointly inferred from the intensity polarization plots together with phase of the linear electro-optical response. Down- scaling the electro-optic response to nano-crystals opens-up new applications towards sub-diffraction electro-optic nano-labels for nonlinear microscopy with applications to nano-sciences and biophotonics. By using a low power He-Ne laser source and a low intensity illumination beam, PLEOM bears the potential of a new low-cost non-imaging method in biology, especially relevant for sensitive samples.
Single nanoparticle imaging is a powerful method to characterize nanoobjects and gain better understanding of their structural and optical properties. In our research we focus on plasmonic nanoparticles and particularly on anisotropic gold nanorods, which present interesting, polarization-dependent optical properties strictly correlated with their surface plasmon resonances. Here we discuss our results on two-photon excited luminescence imaging of a single gold nanorod. We analyze the dependence of the two-photon luminescence of a nanorod on the excitation wavelength, incident laser power and polarization, and contrast them with the data available in the literature.
In this work we study optically pumped polymer-based lasers doped by various organic dyes in two different
configurations, namely plane cavities of various shapes and vertical external cavities ("VECSOL"). The intrinsic
fluorescence anisotropy of specific dye molecule together with the polarization state of the pump beam defines the basic
emission properties of such dye-doped polymer system. The nonlinear enhancement of amplified spontaneous emission
(ASE) and lasing results in the forcing of the emission properties and particularly of their polarization features. However,
we demonstrate experimentally that it is possible to release this constraint and to obtain laser emission with a
polarization state different from that of the pump.
In this paper we report on the design and fabrication of polymeric microracetracks optical resonators for optofluidic
label-free biosensing. In the domain of optical integrated devices, polymer materials offer the advantages of low cost,
easy fabrication, low scattering loss on waveguide sidewalls, and high coupling efficiency to optical fibres and
waveguides. Moreover, for biochemical sensing, polymer surfaces can be easily modified to immobilize a wide choice of
target molecules. Polymers are also well compatible with microfluidic circuits, favoring the insertion of photonic circuits
into optofluidic cells. The vertical coupling configuration, in which resonators are vertically coupled to the buried bus
waveguide, presents several advantages in comparison with the lateral coupling configuration, particularly in the context
of optofluidic biosensors. Polymeric microracetracks were fabricated using the SU-8 negative photoresist and the
CYTOP fluorinated polymer, using a combination of a simple near UV lithography and reactive ion etching technology.
Vertically coupled microracetracks immersed in deionized water display high Q-factors (> 35000) and finesse up to 25.
Surface sensing experiments performed with these microresonators using TAMRA-cadaverine as a test molecule, which
can be quantified through fluorescence analysis, demonstrated a very low detection limit of 0.22 attogram.
We propose new strategies to increase and control molecular second-order nonlinearities, byusing photoswitching
processes or plasmonic resonance. First, we report on reversible switching of nonlinear optical (NLO) properties, based
on the use of dipolar or octupolar metal complexes containing photochromic ligands like dithienylethene (DTE)
derivatives. DTE undergo a reversible interconversion between a non-conjugated open form and a π-conjugated closed
form. A strong relative change of the quadratic molecular nonlinearity upon visible light exposure (more than one order
of magnitude) is evidenced by second harmonic generation experiments. This process is fully reversible. On another
hand, we explore the quadratic NLO properties of highly NLO dyes (stilbazolium derivatives) grafted onto the surface of
gold nanoparticles (NP). In spite of the fact that the plasmon resonance wavelength of gold NPs lies far from that of the
second harmonic signal at 820 nm, a significant increase of the nonlinear response of this dye (when linked to a gold
nanoparticle) due to surface Plasmon resonance with gold NPs is shown by Harmonic Light Scattering at 1.64 μm. The
nature of the linker has a significant influence of hyperpolarizability values, and a similar, but weaker enhancement
effect, is also reported in the case of dye/NP mixtures.
