Evaluation of radio-over-fiber link for 45-GHz- and 60-GHz-band simultaneous transmissions

This paper presents an experimental study for evaluating the frequency response of the radio-over-fiber (RoF) system by using a vector network analyzer. An optical modulator and an optical-to-electrical (O/E) converter with a 3-dB bandwidth at 65 GHz and 100 GHz, respectively were used. In general, because the dispersion of a transmission optical fiber degrades the signal quality and limits the transmission distance, an optical band-pass filter (OBPF) is used for the suppression of the single-sideband (SSB) components, that is, the RoF transmitter functions as an SSB transmitter. An erbium-doped fiber amplifier with an OBPF at the receiver optimizes the optical power launched into the O/E convertor. The fluctuation in the observed responses is approximately 2 dB_p-p. In the IEEE802.11ad standard, the tolerance of the fluctuation in the constellations in each subcarrier, under an orthogonal frequency-domain multiplexing scheme, at the transmitter is within +2/-4 dB, which is less than 6 dB. From this viewpoint, the observed fluctuations are less than the tolerance level. The linearity issue is one of the most important factors for the RoF link. The observed responses do not drastically change with an input radio power of 22 dB. Thus, the RoF link with an extremely high-bandwidth RoF transceiver can be used for simultaneous transmissions of 45-GHz and 60-GHz-band radio.