Optical trapping is the science of holding and immobilizing particles and cells, for further manipulation and spectroscopic studies. Enhancing the application of optical trapping is limited by size and flexibility of this tool, mostly limited to high numerical aperture objectives. In this work, we show the potential of using structured light to further enhance the capabilities of optical fibres as optical tweezers, to be used for applications in which space and throughput are of importance. Using femtosecond two photon direct laser writing, we produce accurately designed micro-optic probes at the tip of optical fibres to enhance the light field for trapping single particles as well as single live cells. Enhanced trapping efficiency, ease of transporting trapped particle, and potential of performing wide spectrum spectroscopy on the trapped entity are the advantages of the present approach.
An original approach of highly efficient fiber-based optical tweezers using 3D printed diffractive optical elements at an optical fiber facets is presented. As an example Fresnel lens structures, with focal lengths in the range of 50 to 200 µm, are fabricated by femtosecond two photo lithography. Compared to conventional fiber tip tweezers based on chemically wet etched fiber tips, significant trapping efficiency enhancement by a factor of up to 50 is observed in both axial and transverse direction. An outlook on further concepts of enhanced optical fiber tweezers based on 3D diffractive structures will complete the presentation.
We report stable and reproducible optical trapping of Eu-doped NaYF4 anisotropic nanorods using single fiber tip optical tweezers for investigating the orientation resolved emission spectra. The nanorods were elaborated by the hydrothermal process followed by annealing and centrifugation steps, resulting in a well-defined size distribution. Nanorod trapping was observed at two positions, first, in fiber tip contact and second, at a finite distance of 4 - 6 µm away from fiber tip in the axial direction. The nanorod trapped with tip contact was highly stable and stay trapped for several hours. They were aligned with the fiber axis with a residual angular distribution width of 4° at a light power of 34.8 mW. Moreover, we have determined trap stiffness of the off-tip trapped nanorod by applying the Boltzmann statistics and power spectra analysis of position fluctuations.
Subsequently, the trapped NaYF4:Eu nanorods were used for studying the Eu3+ emission spectra in two orthogonal directions: perpendicular and parallel to the nanorod axis. The influence of anisotropic polarization was observed in the perpendicular direction whereas emission remained isotropic polarization in the parallel direction. The observed emission spectra have been analyzed for the well-defined peaks at 590 and 614 nm corresponds to the magnetic and electric dipole transitions. The experimental investigations were completed by studying the polarization-dependent emission spectra in the perpendicular direction.
A new approach of a highly efficient counter propagating optical fiber based tweezers using 3D printed Fresnel lenses at the fiber facets will be presented. In contrast to conventional fiber tip tweezers the emitted beams of the Fresnel lens fibers are converging resulting in a significantly enhanced trapping efficiency in both axial and transverse direction. The used polymer diffractive Fresnel lens structures are fabricated by femtosecond two photo lithography using a commercial system. The measured trapping efficiencies are found to be up to 90 times higher than for similar results using chemically wet-etched fiber tips. A short outlook on further concepts of enhanced optical fiber tweezers based on 3D diffractive structures will also be given.
We propose and experimentally demonstrate an alternative WGR coupling scheme that is easy to make, requires little alignment, and is both convenient and stable with no need for phase matching. It relies on cavity enhanced Rayleigh scattering. This is the first, single-ended, fiber-based optical nano-antenna that can be used to simultaneously excite and collect light from the WGMs of a microresonator, coupling efficiency as high as 13% is observed, making it very promising for optical sensing applications or cQED.
Nanoparticles of different compositions, sizes, and shapes are elaborated and trapped in a reproducible and stable manner using our optical fiber tip tweezers. Here we report trapping of spherical YAG : Ce3 + particles of 300 and 60 nm diameters and of NaYF4 : Er3 + , Yb3 + nanorods of lengths from 640 nm to 1.9 μm. The properties of the tweezers are analyzed by video observations using Boltzmann statistics and power spectra analysis. Efficient trapping is found for the spherical particles and the small nanorods, whereas the large nanorods are efficiently trapped with only one fiber tip. The optical emission of a trapped nanorod completes the experimental results. Force calculations using the exact Maxwell stress tensor formalism are conducted to explain the experimental observations.
We report stable and reproducible trapping of different micro and nanoparticles using a far field dual fiber tip optical tweezers. The tweezers properties are analyzed by studying the trapped particles residual Brownian motion. The trapping potential is harmonic and the trapping forces in transverse direction are typically three times larger with respect to axial direction. Interference fringe trapping is observed for 300 nm YAG particles. Depending on their length, NaYF4 nanorods are trapped in single or dual fiber tip configurations. Longest rods could be trapped with one single fiber tip at 5 μm away from tip. The experimental results are discussed using numerical simulations based on exact Maxwell Stress Tensor approach.
