Fiber-coupled laser systems for high-power and high-brightness applications

Fiber-coupled systems based on broad-area multimode emitters require complicated optical trains in order to transform their poor quality output beam into a usable form. Recently, Nuvonyx has reported implementations of a single spatial mode, high-brightness laser diode bar with significantly improved beam quality. These laser bars represent a broad technology platform at the core of many Nuvonyx systems. The low output divergence of these devices enables efficient coupling into a 400 mm core, 0.22 numerical aperture fiber with a single focusing lens. Larger systems using stacks of high-brightness diode laser bars can achieve greater than 1.7 kW output from this same fiber size, corresponding to a power density level exceeding 1.4 MW/cm 2 . The high-brightness bars reported here are compatible with techniques for achieving high spatial or spectral brightness. Using external feedback elements such as a volume Bragg grating, the output spectrum can be narrowed to less than 0.25 nm and is stabilized to dλ/dI = 4 pm/A and dλ/dT = 2 pm/°C. Using spectral beam combination, a single high brightness bar can be coupled into a 100 mm core, 0.22 NA fiber with approximately 90% efficiency.