The best error vector magnitude provided using a cascaded SOA-MZIs link is 15.5% at the mixing frequency of 101.9 GHz for up-conversion and 18% at 86.3 GHz for down-conversion at the bit rate of 40,500 Mbit/s. Positive conversion gains are obtained at the highest mixing frequency of 101.9 and 86.3 GHz for up- and down-conversions, respectively. Using the virtual photonics integrated (VPI) simulator, it has been shown that the optical transmission system based on a cascaded SOA-MZIs link has a better efficiency and more endurable quality of the frequency mixing of QPSK signals and the higher frequency range for up- and down-conversions. In addition, this up-converted signal is concurrently up- and down-converted at the SOA-MZI2 output at mfs+nfs±f1 and |nfs±f1-mfs|, respectively, where m is the harmonic rank of the second sampling signal. The intermediate frequency (IF) signal carrying quadratic phase shift keying (QPSK) data at a frequency f1 is up-converted at the SOA-MZI1 output at nfs±f1, where n is the harmonic rank of the first sampling signal. In this paper, a simultaneous frequency up- and down-conversion is performed using a cascaded semiconductor optical amplifier Mach-Zehnder interferometers (SOA-MZIs) link for radio-over-fiber (RoF) applications. The proposed filter-free photonic image-rejection down-converter is theoretically analyzed and experimentally verified. Moreover, no optical filter is required thus, the image-rejection down-converter can work with a large bandwidth. 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. After the power splitting, orthogonal I and Q IF signals can be obtained by a photonics-based continuously adjustable phase shifter. Afterwards, an LO signal remodulates it through the Y-DPMZM, and carrier-suppressed SSB modulation is fulfilled via another electrical 90 HC. At the center office, the modulated RF signal is injected into a dual-polarization dual-parallel MZM (DP-DPMZM) after a polarization controller (PC). It is then transmitted to the center office by an optical fiber link. The radio frequency (RF) signal from the distributed antenna unit is injected into a dual-drive MachZehnder modulator (DDMZM) through an electrical 90 hybrid coupler (HC), and a single-sideband (SSB) signal is realized. A filter-free photonic image-rejection down-converter with immunity to dispersion-induced power fading is proposed and demonstrated. Photonics-assisted frequency conversion and transmission based on cascaded modulators is an effective way to satisfy the requirements of distributed antenna array applications. Very high isolation of more than 70 dB between the LO and RF signal ports is also demonstrated. We present experimental results demonstrating that the proposed structure can be used to realize high conversion efficiency frequency downconversion over wide RF and intermediate frequency (IF) signal frequency ranges as the reported dual-parallel-modulator-based microwave photonic frequency downconverter. The new structure allows the modulators for the RF signal and local oscillator (LO) modulation to be placed in different locations suitable for antenna remoting applications, and it has infinite isolation between the LO and RF signal ports. It is based on utilizing the polarization-dependent modulation efficiency property in LiNbO3 electro-optic modulators. A new cascaded modulator structure that has the ability to realize high conversion efficiency microwave frequency downconversion, while at the same time able to overcome two fundamental limitations in the dual-parallel modulator approach, is presented.
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