VCSELs have various applications in different fields, including datacom, optical interconnects, printers, and sensors. However, VCSEL technology has not been applied in laser material processing that needs a light source with high power density. This is because single-mode (SM) VCSELs have fundamental difficulty in producing beams having an output power of more than several milliwatts. On the contrary, the application range of VCSEL amplifiers is expected to be extended into fields that simultaneously require lasers with high power and high beam quality because they have the potential to attain both characteristics.
In this paper, we demonstrate the CW operation of high-power SM 2 mm to 1 cm long VCSEL amplifiers that had an output power of several watts at 20 °C. By optimizing the top-mirror reflectivity and seed-laser wavelength, the output power was linearly proportional to the amplifier length when the growth of amplified spontaneous emission (ASE) was suppressed. The I–L characteristics for different amplifier lengths were measured. All devices emitted narrow beams with divergence angles of approximately 0.1°. The maximum SM output power of the devices with lengths of 2 mm, 6 mm, and 1 cm were 0.62, 2.13, and 3.25 W, respectively. This result shows the possibility to achieve high power and high beam quality for direct semiconductor laser processing.