Mauro Varasi

Instrumentation development in support of fiber grating sensor arrays

This paper discusses the use of fiber gratings as sensing devices and the measurement limitations imposed by conventional laboratory instrumentation. Work that is currently in progress on instrumentation development to alleviate some of these limitations to yield practical, robust systems is discussed. Research activities concerning 2 system configurations are addressed in some detail: (1) sensor arrays in a system based on broadband optical transmitters with narrowband optical receivers using conventional optical filters or acoustically-tuned, integrated optic filters, and (2) sensor arrays in a system based on narrowband, optical transmitters with laser diodes or fiber lasers that make use of fiber gratings as wavelength tuning elements in conjunction with simple, broadband optical receivers.

A high-resolution integrated optical spectrometer with applications to fibre sensor signal processing

An integrated optical device has been developed to realize the instrumentation for the processing of the optical signal such as those from fibre optic Bragg grating sensors (FBG) embedded in composite materials. The optical circuit integrates on X-cut an acousto-optical TE - TM converter included between two crossed polarizers, in order to realize a tunable high-resolution optical filter. The design and fabrication process parameters and solutions adopted with the aim of obtaining very-high-resolution filters ( FWHM < 0.45 nm at 1300 nm) are discussed. The device has been demonstrated to allow the polarization-independent spectrum analysis of in-fibre optical radiation, exploiting the heterodyne detection of the optical signals from the output of the acousto-optical tunable filter. The application as instrumentation for the processing of optical signals from such sensors is described and the experimental results are presented for the monitoring of static and dynamic deformations of composite material structures such as those in which the FBG sensors have been embedded.

Integrated optical coherent architecture for beam forming in phased-array active antennas

A new architecture is proposed for the optical beam forming in Phased Array Active Antennas (PAAA) in which the integrated optical technologies allow to realize a simple and effective coherent optical processor. The system proposed here combines the advantages of the microoptics systems (all optical processing) with the ruggedness and small size of the integrated optical circuits. These results are obtained by the use of optical multifunctional circuits integrated on LiNbO3 performing all the necessary processing. The resulting network consists of a single integrated optical chip for each antenna row and the optical fibers for the distribution of the signals (frequency, phase) to the active radiating elements. The system architecture will be discussed and technological results in the fabrication of the integrated optical circuit will be presented.

Lithium niobate proton-exchange technology for phase-amplitude modulators

The PE technology has been applied in the fabrication of a wide bandwidth interferometric modulator in X-cut Lithium Niobate. The utilization of dilute melt of Benzoic Acid and Lithium Benzoate as source in the H-Li exchange process, and the introduction of a subsequent appropriate thermal annealing allow to obtain high quality channel waveguide characterized by high long term stability, high electrooptical efficiency , low propagation losses, low fiber-waveguide insertion losses and high resistance to the laser radiation induced damage. The main advantages of this modulator in comparison with the similar Ti-induffusion based device are the lower fabrication cost and the possibility to handle higher optical power, allowing higher dynamic range of the signal processing system.

Codoped silica-on-silicon waveguides fabricated by PECVD technique

Silica-on-silicon waveguides have been fabricated doping core layer with phosphorus and germanium. Plasma Enhanced Chemical Vapor Deposition has been used to grow all layers starting from liquid metalorganic compounds. Co-doping assures chemical (Ge) and geometrical (P) homogeneity with optical fibers and allows to propagation losses of 1 dB/cm (not reflowed samples). Low cost, high realization rate and process compatibility with other microelectronic components make this technology very attractive for industrial production.

Second-harmonic generation in PMMA films doped with organometallic complexes

Abstract We have prepared and characterized PMMA films doped with three new Pt-containing acetylides for second-order optical nonlinearity. The noncentrosymmetric order of chromophores in the matrix was achieved through corona poling and monitored in situ with measurements of second-harmonic generation. The values of second-harmonic coefficient are of the same order as in DR1-doped films with the advantage of a lower absorption in the visible region. The data of the orientational decay confirm the relaxation dynamics of doped PMMA.

Polarisation independent integrated optical spectrometer (PIIOS)

A new integrated optical device is demonstrated for the polarization independent spectrum analysis of in fiber optical radiation. The device exploits the heterodyne detection of the optical signals from the output of an acousto-optical tunable filter fabricated on XY LiNbO3. The device is used to analyze and multiplex the optical signals from Fiber Bragg Grating sensors.

Acousto‐optic performance of monomode dilute melt proton exchange waveguiding Bragg cells

The acoustic and acousto‐optic performance of surface acoustic wave Bragg cells using waveguides fabricated by Ti diffusion and dilute melt proton exchange have been compared. All waveguides were monomode at 0.83 μm, and we report for the first time essentially identical acousto‐optic performance for the two waveguides, with no significant degradation of properties being caused by the dilute melt proton exchange process.