Transverse mode instability and thermal effects in thulium-doped fiber amplifiers under high thermal loads

In-band pumped, Q-switched thulium-doped fiber laser system delivering 140 W and 7 mJ pulse energy

We report on a highly efficient, in-band pumped, Q-switched, Tm-doped, rod-type master oscillator power amplifier (MOPA) system delivering up to 140 W average output power and 7 mJ pulse energy with a slope efficiency of 77% at 20 kHz repetition rate. The amplifier is pumped with Raman-shifted fiber lasers centered at 1692 nm. This in-band pump scheme for Tm-doped fiber lasers can significantly mitigate their quantum defect-related heat load limitations. At the same time, this pump wavelength yields a similar amount of storable and extractable energy to the state-of-the-art pumping at 793 nm. This approach has allowed for the development of highly efficient Tm-doped fiber laser systems combining a high average power and a high output pulse energy.

A 2 μm Wavelength Band Low-Loss Spot Size Converter Based on Trident Structure on the SOI Platform

A 2 μm wavelength band spot size converter (SSC) based on a trident structure is proposed, which is coupled to a lensed fiber with a mode field diameter of 5 μm. The cross-section of the first segment of the tapered waveguide structure in the trident structure is designed as a right-angled trapezoidal shape, which can further improve the performance of the SSC. The coupling loss of the SSC is less than 0.9 dB in the wavelength range of 1.95~2.05 μm simulated by FDTD. According to the experimental results, the lowest coupling loss of the SSC is 1.425 dB/facet at 2 μm, which is close to the simulation result. The device is compatible with the CMOS process and can provide a good reference for the development of 2 μm wavelength band integrated photonics.

High-power tunable Raman soliton generation in large core diameter passive fibers via a precise fundamental-mode matching technique

We demonstrate tunable high-power, high-energy Raman solitons with the range of 1.9-2.3 µm in large mode area (LMA) fibers and an optimized fundamental-mode matching technique for coupling LMA silica fibers. Finally, we obtained Raman solitons with a maximum output power of 5.8 W and a maximum pulse energy of 105 nJ in a LMA passive fiber with 32 µm core diameter, the tuning range of Raman soliton is 1.96-2.35 µm. In addition, we obtained Raman solitons with a maximum output power of 7.3 W and a maximum pulse energy of 126 nJ in a LMA passive fiber with 48 µm core diameter, the tuning range of Raman soliton is 1.96-2.27 µm. The output power of 7.3 W is the highest Raman soliton power currently available in silica fibers, and the result fills a gap in the generation of both high-power and high-energy Raman solitons in a LMA silica fiber.

Compact, ultrastable, high repetition-rate 2 μm and 3 μm fiber laser for seeding mid-IR OPCPA

We report a compact and reliable ultrafast fiber laser system optimized for seeding a high energy, 2 μm pumped, 3 μm wavelength optical parametric chirped pulse amplification to drive soft X-ray high harmonics. The system delivers 100 MHz narrowband 2 μm pulses with >1 nJ energy, synchronized with ultra-broadband optical pulses with a ∼1 μm FWHM spectrum centered at 3 μm with 39 pJ pulse energy. The 2 μm and 3 μm pulses are derived from a single 1.5 μm fiber oscillator, fully fiber integrated with free-space downconversion for the 3 μm. The system operates hands-off with power instabilities <0.2% over extended periods of time.

Temperature-dependent cross section spectra for thulium-doped fiber lasers

An investigation on the temperature dependence of spectroscopic parameters of trivalent thulium ions is important for the design of high-power, thulium-doped fiber lasers and amplifiers. In this Letter, the thulium absorption/emission cross sections are determined in the spectral range 700-2200 nm and in the temperature range from -196°C to 300°C. The spectra are obtained from the absorption and emission measurements of a thulium-doped fiber and from measured thulium concentration profiles. Attempts were made to estimate the temperature dependence of the spectra where the measurements are not accessible. Firstly, the spectra are fitted to a multi-Gaussian model with temperature dependent parameters. Secondly, a physically motivated model of the cross section spectra is proposed and analyzed.

Inband-pumped, high-power thulium-doped fiber amplifiers for an ultrafast pulsed operation

We investigate the influence of the pump wavelength on the high-power amplification of large-mode area, thulium-doped fibers which are suitable for an ultrashort pulsed operation in the 2 µm wavelength region. By pumping a standard, commercially available photonic crystal fiber in an amplifier configuration at 1692 nm, a slope efficiency of 80 % at an average output power of 60 W could be shown. With the help of simulations we investigate the effect of cross-relaxations on the efficiency and the thermal behavior. We extend our investigations to a rod-type, large-pitch fiber with very large mode area, which is exceptionally suited for high-energy ultrafast operation. Pumping at 1692 nm leads to a slope efficiency of 74 % with a average output power of 67 W, instead of the 38 % slope efficiency obtained when pumping at 793 nm. These results pave the way to highly efficient 2 µm fiber-based CPA systems.

Ultrafast Tm-doped fiber laser system delivering 1.65-mJ, sub-100-fs pulses at a 100-kHz repetition rate

High-energy, ultrafast, short-wavelength infrared laser sources with high average power are important tools for industrial and scientific applications. Through the coherent combination of four ultrafast thulium-doped rod-type fiber amplifiers, we demonstrate a Tm-doped chirped pulse amplification system with a compressed pulse energy of 1.65 mJ and 167 W of average output power at a repetition rate of 101 kHz. The system delivers 85 fs pulses with a peak power of 15 GW. Additionally, the system presents a high long- and short-term stability. To the best of our knowledge, this is the highest average output power short wavelength IR, mJ-class source to date. This result shows the potential of coherent beam combining techniques in the short wavelength infrared spectral region for the power scalability of these systems.