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.
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...
Photopolymerizable materials are capable of recording high-efficiency volume holograms by changing the refractivity of the layer, for fringe spacing between 0.2 and 10 ?m. As the photosensitive emulsion is embedded between two glass plates, it is possible to open the sandwich after the recording and to analyze the free polymer surface using pulsed force mode of an atomic force microscope. The modulation of properties between the bright and dark fringes, photoinduced by an interference pattern are analyzed in terms of : - relief amplitude (the surface corrugation appearing after opening is due to the relaxation in surface of the constraints stored during the grating formation) ; - local variations of the mechanical polymer properties (they are related to the coupling of the spatially controlled photopolymerization with mass diffusion processes, giving rise to the microstructuration, e.g. regions with various segment densities). Taking into account all these data, improvement of the material is possible in view of applications in data storage or creation of optical diffractive elements. In particular, in the case of multiplexed gratings, it provides a means for visualizing the Young’s modulus pattern associated with each individual record and, therefore, optimizing the recording procedure.