Single-frequency fiber lasers have drawn intense attention for their extensive applications from high-resolution spectroscopy and gravitational wave detection to materials processing due to the outstanding properties of low noise, narrow linewidth, and the resulting long coherence length. In this paper, the recent advances of single-frequency fiber oscillators and amplifiers are briefly reviewed in the broad wavelength region of 1–3 μm. Performance improvements in laser noise and linewidth are addressed with the newly developed physical mechanisms. The solution to achieving higher power/energy is also discussed, accompanied by the start-of-the-art results achieved to date.

Review of recent progress on single-frequency fiber lasers [Invited]

Lidar imaging systems are one of the hottest topics in the optronics industry. The need to sense the surroundings of every autonomous vehicle has pushed forward a race dedicated to deciding the final solution to be implemented. However, the diversity of state-of-the-art approaches to the solution brings a large uncertainty on the decision of the dominant final solution. Furthermore, the performance data of each approach often arise from different manufacturers and developers, which usually have some interest in the dispute. Within this paper, we intend to overcome the situation by providing an introductory, neutral overview of the technology linked to lidar imaging systems for autonomous vehicles, and its current state of development. We start with the main single-point measurement principles utilized, which then are combined with different imaging strategies, also described in the paper. An overview of the features of the light sources and photodetectors specific to lidar imaging systems most frequently used in practice is also presented. Finally, a brief section on pending issues for lidar development in autonomous vehicles has been included, in order to present some of the problems which still need to be solved before implementation may be considered as final. The reader is provided with a detailed bibliography containing both relevant books and state-of-the-art papers for further progress in the subject.

An Overview of Lidar Imaging Systems for Autonomous Vehicles

In this paper, we report the mode area scaling of a rare-earth doped step index fiber by using low numerical aperture. Numerical simulations show the possibility of achieving an effective area of ~700um2 (including bend induced effective area reduction) at a bend diameter of 32cm from a 35μm core fiber with a numerical aperture of 0.038. An effective single mode operation is ensured following the criterion of the fundamental mode loss to be lower than 0.1dB/m while ensuring the higher order modes loss to be higher than 10dB/m at a wavelength of 1060nm. Our optimized modified chemical vapor deposition process in conjunction with solution doping process allows fabrication of an Yb-doped step index fiber having an ultra-low numerical aperture of ~0.038. Experimental results confirm a Gaussian output beam from a 35μm core fiber validating our simulation results. Fiber shows an excellent laser efficiency of ~81%and aM2 less than 1.1.

Demonstration of ultra-low NA rare-earth doped step index fiber for applications in high power fiber lasers.

Stimulated Raman scattering gives back reflection sensitivity to a high power fiber laser. Therefor SRS suppression is necessary in order to realize stable laser processing by a high power fiber laser. A 5-kW single-mode ytterbium doped fiber laser with a 20-m long delivery fiber has been realized. The fiber laser is an all-fiber single-stage Fabry-Perot system in a co-pumping configuration. The optical to optical efficiency was 80% at the output power of 5.0 kW. And the M-squared figure of 1.3 was obtained. The Stokes light by SRS is suppressed to 45 dB below the laser output by using fibers with the effective mode area of 600 μm2 . While SRS was well suppressed, four wave mixing was observed with the frequency shift of ~6 THz. Four wave mixing between the fundamental mode and the secondary modes is believed to take place. Four wave mixing is believed not to give back reflection sensitivity to the fiber laser. The 5-kW single-mode fiber laser was applied to laser processing. Bead-on-plate tests were carried out with a galvanometer scanner. The laser ran without stopping nor damaging the laser system even during processing highly reflective material. This implies that our SRS suppressed single-mode fiber laser can be used practically in most of processing systems.

5-kW single stage all-fiber Yb-doped single-mode fiber laser for materials processing

Single-mode fiber lasers with excellent beam quality and several-kilowatts output power are expected to realize both extraordinary processing speed and high aspect ratio in the material processing field. In this paper, we report an 8-kW output single-stage Yb-doped fiber laser with a BPP of 0.50 mm-mrad. The laser has a delivery fiber with a length of 3 m. To realize an 8-kW single-mode output without excess a stimulated Raman scattering threshold, fibers with a considerably large effective core area are employed. An ytterbium doped fiber is directly pumped by newly developed high-power laser diode modules with a total available pump power over 10 kW through a bi-directional pumping scheme. The laser has a high slope efficiency of 81%. The power of the SRS light around 1120 nm was 22 dB smaller than the fundamental laser power at 1070 nm. To the best of our knowledge, it is the smallest BPP with more than 8 kW output power pumped by an end-pumping regime. We believe the laser will contributes laser processing using a galvano scanner for high speed and high aspect ratio welding.

8-kW single-stage all-fiber Yb-doped fiber laser with a BPP of 0.50 mm-mrad

The physical and engineering challenges in scaling fiber lasers toward 10kW include 1) avoiding non-linear thresholds, particularly SRS, 2) obtaining sufficient pump brightness, and 3) overcoming thermal issues. The methods to overcome these barriers are reviewed and results >6kW SM are provided. Article not available.

Power Scaling of SM Fiber Lasers toward 10kW

The world’s most powerful laser system for industrial applications would be presented. Ytterbium fiber laser combines record 101.3 kW output power, continuous-wave operational mode and an excellent beam quality. Beam parameter product (BPP) does not exceed 16 mm x mrad, when we use 300 μm x 10 m feeding fiber, or near 25 mm x mrad, when fiber-to-fiber output coupler with 500 μm x 50 m process fiber is used. Emission wavelength is 1070 nm. High wall-plug efficiency 35.4%, compact laser cabinet and total weight less than 3600 kg open the new opportunities in different industrial and mobile applications. Keywords—Lasers, fiber; Infrared and far-infrared lasers

/pdf/100-kw-cw-fiber-laser-for-industrial-applications-i0n7wmyeli.pdf

100 kW CW fiber laser for industrial applications

Summary form only given: We report novel all-fiber concept based on parallel combining of multiple nanosecond pulse fiber lasers by means of fused fiber combiners. The radiation of 19 laser modules was coupled into 500 μm core delivery fiber with BPP equalled to 31.6 mm × mrad. Peak power 0.4 MW and pulse energy 40.5 mJ were achieved. Average power was 4.05 kW within 1064 nm wavelength range.

http://ieeexplore.ieee.org/iel7/6877793/6886200/06886451.pdf

A. Ferin

Papers

Power Scaling of SM Fiber Lasers toward 10kW

100 kW CW fiber laser for industrial applications

Multi-kilowatt average power nano pulse fiber lasers