Concurrent Third-Order Replicas in an Electro-Optical SOA1_SOA-MZI_SOA4 Cascade via Four-Wave Mixing and Cross-Phase and Cross-Gain Modulation

Concurrent up- and down-frequency conversion is central to radio-over-fiber (RoF) and millimeter-wave (MMW) system design. However, existing all-optical mixers based on semiconductor optical amplifiers (SOAs) typically exploit a single nonlinear mechanism, such as four-wave mixing (FWM), cross-gain modulation (XGM), or cross-phase modulation (XPM), and therefore generally provide several frequency conversions. Their performance is further constrained by the available mixer bandwidth and by noise contributions from sampling, thermal, and shot noise. Combining multiple such mechanisms in cascade to concurrently generate both up- and down-mixed replicas at GHz-range frequencies has, to our knowledge, not previously been demonstrated. We address this by proposing and experimentally validating a three-stage electro-optical architecture, denoted SOA1_SOA-MZI_SOA4, combining two single SOAs (SOA1, SOA4) with an SOA-based Mach–Zehnder interferometer (SOA-MZI) to generate concurrent third-order replicas through sequential FWM, XPM, and XGM interactions. In the first stage, FWM at the SOA1 output generates third-order components; in the second, these are further processed by XPM-XGM within the SOA-MZI; in the third, the resulting signal is amplified at the SOA4 output. Measured electrical spectra confirm the simultaneous up- and down-conversion of the third-order signal at each stage, reaching a conversion efficiency of up to 14 dB at 15 GHz. These results show that concurrent third-order up- and down-mixing, combining FWM, XPM, and XGM in a single cascaded architecture, is achievable with potential application in high-frequency electro-optical signal processing.