With the expanding application of high-end fiber lasers across various fields, limitations related to mass, size, heat dissipation, and power consumption have become increasingly prominent in priority areas such as scientific research. There is a corresponding growing demand for fiber-coupled modules that are compact, lightweight, and possess a high electro-optical conversion efficiency as well as strong environmental adaptability to ensure stable and reliable operation. As a core component of a fiber laser, the fiber-coupled pump source module directly impacts the key performance of the fiber laser. High-end fiber lasers require semiconductor laser pump sources to possess the characteristics of lightweight design, compact form factor, high efficiency, high power output, wavelength locking in a wide temperature range, full current, and good environmental reliability. Therefore, an ideal fiber-coupled pump source should simultaneously incorporate all these characteristics to meet the diverse application requirements of fiber lasers across various scenarios. However, this presents a significant technical challenge, particularly in terms of the power-to-mass ratio, which still has considerable room for improvement. With the iterative upgrade of compact high-energy laser systems, bottlenecks such as output power, electro-optical conversion efficiency, lightweight design, and thermal management have become more pronounced, and breakthroughs are urgently needed to overcome external constraints in the field of research. Currently, traditional optical paths suffer from the issues of slow-axis collimation with long working distances, wasted optical path space, and large volume dimensions. Volume Bragg grating (VBG) wavelength locking causes beam deflection in the collimation direction and expansion along the slow axis, reduces coupling efficiency, and degrades numerical aperture of the output beam. Single-lens coupling suffers from low coupling efficiency due to aberrations. VBG has a high diffraction efficiency but low beam transmission, resulting in high losses and power attenuation that affect the coupling efficiency of the wavelength-locking module.

Optimization of COS (chip on submount) devices based on high-power, high-efficiency 976 nm semiconductor laser chip packaging is needed to further improve the electro-optical conversion efficiency and reduce the slow axis divergence angle at high operating temperatures. Module adopts an optical-mechanical-thermal integrated balance design, brand-new slow-axis beam expansion collimating lens, optimized optical paths of fast-axis collimation, VBG wavelength locking, slow-axis beam expansion collimation, and separated coupling technology for fast and slow axes. At the same time, small-size and low-diffraction-efficiency VBG is used to develop wide-temperature and full-current wavelength locking. Finally,the combined use of all the above techniques makes the module to achieve a high-performance output . The light source is densely arranged, lightweight alloy materials are selected, a compact structure design is adopted, and thermal simulation optimization is performed to develop a lightweight module with a high power-to-mass ratio.

The laser diode (LD) chips are packaged into COS devices to achieve a high-performance output. Through optimization, the electro-optical conversion efficiency at high-temperature operating points is improved by 2% [Figs. 3(a) and (c)], while the slow-axis divergence angle at high-temperature operating points is reduced by 0.5° [Figs. 3(b) and (d)]. Through the opto-mechanical-thermal integration design and simulation, the module size is 105 mm×33 mm×12.2 mm, and the module mass is 75 g [Figs. 11(a) and (b)]. Compared to traditional fiber-coupled modules, the volume is reduced by 60% and the mass is reduced by 70%. The fiber with a core diameter of 135 μm and a numerical aperture of 0.22 achieves a continuous output power of 280 W, an electro-optical conversion efficiency of 55%, a numerical aperture of 0.17, the center wavelength of 976.3 nm, and a spectral width of 0.4 nm [Figs. 12(a) and 12(b)]. The high-performance, lightweight 976 nm wavelength-locked fiber-coupled module developed in this paper has a power-to-mass ratio of 3.7 W/g and a power-to-volume ratio of 6.6 W/cm3.

This paper is based on a high-power, high-efficiency 976 nm semiconductor laser chip with an emitting area width of 190 μm and a cavity length of 4500 μm. At a current of 25 A, the output power reaches 25.5 W, with a voltage of 1.55 V, an electro-optical conversion efficiency of 68%, and a slow-axis divergence angle of 8° for 95% of the energy. The COS device integrates 18 LD chips of 976 nm and features a space-efficient packaging design and a balanced optical-mechanical-thermal integration. It employs slow-axis beam expansion collimating lens, optimized optical paths combining fast-axis collimation, VBG wavelength-locking, and slow-axis beam expansion collimation, and separated coupling technology for the fast and slow axes. Lightweight alloy materials and a compact structural design are selected along with thermal simulation optimization. A high-performance lightweight 976 nm fiber-coupled module is developed, achieving an output power of 280 W at a core diameter of 135 μm, an electro-optical conversion efficiency of 55%, a numerical aperture of 0.17, a center wavelength of 976.3 nm, and a spectral width of 0.4 nm. This achieves a power-to-mass ratio of 3.7 W/g and a power-to-volume ratio of 6.6 W/cm3, providing a stable and reliable laser for applications with constraints on mass, volume, and power consumption.