Monolithically Integrated Multi-channel Radio-over-Fiber transmitter and Frequency Converter

A multi-channel Radio over Fiber (RoF) transmitter and frequency converter fully integrated in a monolithic indium phosphide (InP) PIC is reported. The PIC accepts four independent intermediate frequency (IF) channels with a bandwidth up to 10GHz that are simultaneously upconverted by a single common local oscillator (LO) with a frequency up to 35GHz. At the output of the PIC, the channels, with different wavelengths, are grouped on a single optical fiber, so that after being routed where necessary they can be easily separated by a wavelength division de-multiplexer (WDM) and retrieved to the electrical domain at their RF frequencies by high-speed photodiodes. In details, the PIC hosts four directly modulated distributed feedback (DFB) lasers responsible for the IF modulation, coupled together and modulated by the LO in a single Mach-Zehnder modulator (MZM). The PIC has been fully characterized in its building blocks as well as in its RF performance, showing a conversion loss of 53dB when upconverting to the Ka-band, and a channel-to-channel isolation in excess of 50dB. The system is also tested with data payloads employing different orders of QAM modulations, demonstrating error-free operation in Ka-band.