Fundamental-transverse-mode ridge waveguide laser chips were recleaved to form C3 lasers with a single-longitudinal-mode output stabilised at a fixed wavelength over a wide range of drive currents and temperature. Lasers operated at 1.55 μm at a bit rate of 2 Gbit/s with on-off ratios greater than 10:1 and side-mode suppression greater than 1200:1. A simple method for mapping the stable operating regime is described.