All-Optical In-Phase/Quadrature Microwave Mixer for Antenna Remoting Applications

• Published in: IEEE photonics journal Vol. 13; no. 5; pp. 1 - 7
• Main Authors: Chen, Hao, Chan, Erwin H. W.
• Format: Journal Article
• Language: English
• Published: Piscataway IEEE 01.10.2021; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Antennas; Bias; Frequency ranges; I/Q mixer; image rejection mixer; Mach-Zehnder interferometers; Microwave antennas; Microwave mixer; Microwave photonics; Mixers; Optical communication; Optical fibers; Optical modulation; optical modulator; Optical polarization; optical signal processing; Phase error; Phase shift; Quadratures; Radio frequency; Rejection; remote antennas; Sagnac interferometers; Sidebands; Signal processing
• ISSN: 1943-0655; 1943-0647; 1943-0647
• DOI: 10.1109/JPHOT.2021.3110589

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.