Zebiao Li

820 Hz linewidth short-linear-cavity single-frequency fiber laser at 1.5 μm

We proposed a short-linear-cavity fiber laser with a virtual-folded-ring configuration, which combines the advantages of ring lasers and short-linear-cavity lasers. An all-fiber quarter-wave plate was used inside the cavity to introduce polarization retardation. By retarding the polarization of the travelling waves, the spatial-hole-burning effect was weakened and the efficient cavity length was extended to nearly twice its physical length. As a result, a single-frequency laser output with a linewidth of less than 820 Hz was obtained from the free-running fiber laser. The relaxation oscillation frequency was observed to be around 280 kHz and the signal to noise ratio of the laser output was >72 dB.

Partially doped fiber design for suppressing transverse mode instability

Transverse mode instability becomes the main limit for power scaling of high power fiber lasers with nearly diffraction-limited beam. Compared to conventional step index fiber, this paper proposes a partially doped fiber, which can decrease coupling coefficient between fundamental mode and higher order mode. Based on a coupled mode model, this designed fiber is proved to suppress transverse mode instability effect and promising for power scaling of fiber lasers. Furthermore, we investigate the impact of doped region on transverse mode instability threshold, and propose a partially doped fiber, which can realize 5 kW in single mode regime theoretically.

Mitigate transverse mode instability by linear inner-cladding fiber

Abstract. Transverse mode instability (TMI) limits power scaling of fiber lasers. A semianalytical model is established to calculate the TMI threshold in high-power fiber laser systems of the multi-kW-class. A linear inner-cladding fiber can mitigate the TMI effect by smoothing the heat profile and decreasing the nonlinear coupling coefficient along the fiber. We investigate strong pump absorption of a linear inner-cladding fiber, which leads to shorter fiber length. Utilizing a 915-nm copumping scheme, the linear inner-cladding fiber can realize 10-kW output power in single-mode regime theoretically.

188 W nanosecond pulsed fiber amplifier at 1064 nm

We report an all-fiber high power nanosecond pulsed laser at a center wavelength of 1064 nm. Optimizing the coiling diameter of the active fiber, 188 W average power is achieved at a repetition rate of 40 kHz. The pulse width is measured as 101 ns, while the peak power can be estimated to 46.5 kW.

Power scaling analysis of high power fiber laser employing online three-section recoating method of splice point

Thermal damage is a major limiting factor in the experimental power scaling of high power fiber lasers. A novel online three-section recoating method is proposed in this work which can remove the leaked light due to interface imperfection and improve the heat transfer of the splicing. More than pump power is injected into the gain fiber through the splice point without damage. Theoretical analysis is carried out with both of the analytical and finite element models. The theoretical results agree in temperature growth slope with the experimental results and the extrapolation implies that it is possible to inject more than pump power into the 30/600 YDF from the single end using this method.

Influence of spectral properties of wavelength-locked and wavelength-unlocked diode laser on fiber laser performances

The influence of the spectral properties of laser diode (LD) pump source, i.e. central wavelength and linewidth, on the fiber laser performances are studied. The absorption degradation ratio (ADR) is introduced and evaluated as a guide for pump selection and fiber laser design. The spectra of wavelength-locked and wavelength-unlocked LDs are measured and they are used for fiber laser amplification. The results show that the efficiency of the wavelength-locked LDs is higher than that of the wavelength-unlocked LDs at full current but the residual pump power of wavelength-locked LDs can be much higher at lower current because of the side band.

Linear inner cladding fiber amplifier suppressing mode instability

We use a semi-analytical model considering pump power saturation in high power fiber laser systems of multi-kW-class to calculate mode instability threshold. A novel designed fiber, linear inner-cladding fiber, can mitigate mode instability effect by decreasing nonlinear coupling coefficient and smoothing heat profile along the fiber. We investigate strong pump absorption of linear inner-cladding fiber, leading to shorter fiber length. With 915 nm pumping, linear inner-cladding fiber can reach 10 kW output power without mode instability in theory.