We introduce and demonstrate a dual-channel radially-polarized surface plasmon microscopy (SPM) system with
capability down to single nanoparticle detection. For nanospheres stained with fluorescent molecules, we are able to
simultaneously collect both fluorescence and elastic scattering images. By using a radial polarizer, the entire incident
beam is TM-polarized, which enables formation of a dark circular ring in the reflected image, thus providing higher
sensitivity to refractive index changes. The fluorescence intensity is clearly enhanced by more than 50% under radial
polarization as compared to a linear one. The complementary signals acquired from the two separated channels jointly
lead to well-co-localized images in scanning mode. This technique is currently extended to study two photon
fluorescence (TPF) signals from nanospheres, as well as second harmonic generation (SHG) signals from noncentrosymmetric
nanocrystals. It also provides a way to compensate for the eventual blinking of the fluorescence, which
does not affect the elastic scattering channel.
Several high-performance polymeric electro-optic modulators have been demonstrated in the last decade. Most of them
have been elaborated using specific high-performance electro-optic polymers designed for their exceptional electro-optic
response and their thermal stability. In this paper we report the high performance of electro-optic modulators made of a
commercial side-chain electro-optic copolymer DR1-PMMA as the active core material and of a passive epoxy polymer
NOA73 as cladding material. The electro-optic polymer used in these modulators is a Disperse Red 1- poly-methylmethacrylate
(DR1-MMA) side-chain copolymer with relative molar concentrations of DR1-substituted (resp. MMA
unsubstituted) groups equal to 30% (resp. 70%). We have designed, elaborated and tested phase modulator and pushpull
Mach-Zehnder modulators in order to optimize their figure of merit VπL. A push-pull Mach-Zehnder modulator
with 2 cm-long electrodes and an inter-electrode distance of 8.8 μm displays a half-wave voltage of 2.6 V at 1550 nm,
corresponding to a figure of merit of 5.2 V.cm. This result was obtained with a moderate poling electric field of 75 V/μm
applied to the core of the modulator waveguide. We report here the best figure of merit which has never been observed in
a modulator realized with a commercial side-chain electro-optic polymer.
We have designed and realized three integrated photonic families of micro-resonators (MR) on multilayer organic
materials. Such so-called 2.5D-MR and 3D-MR structures show off radius values ranging from 40 to 200μm. Both first
and second families are especially designed on organic multilayer materials and shaped as ring- and disk-MR organics
structures arranged upon (and coupled with) a pair of SU8-organic waveguides. The third family is related to hybrid 3D-MR
structures composed of spherical glass-MR coupled to organic waveguides by a Langmuir-Blodgett lipid film about
three nanometers in thickness. At first, polymer spin coating, surface plasma treatment and selective UV-lithography
processes have been developed to realize 2.5D photonic micro-resonators. Secondly, we have designed and characterized
photonic-quadripoles made of 3D-glass-MR arranged upon a pair of SU8 waveguides. Such structures are defined by a
4-ports or 4-waveguides coupled by the spherical glass-MR. We have achieved an evanescent photonic coupling between
the 3D-MR and the 4-ports structure. Spectral resonances have been measured for 4-whispering gallery-modes (WGM)
into such 3D-structures respectively characterized by a 0.97 nm free spectral range (FSR) and a high quality Q-factor up
to 4.104.
We report on the first developments for a new approach of integrated photonic using optical evanescent coupling
from organic microstructures to bundles of hybrid nanotubes (NT). Microstructures are organic disks acting as
photon reservoirs, integrated on a photonic chip fabricated by micro-technologic processes. Biomimetic peptidic/
silica nanotubes are realized by molecular self-assembly allowing high aspect ratio. Such heterostructures
have been included directly on the organic chip as an innovative solution based on nanotubes in situ chipapproach.
The latter allowed us to obtain an adequate evanescent coupling localized between micronic-disks and
bundles of nanotubes. As a result, we highlight a specific photonic propagation along various heterostructured-
NT-bundles featuring distances beyond the centimeter and losses from 1.2 to 6.6 dB/cm. It presents an advantageous
confinement of the optical mode marked with strong energy localizations between nanotubes.
