Abstract

External modulators, which have chirping characteristics smaller than those of laser diode (LD) direct modulation, are desired for 1.55-μm-wavelength long-haul standard fiber transmission systems. The monolithic integration of external modulators with distributed-feedback laser diodes (DFB-LDs)^1,2,3 has attracted much attention because they are smaller and have lower interconnection losses to fibers than do discrete waveguide modulators. Several excellent standard fiber transmission experiments^4,5 using the integrated devices have been reported. On the other hand, it has been pointed out⁵ that quite small residual reflection from the modulator facet is required of DFB-LD/modulator integrated devices for stable fiber transmission characteristics that are insensitive to operating parameters such as LD bias current. However, no clear data with respect to fiber transmission stability, such as power-penalty dependence on operating conditions, have been reported to date, even for a DFB/modulator integrated device with small residual reflection.

© 1994 Optical Society of America