Effect of interaction between the internal cavity and external cavity on beam properties in a spectrally beam combined system.

A high-power beam can be achieved in spectrally beam combined systems due to the interaction between internal and external cavities. In order to investigate effects of the coupled cavity on the combined beam, we started with the derivation of the equivalent reflectance and transmittance of the external cavity based on a multilayer dielectric grating (MDG). Then, photons in active regions of diode lasers with/without feedback were calculated by utilizing Lang-Kobayashi rate equations. The results indicate that the lens and the MDG have an obvious impact on both the reflectance and transmittance of the external cavity, which determine whether the photons of a laser with feedback are larger or smaller than those without feedback. The photons of the laser with feedback and the transmittance of the external cavity codetermine the combining efficiency. Impacts of the confinement factor and spontaneous emission factor of diode laser emitters on the coupled cavity are similar to those on a common laser internal cavity. Spectral compositions of the combined beam have different brightness from each other.