[Paper Review] Design and Fabrication of a Differential MOEMS Accelerometer Based on Fabry Perot micro-cavities

Mojtaba Rahimi, Mohammad Malekmohammad+3 more|arXiv (Cornell University)|Mar 1, 2022

Advanced Fiber Optic Sensors27 references34 citations

TL;DR

This paper presents a differential micro-opto-electro-mechanical systems (MOEMS) accelerometer using dual Fabry-Pérot (FP) micro-cavities on a silicon-on-insulator wafer via bulk micromachining. The device measures proof mass displacement via optical interference, with differential detection doubling sensitivity. Experimental results show 6.52 nm/g optical sensitivity, 153 µg resolution, and 49.6 mV/g electrical sensitivity in dynamic mode, with a resonant frequency of 1372 Hz over a ±1g range.

ABSTRACT

In this paper, a differential MOEMS accelerometer based on the Fabry-Perot (FP) micro-cavities is presented. The optical system of the device consists of two FP cavities and the mechanical system is composed of a proof mass that is suspended by four springs. The applied acceleration tends to move the PM from its resting position. This mechanical displacement can be measured by the FP interferometer formed between the proof mass cross-section and the optical fiber end face. The proposed sensor is fabricated on a silicon on insulator (SOI) wafer using the bulk micromachining method. The results of the sensor characterization show that the accelerometer has a linear response in the range of 1g. Also, the optical sensitivity and resolution of the sensor in the static characterization are 6.52 nm/g and 153ug. The sensor sensitivity in the power measurement is 49.6 mV/g and its resonant is at 1372 Hz. Using the differential measurement method increases the sensitivity of the accelerometer. Based on experimental data, the sensor sensitivity is two times as high as that of a similar MOEMS accelerometer with one FP cavity.

Motivation & Objective

• To overcome the sensitivity-range trade-off in FP-based MOEMS accelerometers.
• To enhance sensitivity using a differential measurement approach with two opposing FP cavities.
• To develop a compact, integrated, and mass-producible accelerometer with high optical and electrical sensitivity.
• To demonstrate high linearity and resolution in both static and dynamic characterization over a ±1g range.

Proposed method

• The accelerometer uses a proof mass suspended by four springs, enabling movement along the Y-axis.
• Two Fabry-Pérot micro-cavities (C1 and C2) are formed between the proof mass sidewall and optical fiber end-faces.
• Differential detection compares the spectral shifts of C1 and C2, which change oppositely under acceleration, doubling the effective sensitivity.
• Optical sensing uses intensity monitoring at 1550 nm, with tunable filters selecting central wavelengths (1547.2 nm and 1551.9 nm) for linear response.
• Finite-difference time-domain (FDTD) simulations model light propagation and optimize cavity parameters.
• The sensor is fabricated using a straightforward bulk micromachining process on a silicon-on-insulator (SOI) wafer.

Experimental results

Research questions

• RQ1 Can a differential FP cavity configuration improve the sensitivity of MOEMS accelerometers beyond single-cavity designs?
• RQ2 How does the differential measurement method affect the optical and electrical sensitivity in a ±1g acceleration range?
• RQ3 What is the achievable resolution and linearity of the sensor in static and dynamic modes?
• RQ4 To what extent does the fabricated sensor’s performance exceed that of existing MOEMS accelerometers in sensitivity and footprint?

Key findings

• The sensor achieves an optical sensitivity of 6.52 nm/g in static mode, which is twice that of a single-cavity MOEMS accelerometer.
• The resolution is 153 µg, calculated from the BraggMETER precision (1 pm) and optical sensitivity.
• In dynamic mode, the electrical sensitivity reaches 49.6 mV/g, confirming the differential method doubles sensitivity compared to single-cavity systems.
• The resonant frequency is 1372 Hz, slightly differing from simulation due to fabrication tolerances.
• The sensor exhibits a linear response across the ±1g measurement range in both static and dynamic tests.
• The footprint is 4 × 3 mm², with a fully integrated, compact, and mass-producible design using bulk micromachining.