We have demonstrated a novel Sagnac loop and micro-ring based laser cavity which is simple and reliable, with accurately controlled reflectivity and negligible excess loss. The resonant wavelength of a 2 μm radius micro-ring is shown to be lithographically controlled to a standard deviation of 3.6 nm. Both C- and O-Band lasers based on Sagnac loop mirror and micro-ring cavity have been demonstrated. The lasers are shown to be able to be modulated at 40 Gb/s.