All-Fiber Mode-Locked Ring Laser With a Sagnac Filter

We present an ytterbium-doped all-fiber all-normal-dispersion laser with a Sagnac filter. The Sagnac filter facilitates the all-fiber configuration without bulk filtering components. In addition, the bandwidth, central wavelength, and modulation depth can be tuned easily by controlling the length of the polarization-maintaining (PM) fiber and polarization controllers in the Sagnac loop. All these properties are independent of the polarization state of the pulses. Stable mode-locked pulses are obtained in this laser with a pulse energy of 3.5 nJ.