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A collimated light beam parallel to the axis of a fused-quartz cylinder impinging on a 90° apex angle concave cone cut in a quartz rod is transformed into a cylindrical wave by total internal reflection. A thin metal film at the quartz–air interface enables excitation of the plasmon mode at the air side that can polarize the cylindrical wave and/or has the potential to monitor physical, chemical, or biological quantities or events at the inner wall of the cone. The present Letter first analyzes the plasmon coupling mechanism and conditions. It then describes the diamond-grinding technique achieving a smooth cone wall and the finest possible tip. The experimental evidence of the polarization conversion is brought on a diamond-grinded section of fused-silica rod and gold coating of the concave wall.

The present paper is concerned with the mechanically extremely sensitive reflection switching concept of a free-space wave impinging on an array of dielectric or semiconductor pillars. Splitting the pillars of a 2D periodic array in its resonant reflection regime at a prescribed wavelength into two parts with a low-index gap of a few nanometers between parts cancels the reflection of a plane wave under normal incidence. The underlying principle lies in the strong and abrupt discontinuity of the electric field component parallel to the pillar axes caused by the gap. The electromagnetic field distribution is consequently deeply perturbed and no longer corresponds to that of an optical resonance of the array; this suppresses the reflection. The electromagnetic analysis of a silicon pillar array leads to the design of a gapless experimental model fabricated by microsystem technologies that exhibits a broad reflection maximum of a few tens of nm at a prescribed wavelength in the visible and near-IR range, and of a pillar structure with nanometer-thick low-index gap exhibiting no reflection peak over this wide wavelength range. A transmission ratio of 1:30 at a 1080 nm peak wavelength between a gapless and a 1.5 index, 30 nm-thick gap structures was measured.

Controlled translational displacement between a large-surface photosensitive planar substrate and a wide and short 1D grating phase-mask enables the printing of large-width, spatially highly coherent gratings of principally unlimited length, using a limited number of opto-mechanical control parameters. The phase-mask is illuminated by a temporally modulated exposure light sheet controlled by a displacement sensor. The proposed method is compared with existing techniques, and its functional elements and their combination are analyzed.

International audience; The roughness of shallow or deep metallic diffraction gratings modifies the propagation of surface plasmon mode along the metallic-air interface. The scattering losses lead to a spectral or angular broadening of the surface plasmon resonance (SPR) and to a shift of the resonance wavelength and coupling angle. This mechanism is deeply analyzed both experimentally and theoretically to overcome these effects when such structures, in particular deep ones, are used as SPR-based sensors.

The aim of this work is to highlight the possibility of local non-intrusive temperature measurements at the interface between a metallic surface and a fluid by analyzing the plasmon resonance on a periodically micro-structured surface. A change in the temperature of the sample surface induces a modification of the local refractive index leading to a shift of the surface plasmon resonance frequency due to interactions between the evanescent electric field and the close environment of the surface. The metallic gratings developed in this study enable a direct excitation of a plasmonic wave, which, in turn, lead to a high sensibility of the local temperature measurement with a very compact and simple device.

The numerical modeling of a directional coupler composed of four identical slab waveguides reveals that the ratio of the field extrema of the four propagating modes is close to the golden ratio ϕ. This is confirmed by an analytical derivation leading to the exact dispersion equation of the eigenmodes of the four-waveguide coupler and to the expression of the ratio between field extrema. A coupled wave analysis gives the analytical expression of the propagation constants of the coupler eigenmodes and of the ratio between extrema in terms of the coupling coefficients between waveguides; it shows that this ratio is strictly equal to ϕ in weakly coupled structures where the coupling coefficient between next-nearest neighboring waveguides is negligible.

