Broadly Tunable Laser Using Double-Rings Vertically Coupled to a Passive Waveguide

A widely tunable laser source based on double microrings is presented which exhibits tuning range up to 46 nm. Two microrings consisting of active GaInAsP/InP material are vertically coupled with a straight transparent waveguide using full wafer bonding techniques. Wafer bonding allows the fabrication of ultra short couplers where the critical coupling gap can be epitaxially controlled. The microrings are operated above threshold and act as laser sources forming a coupled cavity system. Their respective radii are chosen to be slightly different, greatly extending the coupled cavity free spectral range (FSR) providing sufficiently high mode suppression ratio ( MSR > 30 dB). The isolation of adjacent rings allows an individual electrical control and enables a wavelength tuning with pm accuracy. The tuning mechanism benefits from the Vernier effect resulting in a broad range of achievable wavelengths in a systematic and repeatable way.