Molecular Nonlinear Optics, an otherwise well established domain, is currently revisiting and shaking its foundations,
objectives and methods, in the frame of ongoing conceptual as well as methodological revivals. These are based on
correlated advances in chemistry and physics, entailing spectacular advances in the new playground of multiphoton bio-imaging.
For chemistry, we chose to review and highlight a comprehensive multipolar template approach will helps
rationalize and generalize molecular design rules, with current emphasis on multi-functionality and the nano-scale. In
consistence with advances in chemistry, we emphasize for physics the domain of nonlinear micro- and nano-photonics,
in particular with respect to active nonlinear coupling schemes, based on interference of multi-photon absorption
pathways. It permits to encode nonlinear information or guide the displacement of molecular or nano-scale objects by
adequate laser illumination. Building-up on these advances and more, advanced bio-imaging methods such as based on
phase and polarization resolved nonlinear schemes, are currently opening-up new windows onto cellular structures and
mechanisms, with the potential towards unprecedented spatial resolution.
Optoelectronic oscillators have been studied since many years now, their high spectral purity being one of
their most interesting quality for photonics signal processing, communication or radio over fiber systems.
One part of the structure is a long fiber optic feedback loop acting as a delay line. Different techniques have
been introduced such as multiple loops in order to get very narrow spectral lines and large mode spacing.
One of the problems due to long fiber loops is the size and the requirement of temperature control. In order
to go toward integrated solutions it is also possible to introduce optical resonators instead of a delay line
structure (as for classical electronic oscillators). But such resonators should present very high quality factor.
In this paper we demonstrate solutions using resonators based on polymer materials such as PMMA-DCM.
Structures such as micro-rings, micro-disks or stadium-shaped resonator have been realized at the laboratory.
Quality factor of 6000 have already been achieved leading to an equivalent fiber loop of 19 m for an
oscillator at 10 GHz. But it has been already theoretically proved that quality factor greater than one
thousand hundred could be obtained. These resonators can be directly implemented with Mach-Zehnder
optical modulators based on electro-optic polymer such as PMMA-DR1 leading to integrated solutions. And
in the future it should be also possible to add a laser made with polymer material, with a structure as
stadium-shape polymer micro-laser. The fully integrated photonic chip is not so far. The last important
function to be implemented is the tuning of the oscillation frequency.
We predict that nanoparticles of octupolar symmetry (nano-triangles
and nano-tetrahedra), whose orientation cannot be affected by means
of linear optics, subjected to a coherent mixture of fundamental and
second harmonic fields will rotate and orient controlled by the relative
phase between these fields. This is due to the generation of the
second-harmonic polarization and its interaction with the
second-harmonic field. We have described this effect quantitatively
for triangular and
tetrahedral clusters of metal nanospheres where it can be observed
experimentally and used in applications.
We present herein a original concept of electro-optic (EO) probe for high frequency electric field measurements. This sensors is based on a thin organic layer of DR1-PMMA embedded in a high finesse Fabry-Perot cavity. The optimal orientation of DRl molecules, parallel to the face of the micro-cavity, has been obtained thanks to a lateral poling method. A r33 of 2.5 pm/V has been reached for a 16 μm thick polymer layer. The final probe exhibits high sensitivity of 2V.cm-1.Hz-1/2.
