Chip-based microwave photonic frequency mixer (Invited)

A microwave photonic frequency mixer constituted of an optically-carried local oscillator (LO) and a wavelength-division modulator was proposed. The wavelength-division modulator chip, which was consisted of a silicon phase modulator, two micro-ring filters, a photodetector, two optical couplers, and two grating couplers, was designed and fabricated. Based on the chip, a microwave photonic harmonic frequency mixer was implemented. In the experiment, an optically-carried LO was generated by double-sideband suppressed-carrier modulation at a Mach-Zehnder modulator. An RF signal from 6 to 16 GHz was successfully converted into a signal with a frequency of 33 to 23 GHz. In order to suppress the remaining mixing spurs, two solutions, i.e., increasing the rejection ratio of the micro-ring filter to decrease the intensity of the leaked optically-carried LO and introducing an optical phase shifter to correct the phase of the leaked optically-carried LO, were proposed and verified by simulation. It should be noted that the latter is simpler and more suitable for photonic integration.