Studies of reflection effects on device characteristics and system performances of 1.5- mu m semiconductor DFB lasers

The effect of the external optical feedback on the 1.5- mu m distributed feedback (DFB) laser's device and system performance, both unpackaged and packaged, is studied, considering reflection magnitudes, polarizations, and phases. The reflection is introduced into the laser's AR-coated facet and thus resembles the real system condition for both CW and pulsed (modulated) operations. It is demonstrated that all three parameters can affect the device's CW spectral properties, namely, the emergence of a second mode or mode switching and a clear reflection amplitude dependence on the system performance. When the device is modulated at a subgigabit/second rate, the reflection amplitude is the dominant factor that influences the system performance. Under the assumption that reflection phases do not play a role in inducing a second mode when the reflection level is high and under the worst polarization condition, the percentage of unpackaged lasers failing the CW L-I test under maximum back reflection (-3.55 dB) is low (less than 2%). A similar failure rate was found for the packaged lasers.< >