A key parameter for the choice of an erbium-doped material suitable for efficient amplification around 1.55 μm is its ability to isolate Er ions from each other in order to increase the quenching concentration and henceforth to improve pumping efficiency. Encapsulation of Er ions by organic ligands results in quenching concentrations about a few % in a polymer matrix and may therefore induce high gain values at 1.55 μm. In this paper, we report on the elaboration and optical characterization of Erbium complex-doped PMMA thin films and waveguides with different concentrations by spin-coating technique. Refractive index of these thin films and etching conditions for waveguide fabrication are carefully investigated. Strong gain coefficient values (up to 9 cm-1) measured by Amplified Spontaneous Emission are reported at 1.55 μm under 980 nm cw pumping of an erbium-complex-doped PMMA film. A multifunctional polymer material containing an erbium complex together with an electric-field oriented nonlinear optical (NLO) chromophore is shown to simultaneously display good IR gain properties and quadratic NLO response, then qualifying this approach for in-situ amplification of active electro-optic devices for optical signal processing. Rib waveguides made of erbium-doped PMMA have been elaborated using standard lithographic and reactive ionic etching techniques. Gain and loss measurements of these waveguides are characterized for single mode propagation of signal (1.55 μm) and pump (980 nm) waves, and compared to predictions from beam propagation method modelization.
Electro-optic modulators based on polymer material are very promising devices because of the expected very high modulation rate and low cost fabrication process. These modulators are mainly based on Mach-Zehnder structure, but phase modulators associated to polarizer and analyzer can also be used. Until now there are no real devices commercially available. One of the problems concerns the temperature stability. Because of the optical power of the laser beam and the absorption of the polymer material used for the optical waveguide there is a slight temperature evolution of the modulator leading to a change in the bias point of the modulator and then to a slow drift of the bias point leading to a dissymmetry of the optical modulated signal. This evolution can be compensated by adding a small DC value to the voltage applied to the electrodes. A control loop has been designed and tested in order to stabilize the bias point of the modulator. This loop acts as a synchronous detection with a low frequency modulation at 500 Hz and a practical detection at 1 kHz. By this way it is in fact the first order derivative of the signal which is stabilized leading to the signal symmetry control. This low frequency signal can be added without any problem to the informative modulating signal. By using this control loop the modulator can be used for a very longer time than without it. Of course a temperature control of the modulator by a Peltier effect module should also be implemented for a better and complete stabilization.
This paper describes the design of an optical to microwave converter. The physical effect used for the conversion is based on the non-linear behavior of an electro-optic polymer material. The microwave frequency is generated by the way of an optical waves mixing process, which means by the frequency difference of two optical waves propagating simultaneously inside an optical waveguide. If one of these optical waves is modulated by an informative signal, the microwave signal will infer the modulation. The converter is designed for working at the 1.55 μm optical telecommunication wavelength. The active waveguide is built with the crosslinked PMMA-DR1 electro-optic copolymer, and the cladding layers are made of NOA material. For the first characterizations there is no need of a master-slave configuration for the sources, and the two optical waves are produced by highly stable and fine tunable lasers. The microwave signal is collected on a strip line which characteristic impedance has to be adapted to the conversion process. Simulations have been conducted showing the feasibility of the method and by matching the velocities of the microwave signal and of the optical signal it is possible to create constructive microwave photonic mixing at more than 60 GHz. To achieve the conversion it is necessary to work with a traveling-wave configuration. Some special test devices have been built for the determination of the NOA material permittivity leading to a precise adjustment of the effective index of both optical and microwave waveguide. From all these measurements it has been possible to design completely the device, which is now under test.
The purpose of this paper is to present the design of an electro-optic polymer traveling-wave waveguide photodetector operating in the 1.55 μm wavelength optical telecom window; this component seems to be completely new. Thanks to equal light and microwave speeds in the polymer material waveguides, microwave photonic mixing at frequencies as high as 60 GHz should be reached by the traveling-wave device. The component is based on three waves mixing technique; therefore it is a band-pass photodetector. The physical effect of the three waves mixing will be analyzed, and then a design of the component will be proposed.
