Giancarlo C. Righini

Optical Microspherical Resonators for Biomedical Sensing

Optical resonators play an ubiquitous role in modern optics. A particular class of optical resonators is constituted by spherical dielectric structures, where optical rays are total internal reflected. Due to minimal reflection losses and to potentially very low material absorption, these guided modes, known as whispering gallery modes, can confer the resonator an exceptionally high quality factor Q, leading to high energy density, narrow resonant-wavelength lines and a lengthy cavity ringdown. These attractive characteristics make these miniaturized optical resonators especially suited as laser cavities and resonant filters, but also as very sensitive sensors. First, a brief analysis is presented of the characteristics of microspherical resonators, of their fabrication methods, and of the light coupling techniques. Then, we attempt to overview some of the recent advances in the development of microspherical biosensors, underlining a number of important applications in the biomedical field.

Basic element for integrated electro-optical devices based on liquid crystal waveguides

Integrated optical devices based on liquid crystals (LC) features have been generally discarded for a long period mainly due to very high scattering losses. However, in the 90s this situation is rapidly changing. A better understanding of the physical phenomena underlying the observed effects, the use of new materials with improved performances, the discovery of new electro-optical and nonlinear optical effects make the applications of LC in integrated optics more and more attractive. We present here some recently obtained results in this field. In particular, we have designed and realized an integrated device in a three-stage planar waveguide, having as middle stage a nematic liquid crystal (NLC) film. We studied the device performance in different geometries using TE polarized light. By a proper choice of the material parameters we measured time responses in the microsecond rage. Our experimental results confirm the possibility of employing such a device working as an optical switch and/or beam deflector.

Testing of optical waveguides (TOW) cooperative project: preliminary results of the characterization of k-exchanged waveguides

The preliminary results of a round-robin test to check the reproducibility of the measurement of the main optical characteristics of gradient-like planar waveguides are reported. The test involves seven research laboratories in Europe and Canada. The effective indexes of a set of planar waveguides produced by K+/Na+ ion-exchange have been measured in each laboratory and the refractive-index profiles have been reconstructed by various numerical methods. The comparison between the reconstructed profiles and the directly measured one is also shown for one of the waveguides under test.

Optical Fibres For Medical Applications : Output Beam Shaping

In medical applications of the laser, particular radiation patterns of light on the tissue to be treated are often required. This need can be satisfied by unconventionally shaped fibre tips. The most promising examples of such tips are briefly reviewed. The most important fa-brication methods are also considered as well as the medical or surgical applications which are under investigation.

Characterization of laser-written sol-gel strip waveguides

The realization of low-loss optical waveguides by the sol-gel method and the subsequent production of strip waveguides by direct laser densification are described. These waveguides have been characterized by both the optical and structural point of view, and the results are discussed.

Axially - And Side - Radiating Optical Fibres For Medical Applications

Laser surgery and photoradiation therapy are still rapidly developing: they are therefore placing new requirements and conditions on the associated technology. Thus, optical fibers are often requested to have a particular output which matches the needs of the considered applications. Integral fibre tips are a very convenient solution to many optical systems. The fabrication techniques and the experimental characteristics of different kinds of fibre tips are described.

Near-surface optical analysis of ion-exchanged glass waveguides

Results form our near-surface approach for inhomogeneous films are compared with those from the standard m-line technique in K+ and Ag+ ion-exchanged, graded- index waveguides. We focused our attention on the determination of the refractive index at the film-air interface, and we conclude, from fundamental reasoning as well as from experimental evidence, that the direct near- surface approach can provide higher accuracy than the usual extrapolation from the modal effective indices.

Microlens - Ended Fibres: A New Fabrication Technique

The formation of spherical or elliptical terminations on optical fibres by heating produces an integral microlens element which can be used to improve the coupling efficiency between a laser diode and a fibre or between two fibres, or to focus the output beam for biome-dical applications. A novel fabrication technique is outlined, which uses the laser light energy delivered by the fibre itself. The method is easy and reliable, and is applicable to all types of multimode fibres, even of large core diameter.

Side Radiation Optical Fibers for Medical Applications

The multimode optical fibers, commercially available, are today a very convenient system for delivering the laser radiation to the tissue, in surgical as in therapeutic applications. When the optical fibers are used in combination with the endoscopic techniques they represent a powerfull and not destructive method for reaching and treating the tissue situated in inaccessible zones of the human body.

Resonance Frequency of Optical Microbubble Resonators: Direct Measurements and Mitigation of Fluctuations

This work shows the improvements in the sensing capabilities and precision of an Optical Microbubble Resonator due to the introduction of an encaging poly(methyl methacrylate) (PMMA) box. A frequency fluctuation parameter σ was defined as a score of resonance stability and was evaluated in the presence and absence of the encaging system and in the case of air- or water-filling of the cavity. Furthermore, the noise interference introduced by the peristaltic and the syringe pumping system was studied. The measurements showed a reduction of σ in the presence of the encaging PMMA box and when the syringe pump was used as flowing system.