Low-loss coupling of VCSELs (vertical-cavity surface-emitting lasers) to optical fibres is a key issue for increasing their use in optical communications and instrumentation systems. However, tolerances on angular tilts and lateral misalignments are tight, particularly in the case of single mode devices. To address this challenge, a new fabrication method based on near-infrared single-mode self-writing (NIR-SM-SWW) of a polymer waveguide was developed and tested for the coupling of two single mode fibers at 850 nm (Thorlabs 780-HP) with a mode field diameter close to that of 850 nm single mode VCSEL. The specificity of our method is to use a writing wavelength identical to that designed for single mode propagation in the fibers, leading to a single step photopolymerization process that will be directly transferable to 850 nm VCSEL-to-fiber coupling. First results show coupling losses at 850 nm as low as 0.86 dB for a distance between the fibers of 100 μm.
Micro- and nanopatterning of metal oxide materials is an important process to develop electronic or optoelectronic devices. ZnO is a material of choice for its semiconducting and photoluminescence properties. We have developed and investigated a new process that relies on direct write laser patterning in the DUV range to prepare photoluminescent microstructures of ZnO at room temperature, under air. This process is based on a synthesis of colloidal ZnO nanocrystals (NCs) with a careful choice of the ligands on the surface to obtain an optimal (i) stability of the colloids, (ii) redissolution of the non-insolated parts and (iii) cross-linking of the DUV-insolated parts. The mechanisms of photocrosslinking are studied by different spectroscopic methods. This room temperature process preserves the photoluminescence properties of the NCs and the wavelength used in DUV allows to reach a sub-micrometer resolution, which opens new perspectives for the integration of microstructures on flexible substrates for opto-electronic applications. We also show that this concept can be extended to other metal oxide nanoparticles.
DUV photolithography, as the major process of nanofabrication, typically requires high volumes of toxic chemicals within resist formulation, solvent and developer. In this context, alternative chemistries to current petroleum-derived photoresists are proposed to reduce environmental impacts. Chitosan represents a bio-sourced resist allowing water-based patterning processes free of organic solvent and alkali-based developers, by substitution with a green solvent (deionized (DI) water). This paper present last stepwise process in the patterning integration with a chitosan-based resist. Preliminary results using a 300 mm pilot line scale at CEA-Leti demonstrate patterns resolution down to 800 nm along with plasma etch transfer into Si substrate. Finally, the environmental impact through life cycle analysis (LCA) of the whole process based on chitosan resist is assessed and compared to conventional solvent-based processes.
Biopolymers represent natural, renewable and abundant materials. Their use is steadily growing in various areas (food, health, building …) but, in lithography, despite some works, resists, solvents and developers are still oil-based and hazardous chemicals. In this work, we replaced synthetic resist by chitosan, a natural, abundant and hydrophilic polysaccharide. High resolution sub-micron patterns were obtained through chitosan films as water developable, chemically unmodified, positive tone mask resist for an eco-friendly electron beam and deep-UV (193 nm) lithography process. Sub-micron patterns were also successfully obtained using a 248 nm photomasker thanks to the addition of biosourced photoactivator, riboflavin. Patterns were then transferred by plasma etching into silica even for high resolution patterns.
In this paper a new type of polymeric fiber optic tweezers for single cell manipulation is reported. The optical trapping of a yeast cell using a polymeric micro lens fabricated by guided photo polymerization at the fiber tip is demonstrated. The 2D trapping of the yeast cells is analyzed and maximum optical forces on the pN range are calculated. The experimental results are supported by computational simulations using a FDTD method. Moreover, new insights on the potential for simultaneous sensing and optical trapping, are presented.