B. Bêche, N. Pelletier, E. Gaviot, R. Hierle, P. Papet, F. Poncin-Epaillard, D. Debarnot, A. Goullet, A. Granier, C. Cardinaud, J.P. Landesman, J. Zyss
The authors present a successful design, realisation and characterisation of single-mode TE00-TM00 rib optical waveguides composed of SU-8/SOG polymers subjected (or not) to an apt fluorine-plasma treatment. Such techniques based on radiofrequency fluorine plasma treatment (CF4) proved to strongly modify the properties regarding optical losses due to propagation (selectivity on the polarisation modes, and so on). After realisation of sundry single mode optical waveguides (straight, S-bends, Y-junctions, Mach-Zehnder (MZ) interferometers), the linear absorption coefficient of energy αTE-TM of such rib waveguides have been measured for both optical modes TE00 and TM00 on Si/SiO2/SU-8 structures that yield optical losses of 1.36 dB/cm and 2.01 dB/cm respectively. Optical losses ascribed to Si/SiO2/SOG/SU-8 microstructures have been evaluated to 2.33 dB/cm and 2.95 dB/cm for both polarisations. Concerning the fluorine plasma treatment on SU-8 polymer waveguides, the optical losses regarding Si/SiO2/Fluorinated SU-8 microstructures have been evaluated to 1.25 dB/cm for TE00 polarisation, having then been reduced by 0.11 dB/cm, compared to propagation in pure SU-8. Moreover, such a specific plasma treatment leads to a substantial selectivity on optical polarisation states regarding the TM00 optical mode which has been advantageously used. Thereby, integrated optical polarizers have been achieved on fluorinated SU-8. Hence, as a crucial step for designing polymer components devoted to microsensors applications, the SU-8 (fluorinated or not) polymer appears as a promising candidate for integrated optics with low optical losses.
We present the investigation of optically-induced rotation of single DCM (4-(dicyano methylene)-2-methyl-6-(p-dimethyl aminostyril)-4H-pyran) molecules in a low-Tg polymer matrix. The rotation process is based on the photo-isomerization of the molecule occurring upon a resonant linearly polarized optical excitation. This pumping process creates a photo-selection angular cone, resulting in a motion of the molecular dipole perpendicularly to the linear excitation, stabilized by the polymer re-organization. Ensemble measurements are seen to be biased by the difficulty to discriminate between the re-orientation process and angular selective photo-bleaching. Such photo-bleaching effect can however be observed independently in single molecules data. The thermal rotational motion of single molecules in the polymer were first investigated, showing heterogeneous behaviors with orientational fluctuations of a about ten seconds time scale, due to the local viscosity and elasticity of the polymer environment. Under a linearly polarized pump at several hundreds of W/cm2 intensity, a photo-induced orientation motion towards the perpendicular direction to the pump was observed for 50% of the molecules, within a typical time of a few tens of seconds. The remaining molecules showed orientational fluctuations dominating over the pump effect.
On the basis of spectral-expansion Green’s function theory, we theoretically describe the topography, polarization,
and spatial-coherence properties of the second-harmonic (SH) local fields at rough metal surfaces. The spatial
distributions of the fundamental-frequency and SH local fields are very different, with highly-enhanced hot spots
of the SH. The spatial correlation functions of the amplitude, phase, and direction of the SH polarization all
show spatial decay on the nanoscale in the wide range of the metal fill factors. This implies that SH radiation
collected from even nanometer-scale areas is strongly depolarized and dephased, i.e., has the nature of hyper-
Rayleigh scattering, in agreement with recent experiments. The present theory is applicable to nanometer-scale
nonlinear-optical illumination, probing, and modification.
Photonics devices based on polymer optical waveguides are widely studied now and some commercial announcements have already been published. Nevertheless they are not been followed by really available products and it is still necessary to improve such kind of devices. The aim of this paper is to present a new structure for a polymer electro-optic modulator. The electro-optic polymer material is PMMA-DR1. This electro-optic polymer is well known by its high frequency bandwidth of modulation and its functional robustness. Nevertheless, its half-wave voltage remains relatively high, that is why a new configuration is proposed decreasing the half-wave voltage. The new device, which is fully described, is based on the classical Mach-Zehnder optical modulator structure, to which a completely new loop structure is added. Thus the optical waveguides are designed in order to increase the active length and so reducing the half-wave voltage. Otherwise the device is designed for a complete planar realization. The RF strip lines are also designed according to the loop structure with 50Ω characteristic impedance. A device has been realized and its optical are checked at 1.55μm wavelength. Electronic characteristics should be determined by the way of spectrum and network analyzers at frequencies up to 2GHz. All the measurements should show the feasibility and efficiency of the new structure.
