New Approach to Laser Characterization Using Delayed Self-Heterodyne Interferometry

A new technique to measure phase noise properties of highly coherent lasers based on delayed self-heterodyne interferometer (DSHI) is suggested where the Allan variance of the beat note frequency is obtained via digital signal processing and then used to determine laser linewidth and phase noise properties. This method is capable of determining both white frequency noise and flicker-noise contributions and has been used to characterize various types of lasers. A simple numerical model generalizing previous analytical results has been developed and verified. The corresponding requirements imposed on the DSHI optical delay are consistent with numerical modeling results. The measurement results are in agreement with our previous experiments based on direct heterodyning of the same lasers. The technique is particularly suitable for real-time monitoring of the laser phase noise over long periods of time, which is useful for testing and engineering of highly coherent lasers.