We report on second harmonic generation in a photonic crystal L3 cavity drilled in a thin self-suspended lithium niobate membrane. The cavity, resonant for the pump beam in the telecom wavelength range, exhibits a quality factor of around 500. Second harmonic generation has been measured with a low power continuous laser. A conversion efficiency of 6.4×10-9 has been estimated with an input coupled power of 53 µW

Nanoscale waveguides are basic building blocks of integrated optical devices. Especially, waveguides made from nonlinear optical materials, such as lithium niobate, allow access to a broad range of applications using second-order nonlinear frequency conversion processes. Based on a lithium niobate on insulator substrate, millimeter-long nanoscale waveguides were fabricated with widths as small as 200 nm. The fabrication was done by means of potassium hydroxide-assisted ion-beam-enhanced etching. The waveguides were optically characterized in the near infrared wavelength range showing phase-matched second-harmonic generation.

We report on the light propagation in a one-line-defect photonic crystal waveguide (W1 PhC WG) patterned into a 450 nm thick free-standing lithium niobate membrane by ion-beam enhanced etching. The Bloch wave vectors and transmission spectrum of this PhC WG were retrieved from optical near-field images. The experimental data show good agreement with simulations performed with the three-dimensional (3D) finite-element method and the 3D finite-difference time-domain method. Those results are promising for the development of integrated optics devices operating at telecom wavelengths and based on free-standing lithium niobate PhC membranes.

The performance of lithium niobate (LN) photonic crystals (PhCs) is theoretically analyzed with transmission spectra and band diagrams as calculated by the 3-D Finite-Difference Time Domain (FDTD) method. For a square lattice of holes fabricated in the top surface of an Annealed Proton-Exchange (APE) waveguide, we investigate the influence of both finite hole depth and non-cylindrical hole shape, using a full treatment of the birefringent gradient index profile. As expected, cylindrical holes which are sufficiently deep to overlap the APE waveguide mode (centered at 2.5microm below the surface) produce transmission spectra closely resembling those predicted by simple 2-D modeling. As the hole depth decreases without any change in the cylindrical shape, the contrast between the photonic pass- and stop-bands and the sharpness of the band-edge are slowly lost. We show that this loss of contrast is due to the portion of the buried APE waveguide mode that passes under the holes. However, conical holes of any depth fail to produce well-defined stop-bands in either the transmission spectra or band diagrams. Deep conical holes act as a broad-band attenuator due to refraction of the mode out of the APE region down into the bulk. Experimental results confirming this observation are shown. The impact of holes which are cylindrical at the top and conical at their bottom is also investigated. Given the difficulty of fabricating high aspect-ratio cylindrical holes in lithium niobate, we propose a partial solution to improve the overlap between shallow holes and the buried mode, in which the PhC holes are fabricated at the bottom of a wide, shallow trench previously introduced into the APE waveguide surface.

The realization of photonic crystals in self-suspended lithium niobate membranes by means of focussed ion beam writing and ion-beam enhanced etching is presented. The influence of gallium contamination is discussed and considered in the realization of a L3 photonic crystal resonator that is showing the designed linear optical response in a cross-polarization resonant scattering experiment

This work aims to investigate the initial build-up stages of polyelectrolyte multilayers formed by the successive deposition of the weakly charged Poly(Allyl amine, HCl), PAH and the strong acid Poly(Styrene Sulfonate), PSS, on silica at pH = 9. Two complementary tools were used: laser reflectometry to determine the step-by-step deposited weight of each polymer and Atomic Force Microscopy (AFM) to characterize the topography and measure the thickness of the film. The experiments show that the deposited weight of PAH is the same at each step (around 0.5 mg.m− 2), whereas that of PSS increases more or less linearly along with the step number. Starting at the second polymer deposit (PSS), the structure of the film is very heterogeneous, with a thin polymer layer and bumps that are attributed to the presence of PSS/PAH hydrophobic complexes. The amount of bumps and their height were determined at each of the ten first polymer deposits. The film thickness between the bumps was evaluated by scratching small areas with an AFM tip. Our results support a former description of film growth, based on the electrostatic interactions between the two polymers and the substrate. They also reveal different the roles of the two polymers in the growth of the films: PAH is responsible for the progressive bi-dimensional coverage of the surface area and PSS for the increase in the thickness of the film

