Efficient semiconductor ring lasers made by a simple self-aligned fabrication process

We present what we believe is the highest efficiency and lowest threshold current density ever reported for semiconductor ring resonator lasers. Ring lasers are interesting components, e.g. for fiber-to-the-home systems, because they can readily be integrated and their very simple fabrication process, which is discussed and compared with other common approaches, does not require overgrowth or the fabrication of high-precision gratings. An asymmetric coupler geometry has been tested that leads to a further increase in efficiency, but is more sensitive to changes in the input field than the symmetric equivalent