Simultaneous frequency stabilization, wavelength multiplexing and improvement of beam quality using a self-optimizing external cavity diode laser

The combination of a dense wavelength division multiplexer based on volume Bragg gratings (VBGs) and a subsequent feedback mirror forms an efficient single-stage frequency stabilization and multiplexing system. The laser emission of the connected diode laser sources is automatically forced to amplify the wavelengths with the maximum feedback and the minimum losses, respectively. Therefore, different transversal modes of a single emitter may be linked to different wavelength regions that fulfill the Bragg conditions of the VBGs with high efficiency. We demonstrate a multiplexing system with a channel spacing of 1.5 nm and an optical efficiency of 86%, up to 90% being feasible with modifications. The emission bandwidth of the diode laser single emitters is reduced to <300 pm. Due to transversal mode selection, the lateral beam quality factor M-2 of the single emitters decreases by a factor of 1.4 on average, compared to the free running sources.