In this work, the trapping efficiency of new fiber optical tweezers structures fabricated using photo polymerization and focused ion beam milling techniques is evaluated. The first fabrication methods may present limited capabilities on the tailoring of the structures, and therefore limited operation features. On the other hand, with focused ion beam milling a vast myriad of structures may be accurately fabricated, and contrarily to conventional fabrication methods, more specialized manipulation tools can be developed. In this regard, the performance of FOT for the trapping of yeast cells using spherical lenses (photo polymerization) and spiral phase lenses (FIB) will be presented. In addition, finite difference time domain (FDTD) simulations of the full vectorial optical propagation through the designed structures and the corresponding calculation of the optical forces are presented and different designs are evaluated.
This work reports a new type of optical fiber tweezers based on polymeric micro-lenses. The lenses are achieved by means of an economical and fast fabrication process, using an in-fiber photo-polymerization technique. The polymerization radiation is guided towards the fiber tip creating a polymeric waveguide. The method allows tailoring the geometry of the tip by adjusting the fabrication parameters. Furthermore, more complex shapes can be fabricated by exploring modal effects at the polymerization/trapping wavelengths, which can be used for different applications such as trapping, beam shaping and patterned illumination.
A method to control the output intensity profile of optical fibers is presented. Using guided wave photopolymerization in multimode structures the fabrication with modal assisted shaping of polymeric micro lenses is demonstrated. Results showing that a given linear polarized mode can be selectively excited controlling the intensity distribution at the fiber tip are presented. This pattern is then reproduced in the polymeric micro structure fabricated at the fiber tip thus modulating its output intensity distribution. Such structures can therefore be used to obtain at the fiber tip predetermined intensity patterns for attaining optical trapping or patterned illumination.
This paper presents a study of optical forces acting on dielectric particles in media of distinct refractive index. The radiation pressure forces produced by optical tweezers are calculated using the finite difference time domain method as well as the Lorentz force on electric dipoles. The model considers a 2-dimension structure composed of a waveguide and a dielectric microparticle. Furthermore, the paper presents preliminary experimental results concerning the implementation of fiber optical tweezers system based on polymeric lensed fibers.
We present recent results on the integration of polymer microlenses on single mode Vertical-Cavity
Surface-Emitting Lasers (VCSELs) to achieve output beam control. We describe in particular low
cost and collective fabrication methods developed to allow for a self-alignment of the lens with the
laser source. These approaches are based either on surface tension effects or on a self-writing
process using novel Near Infra-Red (NIR) photopolymers. Results on beam collimation at 850nm are
presented and compared to a fully vectorial and three-dimensional optical model that takes into
account the complete geometry of laser resonator is used. Results on short distance focusing using
self-aligned microtips are presented. Considerations to achieve an active beam control by means of
polymer-based MEMS (Micro-electro-mechanical System) are also discussed. Potential applications
may concern the improvement of VCSEL insertion in optical interconnects or sensing systems, as
well as the fabrication of optical micro-probes for near-field microscopy.
A technique for the fabrication of luminescence based fiber optic optrodes with multiple analyte sensitivity is proposed.
Combination of photosensitive polymers doped with different luminescent indicators was used to produce fiber probes,
by self-guiding photopolymerization, having different geometries and sensing capabilities. Results demonstrating the
method flexibility are shown with luminescent probes doped with CdSe/ZnS quantum dots and an organometalic
ruthenium complex for simultaneous detection of oxygen and temperature.
The recent developments in optics and photonics require novel, simple and fast methods of fabrication of miniaturized
integrated devices with well controlled optical functions. Among other optical elements, microlenses or microcavities
integrated on optical fibers, waveguides of miniaturized laser sources revealed of great interest due to their applications
for coupling, focusing of collimating light. A simple and low cost technique to implement a polymer micro-component at
the extremity of optical fiber was proposed. The process is based on a spatially controlled photopolymerization that is
induced by a laser beam emerged from the optical fiber. Thus, the microlens is directly aligned with the fiber core. The
polymer tips have shown to exhibit various shapes as a function of the photonic parameters and the chemical
composition of formulation. In this paper, we will detail the mechanisms leading to the building up of the polymer
microtips by self-guiding polymerization and we will illustrate the great flexibility of this process in terms of materials,
geometry and writing wavelength. Then we will focus on some applications in optical coupling between fibers and
sensors in order to demonstrate the interest of this simple and flexible approach for polymer micro-optics
implementation.
