Technological challenges for CW operation of small-radius semiconductor ring lasers

En: Semiconductor Lasers and Laser Dynamics II Daan Lenstra, Markus Pessa, Ian H. White. --Strasbourg, FranceTheoretical investigation and device measurements are reported to demonstrate the strict fabrication requirements of small diameter shallow etched semiconductor ring lasers. A very accurate control over the dry etching depth is crucial to both minimise the bending losses and achieve very precise control of the coupling ratio in directional couplers. A reactive ion etching process was developed on Aluminium-quaternary wafer structures, showing selectivity greater than 30 between the AlInAs core layer and the InP upper cladding. The process proved very effective in providing a complete and controllable etching of directional couplers with 500nm wide gaps. Assessment on the effect of the bending losses and on the minimum ring radius was performed through characterisation of half ring lasers. A minimum current threshold of 34mA is reported on 150μm ring radius devices emitting at 1300nm.S.F. would like to acknowledge EPSRC (Engineering and Physical Sciences Research Council, UK) for financial supportPeer reviewe