Spectrogram of Carrier Transient in Semiconductor Optical Amplifier with Dispersive Pump-Probe Spectroscopy

Spectrogram of carrier transient in semiconductor optical amplifiers (SOA) is of great significance for its input conditions and ensuring the quality of the output signal. As the carrier transient process usually happens in picosecond time scale, sub-picosecond temporal resolution is required to resolve this dynamic process. Therefore, the ultrafast pump-probe technology is introduced, and it requires this transient process to be repetitive and stable for a long time, to retrieve the intensity profile with high temporal resolution. To further capture the ultrafast spectrogram with identical temporal resolution, a spectroscopy is required to cascade to the pump-probe technology, which means the acquisition frame rate of the spectroscopy should be equivalent to that of the pump/probe pulses. Although it is challenging for the conventional spectroscopy, the recently developed dispersive time-stretch spectroscopy can realize this megahertz range acquisition frame rate. As a result, a dispersive pump-probe spectroscopy is demonstrated with 1.35-ps temporal resolution and 91.86-MHz spectral frame rate. Therefore, the entire carrier transient process in SOA is captured within 0.2 ms, which makes it robust for most of the low frequency environmental interferences. Moreover, the spectral dependence of carrier recovery process is analyzed in detail, and an abnormal overshoot is observed, which can essentially accelerate the carrier recovery time.