Investigation of ion-ion interaction effects on Yb3+-doped fiber amplifiers.

Ytterbium (Yb3+)-doped materials have been widely used for high efficiency high energy laser sources at the 1 µm wavelength region because of their very low quantum defect and the unique simple energy level structure of Yb3+, resulting in no excited-state absorption and low occurrence probability of deleterious ion-ion interaction processes. It has been generally recognized that these ion-ion interaction processes have very little influence on the operation of Yb3+-doped fiber lasers at low and moderate power levels. However, our recent study shows that the performance of Yb3+-doped fiber amplifiers operating at low power levels is still influenced by the ion-ion interaction processes due to the large amount of population at the upper laser level 2F5/2. In this paper, experimental evidences of the ion-ion interaction effects in Yb3+-doped fiber amplifiers are presented and a new model including these effects is developed for the numerical simulation. Our experimental and numerical investigations on the 976 nm and 1030 nm Yb3+-doped silica and phosphate fiber amplifiers show that ion-ion interaction has non-negligible impact on the performance of Yb3+-doped fiber amplifiers indeed, and compared to Yb3+-doped silica fibers, Yb3+-doped phosphate fibers suffer much less from the ion-ion interaction effects due to the much less clustered ions.

Single-frequency blue laser fiber amplifier.

An all-fiber amplifier for a single-frequency blue laser was demonstrated for the first time, to the best of our knowledge. Over 150 mW continuous-wave single-transverse-mode blue laser output was obtained with a 10 m 1000 ppm thulium-doped fluoride fiber pumped by a 1125 nm fiber laser at a power of 2 W. The output power was limited due to the onset of the competitive lasing at 783 nm. Photodarkening and photo-curing of the thulium-doped fiber amplifier were also studied and analyzed.

Power scalable 10 W 976 nm single-frequency linearly polarized laser source.

A 10 W level 976 nm single-frequency linearly polarized laser source was demonstrated with a two-stage all-fiber amplifier configuration. The continuous-wave output power of 10.1 W was obtained from the second stage amplifier by using a 20/130 µm single-mode, polarization maintaining, 1.5 wt. % ytterbium-doped phosphate double-clad fiber. This all-fiber single-frequency laser source is very promising for watt-level deep ultraviolet laser generation via frequency quadrupling.

Graphene Q-switched Ho(3+)-doped ZBLAN fiber laser at 1190 nm.

We report Q-switched pulse operation of holmium (Ho(3+))-doped ZrF(4)-BaF(2)-LaF(3)-AlF(3)-NaF (ZBLAN) at ∼1190 nm in an all-fiber ring laser by using a fiber-optic graphene saturable absorber, which was fabricated by depositing graphene onto the flat surface of a side-polished D-shaped fiber. Stable Q-switched operation was established at a pump power of 180 mW with a repetition rate of 24 kHz and pulse width of 5.7 µs. When the pump power was increased to 1125 mW, 0.44 µJ Q-switched pulses with a repetition rate of 111 kHz and a pulse width of 0.8 µs were generated.

Watt-level short-length holmium-doped ZBLAN fiber lasers at 1.2 µm.

In-band core-pumped Ho3+-doped ZBLAN fiber lasers at the 1.2 µm region were investigated with different gain fiber lengths. A 2.4 W 1190 nm all-fiber laser with a slope efficiency of 42% was achieved by using a 10 cm long gain fiber pumped at a maximum available 1150 nm pump power of 5.9 W. A 1178 nm all-fiber laser was demonstrated with an output power of 350 mW and a slope efficiency of 6.5%. High Ho3+ doping in ZBLAN is shown to be effective in producing single-frequency fiber lasers and short-length fiber amplifiers immune from stimulated Brillouin scattering.

Single-frequency Ho(3+)-doped ZBLAN fiber laser at 1200 nm.

A single-frequency (SF) fiber laser at 1200 nm was developed with a distributed Bragg reflector (DBR) configuration by splicing a 22 mm long highly holmium-doped ZBLAN (ZrF(4)-BaF(2)-LaF(3)-AlF(3)-NaF) fiber with a pair of silica fiber Bragg gratings. The linewidth was estimated to be less than 100 kHz based on the measured frequency noise. The relative intensity noise was measured to be <110 dB/Hz at the relaxation oscillation peak and the polarization extinction ratio was measured to be >19 dB. Our results highlight the exciting prospect that wavelength coverage of SF DBR fiber lasers can be expanded significantly by using rare-earth-doped ZBLAN fibers.