###### Abstract  
Simulation and experimental performance analyses of simultaneous up-converted signals, for the first time, were investigated utilizing a semiconductor optical amplifier Mach-Zehnder interferometer (SOA-MZI) sampling mixer in co- and counter-directions for standard and differential modulation modes. An optical pulse source at a sampling frequency of \(f_{S}\) = 15.6 GHz was used as a sampling signal. The IF signal channels carrying quadrature phase shift keying (QPSK) data at frequencies \(f_{m}\) were up-converted at different mixing frequencies up to 195.5 GHz. Using the Virtual Photonics Inc. (VPI) simulator, we realized mixed QPSK signals and studied their characteristics through a conversion gain and an error vector magnitude (EVM). Simulations of up mixing operated in a frequency range up to 158 GHz. For the standard modulation in the co-direction, the conversion gain decreased from 43.3 dB at the mixing frequency of 16.6 GHz to 21.8 dB at 157 GHz for the first channel and from 43 dB at 17.6 GHz to 21 dB at 158 GHz for the second channel. The use of the differential modulation principle improved the conversion gain by about 10 dB at 195.5 GHz compared to standard modulations in co- and counter-directions. The EVM reached, respectively, 15.5 and 17.5% for the differential modulation in both configurations, at the bit rate of 100 Gbit/s at 195.5 GHz. The benefit provided by the differential modulation was that EVM values were shifted by 20% for all channels in both configurations at 100 Gbit/s. In the real measurement, we confirmed that co-directional conversion exhibited a better performance than the counter-directional operation. In addition, the real mixed signal exhibited lower efficiency and quality in comparison with simulated signals due to the sensitivity of the receiver. all-optical sampling mixer; frequency up-conversion; SOA-MZI; quadrature phase shift keying 2022990  
Some mixing techniques include photonic signal frequency up conversion, which shifts a signal from an intermediate frequency (IF) to a RF domain. There are different schemes of these techniques to achieve frequency mixing based on different optical mixers such as the electro-optic modulator (EOM) [7; 8], the electro-absorption modulator (EAM) [9] based on the cross-absorption modulation (XAM) [10], and the nonlinear photo-detection [11; 12]. These mixing techniques offer features including a wider bandwidth than the technique utilizing an electric mixer. Moreover, various architectures of mixing exploit the nonlinear effects in a semiconductor optical amplifier (SOA), such as cross-gain modulation (XGM) [13; 14], four-wave mixing (FWM) [15; 16] or cross-phase modulation (XPM). The XPM effect is exploited within a SOA-MZI (SOA Mach-Zehnder interferometer) for up-conversion [17; 18], and up and down conversions for full-duplex applications [19]. Sampling techniques [20; 21] based on a sampling signal driven by an optical pulse source can be used in electronic or optical digital systems for frequency mixing [22; 23; 24; 25]. Furthermore, several techniques are used to implement a RoF system for increasing the channel capacity of a single-mode fiber (SMF) [8; 26; 27]. Recently, a similar SOA-MZI-based system by all-optical sampling for a signal channel [22] reported conversion gains for multiple mixing frequencies. Specifically, a signal at 0.5 GHz was up-converted at mixing frequencies between 8.3 GHz related to the first harmonic of the optical pulse source, and 39.5 GHz related to the fifth one. The conversion gain achieved in this range of frequencies was reduced from 15.5 to \(-\)13.4 dB. During our previous work in [22; 23; 24; 25], the maximum frequency range that corresponded to the highest mixing frequency of the up-converted signals was obtained up to 39.5 GHz. In other studies, the maximum frequency range was observed up to 60 GHz without the use of the sampling technique. However, the latest studies did not achieve a good performance of the system.