The modeling of the scattering of a plane wave at a rough aperiodic surface-as well as its diffraction by a microstructured surface-is possible only by limiting the infinite surface to a window of finite width D. We show that the scattering spectrum at infinity in the Fraunhofer zone can be obtained from the diffraction modeling of a grating of period D whose surface profile coincides with the aperiodic surface in this window. This is justified by adopting the corpuscular representation of light and resorting to Heisenberg's uncertainty relation applied to the photon's canonically conjugate variables momentum and position. This approach gives a deep and comprehensive representation of scattering phenomena, and also the limit of what can be meaningfully calculated and measured. Numerical examples of grating profiles demonstrate that results obtained under the widely used Beckmann-Kirchoff approximation are matched. The described approach can solve scattering problems that usual methods cannot, or face difficulties, such as when there is significant roughness with respect to the wavelength.

A close-to-the-theoretically-largest TM resonant reflection of a free-space wave from a free-standing undulated gold layer immersed in a liquid host medium is demonstrated experimentally. It is mediated by the grating-excited long-range plasmon mode propagating along the continuous metal film with particularly low loss.

Ultrashort pulse lasers have been established as precise and universal tools for the micromachining of solid materials (cutting, texturing …). For these applications the quality of the cutting cross-section is important. The use of a Gaussian beam profile and linear polarization leads to tapered cutting sidewalls. It is possible to change the polarization orientation in order to machine a material for obtaining straight and vertical sidewalls. For this purpose a specific polarization converter was used. The transformation of the polarization distribution from linear to radial and azimuthal is done by a subwavelength, binary grating creating a π phase shift between the TE and TM transmitted waves. In this paper we report on investigations on the influence of laser polarization (radial, azimuthal, circular, linear) on the ablation characteristics of molybdenum and PZT using an Yb doped crystal laser (500 fs) and compare these results with previously published results.

Whereas noble metal films deposited directly onto an undulated photosensitive polymer exhibit plasmon-mediated resonant transmission of free-space waves accompanied by excess losses of approximately 40 %, adequate hard baking of the photosensitive polymer, together with pre- and post-deposition of nanometer-thick ZnS or MgF2 dielectric interfacial layers, restores excellent propagation conditions for the long-range plasmon mode, reducing resonant transmission excess losses to 10 %, and creating the conditions for the experimental evidence of the long-sought plasmonic anomalous reflection phenomenon.

The plasmon-mediated transmission across a subwavelength-undulated, nanometer-thick continuous metal film embedded in a polymer exhibits an, as yet, unexplained loss, reducing the resonant transmission to half its theoretical value, precluding practical applications of this interesting spatially resolved polarization- and wavelength-selective effect. Slow chemical dissolution of the surrounding polymer while measuring the transmission spectrum under floating conditions reveals near complete recovery of the missing photons. The excess losses originate in nanoclusters of overheated polymer spots at the metal interface giving rise to index and geometrical nonuniformities where the mediating plasmon modes have their field maximum.

Design and fabrication of a high efficiency phase mask have been performed for printing submicron period gratings along 8 mm diameter glass cylinders. In this article, the authors present the radial phase mask specially designed and manufactured for a cylindrical surface micro-structuring under UV photolithography. Its period is sub-micron (480 nm < ΛPM < 720 nm). The authors describe then the phase mask based UV lithography set-up using the interference between the transmitted beams of +1 and -1 orders generated by the phase mask. Preliminary results of printed gratings on a cylinder are described on a sol-gel TiO2 thin film layer, enabling direct photo patterning on functionalized layer. The feasibility of a grating printed with a period of Λcylin = 960 nm on an 8 mm diameter cylinder with this dedicated mask has been demonstrated.

Dedicated photolithographic and reactive ion etching processes applied to the plasma-enhanced chemical vapor deposition (PECVD) hydrogenated amorphous silicon layers of solar cells have been developed in the objective of the low-cost manufacturing of efficient, depth-limited subwavelength gratings transforming a linearly polarized beam into a radially and azimuthally polarized beam in the 1.0-1.1-μm wavelength range.

