2003
Autores
Abe, I; Frazao, O; Kalinowski, HJ; Schiller, MW; Nogueira, RN; Pinto, JL;
Publicação
SBMO/IEEE MTT-S International Microwave and Optoelectronics Conference Proceedings
Abstract
Fiber Bragg grating (FBG) written in normal and reduced diameter high birefringence (HiBi) optical fibers have been studied. Chemical etching is used to reduce the fiber diameter while the optical properties of the FBG spectrum are measured. The obtained results agree qualitatively with the stress enhanced chemical etching. They also permit to determine the birefringence of the fiber as a function of the diameter. Optical characterization of the FBG under transversal strain and temperature is performed. The obtained results permit the simultaneous measurement of those parameters with a HiBi FBG sensor.
1999
Autores
Frazao, O; Tavares, P; Cunha, AF; Ribeiro, L; Ferreira da Rocha, J;
Publicação
Proceedings of the Annual IEEE International Frequency Control Symposium
Abstract
An experimental set-up configuration, which allows the self-pulsation frequency of an optical oscillator to be modified by simply adjusting the bias current between 25 and 100 mA, is presented. For lower currents, the self-pulsation frequency is near 6 GHz and the device is stable. For higher currents, the self-pulsation frequency increases to near 11 GHz.
1998
Autores
Frazao, O; Cunha, AF; Tavares, P; Ribeiro, L; da Rocha, JF;
Publicação
Proceedings of the IEEE International Conference on Electronics, Circuits, and Systems
Abstract
This paper reports a technical assessment of an all-optical 4×10 Gbps clock extraction technique in the context of fiber optic digital communication systems. The technique consists in putting a 1320 nm semiconductor laser in a self pulsating mode through injection locking to a CW source. The pulsations are triggered by a fast drive current step. The useful self pulsation region has been explored after extensive simulation providing a valuable knowledge for on-going experiments. Actual synchronization with optical data stream was observed both considering all ones and pseudo-random sequences. Phase sustaining of the clock over moderate-length sequences of zeros was noticed as the most encouraging result of this work.
2011
Autores
Ramos, CA; de Oliveira, R; Marques, AT; Frazao, O;
Publicação
OPTICA APPLICATA
Abstract
This study seeks the development of adaptive composites capable to monitor and actively damp vibrations. In the proposed material, vibrations measurements are performed by an embedded low finesse optical fibre extrinsic Fabry-Perot interferometer, while active damping will be performed by embedded piezoelectric ceramics. This paper focuses on the development of the monitoring procedure. The proposed interrogation procedure for the low finesse optical fibre extrinsic Fabry-Perot interferometer was successfully used to monitor the composite plate when submitted to four-point bending dynamic tests at different frequencies. The embedding of both sensing and actuating components in carbon-fibre reinforced composite laminates is also presented. In the case of the actuator, the efficiency of the embedding process was merely analysed from the capability of the piezoelectric ceramic to monitor dynamic strain of the composite using the PZT piezoelectric inverse effect.
2001
Autores
Frazao, O; Araujo, FM; Vieira, A; Correia, N; Novo, C; Costa, AN; Marques, AT;
Publicação
COMPOSITES IN CONSTRUCTION
Abstract
This paper presents a smart composite for structural monitorisation, based on fibre Bragg grating sensors. The sensor plate, a carbon fibre reinforced plastic laminate having an embedded optical strain gauge rosette, was designed, produced, and tested. These instrumented carbon fibre laminates can be used for monitoring of reinforcement and protection of structures, playing an important role in the control of repaired constructions. The smart structures developed are shown to have the ability of measuring temperature and strain.
1999
Autores
Tavares, P; Frazao, O; Cunha, A; Ribeiro, LB; da Rocha, JF;
Publicação
18TH CONGRESS OF THE INTERNATIONAL COMMISSION FOR OPTICS: OPTICS FOR THE NEXT MILLENNIUM, TECHNICAL DIGEST
Abstract
We report the development of a lab prototype for all optical synchronization at 10GHz. Adjusting the distance between the AR coated facet of the MQW semiconductor laser and the ferrule it was possible to 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.
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