Design and Fabrication of 10-/40-Gb/s, Uncooled Electroabsorption Modulator Integrated DFB Laser With Butt-Joint Structure

This paper describes the wide temperature range operation of an electroabsorption modulator (EAM) integrated with DFB laser diodes (LDs) (EML) designed to reduce the power consumption and size of optical transmitters. We optimized the multiquantum wells (MQWs) for LD and EAM separately to realize uncooled operation. We employed a conduction band offset (??Ec) of around 250 meV for the LD and 150 meV for the EAM. The number of well layers was set at 6 for the LD and 12 for the EAM, respectively. We fabricated the EML using a butt-joint (BJ) process to allow us to design the LD and the EAM independently. We introduced a ridge waveguide structure for the LD and EAM waveguides, and designed the width of the LD and EAM mesa to achieve a high optical coupling efficiency between the LD and the EAM. We then used the 200-?? m-long EAM for 10-Gb/s operation and the 150- ??m-long EAM for 40-Gb/s operation, and thus obtained a dynamic extinction ratio of over 9 dB at 10 Gb/s from -25 ??C to 100 ??C and of 8.2 dB at 40 Gb/s from -15 to 80??C. We achieved a power penalty of less than 2 dB after an 80-km single-mode fiber (SMF) transmission at 10 Gb/s and a 2-km SMF transmission at 40 Gb/s over a wide temperature range. These results confirm the suitability of this EML with a BJ structure for use as a 10-Gb/s or 40-Gb/s uncooled light source.