Large-scale photonic integrated circuits (PICs) are essential for reducing the cost and power consumption of optical networks. Selective doping by means of thermal diffusion and ion implantation is suitable for fabricating PICs because it enables doping into desired regions without crystal growth. In this paper, we report the fabrication of a lateral-p-i-n-diode-structure electro-absorption modulator (EAM) integrated with a DFB (EADFB) laser. Owing to the lateral p-i-n structure, we are able to use the broadening of the exciton absorption peak that occurs when the electric field is applied parallel to the quantum well. By comparing the calculated absorption spectrum change for parallel and vertical electric fields, we found that it occurs with a low electrical field, although the amount of absorption coefficient change is small for the parallel one.
Thus, in our design, we make the EAM length larger than that of the conventional vertical electric field EAM. However, because of the low parasitic capacitance of the lateral EAM, we can expect to achieve high-speed operation. With a fabricated device with a 200-μm-long EAM, we have achieved 50-Gb/s operation with clear eye opening. We have also achieved a side-mode suppression ratio of more than 50 dB by using a surface grating. These results indicate that our lateral EADFB laser is very promising as an integrated light source for large-scale PICs and that our fabrication process based on selective doping is suitable for them.