Self-injection locking dynamics with Raman actions in AlN microresonators

Abstract

Self-injection locking (SIL) of semiconductor lasers to on-chip microcavities enables significant laser noise purification and diverse nonlinear optical actions. Realizing nonlinear SIL in new material platforms is essential for advancing photonic integrated circuits. Here, we demonstrate nonlinear SIL in AlN microcavities that generates stimulated Raman lasers (SRLs) and microcombs. We achieve SRL emission with an output power exceeding 10 mW and a fundamental linewidth below 70 Hz in the 1750 nm band. The Kerr effect further mediates stimulated emissions at the 2nd-Stokes and anti-Stokes frequencies. Multi-time-scale thermal relaxations during turnkey SIL enable GHz-level frequency sweeps of the SRL and pump. Raman actions also render a Stokes platicon microcomb state with co-emission in the pump and Stokes bands. Hybrid-integrated crystalline microresonators can be a versatile platform to investigate nonlinear photon-phonon interactions.

Figures (4)

• Figure 1: (a) Picture of a DFB laser butt-coupled to the AlN photonic chip. The false color highlights the used microcavities. (b) Optical spectrum of the SIL-SRL. (c) Single sideband frequency noise spectra of the free-running pump (yellow), SIL pump (blue), and SRL (purple). The gray dashed line is the simulated thermo-refractive noise (TRN) for the AlN microcavity, and the green curve is the relative frequency noise between the pump and the SRL.
• Figure 2: (a) Optical spectra when pumping the AlN microcavity with a pump power of 20.8 mW and 51.3 mW, respectively. The diagrams illustrate the generation dynamics for the anti-Stokes (AS) and 2nd-Stokes (2S) emissions via the Kerr effect. (b) Measured SRL power and its square-root fit. (c) Measured AS power changes for the AS and 2S emissions and their fits.
• Figure 3: (a) Measured pump and SRL power when turning on/off the pump laser by square waves. (b) SRL interference signal measured by a Mach-Zehnder interfereometer. (c) Frequency change of the pump and SRL during the turnkey operation. Five thermal relaxation processes are used to fit the measured frequency change. The inset shows the ratio between $\delta\nu_{\rm R}$ and $\delta\nu_{\rm P}$, which is close to $m_{\rm P}/m_{\rm R}$. (d) Simulated frequency change and effective detunings for the pump and SRL. (e) Measured magnitude of frequency change of for the pump and the SRL under different pump powers. The solid lines corresponds to linear fits.
• Figure 4: (a) Measured and simulated platicon microcomb with comb lines emerging in the Raman band. The inset shows the simulated comb generation dynamics. (b) A platicon microcomb without the Raman band lines generated by tuning the laser-to-chip phase delay $\phi_B$. (c) Simulated platicon waveforms with (upper) and without (bottom) the Raman band lines.