Advanced DSP technique for dynamic range improvement of a phase-modulation and coherent-detection microwave photonic link

Abstract

Microwave photonic (MWP) links based on intensity modulation and direct detection (IM/DD) have been intensively investigated in the last few years, but the dynamic range is still limited due to the inherent nonlinearity of the electrical-to-optical modulation. Thanks to the inherent linear operation, MWP links based on phase modulation and coherent detection (PM/CD) have been proposed to increase the dynamic range. For a PM/CD MWP link, the dynamic range is mainly limited by the coherent receiver with the amplitude and phase imbalance between the two orthogonal outputs and the phase ambiguity effect when demodulating the phase information in at coherent receiver. In this paper, a DSP technique is proposed to correct these two effects to further improve the dynamic range of a PM/CD MWP link. An experiment is performed. The suppression of the 3 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rd</sup> order intermodulation distortion (IMD3) of more than 30 dB is achieved and the linear demodulation of an input signal with a peak voltage over the half-wave voltage without phase ambiguity is enabled. An improvement in the spurious free dynamic range (SFDR) of 10.2dB-Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2/3</sup> is realized, which leads to a projected shot noise limited SFDR of 128.8dB-Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2/3</sup> .