Ultra-High Data Rate, Terahertz, and Femtosecond Concurrent Up- and Down-Conversion Based on an Electro-Optical SOA-MZI Differential Modulation

This paper presents a comprehensive investigation of a concurrent electro-optical up- and down-conversion architecture based on a semiconductor optical amplifier Mach–Zehnder interferometer (SOA-MZI) operating under a differential modulation configuration. The proposed system employs a high-repetition-rate optical pulse clock (OPC) to generate the sampling control signal required for concurrent frequency conversion. A 4096-QAM data signal modulated at 100 GHz is simultaneously up- and down-converted at the SOA-MZI output through the interaction between the optical sampling signal and the electrically driven SOA branches. The influence of the OPC repetition rate and pulse width on the conversion performance is experimentally analyzed. By increasing the sampling repetition rate to 150 GHz with a pulse width of 0.5 ps, concurrent frequency conversion is achieved over a wide frequency range extending up to 1.6 THz. The performance of the converted signals is evaluated using error vector magnitude (EVM) measurements and temporal characterization. For the up-converted replicas, an EVM of 5.5% is obtained at 1.6 THz for a 1 Tbit/s 4096-QAM transmission. For the down-converted replica at 50 GHz, the EVM reaches 4% at a data rate of 10 Tbit/s. In addition, pulse compression based on a parallel grating pair connected by a 3 km optical fiber is investigated for temporal characterization of the concurrent signal. A compressed pulse width of 45 fs is achieved at full width at half maximum (FWHM). Experimental results demonstrate that the proposed electro-optical SOA-MZI differential modulation architecture provides improved conversion efficiency, reduced noise floor, ultra-wide frequency operation, and high-capacity data transmission capability, making it suitable for terahertz communications, microwave photonics, and ultra-high-speed optical transmission systems.