Absolute Deflection Measurements in a Micro- and Nano-Electromechanical Fabry-Perot Interferometry System

Area of Science:

• Physics
• Mechanical Engineering
• Materials Science

Background:

• Fabry-Perot laser interferometry is a standard technique for analyzing micro- and nano-electromechanical systems (MEMS/NEMS).
• Current methods rely on the substrate as a reference mirror, encoding device motion in reflected laser power.
• Existing calibration approaches can be limited by material properties and geometric constraints.

Purpose of the Study:

• To develop a general and robust calibration method for optical systems interrogating MEMS/NEMS.
• To enable direct measurement of the system's transfer function by utilizing optical nonlinearity.
• To provide a calibration scheme independent of MEMS/NEMS material and geometry.

Main Methods:

• Utilized large-amplitude motion exceeding half the laser wavelength to exploit optical nonlinearity.
• Developed a method for direct measurement of the motion-to-detected-voltage transfer function.
• Experimentally validated the technique on silicon nitride and silicon cantilevers, including spatial mapping of deflections.

Main Results:

• Successfully measured vibration amplitudes and equilibrium position changes in MEMS/NEMS devices.
• Demonstrated spatial mapping of static and dynamic deflection profiles, validated against optical profilometry.
• Extended the calibration to small-amplitude linear regimes and frequency-domain measurements using a lock-in amplifier.

Conclusions:

• The presented calibration scheme is material and geometry independent.
• The method effectively negates nonlinear optical transduction effects.
• Enables accurate assessment of excitation forces and MEMS/NEMS material properties through precise vibrational response measurement.