Photonic transmission systems using a direct detection receiver have the advantages of simplicity and low cost for the end user. The laser transmitter in such systems can be modulated by frequency shift keying (FSK) to avoid a large modulating current and excessive frequency chirp associated with amplitude shift keying (ASK). The FSK signal typically consists of two separate frequency tones, each representing the "1" or "0" data bits. The FSK signal can be demodulated by passing it through a tunable Fabry-Perot (F.P.) optical filter tuned to only one tone, thereby converting the FSK signal into ASK format for direct detection.1-2

© 1990 Optical Society of America

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