Abstract
A new microwave photonic signal processing structure for realising in-phase/quadrature (I/Q) mixing is presented. It is based on a dual-drive Mach Zehnder modulator (DDMZM) and an optical phase modulator inside a Sagnac loop interferometer. Two output IF signals with a quadrature phase difference are obtained by using two photodetectors to detect the upper and lower sidebands of the optical signal at the Sagnac loop output. A quadrature phase difference in the two IF signals is realised by biasing the DDMZM at the quadrature point. This has the advantage of very little quadrature phase errors as a standard modulator bias controller can accurately lock the DDMZM bias point. The optical phase modulator driven by an RF signal can be placed in a remote location for antenna remoting. Theoretical analysis and simulation show using the proposed I/Q mixer for image rejection can overcome the modulation index dependent image rejection ratio problem in the reported I/Q mixers based on a cascaded modulator structure. The Sagnac loop based I/Q mixer is experimentally verified with results show only ±1° quadrature phase error and more than 50 dB image rejection ratio over the operating frequency range of 6 to 20 GHz.
Highlights
Afrequency mixer is a crucial component in communication and electronic warfare (EW) systems
An I/Q mixer implemented by two phase modulators inside a polarisation beam splitter (PBS) loop [20] can overcome the problems in the cascaded modulator structure while having the antenna remoting ability
It is based on a Sagnac loop interferometer consists of a dual-drive Mach Zehnder modulator (DDMZM) and a phase modulator (PM)
Summary
Afrequency mixer is a crucial component in communication and electronic warfare (EW) systems. An I/Q mixer implemented by two phase modulators inside a polarisation beam splitter (PBS) loop [20] can overcome the problems in the cascaded modulator structure while having the antenna remoting ability. It has a complex structure as it requires polarisation controls of two optical signals in front of two PBSs followed by two sets of balanced detectors. We present a microwave photonic I/Q mixer for antenna remoting applications It is based on a dual-drive Mach Zehnder modulator (DDMZM) for LO modulation and an optical phase modulator (PM) for RF signal modulation inside a Sagnac loop. Results demonstrate a 6 to 20 GHz operating frequency range, only ±1 quadrature phase error and over 50 dB modulation index independent image rejection ratio (IRR)
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