NaYF4:(Er,Yb,Gd) nanorods of different size were trapped using our original optical tweezers consisting of two fiber tips facing each other. Trapping properties were found to depended drastically on the actual particle size. Small rods were efficiently trapped whereas long rods were strongly attracted by the fiber tips and their stable trapping position was situated at the apex of one single fiber tip. In the case of the long particles the trapped particle modified the fiber tip emission properties and trapping of a second nanorod at distances of some microns from the first one is observed. These experimental results will be explained by numerical simulations using the exact Maxwell Stress Tensor approach.
The unique optical properties of fluorophores nanoparticles doped with rare earth elements have attracted a lot of attention in the scientific community due to their potential application from biological imaging to quantum information.
In this work, we compare the photoluminescence of nanoparticles measured by two different means: traditional objective based microscopy and fiber based optical tweezers.
Our doped NaYF4 nanocrystals are prepared through solvothermal synthesis. Ytterbium and erbium codoping provides nanoparticles with luminescence properties. Under IR laser excitation, the nanoparticles present strong and photostable upconversion signals in the visible range. In addition, by changing the gadolinium content of the host matrix, we obtain nanorods with a controlled aspect ratio up to 20 and a well defined crystalline structure.
The high anisotropy of the nanoparticles results in a strong polarisation of the photoluminescence. To investigate this property, we observed our nanoparticles using a confocal microscope and studied the dependency of the polarisation with the length of the particles.
To complete our characterization, we used optical tweezers to trap nanoparticles in water. We first show the possibility to trap these nanoparticles with an original optical tweezers based on two chemically etched fibers. Due to the optical forces applied by the laser beam coupled into the fibers, the nanorods align themselves between the two fibers along their long axis.
Afterwards, the fibers are not only used to trap the particles but also to collect the luminescence emitted only by the trapped nanoparticles. By this mean, we can analyse the emitted light with a spatial resolution. This result will be compare to previous observation done on the same particles with our confocal microscope.
Moreover, an orthogonal third fiber was implemented in the set up. This fiber can move along the particle and collect the light emitted at different point. We present the link between the photoluminescence properties and the emission point by moving this last fiber.
In addition, our optical tweezers are associated to a traditional objective-based optical microscope. We compared the photoluminescence emitted by particles in a homogeneous medium (water) or at an interface when drop casted on a coverslip.
The optical transmission between two metalized optical fiber tips with sub-wavelength open apertures was studied
for tip-to-tip distances down to ten nanometers. Transverse transmission maps with sub-wavelength structures
clearly indicated optical near-field coupling. Depending on light polarization in the emission fiber tips one or
two transmission peaks were observed. All these results were explained by a straightforward analytical model.
We present the stable trapping of luminescent 300-nm cerium-doped YAG particles in aqueous suspension using a dual fiber tip optical tweezers. The particles were elaborated using a specific glycothermal synthesis route together with an original protected annealing step. We obtained harmonic trap potentials in the direction transverse to the optical fiber axes. In the longitudinal direction, the potential shows some sub-structure revealed by two peaks in the distribution statistics with a distance of about half the wavelength of the trapping laser. We calculated intensity normalized trapping stiffness of 36 pN•μm-1W-1. These results are compared to previous work of microparticle trapping and discussed thanks to numerical simulations based on finite element method.
An original optical tweezers using two chemically etched fiber nano-tips is presented. Optical trapping of 1 micrometer polystyrene spheres is demonstrated at optical powers down to 2.6 mW and tip-to-tip distances up to 28 µm. Harmonic trap potentials are found by analyzing the trapped particle position fluctuations. The trap stiffness is deduced using three different models. Consistent values of up to 0.5 fN nm-1 are found. The trap stiffness is linearly decreasing with decreasing light intensity and increasing fiber tip-to-tip distance.
The spectral properties of Er3+-doped As2S3 and Ge33As12Se55 chalcogenide glasses are presented and discussed. Bulk samples and thin films have been studied. Bulk samples have been obtained by melt-quenching. Thin films have been obtained by RF sputtering. Sputtering targets have been fabricated from home-made cut and polished doped bulk samples and from commercial undoped targets with erbium pieces on the surface. The film morphology has been analysed by AFM and a column-like structure has been observed for the Ge33As12Se55 films. The presence of Er3+ ions in As2S3 and Ge33As12Se55 films has been confirmed by PL emission at 1.55 µm. A PL lifetime of 4 ms has been measured in Er-doped As2S3 films. Single mode waveguides have been fabricated by wet etching in Ge33As12Se55 films.
Photocurable thin films have been deposited using the Aerosol-gel process. 3-(Trimethoxysilyl) propyl methacrylate and tetraisopropyl-orthotitanate complexed with methacrylic acid have been used as sol-gel precursors. The films were characterized with respect to their chemical, structural, optical, and photopolymerization properties.
