RoF-Predistortion circuit

Radio-over-Fibre (RoF) networks performances are typically influenced by the non-linearities due to the modulating devices: lasers in direct modulation schemes, electro-optical modulators in external modulation schemes. A completely analog predistortion circuit has been developed to compensate the non-linearities generated by directly modulated semiconductor lasers. This low-cost circuit, of industrial interest, has a multi-decade correction capability, from 300 MHz up to 2 GHz; thus, it can be used effectively to reduce second and third order harmonic (HD2 and HD3) and intermodulation (IM2 and IM3) distortions generated inside the CATV, GSM/DCS, GPRS and UMTS bands. An average broadband compensation of at least 10 dB has been recorded during measurements; the compensation magnitude can be further enhanced by specifically tuning the circuit for CATV or cellular bands, alternatively.