Single-mode monolithic fiber laser with 200 W output power at a wavelength of 1018 nm

High-power 1018 nm Yb3+ doped fiber lasers with different YDF core and coiling diameters: theoretical and experimental study

In this paper, the effect of the active fiber's core/cladding area ratio on the output parameters of 1018 nm fiber lasers has been investigated. In this regard, we conducted a comprehensive study of two fiber lasers that utilized 25/400 and 30/250 µm ytterbium-doped fibers (YDFs), both theoretically and experimentally. The optimum length of YDFs required for 40 dB of amplified spontaneous emission suppression was calculated. Theoretical studies also identified the YDF breaking zone for lengths greater than the optimum. The experimental results showed that selecting the proper dimensions and coiling diameter for the active fiber significantly increased the power and efficiency of the YDF laser. We obtained an output power of 943 W with a 75.5% slope efficiency for the co-pumped 30/250 µm YDFL which, to the best of our knowledge, is the highest reported value for the 1018 nm co-pumped fiber laser. An analysis of the experimental and theoretical results revealed that YDFs with a core/cladding area ratio greater than 1% are more suitable for realizing a high-power 1018 nm fiber laser. The findings of this study are crucial for the development of high-power 1018 nm fiber lasers with improved performance.

Towards Ultimate High-Power Scaling: Coherent Beam Combining of Fiber Lasers

Fiber laser technology has been demonstrated as a versatile and reliable approach to laser source manufacturing with a wide range of applicability in various fields ranging from science to industry. The power/energy scaling of single-fiber laser systems has faced several fundamental limitations. To overcome them and to boost the power/energy level even further, combining the output powers of multiple lasers has become the primary approach. Among various combining techniques, the coherent beam combining of fiber amplification channels is the most promising approach, instrumenting ultra-high-power/energy lasers with near-diffraction-limited beam quality. This paper provides a comprehensive review of the progress of coherent beam combining for both continuous-wave and ultrafast fiber lasers. The concept of coherent beam combining from basic notions to specific details of methods, requirements, and challenges is discussed, along with reporting some practical architectures for both continuous and ultrafast fiber lasers.

Comprehensive investigations on the tandem pumping scheme employing the pump fiber laser operating at an extremely short wavelength

In this work, with the aim of improving the nonlinearity threshold in tandem-pumped fiber amplifiers for higher output power, theoretical and experimental work was carried out to enhance the pump absorption and thereby decrease the required length of ytterbium-doped fiber by employing shorter-wavelength fiber lasers as the pump sources. Systematical simulations were first carried out to optimize the cavity parameters of a short-wavelength fiber oscillator at 1007 nm, and subsequently, the performance of the 1007 nm fiber laser in tandem pumping was simulated and compared with that of the 1018 nm fiber laser pumped results. Considerable absorption increment and efficiency improvement could be realized in the 1007 nm fiber laser pumped fiber amplifier relative to the 1018 nm fiber laser pumped one. Furthermore, according to the simulation results, a fiber laser operating at 1007.7 nm with the output power of ∼170 W and a slope efficiency of ∼72.90% was experimentally demonstrated. By applying this fiber laser in tandem pumping a 1080 nm fiber amplifier with different gain fiber lengths, improved performance was acquired in comparison with the 1018.6 nm tandem pumping scheme, the experimental results of which were coherent with the simulation results. This work could provide an effective approach for improving the nonlinearity threshold of tandem-pumped fiber amplifiers and paving the way for higher output power.

Experimental investigation of a high-power 1018 nm fiber laser using a 20/400 μm ytterbium-doped fiber

A 472 W monolithic fiber laser, operating at 1018 nm by employing an active fiber with a low core/cladding diameter ratio of 20/400 μm, is reported in this paper. The slope efficiency and beam quality factor (M²) of the fiber laser are, respectively, 49.4% and 1.17. To realize the setup, the effects of the characteristics of the experimental elements-reflectivity of the output coupling fiber Bragg grating, length of the active fiber, etc.-on the output behavior of the system have been investigated. These are the highest recorded output signal power, efficiency, and beam quality factor in monolithic 1018 nm ytterbium-doped fiber lasers using fibers with a core/cladding diameter ratio of 20/400 μm.

Laser micromachining of periodic surface radius change on the optical fiber circumference

In this paper, we are showing that holes and marking spots with sizes that are comparable to the wavelength of a CO₂ laser at λ=10.6  μm can be achieved reproducibly on a conventional optical fiber SMF28 when it is positioned at the focal point. Some theory on Gaussian beam propagation is briefly reviewed and readily applied to drill a fiber on its axis near the focal point. As the fiber was moved from the focal point, it was found that some features, such as ridges along the fiber circumference, were also micromachined by the laser. It was demonstrated that the fabrication of surface nanoaxial photonic fibers, long-pitch grating fibers, and pump laser strippers can be envisaged on a conventional SMF28 with a cladding diameter of 125 μm.

