Relative intensity noise measurements of 5 μm quantum cascade laser and 1.55 μm semiconductor laser

The magnitude of the relative intensity noise (RIN) of a 5 mum distributed-feedback quantum cascade laser (DFB-QCL) was compared with a conventional 1.55 mum DFB laser diode (LD). The RIN for the DFB-QCL at a frequency of 1 MHz was 157 dBm at 10 mW light output, about 5 dB higher than that of the DFB-LD, which could almost be fully explained by the semi-classical noise model. The resonant tunnelling induced noise, which might be a cause of the RIN degradation, was not observed.