Weihua Guan

Dual-Frequency Operation in a Short-Cavity Ytterbium-Doped Fiber Laser

A dual-frequency 2-cm silica fiber laser with a wavelength spacing of 0.3 nm has been demonstrated using a polarization-maintaining (PM) fiber-Bragg-grating (FBG) reflector. The birefringence of the PM FBG was used to generate the two single-mode (SM) lasing frequencies of orthogonal polarizations. The SM operation in each wavelength has been verified. The output power reaches 43 mW with the optical signal-to-noise ratio of greater than 60 dB. The fiber laser shows stable dual-frequency output under pump variations

Complete elimination of self-pulsations in dual-clad ytterbium-doped fiber lasers at all pumping levels.

We have demonstrated suppression and elimination of self-pulsing in a watt-level, dual-clad, ytterbium-doped fiber laser. The addition of a long section of passive fiber in the laser cavity makes the gain recovery faster than the self-pulsation dynamics, allowing only stable cw lasing. This scheme provides a simple and practical method for eliminating self-pulsations in fiber lasers at all pumping levels.

Single-frequency 1 W hybrid Brillouin/ytterbium fiber laser.

A high-power hybrid Brillouin/ytterbium fiber laser has been demonstrated with an output power of 1 W. The laser operates in the single-frequency regime with an optical signal-to-noise ratio greater than 55 dB in a 0.1 nm bandwidth.

Pump-induced, dual-frequency switching in a short-cavity, ytterbium-doped fiber laser.

Using a short linear cavity composed of a section of highly ytterbium-doped fiber surrounded by two fiber Bragg gratings, dual-frequency switching is achieved by tuning the pump power of the laser. The dual-frequency switching is generated by the thermal effects of the absorbed pump in the ytterbium-doped fiber. At each frequency, the laser shows single-longitudinal-mode behavior. In each single-mode regime, the optical signal-to-noise ratio of the laser is greater than 50 dB. The dual-frequency, switchable, fiber laser can be designed for various applications by the careful selection of the two gratings.

Power Scaling of Single-Frequency Hybrid Brillouin/Ytterbium Fiber Lasers

A coupled-wave rate-equation model, including multiple-order stimulated Brillouin scattering (SBS), is used to study power scaling of hybrid Brillouin/ytterbium fiber lasers. To validate the model, a single-frequency, Brillouin/ytterbium fiber laser was built with a laser output of 40 mW and an optical signal-to-noise ratio greater than 50 dB. The numerical model simulation agrees with the measurements in both fully and partially injection locked regimes. To scale up the lasers output power, a dual-clad architecture is proposed. In this new configuration, the active Yb-doped fiber provides the nonlinear SBS gain as well as the gain resulting from the excited Yb ions. Numerical modeling including three Stokes orders shows that over 5 W of single-frequency laser output can be achieved with a side-mode suppression ratio (SMSR) of greater than 80 dB. Beyond this power, multi-order SBS affects the laser efficiency and SMSR.

Suppression of self-pulsations in dual-clad, ytterbium-doped fiber lasers

Regimes of self-pulsing in fiber lasers have been characterized. Experiments show that the addition of a long section of passive fiber in the laser cavity can stabilize the laser and largely suppress the self-pulsations.