W.G. Zheng

Digital-wavelength ytterbium fiber laser mode-locked with MoS2

In this letter, we report a digital-wavelength ytterbium-doped fiber laser passively mode-locked with layered molybdenum disulfide (MoS2). The MoS2 based saturable absorber (SA) is made by solution coating the MoS2 solution on a gold mirror, showing modulation depth and saturation intensity of 11.4% and 1.37 MW cm−2, respectively. The output pulse has duration of ~300 ps, 3 dB spectral width of ~0.5 nm and maximum output power of 2.6 mW. The mode-locked fundamental frequency is 2.67 MHz with a ~36 dB signal-to-noise ratio. Through tuning the polarization controller (PC) and squeezing/stretching the single mode fiber in the ring cavity, four-bit digital wavelength emission is achieved. It is proposed that the digital-wavelength tuning feature of fiber lasers can be employed in coding and signal processing.

Characterization of 355?nm laser-induced damage of mitigated damage sites in fused silica

The laser-induced damage threshold (LIDT) is one of the important methods to determine the mitigation efficiency of mitigated damage sites in fused silica optics. In this work, two sizes of laser beam with a wavelength of 355 nm and a pulse width of 6.3 ns are used to test the LIDTs and properties of mitigated damage sites. Meanwhile, the R-on-1 average threshold and threshold distribution are used to analyze damage behavior of mitigated sites. It is found that the R-on-1 average threshold shows an S-shaped curve and the threshold distribution obeys a normal law for the mitigated damage sites, which is similar to the law of pristine substrates reported before. The LIDT discrepancy of mitigated sites tested with different sizes of laser beam is attributed to the spot-size effect of the test laser beam, i.e., the LIDT of the mitigated site increases with decreasing test laser spot size. It is shown that most damage occurs at the edge of the laser affected zone, which could be ascribed to the weak location between laser affected and unaffected zones. Finally, the correlations between damage size and the laser fluence which causes damage initiation or damage growth are investigated for the pristine substrate and mitigated sites, and can be fitted by an exponential law.

All-fiber arbitrary and precise pulse spectral shaping

A fiber-loop-based electro-optic (EO) modulation system is proposed and demonstrated to realize both broadband and high-resolution spectral shaping of laser pulses through direct phase modulation. With this fiber-loop EO modulator, arbitrary spectral shape can be carved and the modulation precision is up to 0.004 nm. The laser spectral bandwidth can be steadily broadened from several MHz to several nanometers through tuning the pulse cycle times and the programmable driving signal. One representative shaped spectrum is presented with a <0.01 nm mismatch to the simulated results, which is used to effectively pre-compensate the pulse spectral distortion during amplification.

Single frequency high-peak-power fiber laser by suppression of SBS

We report a single frequency Yb-doped fiber laser with a high peak power at the wavelength of 1064 nm. The laser consists of a single-frequency diode seed and two amplifier stages. In the pre-amplifier, double-pass amplification is adopted by integrating a specially designed fiber Bragg grating to filter out amplified spontaneous emission and achieve high signal-to-noise ratio. The stimulation Brillouin scattering is suppressed by the linewidth broadening due to the cross phase modulation between the signals propagated in the backward and forward directions. In the boost amplifier, a disaster area of the stimulated Brillouin scattering is found and is stepped over by management of both the signal and pump power. The laser generates the peak power of 2.2 kW in single-mode linearly polarized output with a linewidth of around 230 MHz.