Laser beam shaping is a key issue for the photonic integration of VCSEL sources. Most of the techniques
proposed to integrate micro-optics elements onto VCSEL devices imply either a hybrid assembly or a photolithography
step, whose precision limits the accuracy of lens alignment relatively to the VCSEL source. We present here a new
method for self-fabrication of microtips on Vertical-Cavity Surface-Emitting Lasers (VCSELs) by means of Near Infra-
Red (NIR) photo-polymerization. This approach is based on a single fabrication step, implementing novel
photopolymers sensitive at the lasing wavelength. Consequently the process is triggered by the laser source itself and can
be applied easily to VCSEL devices during their electro-optic characterization. The method we have developed for tips
fabrication is detailed as well as corresponding optical properties. The applications of this new and simple method
concern laser light focusing and collimation for integrated micro-systems, coupling to fibers for optical communications
as well as novel micro-probes fabrication for near-field optical microscopy.
This letter provides a brief summary on early work and developments on both controlling and studying the optical
properties of resonant metal nanoparticles and reports on all progress achieved since two years. Our approach is based on
controlled nanoscale photopolymerization triggered by local enhanced electromagnetic fields of silver nanoparticles
excited close to their dipolar plasmon resonance. By anisotropic polymerization, symmetry of the refractive index of the
surrounding medium was broken: C1v symmetry turned to C2v symmetry. This approach has overcome all the
difficulties faced by scanning probe methodologies to reproduce the form of the near field of the localized surface
plasmons and provides a new way to quantify its magnitude. Furthermore, this approach leads to the production of
polymer/metal hybrid nano-systems of new optical properties.
Micro and nano-patterning of photopolymer materials was successfully carried out by using near-field irradiation
configuration. In particular, Evanescent Waves created by total internal reflection were used to induce the
photocrosslinking of an acrylate-based photopolymer sensitive at 514 nm. We demonstrate here that the thickness of the
polymer layer can be tuned from few tens of nm to several microns by controlling the irradiation conditions. The sample
was characterized by profilometry, Atomic Force Microscopy and spectroscopy.
In addition, relief gratings with adjustable fringe spacing were recorded by interferometric method. Effect of photonic
parameters on the gratings geometry is discussed. By changing the irradiation conditions, it is possible to easily obtain
patterns with different geometries, which emphasizes the high versatility of the process.
This study presents high fundamental interest in the frame of nanofabrication since it provides important information on
the effects of confinement at a nanoscale of the photopolymerization reaction. Such data are of primary importance in the
field of nanolithography since the effect of parameters such as dye content, oxygen quenching, photonic conditions can
be evaluated. Moreover, since the choice of the monomer can be done in a wide range of composition, such
nanopatterned polymers surfaces present many interests in the field of optical sensors, photonic crystals, optics, biology...
We present here a simple method to synthesize organic-dispersible colloids and a scenario for the ultra-fast
fabrication of silver/polymer nanocomposite by light-induced crosslinking polymerization. The objective of this
work was to apply UV-curing technology for the fabrication of nanocomposite materials containing silver
nanoparticles dispersed in a polymer binder. This new route allows processing operations to be simplified and
the properties of the final product to be improved. A special attention has been paid to the synthesis and
dispersion of metal nanoparticles in various monomers and oligomers and to the photopolymerization kinetics.
