Ultrahigh resolution spectral analysis based on a Brillouin fiber laser.

We report what we believe to be a novel experimental heterodyne technique for the spectral analysis of continuous optical wave sources. The achieved resolution is as low as the kilohertz level, with a dynamic range in excess of 90 dB. The technique is based on a heterodyne detection between the source under test (SUT) and a Brillouin fiber laser generated by this SUT. Contrary to standard self-heterodyne techniques only a few tens of meters of optical fiber is required without the need of any optical modulators. This spectrometer has been used to characterize a distributed-feedback laser diode and a Brillouin fiber laser.