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.
Progress towards semiconductor laser frequency stabilization using optical feedback from microtoroidal resonators
is presented. A simple model of the feedback mechanism is provided, and equations of motion describing the
system fields are given. Reactive ion etcher based fabrication of microtoroidal resonators with intrinsic quality
factors as high as 1.6 x 10<sup>5</sup> is demonstrated. This fabrication technique enables improved silicon surface quality
and greater control of the physical structure of the microresonators.