High-power Fiber Laser Sources Research Articles

The effect of in-source spatial beam shaping on the laser welding of e-mobility metals and alloys

Electromobility applications require several welded connections using demanding materials often in dissimilar combinations. Copper, aluminium, or steel alloys are laser welded for energy storage and traction related components. On the one hand, high power fiber laser sources provide in-source beam shaping solutions able to modify the irradiance profile towards ring-shaped beams. On the other hand, research focused on the effect of the beam shapes on the melting mechanisms and process quality is still in progress. This work studies the effect of different beam profiles on AISI301LN, AA6082 and pure Cu with a 5 kW fiber laser. Linear trends of power over penetration depth as a function of speed confirms the validity of employing the lumped heat capacity model for ring-shaped beams. Moreover, the specific melting fluence is observed to exhibit an exponential decaying trend with the proportion of power allocated in the fiber core, irrespective of tested material.

Real-time complex amplitude reconstruction method for beam quality M2 factor measurement.

We present a real-time complex amplitude reconstruction method for determining the beam propagation ratio M2 of laser beams based on the transport of intensity equation (TIE). In this work, a synchronous acquisition system consisting of two identical CCDs is established. Once two beam intensity images at different cross-section positions along the optical axis are captured simultaneously by the system, the complex amplitude of the laser beam can be rapidly reconstructed using TIE algorithm. Then the beam intensity distribution at any section position along its propagation direction can be obtained by using angular spectrum (AS) theory. The beam quality M2 factor is therefore calculated utilizing the second-order moments and hyperbola fitting methods, which conform to the ISO standard. The suitability of this method is verified by the numerical analysis and experiments with the He-Ne and high-power fiber laser sources, respectively. The experimental technique is simple and fast, which allows to investigate laser beams under conditions inaccessible to other methods.

A Novel Technique for Designing High Power Semiconductor Optical Amplifier (SOA)-Based Tunable Fiber Compound-Ring Lasers Using Low Power Optical Components

A simple, stable and inexpensive dual-output port widely tunable semiconductor optical amplifier (SOA)-based fiber compound-ring laser structure is demonstrated. This unique nested ring cavity enables high optical power to split into different branches where amplification and wavelength selection are achieved by using low-power SOAs and a tunable filter. Furthermore, two Sagnac loop mirrors, which are spliced at the two ends of the compound-ring cavity not only serve as variable reflectors but also channel the optical energy back to the same port without using any high optical power combiner. We propose and discuss how the demonstrated fiber compound-ring laser structure can be extended in order to achieve a high power fiber laser source by using low power optical components, such as N × N couplers and (N > 1) number of SOAs. A coherent beam-combining efficiency of over 98% for two parallel nested fiber ring resonators is achieved over the C-band tuning range of 30 nm. Optical signal-to-noise ratio (OSNR) of +45 dB, and optical power fluctuation of less than ±0.02 dB are measured over three hours at room temperature.

A Review of Recent Development of Efficient High-Power Continuous- Wave Er-Yb Codoped Fiber Amplifiers

Abstract: In this paper, we will review the recent developments of high-power continuous-wave (CW) Er-Yb codoped fi-ber amplifiers (EYDFAs). Several related patents and a couple of methods of improving the performance of high-power EYDFAs are reviewed. Current research results show that the Yb-band amplified spontaneous emission (Yb-ASE) is the main reason that limits the efficiency and stability of an EYDFA at high pump power. Several methods and experimental results dedicated to suppress the Yb-ASE are introduced. Current and potential future developments of high-power EYD-FAs are summarized in the last part of this paper. Keywords: Erbium, fiber amplifiers, fiber lasers, MOPA, ytterbium 1. INTRODUCTION High-power fiber laser sources in the 1.5-μm band have made a great progress in recent years. Due to their many advantages, such as relatively eye-safe nature, low atmos-phere transmission loss, light weight, low loss in communi-cation fibers, and readily available reliable and cost-effective fiber communication components, they are of great potential for both military and civilian applications, such as laser in-frared radars (LIDARs), free-space communications, mate-rial processing and so on [1-3]. To flexibly control the linewidth, wavelength, and beam quality of a high-power fiber laser source, a master-oscillator power-amplifier (MOPA) configuration is commonly used. In this configuration, the master-oscillator generates a low-power high beam quality seed, and then the seed is amplified through several stages of power-amplifier until the desired output power is achieved. Apparently, the available power and performance of a MOPA system is largely determined by the performance of the power-amplifier(s). The details of the MOPA configuration will be introduced in the next sec-tion. In the 1.5-μm band high-power MOPAs, double-clad erbium-ytterbium codoped fibers (EYDFs) are usually used as the gain media of the power-amplifier. This fiber has an inner cladding surrounding the core and its refractive index is lower than the core but larger than the outer cladding [4]. The cross-sectional shape of the inner cladding is usually non-circular, which can enhance the mode mixing to pro-mote the pump absorption [5].

High-Power Fiber Lasers

The brightness, robustness, and flexibility of high-power fiber laser sources provide an enabling technology for science and industry.