Azimuthal Gratings Deliver 37.9 dB Side-Mode Suppression in O-Band III-V/Si Quantum Dot Microring Lasers

The arXiv preprint from HP Labs and collaborators details how an inner-wall corrugation imposes angular-momentum selection rules that split degenerate whispering-gallery modes into symmetric and anti-symmetric standing-wave supermodes of unequal loss. Finite-element simulations and devices fabricated on 100 mm SOI wafers confirm that second-order Bragg operation symmetry-protects the high-Q anti-symmetric mode, locking emission to one azimuthal order independent of gain peak. Side-mode suppression reached 37.9 dB with hop-free tuning across factor-of-two changes in cavity loading.

This approach decouples lasing wavelength from quantum-dot gain spectrum, turning detuning into a mask-level design variable that sets minimum-threshold temperature. In data-center contexts it directly addresses the multimode instability that has limited microring lasers in dense WDM transmitter arrays for co-packaged optics. Earlier silicon-photonics efforts, such as those reported in Nature Photonics on hybrid III-V/Si DFBs, required multiple epitaxial regrowth steps; the grating method reduces process complexity while preserving direct-modulation bandwidths above 10 GHz.

Next steps include scaling to 8- or 16-channel arrays on the same mask set and testing reliability under 85 °C/85 % RH conditions. If threshold remains below 2 mA at 60 °C across wafers, the architecture could enter foundry PDKs within three years.

The work is a 2026 arXiv preprint; no peer-reviewed version yet exists.