Angularly selective mirrors (ASMs) are proposed as a means to expand the mode area and modal discrimination of microchip lasers. ASMs used as output couplers selectively reflect incoming k vectors over a narrow angular range, while they transmit more inclined components. The eigenvalue problem of a microchip resonator equipped with a Gaussian ASM is solved analytically in the paraxial optics approximation using the ABCD matrix formalism. The narrow angular distribution of the reflected beam produces, through the laws of diffraction, a significant increase of the mode size and improved transverse mode discrimination, at the expense of higher oscillation threshold due to larger output coupling losses. Simulations performed using the parameters of Yb3+-doped YAG material show that one order of magnitude increase of the mode area can reasonably be achieved without causing overheating and thermal fracture. ASMs can be directly deposited on the active material in the form of a resonant grating mirror. This technology involves only planar batch processes that retain the mass production advantage of microchip lasers. The significant increase of brightness of microchips expected from this innovation will give rise to more effective and more compact devices and new applications.

A resonant grating mirror was monolithically integrated to an ytterbium-doped ceramic Y3Al5O12 microchip laser to produce a linearly polarized laser beam emitting at 1030 nm with a polarization contrast ratio up to 1000. The device was pumped with a fiber-coupled laser diode bar emitting 2-ms pulses at 50 Hz at 940 nm. Up to 13-W peak output power was obtained from 20-W absorbed pump power at room temperature. The obtained slope efficiency with respect to the absorbed pump power was about 80%.

Long and stitchingless gratings are printed by means of a read/write head comprising a phase mask illuminated by an intensity modulated laser beam and a reference grating displacement sensor which dictates the modulation period real time. A nearly perfect grating copying is achieved by fixing the sensor grating scale and the written grating substrate on a long platform sliding under the read/write head.

The conditions for maximum longitudinal electric field of a TM mode at the surface of a step index slab waveguide, and the value of this maximum are given in a normalized analytical form. They are applied to a grating coupling structure corresponding to a resonant laser mirror or to optical interconnects involving a normally incident free space wave and a singlemode slab waveguide.

Two novel methods to control the polarization of laser radiation are presented. The discrimination between different polarization distributions isperformed with a corrugation grating in the top high-index layer of a multilayer mirror, which couples the undesired polarization into a lossy waveguidemode of the multilayer. The generation of radially polarized radiation in a laser resonator is presented as a practical verification of the principle.

We study the far infrared electromagnetic response of grating devices by THz time-domain spectroscopy. We flrst show that THz waves are efflciently injected into silicon waveguides using grating couplers. Moreover, changing the waveguide material parameters by white-light illumination allows us to strongly modify the coupling e‐ciency. Then we demonstrate resonant efiects in segmented grating structures that act as perfect mirrors at selected wavelengths even for focused beams. About 10 periods of the grating participate in the phenomenon, nevertheless the resonance frequency width of the device remains narrow. This collection of experiments shows that millimeter-size mock-ups and THz waves can be efiectively used to extrapolate the optical response of micron-size actual devices.

This paper describes a compact and low cost micro-opto-electro-mechanical displacement sensor. Our purpose is the fabrication of a long range, nanometer resolved encoder using a standard CMOS technology, in order to integrate the optical metrology system (photodiodes, analog and digital circuits) on a single chip. We introduce the interferometric linear encoder principle using diffraction gratings; then we present results of optical and electrical characterization of an optoASIC including photodiodes and associated electronic integrated on a standard 0.6 μm CMOS process. This CMOS circuitry is then included inside of a prototype of linear displacement encoder using the principle of diffraction gratings in reflection. Finally, we present the fabrication of micrometer and sub-micrometer diffraction gratings etched in silicon material, in order to obtain a higher encoder integration.

A multilayer planar structure comprising a highly reflective multilayer dielectric mirror and a corrugated waveguide is proposed for use as a narrow passband optical filter. The proposed filter has a much narrower linewidth than a usual Fabry–Perot cavity with two multilayer dielectric mirrors. It is shown that the narrowing of the linewidth is due to the strong spectral dependence of the phase of the wave reflected from the waveguide grating mirror. The shape of the pass band can be made symmetrical by a proper choice of the grating groove profile.

