A 10W Miniaturized Fiber-Coupled Laser Diode System for Pumping of Fiber Lasers*

In recent years, the significance of the high-power micro-sized fiber-coupled laser diode (FCLD) system has grown considerably, serving as a vital pumping source for fiber lasers. The demand for high efficiency and brightness with a single-wavelength pump source in fiber laser has led to significant attention on the high-power FCLD system, renowned for its reliability, compactness, high electro-optical efficiency, symmetrical energy distribution, and high pointing stability. In addition to these features, high-power FCLD systems find application in diverse fields such as material processing, optical fiber communication, surface treatment, and illumination. However, the primary limiting factor that degrades the performance of the FCLD system is the different cross-section of laser diode (LD) output beam and multimode fiber (MMF).  The cross-section of the laser beam is elliptical, with different beam divergence angles in the fast-axis and slow-axis, whereas the cross-section for the MMF is circular in shape.

In the present work, the design of an efficient FCLD system as a high-energy laser source is proposed. FCLD technology aims to create a high-intensity beam spot by converting the elliptical beam emitted from LD into a circular shaped beam. The proposed system consists of toric lenses to reconstruct the wavefront in the fast axis and slow axis, respectively. Based on the beam collimation and mode-matching method, the output of a 10 W single-emitter laser diode is coupled into the MMF. The designed micro-sized system produces an output power of 9.5 W through an optical fiber having a numerical aperture (NA) of 0.22 with core diameter of 200 µm. The suggested design of miniaturized FCLD system involving toroidal surfaces is highly advantageous over the spherical optics to obtain an enhanced coupling efficiency by reducing the optical aberrations.