Abstract
We report the development of two lab prototypes for all optical clock recovery and optical synchronization, composed by a DFB semiconductor laser driven by a ultra-fast switching current circuit. It was verified that a fast switch of the laser bias current accomplished by the strong feedback in the external cavity induce the self-pulsation needed for correct operation. In the presence of optical RZ signals, the device leaves is natural pulsation frequency synchronizing with the input data.

Abstract
In this paper we report the implementation of fiber Bragg gratings with variable negative mean refractive index perturbation, in a highly germanium-doped fiber, resultant from a type IIa exposition regime. The obtained grating presents a favorable group delay characteristic for dispersion compensation applications with reduced bandwidth.

Abstract
This paper summarizes the research activities of the optical communications group at University of Aveiro and Institute of Telecommunications - Aveiro pole. Several activities like clock recovery systems, both electrical and all optical, electrical equalizers for very high bit rate DST systems, post-detection filters for multigigabit optical receivers, soliton systems, simulation work on WDM, DST, EDFA and short pulse generation for high bit rate systems are presented.

Abstract

Abstract
In this work is studied the response of optical fiber long period grating (LPG) to changes of the refractive index of the external media relatively to variations of wavelength and in transmission. The response of the LPG to refractive index greater and lesser than to cladding is investigated. A nanolayer was deposited onto the fiber to increase the sensitivity of the LPG to refractive index of the external media higher than cladding. The film modifies the rates of effective modes of cladding, thus improving the response of the changes in the refractive index of the external media higher than that in the refractive index of the cladding (n(cl) approximate to 1.457). The Langmuir-Blodgett technique was used for the deposition of the nanolayer.

Abstract
The analysis of the quality of food oils is of paramount importance because the degradation of oils can lead to formation of harmful substances to the human organism With the increase of the degradation of oils an increase of its refractive index occurs The objective of this work is to develop and to characterize optical fiber refractometers sensitive to variations of refractive index of food oil samples The optical fiber refractometers thanks to the intrinsic characteristics make them suitable for monitoring the quality of frying oils They possess the advantages to require small volumes of sample for analysis do not contaminate the sample and supply the response in real time In this work a long period grating (LPG) as refractometer is used because of their sensitivity to refractive index of the external media degraded and not degraded frying oil samples The oil samples had been characterized by the analysis of total polar components The refractive index of oil is above 1 47 this region the LPG does not show enough sensitivity a nanolayer of an organic material was coated onto the fiber Using the Langmuir-Blodgett technique the response of LPG is modified according to the refractive index and thickness of the film (he deposition of the film modifies the rates effective modes of cladding thus improving the response of the changes in the refractive index of the external media higher than that the refractive index of the cladding (n = 1 457)