Thermally Tuned High-Performance III-V/Si₃N₄ External Cavity Laser

Silicon nitride (Si ₃ N ₄ ) has a higher nonlinear threshold compared to silicon, which reduces the effect of two-photon absorption. However, the low thermo-optic coefficient and the reduced refractive index contrast of thin Si ₃ N ₄ waveguides lead to a low thermal tuning speed and low thermal efficiency. This paper demonstrates a widely tunable III-V/Si ₃ N ₄ hybrid-integrated external cavity laser with a relatively faster switching time. The Si ₃ N ₄ external feedback circuit is based on 800-nm-thick Si ₃ N ₄ waveguides with an optical confinement factor of 87%. It allows the reduction of the oxide under-cladding layer thickness to 4 μm and the oxide upper-cladding layer to 1.7 μm without additional loss. The switching time between two non-adjacent lasing wavelengths is 60.7 μs. The maximum output power is 34 mW under 500 mA injection current. The side mode suppression ratio is more than 70 dB over the tuning range of 58.5 nm. The laser intrinsic linewidth is 2.5 kHz.