Wavelength-stepped, actively mode-locked fiber laser

Abstract

Wavelength-swept lasers are fast becoming a key element of optical coherence tomography (OCT) with high speed, resolution, and sensitivity. Various designs of wavelength-swept lasers have been investigated to improve the performance for OCT applications, especially to increase the sweep speed. For a decade, the fundamental limit of the sweep speed of laser has been solved with novel designs based on km-long optical fiber cavity and a very small cavity tuned by micro-electromechanical systems. But relying on the mechanical tuning for wavelength sweep is a drawback concerning the long-time stability and improving the speed even more. There have also been increasing concerns about the insufficient bandwidth of data acquisition for high-speed OCT with extended depth range. To solve the addressed problems efficiently, wavelength-stepping without movable components is required. In this thesis, we have developed and characterized a wavelength-stepped fiber laser in combination with the simple active mode-locking technique. Individual control and noise characterization of each wavelength step were demonstrated for the first time. This novel design provides possibilities for a high number of wavelength steps, high repetition with shorter cavity length, and narrow optical linewidth, that are advantageous for applications including optical coherence tomography.