Background Since the breakthrough in blue laser diode chips, blue lasers have found extensive applications in welding, cutting, and material processing, owing to their high material absorptivity and superior photon energy. In particular, fiber-coupled laser diodes offer enhanced reliability and practicality.

Purpose To achieve high power and high brightness, spectral beam combining (SBC) is considered an effective and mature technology. Therefore, there is a critical need to develop narrow-linewidth, tunable lasers that can serve as high-quality sub-beams for SBC, as narrower linewidths allow for a larger number of combining channels. Traditional spectral locking approaches, primarily based on volume Bragg gratings (VBG), distributed Bragg reflectors (DBR), and distributed feedback (DFB) lasers, are hindered by the inability to achieve continuous wavelength tuning. To overcome this limitation, we employ a Littrow-configuration planar grating as the wavelength-selective element to enable both spectral narrowing and continuous tuning.

Methods Using a single emitter with a 5 W output power and a 45 μm stripe width as the fundamental light-emitting unit for semiconductor laser fiber coupling, a "7+7" configuration was adopted for spatial multiplexing along the fast axis and polarization combining along the slow axis.

Results Optical and structural designs were carried out to achieve a power output exceeding 50 W, with a fiber core diameter of 50 μm and a numerical aperture (NA) of less than 0.2. A planar grating was placed behind each emitter as the spectral control element, and a Littrow-type structure was utilized for mode and spectral selection along the slow axis, yielding a spectral tuning range of over 5 nm and a locked linewidth of under 0.5 nm (FWHM, full width at half maximum).

Conclusions Compared with spectral locking methods such as VBG and DBR, this approach offers enhanced spectral controllability, enabling both narrow linewidth operation and continuous wavelength tuning. This light source can therefore function as a high-quality sub-beam for high-brightness blue-light spectral beam combining, providing valuable technical support for the development of high-brightness blue light sources.