Abstract

The actively mode-locked laser diode (LD) with an external mirror configuration suffers from trailing pulses, which are caused by the residual reflection at the LD facet even with an antireflection coating (R_a < 10^-4).¹ To avoid the undesired trailing pulses, two possibilities were shown to exist:² (1) increasing the LD length and/or decreasing the injection current fall time until the LD roundtrip time is longer than the injection current fall time; and (2) decreasing the internal facet reflectivity R_a well below 10^-4. However, these are not so easy to realize. Insertion of a saturable absorber into the laser cavity was also proposed.³ When the cavity length is relatively long (~ few GHz) and the bias and RF currents are large, we also observe trailing pulses caused by the excess gain, which is similar to the relaxation oscillation of direct modulation.

© 1994 IEEE