Demonstration of 155-Gbaud PAM4 and PAM6 Using a Narrow High-Mesa Electro-Absorption Modulator Integrated Laser for 400 Gb/s Per Lane Transmission

With the rapidly increasing speed of optical communication, electro-absorption modulator integrated lasers (EMLs) could be promising candidates for next-generation high speed optical transceivers. In this study, we developed a high-speed EML with a narrow high-mesa electro-absorption modulator (EAM) and experimentally demonstrated 155-Gbaud four-level pulse amplitude modulation (PAM4) (310 Gb/s) and 155-Gbaud six-level pulse amplitude modulation (PAM6) (400 Gb/s) operations. We fabricated two types of EML chips: one had a high-mesa EAM with the same waveguide width as the EAM for the 100-Gbaud operation (Uchiyama et al., 2024) (conventional EML) and the other had a high-mesa EAM with a narrower waveguide to reduce the capacitance of the EAM absorption layer (narrow EML). The fabricated narrow EML demonstrated a 3-dB down frequency bandwidth of 85 GHz, which was 4 GHz wider than that of the conventional EML. The narrow EML showed approximately the same extinction ratio as that of the conventional EML at 50 °C. Therefore, the tradeoff between the frequency response and the extinction ratio was improved with the narrow EML. We also demonstrated the 155-Gbaud PAM6 (400 Gb/s) operation of the narrow EML, and a clear eye diagram was obtained after 500-m transmission. We believe these results suggest the possibility of 400 Gb/s per lane intensity-modulated and direct detection operation.