Measuring frequency noise and intrinsic linewidth of a room-temperature DFB quantum cascade laser

The frequency-noise power spectral density of a roomtemperature distributed-feedback quantum cascade laser emitting at lambda = 4.36 mu m m has been measured. An intrinsic linewidth value of 260 Hz is retrieved, in reasonable agreement with theoretical calculations. A noise reduction of about a factor 200 in most of the frequency interval is also found, with respect to a cryogenic laser at the same wavelength. A quantitative treatment shows that it can be explained by a temperature-dependent mechanism governing the transport processes in resonant tunnelling devices. This confirms the predominant effect of the heterostructure in determining shape and magnitude of the frequency noise spectrum in QCLs. (C) 2011 Optical Society of America