Tin-doped silica samples were prepared by the sol-gel method. Optical absorption and electron paramagnetic resonance measurements were carried out before and after exposure to 266-nm pulsed radiation from the fourth harmonic of the Nd-YAG ͑yttrium-aluminum-garnet͒ laser. The laser-induced change of refractive index was analyzed at different power densities ͑from 1 to 6ϫ10 7 W/cm 2 , 6-ns pulse duration͒ and exposure times. Positive changes of the refractive index up to 4ϫ10 Ϫ4 were observed. The presence and the consequent laser-induced bleaching of the 5-eV absorption band due to oxygen deficient centers, does not appear relevant, since good positive photosensitivity was observed in samples without detectable absorption at this energy.Exposure of silica-based glasses to ultraviolet ͑UV͒ radiation causes a change of the refractive index of the material. 1 This effect is currently studied for applications in optical devices for fiber-optics telecommunications. 2 Optical filtering and other more complex signal processing functions can be implemented in optical fibers or planar waveguides by exposing the material to uv radiation patterns generating modulated changes of refractive index. It was demonstrated that GeO 2 doping of silica, usually employed to produce the core of commercial optical fibers, has a role in this photosensitivity. 1,2 Other kinds of doping are investigated to enhance this property. 1 In particular, recent works showed that SnO 2 doping can give rise to strong and thermally stable photosensitivity. 1,3,4 However, it is not clear whether the microscopic mechanisms involved are those proposed to be responsible for the photosensitivity of GeO 2 -doped silica photoconversion of optically active defects induced by doping and structural compaction of the doped network. 1,2 Contemporaneously to these works, we investigated SnO 2 -doped silica produced by the sol-gel method in order to find the compositional domain compatible with the introduction of diluted tin atoms in Si sites. 5,6 In this paper, we present the results we have obtained on SnO 2 -doped silica samples from the sol-gel method, where Sn substitutional dilution has been achieved. The analysis of the kinetics of the refractive index change vs power density and exposure time gives evidence to two types of mechanisms in substitutional SnO 2 -doped silica, one which involves two-photon processes.Silica xerogels were prepared with a tin content between 0.4 and 0.5 mol%, by the sol-gel method employing hydrolysis of tetraetyl ortosilicate Si͑OEt͒ 4 and dibutyl tin diacetate. 5 Samples were treated at 1050°C by a very slow thermal program comprising a ramp of 4°C/h in vacuum between 450 and 950°C, obtaining complete densification at 1050°C. Samples were then characterized by means of uv absorption spectroscopy ͑Varian Cary 50͒. The indication of the presence of doping-related oxygen deficient centers ͑ODC's͒ was obtained from the 5-eV absorption band. This band arises from twofold-coordinated -Si-cation sites in pure silica, and -Ge-or -Sn-site...

Effects induced by KrF ultraviolet excimer laser on Sn-doped silica fiber performs were analyzed by means of optical and electron paramagnetic resonance (EPR) techniques. Bond breaking in substitutional Sn sites was evidenced by the Sn–E′ EPR signal due to sp3 unpaired electrons in threefold coordinated Sn sites. Red photoluminescence excited at 633 nm, due to nonbridging-oxygen sites, was also observed after laser exposure. The intensity of this emission did not follow the Sn concentration profile, being observed at the core–cladding interface and in the core center. Birefringence data showed that these effects are accompanied by stress relief in the Sn-doped region. Different structural features of core and cladding were evidenced by micro-Raman measurements and related to the observed photosensitivity.

Silicon is increasingly considered as the next future platform for photonic integrated circuits. Low loss Si waveguides and in particular the microring resonator approach seems to be very promising toward the realization of ultra compact, low cost, multi-functionality integrated devices. A novel solution to achieve hit-less tunable add and drop filter on SOI platform is reported on. The device architecture, designed for metro core/access networks, provides full C-band tunability, hit-less tuning operation, polarization independence and very low power consumption.

Silicon is the dominant material in the microelectronic industry and silicon photonics is rapidly gaining importance as a technological platform for a wide range of applications in telecom, and optical interconnect. It allows the implementation of many photonic functions through the use of wafer-scale technologies normally used for advanced CMOS-processing. In this paper some of the most important issues toward a practical implementation of Silicon photonics into an industrial device will be addressed: low loss waveguides, polarization handling, tunability, hitless switching. A tunable Add-Drop multiplexer has been chosen as a case Study of a fully integrated device