Microwave photonic mixers with high spurious free dynamic range

Abstract

Microwave photonic signal processing offers unprecedented features for processing high bandwidth signals. It puts forward a new prospect for overcoming the inherent bottlenecks caused by the limitations in conventional microwave signal processors. The motivation stems from the great potential of exploiting the unique, high time-bandwidth product, low loss, and immunity to electromagnetic interference (EMI) capabilities of photonic signal processing. Microwave photonic signal processing is the new paradigm for processing wideband microwave signals with high tunability and reconfigurability. Amongst the different photonic signal processors, the photonic frequency downconverter is important in many remote antenna, defence and radar systems. Two new microwave photonic mixers are presented in this thesis. The performance of these mixers is substantially improved compared to previous approaches. A new linearised photonic mixer structure, which can fully eliminate the third order intermodulation distortion, is presented. It is based on an integrated dual-parallel Mach-Zehnder modulator to which an optimised RF split and an optimised optical phase shift is applied, in series with a Mach-Zehnder modulator driven by the LO. The mixer achieves a very high spurious free dynamic range performance, it enables essentially infinite isolation between the RF and LO ports, and it has the ability to function over a multi-octave frequency range. Experimental results demonstrate a record measured spurious free dynamic range performance of 127 dB∙Hz4/5, which is over 22 dB higher than that of the conventional dual-series Mach-Zehnder modulator based microwave photonic mixer. In addition, another new wideband linearised photonic mixer structure is presented. It is based on using stimulated Brillouin scattering effects to suppress the optical carrier, together with a single drive integrated dual-parallel Mach-Zehnder modulator for linearisation. The new structure offers enhanced conversion efficiency through the carrier suppression technique. It also suppresses the third order intermodulation distortion to consequently increase the spurious free dynamic range performance through optimising the bias condition of the dual-parallel Mach-Zehnder modulator. Additionally, the new structure enables multioctave operation, and infinite isolation between the RF and LO ports. Simulation results showed a spurious free dynamic range of 120.4 dB∙Hz4/5, and a conversion gain of 8.45 dB, corresponding to 15 dB, and 8.8 dB improvements respectively when compared to the conventional dual-series Mach-Zehnder modulator based microwave photonic mixer. Experimental results demonstrate a measured spurious free dynamic range performance of 120.8 dB∙Hz4/5, which corresponds to 16 dB improvement compared to the conventional photonic mixer structure.