Wang Mingkang, Perez-Morelo Diego J, Aksyuk Vladimir
Microsystems and Nanotechnology Division, National Institute of Standards and Technology, Gaithersburg, MD 20899 USA.
Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, MD 20742 USA.
Microsyst Nanoeng. 2021 Jul 7;7:52. doi: 10.1038/s41378-021-00281-y. eCollection 2021.
Advances in integrated photonics open up exciting opportunities for batch-fabricated optical sensors using high-quality-factor nanophotonic cavities to achieve ultrahigh sensitivities and bandwidths. The sensitivity improves with increasing optical power; however, localized absorption and heating within a micrometer-scale mode volume prominently distorts the cavity resonances and strongly couples the sensor response to thermal dynamics, limiting the sensitivity and hindering the measurement of broadband time-dependent signals. Here, we derive a frequency-dependent photonic sensor transfer function that accounts for thermo-optical dynamics and quantitatively describes the measured broadband optomechanical signal from an integrated photonic atomic force microscopy nanomechanical probe. Using this transfer function, the probe can be operated in the high optical power, strongly thermo-optically nonlinear regime, accurately measuring low- and intermediate-frequency components of a dynamic signal while reaching a sensitivity of 0.7 fm/Hz at high frequencies, an improvement of ≈10× relative to the best performance in the linear regime. Counterintuitively, we discover that a higher transduction gain and sensitivity are achieved with lower quality-factor optical modes for low signal frequencies. Not limited to optomechanical transducers, the derived transfer function is generally valid for describing the small-signal dynamic responses of a broad range of technologically important photonic sensors subject to the thermo-optical effect.
集成光子学的进展为使用高品质因数纳米光子腔的批量制造光学传感器带来了令人兴奋的机遇，以实现超高灵敏度和带宽。灵敏度随着光功率的增加而提高；然而，在微米级模式体积内的局部吸收和加热会显著扭曲腔共振，并将传感器响应与热动力学强烈耦合，限制了灵敏度并阻碍了宽带时间相关信号的测量。在这里，我们推导了一个考虑热光动力学的频率相关光子传感器传递函数，并定量描述了来自集成光子原子力显微镜纳米机械探针的测量宽带光机械信号。使用这个传递函数，该探针可以在高光功率、强热光非线性区域中运行，准确测量动态信号的低频和中频分量，同时在高频下达到0.7 fm/Hz的灵敏度，相对于线性区域的最佳性能提高了约10倍。与直觉相反，我们发现对于低信号频率，使用较低品质因数的光学模式可以实现更高的转换增益和灵敏度。该推导的传递函数不限于光机械换能器，通常适用于描述受热光效应影响的各种技术上重要的光子传感器的小信号动态响应。
