An all optical fiber frequency reference using digital interferometry

Abstract

We use digitally enhanced heterodyne interferometry to measure the stability of optical fiber laser frequency references. Suppression of laser frequency noise by over four orders of magnitude is achieved using post processing time delay interferometry. This approach avoids dynamic range and bandwidth issues that can occur in feedback stabilization systems. Thus long fiber lengths may be used resulting in better frequency discrimination, a reduction in spatially uncorrelated noise sources and an increase in interferometer sensitivity. We achieve an optical stability of 30 Hz/√Hz for quasi-static frequencies as low as 20 mHz.