AI 中文总结
本研究在异质集成Si$_3$N$_4$/LiNbO$_3$平台上实现片上$f$-2$f$自参考，通过空间分离超连续谱产生与二次谐波产生，检测到30 dB信噪比的载波包络偏移频率，为低损耗氮化硅光子学提供自参考超快脉冲源方案。
AI 中文摘要
异质集成在单一光子平台上结合了互补的材料特性。在此，我们在异质集成的 Si$_3$N$_4$/LiNbO$_3$ 平台上演示了片上 $f$-2$f$ 自参考，其中 Si$_3$N$_4$ 波导中的超连续谱产生和 LiNbO$_3$ 层中的二次谐波产生在空间上分离，并通过绝热升降耦合器连接。通过 1560 nm 锁模激光器泵浦，片上脉冲能量为 75 pJ，我们在 300 kHz 分辨率带宽内检测到载波包络偏移频率，信噪比为 30 dB。对比测量证实二次谐波源自 LiNbO$_3$ 层，并表明通过周期性极化有进一步改进的机会。这些结果确立了异质 Si$_3$N$_4$/LiNbO$_3$ 集成作为低损耗 Si$_3$N$_4$ 光子学中自参考超快脉冲源的可行构建模块。
英文摘要
Heterogeneous integration combines complementary material properties in a single photonic platform. Here, we demonstrate on-chip $f$-2$f$ self-referencing in a heterogeneously integrated Si$_3$N$_4$/LiNbO$_3$ platform, in which supercontinuum generation in a Si$_3$N$_4$ waveguide and second-harmonic generation in a LiNbO$_3$ layer are spatially separated and linked by adiabatic escalator couplers. Pumped by a 1560 nm mode-locked laser with 75 pJ on-chip pulse energy, we detect the carrier-envelope offset frequency with 30 dB signal-to-noise ratio in 300 kHz resolution bandwidth. A comparative measurement confirms that the second harmonic originates in the LiNbO$_3$ layer and indicates opportunity for further improvements through periodic poling. These results establish heterogeneous Si$_3$N$_4$/LiNbO$_3$ integration as a viable building block for self-referenced ultrafast pulse sources in low-loss Si$_3$N$_4$ photonics.
