An inserting pilot frequency-doubling millimeter wave radio over fiber system without bit walk-off effect by polarization modulator

Abstract An inserting pilot frequency-doubling millimeter-wave (MMW) radio over fiber (ROF) system without bit walk-off effect by polarization modulator (PolM) is proposed. At the central station, the optical carrier is first split into two beams, one beam is used as the pilot, and the other is modulated by a PolM with a composite radio frequency drive signal which is formed by combining the phase modulated data signal and the amplified data signal. By adjusting key parameters of the system, the output main components of the PolM are ±1st order sidebands, the downlink data signal is modulated only on the +1st order sideband. At the BS, the pilot is reflected out by a fiber Bragg grating (FBG) and used as the optical carrier of uplink for carrier reuse. Injecting the output signal of the FBG into the photodetector, the frequency-doubling MMW signal with downlink is produced. In the case of BER is 10-9, and the length of fiber is 40km and 80km, the power penalty is 0.51 dB and 2.54 dB for the downlink, 0.49 dB and 4.72 dB for the uplink, respectively. Comparing to downlink of conventional ROF system, in the 40km and 80km fiber transmission distance, our scheme raises the sensitivity of the receiver to 3.42dB and 2.85dB, respectively. Our designed ROF system can overcome the bit walk-off effect and have no problems of extinction ratio limitation and the DC drift. Carrier reuse realized by inserting a pilot can overcome the problems of downlink performance degradation and tunability restriction caused by conventional carrier reuse methods