Optimization of high frequency radio over fiber system using cascaded amplifier and dispersion compensation fiber

High spectral quality millimeter (MM) wave is desired for obtaining signal with high conversion efficiency and lesser nonlinear distortion. To enhance the spectral quality, the power of desired sidebands should be maximized and undesired sidebands should be completely suppressed. This paper reports the generation of tunable, high spectral purity and filterless high frequency MM wave with tunable sideband suppression ratio (SSR). Two Mach-Zehnder Modulators with gain in parallel configuration are utilized for obtaining spectrally pure fourth order sidebands. Beating of fourth order sidebands in the photodetector results a high frequency MM wave. Direction of polarization controller, phase shift relationship of local oscillator (LO) signal and appropriate value of gain is used to optimize the carrier suppression ratio. Cascaded erbium-doped fiber amplifier and dispersion compensation (DC) fiber is employed to compensate the nonlinear distortion for enhancing the system performance. 80 GHz MM wave with 59 dB optical sideband suppression ratio and 42 dB electrical sideband suppression ratio is realized from 10 GHz LO signal at a very low modulation index of 2.436. Variation of non-ideal factors such as extinction ratio and modulation index from their ideal value is examined for verifying the SSR optimization in the proposed radio over fiber (RoF) link. Sideband suppression ratio higher than 45 dB can be easily achieved at lower extinction ratio of 30 dB which goes to a maximum of 59 dB at higher extinction ratio. This shows a highly stable system with extinction ratio tolerance. Furthermore, the transmission effectiveness of the resulting MM wave with 10 Gbps non-return-to-zero data is analyzed by using with and without post-compensation technique through DC fiber. Transmission distance of 120 km through optical fiber and 20 km through DC fiber is reported with 6.65 Q factor, 3.8 dB power penalty and 1.45 e(-11) BER by employing post-compensation technique. Proposed system offers longer transmission distance to high data rate RoF transmission system with lesser nonlinear distortion.