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We investigate a frequency up/down-converter based on a single cascaded semiconductor optical amplifier (SOA)-electroabsorption modulator (EAM) configuration for bi-directional 60-GHz-band radio-on-fiber (RoF) system applications. SOA cross-gain modulation and photodetection in EAM are used for frequency up-conversion, and EAM nonlinearity is used for frequency down-conversion. In our scheme, both 60-GHz local-oscillator (LO) signals and IF signals are optically transmitted from a central station to base stations. We characterize the dependence of frequency up/down-conversion efficiencies on EAM bias and optical LO power. For frequency up-conversion, maximum conversion gain of approximately 8 dB was obtained and, for frequency down-conversion, more than approximately 18-dB conversion loss was measured. Utilizing this frequency up/down converter, we demonstrate a 60-GHz bi-directional RoF link. Optically transmitted downlink 10-Mb/s quadrature phase-shift keying (QPSK) data at 100-MHz IF are frequency up-converted to the 60-GHz band at the base station, and uplink 10-Mb/s QPSK data in the 60-GHz band are frequency down-converted to 150-MHz IF and transmitted to the central station. In addition, the dependence of error vector magnitudes on IF signal power and wavelength is investigated.
Microwave Theory and Techniques, IEEE Transactions on (Volume:54 , Issue: 2 )
Date of Publication: Feb. 2006