A multilayer planar structure containing a corrugated waveguide and a highly reflecting mirror is described. The structure is used as a narrow-band optical filter operating in two different regimes. The efficiency of the proposed filters is demonstrated experimentally in the lasing regime.

The problem of grating coupling of a focused incident beam under non-normal incidence into a slab waveguide is given a complete three-dimensional (3D) solution. The diffracted field is expressed as the Fourier integral of a regular part and of a singular part resulting from the existence of the coupled guided mode. A suitable expression of the field in the neighborhood of the pole and a rigorous definition of the modal field lead to a generalized coupled mode equation relating the incident field and the two-dimensional (2D) modal field propagating in the plane of the slab waveguide. The phenomenological parameters involved in the coupled wave equation: the propagation constant, the radiation coefficient as well as the modal field shape are derived from the exact treatment of plane wave diffraction in the same structure. The solution of the complete coupling problem is given in the particular case of a Gaussian incident beam, and of a high index step-index waveguide.

A high-resolution diffractive measurement technique reveals that a wafer scale grating fabricated by an ASML PAS 5500 step and repeat camera exhibits a stitching error less than 10 nm and a variation of a nominally constant period of 1 μm of less than 20 pm.

A displacement measurement technology of diffractive interferometry has been developed in the objective of miniaturization. The interference principle has been implemented in the form of a miniature read head prototype according to a novel device configuration after a discussion on the fabrication and mouting tolerances has been made conducting to a high resolution micro-optical encoder. A read-out grating acting simultaneously as a subwavelength and a two order grating enables the miniaturization of a diffractive interferometric optical displacement sensor of the reflection type.

In this article we present a radial phase mask specially designed and manufactured for direct micro-structuration under UV photolithography of a cylindrical surface covered by a photoresist TiO2 film. The period of the phase mask is sub-micron (between 480 nm and 720 nm) and allows direct printing on several types of cylindrical components. With this dedicated reversible phase mask we have demonstrated the feasibility of a TiO2 grating with a period of 960 nm, printed on a SiO2 cylinder or inside a SiO2 tube of 8 mm diameter., published version, peerReviewed

Surface plasmon coupling of a TM polarized free space incident beam by means of the + 1st or the -2nd order of a smooth corrugation grating at a metal surface causes the cancellation of the diffracted -1st order free space beam and a maximum of the 0th order Fresnel reflection whereas the converse occurs midway between these two conditions. This implies that angular tilting of the element or wavelength scanning provokes the switching between the -1st and 0th reflected orders. This plasmon-mediated effect on propagating free-space beams exhibits remarkably low absorption losses.

Functional demonstration of a wide band, wide angular width “wire-grid polarizer” has been made in the framework of a User Project of the European project ACTMOST (Access To Micro-Optics Expertise, Services and Technologies). The polarization function relies upon linear polarizers using the “wire-grid” polarizer principle by means of a metal grating of unusually large period, exhibiting a large extinction of the transmission of the TE polarization in the 850 nm wavelength range. This grating achieves a broadband and especially high angular aperture reflection with low loss and permits resorting to very low cost incoherent light sources of the transmitted TM polarization. The paper will describe the design, the modeling optimization, and the complete technological process chain which has been used: from the photoresist grating printing using phasemask UV-based lithography to the uniform galvanic growth of very shallow gold grating on transparent conductive layer deposited on a glass substrate. Transmission curves for both polarizations on the first demonstrators will be presented.