Optically active films in the system Y2Ti2O7-Er2Ti2O7 have been deposited using the Aerosol-gel process. Photoluminescence properties closely depend on the film crystallization state. Dilution of erbium ions within a crystalline Y2Ti2O7 matrix allows to prevent photoluminescence concentration quenching induced by short range distance interactions. Consequently, heavily doped films with good photoluminescence properties can be obtained.
Hybrid organic-inorganic thin films doped with lead sulfide nanocrystallites were synthesized by a combination of colloidal chemistry and sol-gel processing. In order to study the influence on the spectroscopic properties of the crystallite surface, and hence the related defect states, PbS-doped films with different sulfur to lead ratios and different surface capping agent concentrations were fabricated. X-ray diffraction measurements showed the presence of nanoparticles with a mean diameter raging from 3 to 5 nm. The absorption spectra showed a large blue shift of the absorption edge to shorter wavelength, indicating strong quantum confinement. Strong photoluminescence emission in the near infrared was found by pumping at 514 or 532 nm. The emission intensity and its position were found to be dependent on the elaboration parameters. The film fabrication process influences only slightly the good particle size distribution of the colloidal PbS solutions. Best results were obtained for films with low sulfur to lead ratio or with high capping agent concentration.
Sol-gel films doped with MeS (Me=Cd or Pb) nanocrystals or with MxOy (M=Ni or Co) nanocrystals have been fabricated. Two different strategies were used: for the sulfides a colloidal doping sol was prepared at room temperature and then mixed with the matrix sol. For the oxides a bifunctional ligand was used, bearing either an amine group capable of coordinating the M ions and hydrolysable siloxane groups for anchoring the metal complex moiety to the silicate matrix. In this case the oxide nanocrystals precipitate at 500°C. Films containing MeS nanocrystals showed both non-linear and active optical properties. Nanocomposite films doped with MxOy showed optical gas sensing properties.
YETO (Y2-xErxTi2O7) thin films of good optical quality have been successfully deposited using the Aerosol-gel process. Strong photoluminescence (PL) emission centered at 1.53 μm was detected when pumping in a waveguiding configuration at 980 nm. Different heat-treatment procedures have been used in order to study the relationship between the spectroscopic properties and the thin films microstructure. A clear correlation between microstructure and spectroscopic properties was observed, when passing from amorphous to crystallized YETO. A single exponential PL decay with a lifetime of 7.5 ms was found for crystalline YETO films. The erbium quenching concentration in crystalline YETO is 1021 ions/cm3 and the corresponding PL lifetime is 3.5 ms. Our work shows that the dilution of the erbium ions within a Y2Ti2O7 (YTO) matrix allows to prevent short range distance interactions between the active Er3+ ions and therefore improves the spectroscopic properties with respect to pure ETO.
Sol-gel is one of the possible production techniques of silica-on-silicon integrated optical devices, combining low cost with a great flexibility. In the frame of a European project, we have investigated the application of the sol-gel technique for the realization of an erbium-doped optical amplifier. In particular we developed GeO2-SiO2-Al2O3 sol-gel waveguides doped with Er. The material was optimized in terms of heat treatments, Al2O3 co- doping content and Er doping level. RBS measurements showed that well densified films could be obtained heating the coatings at 700 degrees C in O2 flux. Waveguide properties were tested measuring the propagation losses at 840 nm. In the planar waveguide pumped at 980 nm, erbium showed fluorescence around 1530 nm with up to 6.5 ms. In order to achieve lateral confinement, the planar waveguides were co-doped with Na2O and channel waveguides were fabricated by ion exchange. The feasibility of sodium-silver and sodium-potassium ion exchange was demonstrated. The influence of the process parameters on passive and active optical properties of the films was studied and straight channel waveguides with Gaussian mode profiles were obtained by the sodium-silver route.
Thin silica-titania planar waveguides doped with different concentrations of lead sulfide (10 - 25 mol%) have been prepared by a sol-gel process. It consist of three steps: (a) preparation of a colloidal sol of semiconductor particles; (b) preparation of an alkoxide solution, precursor of the glass- like matrix; (c) mixing of the colloidal sol and the alkoxide solution. Films were deposited on fused silica by dipping and densified for 1 h at 300 degrees Celsius in nitrogen. The mean particle size is 3 nm and the optical absorption edge is situated around 1100 nm. The nonlinear properties have been investigated using degenerated four wave mixing (DFWM) an a nonlinear m-line technique. Different Nd:YAG lasers with pico- and nanosecond pulses at 1064 nm have been used. Depending on the PbS concentration we measured a high negative nonlinear refractive index of n2 equals -3 to -9 10-8 cm2kW for nanosecond pulses (m-lines) and -1 to -10 10-10 cm2/kW for picosecond pulses (m-lines and DFWM). The response time of the nonlinearity is below 30 ps. All observed nonlinear effects are fully reversible and we did not observe any photodarkening. Straight, monomode channel waveguides have been fabricated on theses films.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.