87-W 1018-nm Yb-fiber ultrafast seeding source for cryogenic Yb: yttrium lithium fluoride amplifier

We demonstrate a compact and robust Yb-fiber master-oscillator power-amplifier system operating at 1018 nm with 2.5-nm bandwidth and 1-ns stretched pulse duration. It produces 87-W average power and 4.9-μJ pulse energy, constituting a powerful seed source for cryogenically cooled ultrafast Yb: yttrium lithium fluoride (Yb:YLF) amplifiers.

Efficient 240W single-mode 1018nm laser from an Ytterbium-doped 50/400µm all-solid photonic bandgap fiber

Lowering the quantum defect by tandem pumping with fiber lasers at 1018nm was critical for achieving the record 10kW single-mode ytterbium fiber laser. Here we report the demonstration of an efficient directly-diode-pumped single-mode ytterbium fiber laser with 240W at 1018nm. The key for the combination of high efficiency, high power and single-mode at 1018nm is an ytterbium-doped 50μm/400μm all-solid photonic bandgap fiber, which has a practical all-solid design and a pump cladding much larger than those used in previous demonstrations of single-mode 1018nm ytterbium fiber lasers, enabling higher pump powers. Efficient high-power single-mode 1018nm fiber laser is critical for further power scaling of fiber lasers and the all-solid photonic bandgap fiber can potentially be a significant enabling technology.

1018 nm Yb-doped high-power fiber laser pumped by broadband pump sources around 915 nm with output power above 100 W

We demonstrate a 1018 nm ytterbium-doped all-fiber laser pumped by tunable pump sources operating in the broad absorption spectrum around 915 nm. In the experiment, two different pump diodes were tested to pump over a wide spectrum ranging from 904 to 924 nm by altering the cooling temperature of the pump diodes. Across this so-called pump wavelength regime having a 20 nm wavelength span, the amplified stimulated emission (ASE) suppression of the resulting laser was generally around 35 dB, showing good suppression ratio. Comparisons to the conventional 976 nm-pumped 1018 nm ytterbium-doped fiber laser were also addressed in this study. Finally, we have tested this system for high power experimentation and obtained 67% maximum optical-to-optical efficiency at an approximately 110 W output power level. To the best of our knowledge, this is the first 1018 nm ytterbium-doped all-fiber laser pumped by tunable pump sources around 915 nm reported in detail.

High-power 1018 nm ytterbium-doped fiber laser with output of 805 W

This Letter presents a high-power 1018 nm ytterbium-doped fiber laser (YDFL) with optimized parameters. A record output power reaching 805 W was achieved, along with a light-to-light efficiency of 64.9% and a beam quality factor of M²=1.80. Further, a higher efficiency of 82.8% of 1018 nm YDFL pumped by wavelength-stabilized laser diodes for the first time, to the best of our knowledge, was shown. At last some attempts were made in bidirectional pumping structure. In this Letter, all the measured spectra showed strong amplified spontaneous emission suppression, and the power curves indicated the potential for further power scaling.

CO2 laser-fabricated cladding light strippers for high-power fiber lasers and amplifiers

We present and characterize a simple CO₂ laser processing technique for the fabrication of compact all-glass optical fiber cladding light strippers. We investigate the cladding light loss as a function of radiation angle of incidence and demonstrate devices in a 400 μm diameter fiber with cladding losses of greater than 20 dB for a 7 cm device length. The core losses are also measured giving a loss of <0.008±0.006  dB/cm. Finally we demonstrate the successful cladding light stripping of a 300 W laser diode with minimal heating of the fiber coating and packaging adhesives.

Core-pumped single-frequency fiber amplifier with an output power of 158 W

Single-frequency laser sources at a wavelength of 1 μm are typically scaled in power with Ytterbium-doped double-clad fiber amplifiers. The main limitations are stimulated Brillouin scattering, transversal mode instabilities and, from a technical point of view, the degree of fiber integration for a rugged setup. Addressing these limitations, we propose an alternative high-power single-frequency amplifier concept based on core pumping. A nonplanar ring oscillator with 2 W of output power at 1 kHz spectral linewidth was scaled by a fiber amplifier up to a power of 158 W without any indication of stimulated Brillouin scattering-using a standard Ytterbium-doped single-mode fiber with a mode field area of only ∼100  μm². A short active fiber length and a strong temperature gradient along the gain fiber yield to efficient suppression of stimulated Brillouin scattering. For deeper understanding of the Brillouin scattering mitigation mechanism, we studied the Brillouin gain spectra with a Fabry-Perot interferometer at different output power levels of the fiber amplifier.