Abstract

We developed a high-speed electro-absorption modulator integrated laser (EML) with a hybrid waveguide structure and experimentally demonstrated 225 Gb/s four-level pulse amplitude modulation (PAM4). This EML has a unique hybrid waveguide structure, which combines a buried heterostructure distributed feedback laser diode for high optical output power and a high-mesa waveguide electro-absorption modulator for a high extinction ratio and wide modulation bandwidth. We fabricated eight chips at wavelengths from 1270.9 nm to 1331.1 nm, which covers the CWDM4 grid. Fabricated EMLs demonstrated a 3-dB down frequency bandwidth of 65 GHz, which is sufficient for 225 Gb/s PAM4 operation. The extinction ratio of more than 3.5 dB and the modulated facet output power of more than 7 dBm were obtained at 50 °C. After 2 km transmission, clear eye diagrams were observed in the wavelength range from 1270.9 nm to 1331.1 nm. After 10 km transmission, clear eye diagrams were observed from 1294.5 nm to 1315.8 nm. The chromatic dispersion dependence of transmitter and dispersion eye closure quaternary (TDECQ), as well as the bit error ratio (BER) characteristics, indicates 800 Gb/s transmission with our EMLs is promising for 2 km on the CWDM4 grid and 10 km on the LAN-WDM grid. In addition, the superior eye quality of 225 Gb/s PAM4 over a wide wavelength range indicates that the use of eight of our EMLs in the proper wavelength range could contribute to the realization of a 1.6 Tb/s system.