We study experimentally the excitation of the radially polarized conical surface plasmon polariton (SPP) in a fully metalcoated conically tapered M-profile fiber which works as a "plasmonic tip" for the scanning near-field optical microscope (SNOM). This structure extends the Kretschmann configuration to the conical geometry. In this plasmonic tip, the radially polarized waveguide mode, propagating inside the fiber, resonantly excites the radially polarized SPP on the metal surface, which consequently gets confined at the apex where the field oscillates longitudinally along the tip axis. We also demonstrate the reverse process, where a longitudinal field excites the radially polarized SPP mode which then resonantly excites the radially polarized waveguide mode. This plasmonic tip combines the advantageous properties of near-field optical probes. Though, it has the shape of an apertureless SNOM tip, it can simplify the detection/excitation procedure and suppresses the background signal by its fiber-based design. Unlike the sharp apertureless SNOM tips that detects only the longitudinal field component or aperture SNOM tips that detect mostly the transversal component, the plasmonic tip detects both longitudinal and transversal field in collection mode and backward-scattering mode, respectively. The plasmonic tip, with further improvements, can become an advanced tool in SNOM due to its ability for background-free near-field detection, ease of operation, and higher conversion efficiency from far-field to near-field than conventional tips. KEYWORDS: plasmonic tip, radially polarized conical SPP, radially polarized fiber mode, longitudinal and transversal field, SNOM, M-profile fiber T he biggest challenge for studying the optical properties of nano-objects arises in efficient delivery and detection of light to and from nanoscale regions. Surface plasmon polaritons (SPPs) help to overcome this limit. 1,2 It enables strong confinement and enhancement of electromagnetic energy below the diffraction limit of light in a variety of structures, particularly in tapered metallic structures with sharp edges or tips. 3,4 Being hybrid electromagnetic waves, SPPs comprise properties of transverse (photon) and longitudinal (plasmon) waves. When propagating in tapered metallic structures toward the sharp edges or apexes, longitudinal component of SPPs field becomes more pronounced. 5−14 This leads to a decrease of the wavelength, thus, allowing it to get localized at the tip apex and resulting in a highly confined and enhanced field at the apex with a strong longitudinal component. 5,7−9 This phenomenon is called SPP superfocusing, and in a metallic cone, it takes place only for the radially polarized SPP mode. 7,8 Tip-enhanced microscopy technique, which provides the highest spatial optical resolution among the optical detection methods, takes advantage of SPP localization at a nanoscale apex of a conical metallic tip. 15−23 The localization can be achieved either by exciting SPPs on a tip shaft 21−23 or simply by placing a tip...

We studied the influence of post-treatment rinsing after the formation of self-assembled polyelectrolyte films made with the weak base poly(allylamine hydrochloride) (PAH) and the strong acid poly(styrene sulfonate) (PSS). The stability of the film was studied using optical fixed-angle laser reflectometry to measure the release of polymeric material and AFM experiments to reveal the change of morphology and thickness. We found that the polymer films were stable upon rinsing when the pH was the same in the solution as that used in the buildup (pH 9). The films released most of the polymeric material when rinsed at higher pH values, but a layer remained that corresponded to a PAH monolayer directly bound with the silica surface. Films containing at least four bilayers were stable upon rinsing at lower pH values, but the stability of thinner films depended on the type of the last polymer deposited. They were stable in the case of PSS as an outermost deposit, but they released a large part of their material in the case of PAH. The stability results were determined using a simple model of the step-by-step assembly of the polymer film described formerly.