Multi-Octave Analog Predistortion Circuit for HD2 and IM2 Compensation in Radio-over-Fiber Telecommunication Apparatuses

We describ here the development of a completely analog, low-cost, multi-octave predistortion circuit for Radio-over-Fiber telecommunication apparatuses. The predistorter is able to reduce of about 10 to 15 dB second-order distortions generated by semiconductor lasers operating in the frequency range 350 MHz ÷ 2 GHz, used with TETRA, GSM and DCS cellular networks. The predistorter has been designed on the basis of a laser circuit model of commercial DFB lasers previously developed. The conguration of the correction circuit has been implemented and realized to obtain the simultaneous correction of the laser second-order harmonic and intermodulation distortion components falling in the abovementioned cellular bands.