Design considerations for high-power external cavity laser diodes

Super large optical cavities can give the desired wide vertical near-field (and narrow vertical far-field), which simplify the optics and feedback in an external cavity laser. However, vertical structures support many higher order modes and may suffer from poor modal discrimination. We examine important additional considerations for the design of external cavity diode lasers. An optical trap can reduce the waveguide width and improve modal discrimination, but some higher order modes are still unavoidable. Thus, the laser materials and growth must be carefully optimised to ensure that light coupled back into the laser cannot propagate in these unwanted modes.