We explore the development of an optoelectronic probe for MF/HF/VHF (up to ∼ 37 MHz) radio frequency bands able to display the complete waveforms. It was built from simple, low cost and robust components. A passive loop antenna generates RF current which modulates an ultra-bright LED of display/illumination. The light signals are transmitted along a PMMA plastic optical fibre (POF) to an optical receiver placed in a remote site. All characterization measurements were carried out in the near-field region. Far-field radio transmissions could also be detected. The probe presented at 0.5 MHz tuning-band has shown a 62 dBµV dynamic range and was able to detect down to Hmin ∼ 0.8 nA cm−1 magnetic field amplitude. A new technique for loss compensation of the fibre link is proposed and successfully tested.
Resumo-Atenuadores ópticos variáveis (VOAs) são dispositivos ativos bastante úteis para enlaces a fibra óptica. Este trabalho, mostra o desenvolvimento de um VOA controlado por luz para fibras ópticas plásticas (POFs)-POF-VOA. O mecanismo de controle é baseado na opacidade foto-induzida em polímeros foto-cromáticos (PFCs) com o uso de LEDs de baixa potência emitindo no ultra-violeta próximo (395 nm). Foi possível induzir ~10 dB de atenuação numa portadora óptica em 525 nm que se propaga pela POF, utilizando < 0,5 mW/mm 2 de densidade de potência óptica de controle.
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