1.2†W single-frequency Tm3+/Ho3+ co-doped fiber oscillator at 2050†nm.

In this Letter, a watt-level single-frequency fiber oscillator at 2050 nm was demonstrated for the first time, to the best of our knowlegde, in a linear laser cavity with a piece of an un-pumped Tm3+/Ho3+ co-doped fiber serving as a saturable absorber. With delicate optimization of mode filtering effect of the dynamic gratings formed in the saturable absorber, a maximum single-frequency laser output power of 1.2 W was achieved under a total bidirectional pump power of 5.8 W at 1570 nm, and the corresponding optical efficiency is 20.7%. This is, to the best of our knowledge, the highest power of a single-frequency fiber oscillator at the wavelength above 2 µm.

High-power, high-efficiency single-frequency DBR fiber laser at 1064†nm based on Yb3+-doped silica fiber.

A high-power, high-efficiency single-frequency fiber laser at 1064 nm was demonstrated based on a distributed Bragg reflector (DBR) all-silica-fiber configuration. A single-frequency laser with an output power of 642 mW and slope efficiency of 66.4% with respect to absorbed pump power was achieved from a 1.2-cm-long commercially available Yb3+-doped silica fiber. To the best of our knowledge, this is the highest single-frequency laser power and efficiency obtained from the DBR all-silica fiber laser. The work presented here paves the way for the development of high-power, robust, and cost-effective single-frequency Yb3+-doped all-silica fiber lasers.

High-energy single-frequency pulsed fiber MOPA at 1064†nm based on a hybrid active-fiber.

We report a single-frequency pulsed Yb-doped fiber master-oscillator-power-amplifier at 1064 nm producing output with pulse energy of 0.6 mJ for a pulse width of 95 ns at a pulse repetition frequency of 5 kHz. Integral to this laser design was the application of a hybrid active-fiber, which integrated a length of heavily Yb-doped phosphosilicate fiber (with a core diameter of 50 µm) with a silica gain fiber (with core diameter of 35 µm). This was used in the power amplifier stage to both suppress stimulated Brillouin scattering and to enhance the gain saturation for improved efficiency and spectral signal to noise ratio. The seed pulses were pre-shaped so that sawtooth-like pulses were obtained after amplification, this having the effect of preventing linewidth broadening induced by self-phase modulation. A spectral linewidth of ∼15 MHz was measured at the maximum peak power of 6.3 kW.

1.7-µm Tm-doped fiber laser intracavity-pumped by an erbium/ytterbium-codoped fiber laser.

In this paper, we demonstrate an efficient 1.7-µm Tm-doped fiber laser whose cavity was embedded in a 1560 nm erbium/ytterbium-codoped fiber laser cavity, which enabled bidirectional pumping and made full use of the circulating pump in the parent laser cavity. A rate equation model was developed to optimize the fiber length and output coupling for a desired output power. In the experiment, a maximum output power at 1720 nm of 1.13 W was obtained under 10 W of 976 nm diode pump power, which correlated well with our modeling. The slope efficiency from the multimode 976 nm diode pump to 1720 nm output was 13.5%, while the slope efficiency in terms of launched 1560 nm pump power reached 62.5%. By using a short Tm-doped fiber to minimize signal reabsorption, a high signal-to-noise ratio over 65 dB was achieved. The prospect for further power scaling was also discussed based on our developed model.

Watt-level 1.7-µm single-frequency thulium-doped fiber oscillator.

Here we demonstrated an efficient high-power single-frequency thulium-doped fiber ring laser operating at 1720 nm. Three cascaded sub-rings were inserted into the main cavity to significantly enlarge the effective free spectral range. By incorporating a fiber Bragg grating, the single longitudinal mode operation was achieved. The maximum single-frequency output power reached up to 1.11 W under 3.75-W launched pump power, while the slope efficiency with respect to the absorbed pump power was 46.4%. The laser linewidth at maximum single-frequency power was measured of 1.9 kHz. Potential power scaling of the single-frequency output power with different quantity and lengths of the sub-rings was also theoretically investigated.

Single-frequency 1.7-µm Tm-doped fiber laser with optical bistability of both power and longitudinal mode behavior.

The single-frequency operation of a thulium fiber laser at a short wavelength of 1720 nm is investigated in a ring resonator. Powerful single-longitudinal-mode operation was realized by utilizing an unpumped thulium-doped fiber as the saturable absorber. The fiber laser delivered 407 mW single-frequency output with a spectral linewidth of 4.4 kHz under 2.7-W launched pump power at 1570 nm, which turned to multi-longitudinal-mode operation at higher pump powers. Additionally, optical bistability of both output power and longitudinal mode behavior, originating from the saturable absorption effect, were observed and discussed. To the best of our knowledge, this is the first efficient 1.7-µm single-frequency fiber laser as well as the first demonstration of optical bistability in thulium-doped fiber lasers.

Efficient multi-watt 1720 nm ring-cavity Tm-doped fiber laser.

Using commercial Tm-doped silica fiber and 1570-nm in-band pump source, we demonstrated an efficient 1720-nm all-fiber laser with ring-cavity configuration. The theoretical model based on rate equations was built up to analyze the laser performance of Tm-doped fiber, which exhibits strong absorption in the 1.7-µm region. The results show that efficient laser operation can be achieved through the optimization of output coupling and the length of Tm-doped fiber. An experimental investigation was performed and agreed with the calculation. By using homemade couplers, we experimentally achieved 2.36-W laser output at 1720 nm under a 6-W launched pump. The slope efficiency with respect to the absorbed pump power and optical efficiency were 50.2% and 39.3%, respectively. Due to the employment of a ring resonator, a narrow laser linewidth of ∼4 GHz at maximum output power was observed.

Power scaling and spectral linewidth suppression of hybrid Brillouin/thulium fiber laser.

In this paper, an ultra-narrow linewidth hybrid Brillouin/thulium fiber laser (BTFL) was demonstrated. By optimizing the output coupling, pump scheme, fiber length and Brillouin pump power for the linewidth narrowing, 344-mW output power with a narrow linewidth of 0.93 kHz was obtained from the BTFL, in which the linewidth of Stokes light was suppressed more than 43 times compared with the 40 kHz linewidth of the Brillouin pump. Besides, the influences of output coupling and pump scheme on the power and linewidth behavior of a single-frequency BTFL were also experimentally investigated, and there exists a performance balance among linewidth narrowing, output power and SBS threshold. The output coupling exerted a significant influence on the BTFL performance.