Microwave Photonic Link With Improved Dynamic Range Through <italic>π</italic> Phase Shift of the Optical Carrier Band

Abstract

A microwave photonic link (MPL) with an improved spurious-free dynamic range (SFDR) by introducing a π phase shift to the spectral complements in the optical carrier band (OCB) is proposed and experimentally demonstrated. The fundamental concept to improve the SFDR is to suppress the third-order intermodulation distortion (IMD3) terms while retaining a high gain for the fundamental terms, which is achieved by introducing a π phase shift to the OCB with the joint use of an electrical 90° hybrid coupler and a dual-parallel Mach-Zehnder modulator (DP-MZM). When detecting the optical signal from the DP-MZM at a photodetector, the IMD3 components originated from the beating between different optical sidebands can be fully cancelled, while the gain for the fundamental terms remains reasonably high. Therefore, the SFDR of the MPL is significantly increased. The proposed MPL is experimentally demonstrated. An SFDR of 108.1 dB·Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2/3</sup> or 120.4 dB·Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2/3</sup> for a noise floor of -146.9 or -163.9 dBm/Hz is achieved, which is 14 dB or 15 dB higher than that of a conventional intensity-modulation direct-detection MPL.