International audience; A polarization rotation is realized by subwavelength binary gratings, where the TE and TM round trip phases of the smallest grating modes are fixed to the smallest possible integer numbers of 2pi that allow a straight-through phase difference of pi This results in a subwavelength grating allowing to realize a half-wave element of almost 100% transmission. The principle is applied to a polarization transformation in the 1030-1064 nm wavelength range, using a segmented polarization rotating element converting a linearly polarized incidence to a radial or azimuthal polarization distribution. The elevated costs of such kind of polarization transformers based on assembled birefringent crystals are avoided by using mass-fabrication compatible silicon on insulator technology on a wafer scale. It shows the general potential of microelectronic technology, concerning the batch manufacturing of wavelength-scale diffractive, grating based elements for processing free space waves.

Abnormal reflecting mirror (ARM) structures, consisting of a corrugated optical waveguiding structure, can serve as a wavelength-selective end mirror in a laser cavity. The ARM structure shows, for each wavelength in a certain region, 100% reflection at a certain angle of incidence. In the vicinity of this angle the waveguide is resonantly excited, leading to strong enhancement of the optical field in the layer structure, which is interesting for efficient second-harmonic generation (SHG). In this paper, experimental results of a first prototype, exhibiting Cerenkov SHG, are reported.

It is shown that the leakage modes of multilayer corrugated dielectric and metal-dielectric structures are extremely important for the achievement of high efficiency of such structures as diffraction gratings. Three types of grating structures are considered: a corrugated waveguide layer on a flat multilayer dielectric mirror (type 1); a multilayer dielectric mirror on a corrugated substrate (i.e., a totally corrugated structure) (type 2); and a structure of the intermediate type (type 3). The performance characteristics of these structures used in the Littrow mounting are compared.

The conditions for the optimisation of any step index waveguide evanescent-wave sensor and for the manufacturing tolerances are given in the form of analytical and normalised expressions. The analysis is made for both TE and TM modes, in both cases where the measurand is homogeneously distributed in the cover, and where it is an ultrathin film on the waveguide-cover interface.

A ray optic description of evanescent wave sensing allows a homogeneous treatment of the sensitivity of free space and guided wave slab sensors. It is shown in particular that the sensitivity of evanescent wave sensors is generally smaller or much smaller than that of a free space wave traversing the probed medium except in the remarkable case of large contrast slab waveguides propagating a restricted number of TM modes where the sensitivity can exceed that of a free space wave.

A multilayer waveguide-grating optical component for laser cavities was proposed, made, and investigated. It is found that corrugation of all the layers of the component makes it possible to obtain a high coefficient of narrow-band (with respect to wavelength) reflection of moderate-power light beams. The possibility of the operation of the component in the laser cavity in narrow-band filter regime is noted.

Closed form analytical expressions and normalized charts rigorously provide the conditions for maximum geometric wavelength dispersion in three-layer slab waveguides. The resulting optimization procedure is illustrated by the design of a dispersive channel waveguide for use in a novel SiON-technology based integrated optical wavelength sensor.

Specific features of the dispersion in step index slab waveguides, such as zero waveguide dispersion and zero group delay difference between modes, are shown to be described by normalized expressions involving two normalized structure parameters only. The complete subset of dual-mode waveguide structures exhibiting wavelength independent propagation constant difference is identified, and its importance for sensor applications is emphasized.

An analysis was made of the operation of a metal — dielectric grating formed by a corrugated film located on a flat surface of a metal. It is shown that the high diffraction efficiency of such a grating for the TE waves is attainable not only in the autocollimation regime (Littrow mounting), but also for a grazing (Θ = 89°) incidence of a light beam on the grating (Littman — Metcalfe mounting). This high efficiency is observed when leaky modes are excited in the dielectric layer. An experimental check of the calculated results is reported.

The problem of existence of a long-range surface electromagnetic wave in an asymmetric structure with a thin metal film is considered. Experimental observations of the anomalous reflection of light from the surface of a corrugated structure are used to demonstrate the excitation of a long-range wave in such a structure. The possibility of using such long-range plasmons in sensor applications, when the plasmons are excited by a diffraction grating, is considered.