Optical Microwave Frequency Up-Conversion Via a Frequency-Doubling Optoelectronic Oscillator

We propose and demonstrate an optical microwave modulator that incorporates a low phase-noise optoelectronic oscillator (OEO) for frequency up-conversion in a radio-over-fiber system. A single Mach-Zehnder lithium-niobate waveguide modulator working as a local oscillator in a frequency-doubling OEO directly up-converts the baseband signals to a carrier band. We demonstrate frequency up-conversion to the 20-GHz band for optical analog signals in the intermediate-frequency (IF) band and for optical digital signals at 1.25 Gb/s. The measured transmission bandwidth for IF modulated signals is greater than 1.5 GHz for transmission over 50.5 km of single-mode fiber.