The octupolar framework provides a promising route towards molecular compounds combining enhanced NLO responses and improved nonlinearity-transparency trade-off. In this perspective, we have designed original three-branched boomerang-shaped nanoscale molecules. Their molecular design is based on the grafting of three conjugated blades bearing either an electron-withdrawing or an electron-releasing end group on a triphenylbenzene core which can act as a (weak) donor or acceptor counterpart. We selected oligomeric phenylene-vinylene conjugated rods to allow for efficient charge transfer between the center and the periphery of the molecule while preserving transparency. Based on this strategy, we have prepared homologous nanoscale molecules with size varying between 2 and 5 nm. These molecules exhibit a definite solvatochromic behavior, in consistence with a multidimensional intramolecular charge transfer (MDICT) taking place between the core and the peripheral groups. Large first-order hyperpolarizabilities could be achieved by taking advantage and boosting of the MDICT phenomenon while maintaining wide transparency in the visible region (up to ||β|| = 800 10-30 e.s.u., with λmax = 377 nm). The superlinear dependence of β on size and their concave shape make elongated analogues attractive candidates for future developments.
A multichromophoric nanoassembly was designed by gathering seven push-pull chromophores on a β-cyclodextrin assembling unit via covalent linkers. Such supermolecule provides a valuable model for the investigation of confinement effects on the linear and nonlinear optical properties of push-pull chromophores in the condensed phase. Push-pull chromophores display a significant ground-state dipole, thus promoting dipolar interactions that are expected to influence both the conformation and the optical properties of the multichromophoric assembly. In this perspective, the photophysical and nonlinear optical properties of the mutichromophoric bundle were investigated and compared to those of the monomeric chromophore. The absorption, circular dichroism and fluorescence investigations provide evidence that the push-pull chromophores do not behave as isolated independent chromophores within the multichromophoric assembly. The nanoscale supermolecule is hypsochromically and significantly hypochromically shifted with respect to its monomeric analogue. In addition, the close proximity promotes excitonic coupling, as well as excimer formation phenomena. The nanoscopic assembly also shows a very large dipolar moment (μ = 38 D), and a significant molecular first-order hyperpolarisability, which reveal a spontaneous sheaf-type self-arrangement of the dipolar chromophores within the supermolecule. Such chiral hyperpolar nanoassemblies are promising candidates as model systems for nanophotonics.
Highly dipolar non-linear optical chromophores with absorption typically in the range of 350-500 nm have been synthesized by the reactions of amines with tetracyanoquinodimethane (TCNQ). These materials show interesting fluorescence properties with the emission strongly dependent on the host environment. One of the advantages of these materials is the large figure of merit ((mu) (beta) ), which is calculated to be -765 x 10-48esu, allowing large non-linear optical coefficients to be obtained. Guest-host polymer films of these materials have been corona poled using a constant current corona triode. These materials are highly dipolar which leads to the formation of aggregates within the doped polymer films. Studies of the second order non-linearities using second harmonic generation (SHG have revealed the presence of such aggregation. The magnitude of the SHG that can be obtained form such systems is therefore severely limited by this aggregation. This phenomenon was then confirmed with optical spectroscopy and electric field induced second harmonic generation (EFISH) studies.
