An SOA-integrated EADFB laser for enhancement of modulated light output power and extension of transmission distances

Electro-absorption modulator (EAM) integrated distributed feedback (EADFB) laser are widely used for 10-, 40- and over 40-km optical communications. In a certain power dissipation condition, there is intrinsic difficulty in increasing the modulated light output power of EADFB lasers, because large insertion loss of the EAM deteriorates the power conversion efficiency. In this study, we investigated an SOA integrated with a EADFB laser to improve the power conversion efficiency of the EADFB laser. The device is called an SOA assisted extended reach EADFB laser, or AXEL for short. For a transmission with a 1.3-μm wavelength, the transmission distance was limited to 40 km because of the large fiber loss of 0.3 dB/km. To overcome this kind of transmission distance limit, we demonstrated a 1.3-μm AXEL with significantly increased power conversion efficiency. In addition, a 25-Gbit/s 80-km transmission by using AXEL and APD-ROSA was firstly achieved beyond the limitation of transmission distance. In contrast, with respect to an L-band wavelength range, a large chromatic dispersion severely limits the transmission distance. Then, we also investigated the AXEL with 1.57 μm wavelength range, and found that the SOA can operate as both optical booster and chirp compensator. Furthermore, the extension of 10-Gbit/s transmission to 80-km and enhancement of modulated light output power to 9.0 dBm were simultaneously achieved by taking advantages of its chirp compensation effect and high power conversion efficiency. The presented results indicate that the AXEL is an attractive candidate for a high-efficiency modulated light source with any wavelength range.