Temperature investigation of low SWaP thulium-doped fiber lasers.

We investigate the temperature dependence of an in-band core-pumped thulium-doped fiber laser with a low SWaP (size, weight, and power) architecture. The temperature investigation is carried out both experimentally and numerically by a simulation model. We demonstrate experimentally that the investigated setup is resistant for temperatures till 353 K. In addition, we explain the observed behavior by considering the temperature depended spectroscopic parameters of thulium-doped silica fibers. Finally, a numerical investigation is carried out for higher temperatures up to 573 K and higher output powers up to 12 W as well as for different wavelengths and show that the considered fiber lasers works still efficient at these temperature ranges. We show the reliability of the considered thulium-doped fiber laser architecture for applications in harsh environment.

High-power continuous-wave Tm3+:Ho3+-codoped fiber laser operation from 2.1 µm to 2.2 µm.

A Tm3+:Ho3+-codoped free-space single-oscillator fiber laser is under investigation with special focus on the power scalability of emission wavelengths from 2.1 µm to 2.2 µm. Using a tunable diffraction grating, a 200-nm tunable laser source is built. Laser output powers above 10 W are delivered from 1990 nm up to 2190 nm, demonstrating the range for stable high-power laser operation. By replacing the diffraction grating by a highly reflective, narrow linewidth volume Bragg grating, power scaling is performed at 2.1 µm and is even enabled at a wavelength of 2.2 µm. Using a volume Bragg grating (VBG) at 2.1 µm, a slope efficiency of 49% is measured with an output power of 262 W. Using another VBG with a center wavelength of 2.2 µm, the fiber laser delivers a record power of 77 W with a slope efficiency of 29%.

Nanosecond pulsed single-frequency two-stage holmium-doped fiber MOPA at 2054 nm and 2090 nm.

A single-frequency polarization-maintaining holmium-doped fiber master oscillator power amplifier operating at signal wavelengths of $2054\;{\rm nm}$ and $2090\;{\rm nm}$ is presented. The two-stage setup delivers up to $240\;{\rm W}$ peak power and $6.7\;\unicode{x00B5} {\rm J}$ pulse energy for a pulse width of $30.2\;{\rm ns}$ at a repetition rate of $100\;{\rm kHz}$. The first amplifier stage is designed by simulation, tailored for high gain at the signal wavelength range, favoring amplification at $2090\;{\rm nm}$. The design is discussed, and the measured values are compared with the simulation. The second stage is investigated regarding the efficiency for co- and counter-pumping. Stimulated Brillouin scattering was found to be the limiting factor for pulse peak power scaling in the second stage. The measured output pulse shapes are discussed and compared to pulse shapes derived with the Frantz-Nodvik model.

High pulse energy ZnGeP2 OPO directly pumped by a Q-switched Tm3+-doped single-oscillator fiber laser.

A mid-infrared ${{\rm ZnGeP}_2}$ optical parametric oscillator pumped by a ${{\rm Tm}^{3 +}}$-doped fiber laser is reported, providing pulse energies of $230 \;\unicode{x00B5}{\rm J}$, pulse widths of 40 ns, and peak powers of ${\sim}6\;{\rm kW} $ with excellent efficiency and beam quality. The pump source is an actively $Q$-switched single oscillator optimized to generate high pulse energies.

25 W 2 µm broadband polarization-maintaining hybrid Ho- and Tm-doped fiber amplifier.

We report the design, evaluation, and performance of a polarization-maintaining (PM) fiber amplifier with a CW output power of >25 W at 2051 nm and a high input signal dynamic range of 34 dB at 25 W. To improve both the output power and dynamic range performance of previous amplifiers, we propose a PM hybrid design with a single-clad Ho-doped preamplifier (HDFA) followed by a double-clad Tm-doped power amplifier (TDFA). The role of the Ho-doped fiber preamplifier is to provide large input signal dynamic range, low noise figure, and moderate output power over an operating bandwidth from ≈2-2.1 µm. The role of the Tm-doped fiber power amplifier is to offer power amplification with good efficiency, taking full advantage of 2-for-1 ion-ion interactions, with the possibility of scaling up the output power to values much higher than 25 W. Our hybrid Ho-Tm-doped design provides a PM fiber amplifier with a combination of large input signal dynamic range, low noise figure, broad operating bandwidth, and high output power. Simulations of the hybrid HDFA/TDFA performance agree relatively well with experimental data.

Simulation of 2µm single clad thulium-doped silica fiber amplifiers by characterization of the 3F4 - 3H6 transition.

We report measurements of absorption, gain, and the lifetime of the transition 3H6 - 3F4 for three commercially available thulium-doped single clad silica fibers. These measurements are used in a steady-state simulation of thulium-doped fiber amplifiers (TDFAs). Comparison of simulation and experimental results yield good agreement for a single stage TDFA at 1952 nm and a tandem TDFA at 1910 nm.

Multistage single clad 2 µm TDFA with a shared L-band pump source.

We report the experimental performance and simulation of a multiwatt two-stage TDFA using an L-band (1567 nm) shared pump source. We focus on the behavior of the amplifier for the parameters of output power Pout, gain G, noise figure NF, signal wavelength λs, and dynamic range. We measure the spectral performance of the TDFA for three specific wavelengths (λs=1909, 1952, and 2004 nm) chosen to cover the low-, mid-, and upper-wavelength operating regions of the wideband amplifier. We also compare the performance of the two-stage shared pump TDFA with a representative one-stage shared pump amplifier. A comparison of experimental results with simulation is presented.