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We report on the experimental realization of two different low-loss single- to multimode fiber coupler designs, each combining more than 5 kW of output power. The adiabatic mode evolution in the seven-fiber input bundle provides a brightness close to its theoretical maximum. The all-glass structures exhibit very low heat loads mainly due to small avoidable contamination, indicating room for improvement. To the best of our knowledge, regarding all-fiber geometrical combined power generation, beam quality and heat stability, the presented results had never been reported before.

To further decrease feature sizes, the semiconductor industry heavily improved the photolithography. Photoresist layers are exposed through photomasks and structured accordingly. The underlying substrate is then selectively altered by adding or subtracting material. The unrivaled precision, resolution, and accuracy allow an unmatched level of miniaturization, and several thousand electrical components can be processed simultaneously. This technology was expanded to the fabrication of sensors and actuators, creating microelectromechanical systems. With silicon, the possibilities of further expanding this technology to new dimensions and applications are limited. Reasons are the stiffness, 2.5-D fabrication, and lack of optical transparency. To enable new applications, we present the successful translation of wafer-level fabrication to millimeter-scale actuators. This was achieved by changing the material to ultraviolet (UV)-curable polymers. Based on the electrostatic zipper actuator, avoiding the common pull-in-effect is essential for the successful realization of an acceptable microactuator. Therefore, the bottom electrodes are split and shaped to adjust the generated electrostatic forces, balancing the mechanical restoring forces. Besides the theoretical design, the fabrication technology based on classic photolithography is explained. Experimental results include voltage-dependent deflection measurements, achieving 110- $\mu $ m deflection with 70 V driving voltage. The dynamic response measurements show resonance frequencies of 1.89 kHz. [2014-0181]

We review the technique of incoherent beam combining and show experimentally the combination of four continuous wave fiber amplifiers to an average power of 2 kW and four pulsed 2 ns fiber amplifiers to an average power of 187 W (pulse energy 3.7 mJ) using binary dielectric gratings. The scaling potential and limitations are discussed in detail.

The first rare-earth-doped fiber lasers were operated in the early 1960s, and produced a few milliwatts at a wavelength around 1 mu m [1], 12]. Since the beginning of the decade, an enormous increase of fiber laser output power has been reported, the realm of kilowatt power has been entered, and power levels as high as 100 kW are envisaged. Apart from the power, fiber laser systems are renowned for their inherent compactness, monolithic architecture, and a power-independent beam quality. This paper reviews the challenges, achievements, and perspectives of highpower continuous-wave (CW) laser generation and amplification in fibers.