Optical multicarrier generator for radio-over-fiber systems

We propose an optical multicarrier generation method for radio-over-fiber (ROF) systems. The multicarrier generator is composed of a phase-modulated laser and two chirped fiber Bragg gratings used as flattening filters. The chirped gratings are spectrally tailored to equalize the intrinsically uneven envelope of the phase-modulated laser spectrum. A flattened multicarrier spectrum with 7 carriers at a frequency spacing of 12.5 GHz is demonstrated with less than 2 dB peak-to-peak variations and 40 dB optical signal-to-noise ratio (OSNR). We evaluate the quality of the multicarrier generator by using it as an externally modulated source for 802.11 compliant signals. We performed error vector magnitude (EVM) measurements on each of the filtered carrier and found an average value of 32.8 dB compared to 36.2 dB for a tunable laser source. The results show that the multicarrier source could be used for error free transmission.