Athermal synchronization of laser source with WDM filter in a silicon photonics platform

In an optical interconnect circuit, microring resonators (MRRs) are commonly used in wavelength division multiplexing systems. To make the MRR and laser synchronized, the resonance wavelength of the MRR needs to be thermally controlled, and the power consumption becomes significant with a high-channel count. Here, we demonstrate an athermally synchronized rare-earth-doped laser and MRR. The laser comprises a Si₃N₄ based cavity covered with erbium-doped Al₂O₃ to provide gain. The low thermo-optic coefficient of Al₂O₃ and Si₃N₄ and the comparable thermal shift of the effective index in the laser and microring cross-sections enable lasing and resonance wavelength synchronization over a wide range of temperatures. The power difference between matched and unmatched channels remains greater than 15 dB from 20 to 50 °C due to a synchronized wavelength shift of 0.02 nm/°C. The athermal synchronization approach reported here is not limited to microring filters but can be applied to any Si₃N₄ filter with integrated lasers using rare earth ion doped Al₂O₃ as a gain medium to achieve system-level temperature control free operation.