Experiments on modulation properties and optical feedback characteristics of laser diodes stabilized by an external cavity or injection locking

In the wavelength range near 1.3-μm, single-mode operation of laser diodes is achieved by means of an external cavity and injection locking. The influence of digital modulation and optical feedback from a directly taper-coupled fiber is investigated. Lasers stabilized by injection locking showed excellent side-mode suppression at CW-operation but strong side modes when the laser was modulated. The frequency of the main mode is neither affected by modulation nor by optical feedback from the fiber. On the contrary the laser stabilized by an external cavity exhibited good side-mode suppression even when it was modulated. However, the frequency stability of the main mode was influenced severely by optical feedback and modulation. A transmission experiment over 21 km at a bit rate of 2.24 Gbit/s showed that this simple stabilization method is sufficient for applications in optical wide-band IM-PCM transmission systems.