RESUMEN

Optical fibre gratings have recently been suggested as optical platforms for chemical and biochemical sensing. On the basis of the measurement of refractive index changes induced by a chemical and biochemical interaction in the transmission spectrum along the fibres, they are proposed as a possible alternative to the other label-free optical approaches, such as surface plasmon resonance and optical resonators. The combination of the use of optical fibres with the fact that the signal modulation is spectrally encoded offers multiplexing and remote measurement capabilities which the other technology platforms are not able to or can hardly offer. The fundamentals of the different types of optical fibre gratings are described and the performances of the chemical and biochemical sensors based on this approach are reviewed. Advantages and limitations of optical fibre gratings are considered, with a look at new perspectives for their utilization in the field.

Asunto(s)

RESUMEN

A miniaturized probe comprising a circular array of optical fibers coupled to a graded-index microlens has been designed for analyzing colloidal solutions by photon correlation spectroscopy (PCS). The system's suitability for PCS measurements was validated by experimental testing performed in bulk solutions and small drops of monodisperse and bimodal test colloidal solutions.

RESUMEN

A fiber-optic sensor designed to operate inside high-power electric plants is presented. The probe is based on a fiber-optic proximity sensor that detects the light intensity modulation induced by an elastic transducer. The nonlinear response of the optical head is exploited in an original manner to obtain the simultaneous and ndependent measurement of temperature and vibration at 100 Hz. The particular working principle provides an intrinsically lead-insensitive response.

RESUMEN

A multimode optical fiber thermometer is described, which makes use of a single fiber for light guiding and a thermochromic solution as a differential absorption temperature transducer. The probe has a novel design and utilizes graded-index microlenses to achieve high coupling efficiency between fiber and transducer. Technical data of the electrooptic unit, along with the working principle of the probe are presented, and calibration tests of the thermometer are given.

RESUMEN

A novel fiber optic vibration sensor is presented, based on the motion detection of an elastic cantilever by means of the optical triangulation technique. The sensor was designed to work at a fixed frequency of 100 Hz for applications in high power electrical plants where insulation and EM immunity requirements make fiber optic sensing the most suitable choice. The working linear range reaches a peak amplitude of 0.25 mm; resolution is 0.1 microm; accuracy is better than +/-3%; and sensitivity is 10 mV/microm. Design details and experimental results are reported.

RESUMEN

The coupling of two fibers terminating in graded-index-rod lenses is analyzed. In particular, power losses due to angular misalignment and to the combined effects of lateral misalignment and spacing are discussed, assuming a Gaussian radiation pattern of the fibers. Criteria for the design of graded-index-rod components are also given.

RESUMEN

Radiation characteristics of multimode fibers with enlarged tapers were investigated on a number of samples obtained by varying the fiber drawing speed with a given law corresponding to a prefixed taper profile. The characterization of the fibers was made by near- and far-field intensity pattern measurements as well as by measuring the losses introduced by the taper. With a suitable choice of parameters the taper constitutes a reasonable low-loss component useful, for example, for either efficient coupling to large-spot high-power density sources or connecting fibers of different sizes. Conversely at the exit of the fiber the taper can be used for beam shaping which is of interest for mechanical or surgical applications.