Effect of Grating Diffraction Efficiency on Output Coupler Free External Cavity Spectral Beam Combining Structure

The output coupler free external cavity spectral beam combining structure uses the beam along 0-order and 1-order diffraction direction as the feedback light beam to realize the wavelength locking of the emitters, which avoids the waste of 0-order and 1-order diffracted beams, and high beam-combining efficiency can be obtained. The diffraction efficiency of the diffraction grating has an important influence on the beam-combining structure's feedback efficiency and output efficiency. In this paper, the influences of grating diffraction efficiency on the wavelength locking of unpolarized light and the beam combining output efficiency are simulated and analyzed, and the stable wavelength locking of emitters can be achieved when the grating diffraction efficiency is 78.9%-92%. As a result, the highest beam-combining output efficiency can be achieved by using this external cavity spectral beam combining structure with output coupler free.