Fenfei Liu

Sub-pg mass sensing and measurement with an optomechanical oscillator

Mass sensing based on mechanical oscillation frequency shift in micro/nano scale mechanical oscillators is a well-known and widely used technique. Piezo-electric, electronic excitation/detection and free-space optical detection are the most common techniques used for monitoring the minute frequency shifts induced by added mass. The advent of optomechanical oscillator (OMO), enabled by strong interaction between circulating optical power and mechanical deformation in high quality factor optical microresonators, has created new possibilities for excitation and interrogation of micro/nanomechanical resonators. In particular, radiation pressure driven optomechanical oscillators (OMOs) are excellent candidates for mass detection/measurement due to their simplicity, sensitivity and all-optical operation. In an OMO, a high quality factor optical mode simultaneously serves as an efficient actuator and a sensitive probe for precise monitoring of the mechanical eigen-frequencies of the cavity structure. Here, we show the narrow linewidth of optomechanical oscillation combined with harmonic optical modulation generated by nonlinear optical transfer function, can result in sub-pg mass sensitivity in large silica microtoroid OMOs. Moreover by carefully studying the impact of mechanical mode selection, device dimensions, mass position and noise mechanisms we explore the performance limits of OMO both as a mass detector and a high resolution mass measurement system. Our analysis shows that femtogram level resolution is within reach even with relatively large OMOs.

Thermo-optomechanical oscillator for sensing applications

We demonstrate a thermo-optomechanical oscillator based on high-Q optical resonance and study its application in sensing. The unique bifrequency oscillation that carries the signature of local thermo-optic and global thermo-mechanical effects is analyzed and characterized.

Mass Sensing With Optomechanical Oscillation

We demonstrate the application of optomechanical oscillator (OMO) as a high-resolution mass sensor. Preliminary experimental results and theoretical analysis show that the optomechanical oscillator can function as a low-power mass sensor with sub-pg sensitivity.

Characterization of Optomechanical RF frequency Mixing/Down-Conversion and its Application in Photonic RF Receivers

We have characterized the process of radio-frequency (RF) frequency mixing and signal down-conversion in radiation pressure driven optomechanical RF oscillators. We have studied the dependence of the optomechanical mixing process on RF frequency, optical pump power and wavelength detuning and verified the existence of a linear regime where down-converted power is proportional to the RF input power. These outcomes show that optomechanical oscillator (OMO) has the potential to be used as frequency down-converter in RF over fiber links and photonic RF receivers. We have verified the fidelity of the optomechanical down-conversion process and demonstrated the first optomechanical voice down-conversion from an RF carrier.

Application of dynamic line narrowing in resonant optical sensing.

We propose a dynamic operational mode and the resulting dynamic line narrowing as a method for enhancing the resolution and the detection limit of high-quality (high-Q) resonant optical sensors. Using a silica microtoroid as an experimental platform, we demonstrate that dynamic line narrowing through the thermo-optic effect can significantly improve the detection limit in both resonant shift and resonance splitting operating modes.

On the Performance of High-

We study the performance of multiring-based optical filters in the presence of resonant frequency mismatch among the microrings induced by fabrication error, optical absorption, and nonlinear optical effects, as well as in the context of silicon-on-insulator technology. A general framework is developed to evaluate the worst-case impact of fabrication error and input power on the performance of a bandpass multiring optical filter with Butterworth response.

Q

We characterize the mass sensing properties of microtoroidal optomechanical oscillator (OMO). We show a record sensitivity slope of 1300 Hz/pg and study the impact of mass distribution, mode selection and noise on mass sensitivity.

Multiring Optical Filters

We demonstrate the application of an optomechanical oscillator (OMO) as a high-resolution mass sensor. The coupling between high-Q optical and mechanical modes of a single optical microcavity results in narrow linewidth mechanical oscillation driven by the radiation pressure of the circulating optical power. The oscillation frequency can be monitored upon detection of the modulated transmitted optical power. Therefore the optical wave plays a dual role as both the driving power and a sensitive probe. The narrow oscillation linewidth, combined with the sensitivity of the mechanical resonance to mass changes, makes OMO an excellent candidate for all-optical mass sensing. Experimental results and theoretical analysis show that OMO can function as a compact, low-power mass sensor with sub-pg sensitivity.

On the performance and sensitivity limit of mass sensing with optomechanical oscillation

We study the performance of integrated multi-ring optical filters in the presence of fabrication and power induced resonant frequency mismatch (RFM) among the microrings particularly in the context of silicon-on-insulator technology.

Mass sensing with optomechanical oscillation

We have studied the generation of harmonics and the resulting RF frequency mixing properties in optomechanical oscillators (OMOs). Preliminary results and theoretical analysis show at small detuning regime OMO functions as square-law frequency mixer