Wavelength switchable mode-locked fiber laser using optical switch

Abstract

Programmable and fast wavelength-switchable ultrashort pulses have important applications in optical communication, optical sensing, micro-wave photonics, and other fields. Multi-wavelength mode-locked lasers are commonly developed to achieve wavelength tunability by using tunable optical filters, fiber Bragg gratings, Lyot filters providing the direct spectral manipulation of the pulses. Actually, manual control is essential in process of wavelength switching, which is very time-consuming and sometimes it is difficult to find the appropriate state of polarization for a certain mode-locking state when utilizing polarization adjustment. So a programmable mode-locked laser which can automatically switch to different mode-locking states is desired. Here, we demonstrate a fast electrically-controlled wavelength-switching scheme in ultrafast nonlinear polarization rotation mode-locked lasers. It is achieved by simply introducing an inline polarization beam splitter (PBS) with two output ports and followed by a 1×2 electrically-controlled optical switch in a fiber ring laser. By utilizing the polarization-maintaining-fiber-pigtailed inline PBS and a polarization controller, a nonlinear polarization evolution (NPE) mode-locking effect as well as a tunable Lyot filter are enabled in the fiber cavity. The optical switch could select the optical path with different polarization state for mode-locking at different wavelength.