Broadband Image-Reject Mixing Based on a Polarization-Modulated Dual-Channel Photonic Microwave Phase Shifter

Abstract

Broadband image-reject mixing using a dual-channel polarization-modulated photonic microwave phase shifter is proposed and experimentally demonstrated. The polarization-modulated photonic microwave phase shifter is realized by an orthogonal circularly-polarized wavelength generator, an optical coupler, two polarizers, and two photodetectors (PDs). When a local oscillator (LO) signal, a radio-frequency (RF) signal, and an image interference are supplied to the polarization-modulated phase shifter, opposite phase shifts would be introduced to the RF-and image-induced intermediate frequency (IF) signals. By carefully adjusting the polarizers to make the two channels of the phase shifter quadrature, a phase difference of −90 degree is introduced to the RF-induced IF signals in the two channels, while 90-degree phase difference between the image-induced IF signals is produced. With an electrical 90 degree hybrid to combine the two channels, the two RF-induced IF signals will be in phase while those from the image are out of phase. As a result, the image in the downconverted signal is cancelled. An experiment is carried out. An image-reject mixer (IRM) with an image rejection ratio of ∼60 dB for a single-frequency signal and 23 dB for a 4-GHz linear frequency-modulated signal is obtained.

A Reconfigurable Local Oscillator Harmonic Mixer with Simultaneous Phase Shifting and Image Rejection

“…Therefore, microwave photonic mixers that possess phase shifting functionalities have become a research hotspot. The previously reported schemes typically implement the phase shift function through three main approaches: adjusting the bias voltage of the modulator [11][12][13], adding a phase modulator (PM) [14], or utilizing polarization-based methods [3,15,16]. For instance, Chen et al achieved the phase shifting function of the mixer by controlling the bias voltage of the modulator, but this method is susceptible to DC bias drift [11].…”

Stimulated Brillouin Scattering Based Image-Reject Microwave Signal Harmonic Down-Converter

“…A straight-forward way to realize the mixer is setting the phase shift of the photonic microwave phase shifter [14]. The other approach for image rejection is based on a microwave photonic filter to select the desired signal and suppress the image [15]. However, since no gain is applied to the RF signal, the image rejection ratio (IRR) of these schemes is limited.…”