By Hyper-Rayleigh Light Scattering (HLS) experiments, we obtained the first-order hyperpolarizabilities (beta) for a series of 1D polyeno-dipolar and C3h polyenoctupolar molecules. Theoretically, we applied the additive model to analyze (beta) for multipolar nonlinear optical (NLO) molecules. The hyperpolarizability is dissected into an additive term and an interaction term, and the equations for evaluating the additive (beta) A and interaction (beta) I terms were derived for multipolar molecules. The structure and substituent effects were analyzed for various planar C3h and C2v multipolar molecules, based on the calculation results of the (beta) ijk from a CNDO/S program. The relations of experimental (parallel)(beta) (parallel) with conjugation lengths were given, which agree well with out theoretical results.
We report on the measurement of the time relaxation of the electro-optic properties of poled side-chin copolymers under illumination with absorbed laser radiation. Films of side- chain Disperse Red 1 substituted poly-Methyl-Methacrylate were sandwiched between ITO and gold electrodes and poled with a standard temperature/electric field cycle. The decay of the electro-optic properties, measured by means of the Teng and Man ellipsometric reflection technique at (lambda) equals 830nm, was measured for several intensities of a circular polarized absorbed laser beam, (lambda) equals 514.5nm, illuminating the sample. The relaxation shows a stretched exponential time dependence, with intensity dependent decay and stretching constants. The relaxation curves are compared with those obtained, for the same sample, in standard temperature stimulated non linear dielectric relaxation measurements.
This paper reviews two emerging approaches towards new materials and related device technologies for nonlinear photonic applications. Hybrid organic-inorganic sol-gel materials are shown to be meeting material engineering requirements, with the electrically poling of Disperse Red1- like chromophores grafted to a syloxane chain exhibiting a remarkably high non resonant second-order nonlinearity together with long-term orientational stability. Furthermore, an all-optical poling method based on the photoinduced orientation of molecules in various matrices, appears as an appealing alternative to the traditional electric field poling, capable to circumvent its intrinsic limitations such as the necessity of a dipolar chromophore. We have experimentally demonstrated the possibility to implement a macroscopic multipolar organizational scheme by way of purely optical photoinduced processes. Adequate choice of the polarization states of fundamental and harmonic <<write>> beams will leave a permanent imprint of any desired symmetry pattern onto the (non)linear material.
Manfred Eich, Hanno Beisinghoff, Bengt Knoedler, Michael Ohl, Martin Sprave, Jan Vydra, M. Eckl, Peter Strohriegl, Michael Doerr, Rudolf Zentel, M. Ahlheim, M. Staehelin, B. Zysset, Julienne Liang, Regine Levenson, Joseph Zyss
Four high Tg side chain polymers have been investigated based on polyimide and acrylate backbones functionalized with DR1 and heterocyclic thiophene chromophores. UV-VIS studies revealed chromophore stability up to 210 degree(s)C. Maximum poling efficiency was found approximately 15 K above Tg. From dielectric relaxation studies and from poling dynamics it is obvious that chromophore reorientation follows an Arrhenius law at temperatures well above Tg leading into a WLF-behavior in the vicinity of Tg. Relaxation of the EO-coefficient could be interpreted in terms of a KWW function. The average relaxation times strongly deviate from the WLF-function at temperatures well below Tg and can be described with an Arrhenius law. Activation energies here are significantly smaller than those in the high temperature limit above Tg, indicating that the chromophore dipoles are incompletely coupled to the polymer (alpha) process. Very good stability was observed for the polyimide P3 with average relaxation times of 104 years at 50 degree(s)C and 4 months at 120 degree(s)C. EO coefficients of up to 12 pm/V at 1541 nm were realized using a poling field strength of 1 MV/cm. EO-coefficient at constant poling field was found to be approximately linearly dependent on chromophore content. Channeled waveguides were fabricated by selective reactive ion etching with small losses of 1 dB/cm at 1318 nm. However, loss varies strongly between 1 dB/cm and 3 dB/cm depending on film quality.
