We tested the long term stability of first order Sapphire Fiber Bragg gratings (SFBG) at 1400°C for a period of 28 days in air. During the whole period temperatures detected by the SFBG differed less than ±2K°C from the temperatures measured by a type B thermocouple. The spectra at the beginning and the end of the installation were identical. The reliable practical application of wavelength-multiplexed two-grating SFBG arrays for quasi-distributed sensing at very high temperatures has been demonstrated.
This paper deals with a 3-D scanning system based on relatively inexpensive, off-the-shelf products. Although there exist
many techniques for obtaining information about object position, size and form, it is still possible to find specific
applications where none of the conventional methods seem to satisfy the requirements. Such applications are
encountered in challenging environments where one has to simultaneously gather information quickly, with high
accuracy and without interaction with the object of interest. The instruments also need to be kept simple, cost effective
and robust. In this paper, we propose and investigate a system that angles a beam from a laser rangefinder along the
object of interest, in order to determine the object's geometrical properties. The beam is angled by means of a
galvanometer scan head. The scanned pattern is conditioned by the assumed object form and position. The pattern is
adjusted during the measurement in an appropriate way so that the scanning time is minimized. The object form assumed
is a series of concentric pipes of relatively small and varying diameter (10 - 50 cm). The system is designed to determine
the position of the joints and the diameters of the pipe sections. The object can be at temperatures ranging from subzero
to over 1300 °C. This article specifies the characteristics of the system and discusses the various parameters limiting the
system performance. Although the system components were not optimal with respect to the measurement requirements,
the system's performance is designated as satisfactory. The system can easily be improved by exchanging the
components with more suitable units.
In a dielectric waveguide, the optical power is confined mostly in the core of the waveguide, where the refractive index is highest. Outside of the core the field is evanescent, i.e., the field strength decreases exponentially with the distance from the core. This evanescent field can be used to manipulate microparticles. For a particle with index of refraction higher than that of the surrounding medium (water), the optical forces due to the evanescent field act to guide the particle along the waveguide. The use of waveguides to trap particles combines the possibilities of conventional optical tweezers with the techniques employed in integrated optics, and it has the added advantage of integration of several functions on a single chip. We have experimentally observed size-dependent trapping and propulsion at velocities up to 33μm/s of polystyrene spheres, of diameters between 3 and 12μm, and in propulsion of 0.25μm diameter gold spheres at velocities up to 500μm/s. A Y-junction with a multimode input waveguide has been used to sort particles. By moving the input fibre relative to the input waveguide, the light goes into one of the two output branches. We have shown that this principle can be used to sort polystyrene microbeads. Recently we have used counter-propagating waves to move particles in both directions and also to stop a particle at a precise location. Experimental results and simulations for polystyrene microbeads, yeast cells and gold particles are presented.
Optical microsphere resonators, with their exceptionally low optical losses and high Q-factors, are attracting a lot of interest in integrated optics and related fields. Not being accessible by free-space beams, whispering gallery modes (WGM) of a microsphere resonator require near-field coupler devices. Efficient evanescent coupling has been demonstrated previously by using thin tapered fibres, fibre half-block couplers, angle-polished fibres and bulk prisms. In this work, we demonstrate WGM excitation in microspheres, from 8 to 15 μm in diameter, by using an integrated optics channel waveguide. Light from a tunable laser was coupled into a single mode K<sup>+</sup> ion-exchanged channel waveguide formed in BK7 glass substrate. Dry borosilicate glass microspheres were dispersed on the substrate surface. Polystyrene microspheres were suspended in electrolyte water solution and confined in a closed cell on top of the waveguide. The light was coupled to the particles sitting on the waveguide surface. The scattered light was observed through the microscope. As the laser wavelength was tuned, the observed images were recorded with a CCD camera. WGM excitation was observed through the increased scattered light intensity at certain wavelengths. In the case of glass microspheres and a Ti:Sapphire tunable laser, the obtained resonance quality (Q-) factors were about 400. The resonances observed in polystyrene microspheres using a tunable diode laser had lower Q-factors and were deteriorating with decreasing particle size.