Photonic Generation of Microwave Frequency Shift Keying Signals

Abstract

A novel approach to generating microwave frequency shift keying (FSK) signals using a polarization modulator (PolM) and a dual-polarization Mach-Zehnder modulator (DPol-MZM) is proposed and experimentally demonstrated. In the proposed system, the PolM is employed to modulate the polarization state of an input linearly polarized lightwave to switch between two orthogonal directions, leading to the generation of a polarization shift keying (PolSK) signal. Then the PolSK signal is sent to a DPol-MZM, which is made up of two polarization multiplexed sub-MZMs by a polarization controller (PC). Two microwave signals with different frequencies are applied to the sub-MZMs. After aligning the orthogonal directions of the PolSK signal with the axes of the DPol-MZM by the PC, the PolSK signal can be converted into a microwave FSK signal. A proof-of-concept experiment is carried out to verify the proposed system. When the sub-MZMs in the DPol-MZM are biased at a quadrature point, a double sideband microwave FSK signal at 3/6.5 GHz with a bit rate of 1.25 Gb/s is generated and transmitted over 10 km of single-mode fiber. When the sub-MZMs are biased at minimum point, an optical carrier suppression microwave FSK is achieved at frequency-doubled 6/14 GHz with a bit rate of 2.5 Gb/s.