A wide choice of push-pull polyenes and carotenoids of increasing length (up to 30 angstrom) and bearing various donor and acceptor end groups has been synthesized in order to investigate the chain-length dependence of their quadratic hyperpolarizability (beta) . (beta) measurements have been performed using the electric field induced second harmonic generation (EFISH) technique. In each series of homologous compounds, the lengthening of the conjugation path results in a pronounced increase in (mu) (beta) values. This behavior leads to very large static (mu) (beta) (0) values for the longest molecules and can be modeled by (mu) (beta) (0) equals kna relationships with respect to the number n of double bonds in the polyenic chain. The exponent value (a) was found to depend on the end groups. The replacement of a double bond by a triple bond in the middle of the polyenic chain results in a blue shift of the charge transfer absorption band and leads to smaller (mu) (beta) (0) values. However, this phenomenon is modulated by the end groups.
The off-resonant (pi) -electronic component of the (beta) tensor, (beta) (pi ), is calculated and analyzed for an octupolar molecule with D3h point group symmetry, 1,3,5-triamino- 2,4,6-trinitrobenzene (TATB), and the related dipolar molecule with C2v point group symmetry, para-nitroaniline (pNA). The (beta) (pi )'s for TATB and pNA are calculated using the semi-empirical INDO/S Hamiltonian combined with single- and double-excitation configuration interaction of singlet (pi) -electron configurations, and Orr and Ward's sum- over-states expression for (beta) .
The quest for more efficient nonlinear optical materials of increased optical quality is being spurred by the development of optical communication systems that require ultrafast broadband optical signal processing functions. Conversely, nonlinear optical phenomena enlarge traditional spectroscopic approaches to encompass more complex and informative multiphotonic pathways. In this stimulating context, organic nonlinear materials have been recognized as forefront candidates for investigations of fundamental and applied natures involving in a joint effort chemists, material scientists, and optical physicists. After reviewing the molecular engineering foundations of the domain, specifically with respect to an efficiency-transparency trade-off, we concentrate on a more specific case that embodies, from the definition of the molecule, all the way down to applied physics end goals, the key-concepts and methodological tools in the field. This is the paradigmatic case of N-4-Nitrophenyl-(L)- Prolinol (NPP) which, after almost a decade of efforts involving crystal growth and ultrafast time resolved spectroscopy, has recently reached sufficient quality to lead to optical parametric oscillation. Stable coherent tunable oscillation in the near IR from 0.9 to 1.7 micrometers has thus been demonstrated for the first time in an organic molecular crystal with specific advantages as compared to mineral candidates and room for further performance improvements. We recall in conclusion that new molecular and crystalline pathways are still opening-up, such as based on molecular nonlinearities of octupolar origin or organo-mineral crystals.
Ellipsometric spectra of thick polymer films for non-linear optics were recorded at several angles of incidence. A non-linear regression analysis is used to compare an isotropic model to a uniaxial one. Analysis in the transparent region unambiguously points out the more suitable model, and the corresponding thickness. These results are subsequently used on all the spectrum, including the absorption domains, so as to give the complex ordinary and extraordinary indices. Relevant structural information on the polymer conformation is then inferred.
As interest in the quadratic nonlinear optical properties of organic molecules and materials keeps strongly increasing, experimental data start accumulating and provide a better understanding of the structure/property relationships. Compounds were usually developed according to the general recipe of having a push (electron donating) group and a pull (electron accepting) group linked by a conjugated segment.
The linear optical and electro-optical properties of new guest-host poled polymeric thin films are reported based on combined ellipsometric and modulated reflection measurements. Wavelength dispersion of the electro-optic coefficient and comparison between second harmonic generation and electro-optic coefficients are in keeping with a two-level model of the quadratic nonlinearities. The large extension of the conjugated systems may account for the remarkable quasi-absence of relaxation of the electro-optic coefficient over a period of months, when incorporated in PMMA. Operation of a waveguide phase modulator has been demonstrated at 1064 nm in a multilayer strip waveguide architecture over a GaAs substrate, and shown to correspond to r33 equals 1.76 pm/V. Further optimization is underway.
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