The silver nanoparticles were generated by reduction of AgNO3 with t-BuONa activated sodium hydride. Ag(0)
particles present a narrow size distribution with an average diameter of 6.5 nm. Transmission electron
microscopy (TEM) analysis has shown that Ag(0) nanoparticles are well dispersed in the acrylic resin. The
curing process was followed quantitatively by FTIR spectroscopy through the decrease upon UV exposure of the
IR bands characteristic of the functional groups. The silver nanoparticles have no detrimental effect on the
photopolymerization kinetics. The incorporation of metal nanoparticles was found to greatly reduce the gloss of
UV-cured coatings. Moreover, the outstanding optical and viscoelastic properties of these UV-cured
nanocomposites opens up interesting perspectives in various fields of applications (optics, nanoelectronic,
biology...).
A flexible method of manufacturing polymer microlenses at the extremity of both single mode and multimode optical fibers has been previously developed. The procedure consists in depositing a drop of liquid photopolymerizable formulation on the cleaved fiber end and using the light emerging from the fiber to induce polymerization leading to the formation of a polymer tip. This process is highly interesting for applications in optical fiber connecting and SNOM
imaging since it is fast, highly flexible (curvature radius can range from 0.2 to 100 μm) and does not require expensive equipment.
Although the fabrication process leads to well-controlled geometrical structures, the mechanism of the polymer tip formation was not fully elucidated. In this work, we particularly focus on the photoinduced physico-chemical processes that occur during the lens formation. The effect of different parameters (irradiation time, light power, received energy, oxygen...) on the final properties of polymer tip (mechanical resistance, curvature diameter) was studied. The building up of the polymer tip was characterized by optical microscopy. This study allowed selecting the synthesis parameters leading to an improvement in the mechanical and optical properties of the polymer tip. From a fundamental point of view, this study appeared to be an interesting means to investigate the photostructuration of polymers at the micro- and nanoscales.
Organic materials are taking a growing place in the development of new materials for data technologies thanks to the potential of molecular engineering, the flexibility of available chemical compositions, the low costs..., but also because of their unique optical and mechanical properties. In this context, photopolymers present specific advantages particularly interesting for high density optical data storage, based on the possibility of structuring their linear and nonlinear optical properties with a great facility by direct optical patterning. In order to understand and control the physico-chemical aspects of the photopatterning, means of investigation at a micro and nanoscopic scales are required. Not only the 3D imaging of the object is needed, but some structural information on the material is necessary to go further in the investigation of the involved phenomena. AFM used in Pulsed Force Mode (PFM) fulfils these requirements: the PFM mode is a non-resonant mode designed to allow approach curves to be acquired along the scanning path. It thereby provides a recording of the sample topography and extends the possibilities of the prevalent contact and intermittent-contact AFM modes to a direct and simple local
characterization of adhesion and stiffness. This paper describes the principle of Pulsed Force Mode AFM and illustrates its usefulness for investigating of the photostructuration of polymer matrixes. In a first part, homogeneously irradiated films were characterized in order to demonstrate the sensibility of the PFM analysis. In particular, the PFM signal is correlated to the monomer conversion
ratio that was measured by FTIR spectroscopy. In a second step, we illustrate the potential of PFM for the investigation of photopatterned films. Holographic gratings were recorded in an acrylate-based formulation and characterized by PFM. We have successfully assigned the different areas of the film that correspond to different incident intensities. Using the information recorded on homogeneous films, it is possible to obtain an estimation of the conversion of the monomer at sub-micronic scale. Such a study is of primary importance in order to understand the mechanism leading to microstructuration and thus to optimize this process in terms of resolution.
Hybrid organic-inorganic materials based on the sol-gel synthesis of organically modified silicon alkoxides have demonstrated their great potential for optical applications. They offer a high versatility in terms of chemical, physical properties and macroscopic shape molding of the final component. In a first step, hydrolysis and condensation reactions are led along the same way as in classical sol-gel glasses. Partial elaboration of the silicate backbone is thus achieved. Then, free-radical polymerization is proceeded by irradiating the sample under UV or visible light. Finally, the material consists of two crosslinked inorganic and organic networks that are interpenetrated. The present paper focuses on a photolithographic process allowing the generation of relief optical elements without requiring a wet treatment to reveal the latent image. It enables a low cost, simple and quick method for the fabrication of integrated micro-optical components with a spatial frequency up to 250 l/mm. The aim of the present work is to give particular attention to the kinetic aspects of the polymerization of the organic component. The control of the C=C double bonds conversion of acrylate functionalized alkoxides in case of photopolymerization is therefore, an essential issue to tailor material properties. The study also focuses on the influence of physico-chemical parameters that govern the relief generation. Kinetics of surface corrugation point out the importance of strain relaxation, mass-transfer by flowing and organic network formation during the photolithographic process. Some illustrations of the generated diffraction gratings are given.
