Characterization of the wide band chirp of laser diodes with time-resolved spectroscopy

This paper reports a high-resolution amplified optical sampling time-resolved spectroscopy technique for characterization of the chirp of laser diodes with no limitations on measuring chirp ranges. The chirp induced by slowly (25 Hz) and rapidly (>100  MHz) varying current waveforms was measured. Although the slowly varying case used a triangular current waveform to modulate a distributed feedback laser diode, a non-linear chirp was measured, and a chirp excursion of 71 GHz was found. For the rapidly varying case, the chirp response of three different laser diodes emitting around 1.55 μm were characterized with direct modulation square current pulses. Chirp excursions of up to 157 GHz were measured. From the measurements results, three thermal time constants, from tens of nanoseconds up to hundreds of microseconds, were obtained for each laser diode.