Easily-wavelength-locked high-efficiency coupler-free external cavity spectral beam combining for diode lasers

In this manuscript, we propose a coupler-free external cavity spectral beam combining (SBC) structure, where the -1st-order and 0th-order diffracted beams are utilized as feedback, allowing wavelength locking of all emitters to be readily achieved without multiple round-trips feedback required in a conventional coupler-free SBC structure. The combined beam is output along the 1st-order diffraction direction of the grating. Using the structure, we demonstrated a combined beam with an output power of 58.30 W, a combining efficiency of 82.80%, a spectral bandwidth of 21.12 nm, and beam quality factors of M_x² = 1.56 and M_y² = 11.99, approaching those of a single emitter. Compared with conventional coupler-free and closed-loop SBC structures, the proposed scheme improved the combining efficiency by 3.09% and 3.54%, respectively. This work presents an SBC structure featuring high combining efficiency and easy wavelength locking, offering a promising route for SBC of diode lasers.