Filter-Free Photonic Image-Rejection Down-Conversion for Distributed Antenna Applications

Abstract

Photonics-assisted frequency conversion based on cascaded modulators is an effective way to satisfy the requirements of distributed antenna array applications. A filter-free photonic image-rejection down-converter with immunity to dispersion-induced power fading is proposed and demonstrated. The radio frequency (RF) signal from the distributed antenna unit is injected into a dual-drive Mach-Zehnder modulator (DDMZM) through an electrical 90° hybrid coupler (HC), and a single-sideband (SSB) signal is realized. It is then transmitted to the center office by an optical fiber link. At the center office, the modulated RF signal is injected into a dual-polarization dual-parallel MZM (DP-DPMZM) after a polarization controller (PC). Afterwards, an LO signal remodulates it through the Y-DPMZM, and carrier-suppressed SSB modulation is fulfilled via another electrical 90° HC. After the power splitting, quadrature I and Q IF signals can be obtained by a photonics-based continuously adjustable phase shifter. Through a combination of the I/Q IF signals with a low-frequency electrical 90° HC, a photonics image-rejection down-converter based on phase cancellation is realized. Moreover, no optical filter is required; thus, the image-rejection down-converter can work with a large bandwidth. The proposed filter-free photonic image-rejection down-converter is theoretically analyzed and experimentally verified.

A Photonics-Assisted Binary/Quaternary Phase-Coded Microwave Signal Generator Applicable to Digital I/O Interfaces

“…An optical spectrum analyzer (OSA, Yokogawa, AQ6370C, Beijing, China) and an oscilloscope (Tektronix DPO75902SX, Beijing, China) are employed to monitor the optical spectra and waveforms, respectively. chromatic dispersion-induced power fading is effectively eliminated over the long-distance single-mode fiber [23].…”

“…When the amplitudes and sequence patterns of the two independent coding signals are set reasonably, a binary or quaternary phase-coded signal can be realized. Due to the CS-SSB modulation of the LO signal in the proposed system both in fundamental and doubling carrier frequency modes, chromatic dispersion-induced power fading is effectively eliminated over the long-distance single-mode fiber [ 23 ].…”

Photonic frequency translation with EML+TIA enabled down-converting receiver

“…While frequency up-conversion techniques are rather well researched and have been demonstrated by means of optical carrier suppression [3,4], independent sideband modulation [5], comb sources with selective modulation of their spectral lines [6,7] and heterodyning with freerunning lasers [8], down-conversion techniques enjoy considerably less attention. Although earlier works have demonstrated the concept to be feasible [1,2,9], its complexity is typically exceeding that of up-conversion techniques.…”