The hybrid sol-gel process is recognized to be an alternative route for production of low cost silica-based integrated optic devices, since it allows the elaboration of ridge waveguides without recourse to high cost processing, like ion etching. However, the high absorption of these materials in the NIR region (1300 and 1550 nm) has limited so far their use.
The main objective of this article is to describe the major factors that lead to high losses in the final material and to give solutions to overcome this drawback. The choice of hybrid precursors and the influence of the experimental conditions of gel preparation are of paramount importance. Appropriate synthesis conditions allow a significant decrease of the gel losses (to 0,5 dB/cm) while keeping good wetability and UV-patternability. Each step of the waveguides elaboration was studied separately (UV-irradiation, etching, overcladding, storage) regarding the losses of the material. Post-baking of the waveguides is a way to significantly decrease the losses at 1550 nm. Under appropriate conditions, the losses measured in the waveguides can be kept below 1 dB/cm.
Sol-gel process is for more than one decade an interesting way to synthesize inorganic-organic composites under a soft chemistry route. Recently a process for the fabrication of self-developing diffractive optical elements has been developed. The inorganic part of the molecule was an alkoxysilane that reacted via hydrolysis and condensation reactions at room temperature, thus leading to a gel. The mild conditions under which the inorganic part of the material was prepared are compatible with the presence of an organic moiety, a methacrylate function. The organic network was produced via spatially controlled UV illumination using amplitude masks. Surface relief gratings were obtained via this photochemical step ; generation of relief resulted from mass-transfer by diffusion and gradient of surface free energy. No etching process was required. Although the hybrid sol-gel material was assumed to perform along the same lines as the one involving all-organic photopolymers, the influence of the inorganic moieties on the photopolymerization of the methacrylate function remained unknown. Characteristics of the photopolymerization process taking place in hybrid sol-gel materials were investigated by UV and FTIR spectroscopies. Besides the study of the organic network, NMR investigations led information relative to the inorganic network formation during the sol ageing. The whole results provide insights into the influence of the temperature during the photochemical step. Relief gratings generated under various conditions and for a large scale of spatial frequencies are presented. Sinusoidal to almost binary profiles were obtained in a one-step process.
Growing interest in miniaturized optical components for various applications such as optical interconnection systems and telecommunication industry have led to the development of several techniques that are used in the fabrication of micro-optical elements. One approach involves the use of polymers as recording materials: these are flexible, highly transparent and cheap. The technique described in the present paper is founded on the ability of self-processing photopolymers to generate refractive microlens arrays. Spatially controlled illumination of a photosensitive layer induces an inhomogeneous photopolymerization involving a mass-transport process of reactive species and generating a relief in the photopolymer layer. The presentation focuses on the fabrication of microlens arrays through photopolymerization with the green line of an argon-ion laser. Surface tension and differential volume shrinkage turned the illuminated area into good quality lenses. The fabricated lens arrays exhibit diameters ranging from less than 20 micrometers to more than 500 micrometers and focal lengths from 100 micrometers to a few millimeters, depending on photonic, optical and physico-chemical parameters. This imaging technique is highly flexible as regards height, shape and optical properties of the lenses that are produced. By starting from the same background, one can also fabricate diffractive optical elements such as gratings and duplicate computer-generated holograms that come increasingly into prominence as the micro-opto-electro-mechanical field expands.
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