Linearization signal conditioning circuit for tri-axial micro-grating MOEMS accelerometer.

This paper proposes what we believe to be a novel linearization signal conditioning circuit for a tri-axial micro-grating micro-opto-electro-mechanical systems (MOEMS) accelerometer. The output of a micro-grating accelerometer varies as a sine/cosine function of the acceleration. The proposed circuit utilizes a subdivision interpolation technique to process these nonlinear intensity variations and render a linear digital output across the full range. Such a linearization circuit was achieved through a 90-degree phase-shift circuit, high-precision DC bias-voltage and subdivision interpolation circuits to reduce the influence of phase, magnitude, and offset errors of the sine-cosine signals on the interpolation factor, improving the resolution and accuracy of acceleration detection. Experimental results demonstrated that the micro-grating MOEMS accelerometer achieves a resolution of sub-mg, cross-axis errors of 3.57%, 1.22% and 0.89% for x-, y- and z-aixs, respectively. The bias instabilities and velocity random walks for the vertical and lateral accelerometer are superior to 26 µg and 38.7 µg/√Hz. The tri-axial micro-grating MOEMS accelerometer exhibits significant potential for applications requiring high sensitivity and large operation ranges, including the automotive industry and military equipment.

Micro-opto-electro-mechanical gyroscope based on the Talbot effect of a single-layer near-field diffraction grating.

We demonstrate a novel, to the best of our knowledge, micro-opto-electro-mechanical system (MOEMS) gyroscope based on the Talbot effect of a single-layer near-field diffraction grating. The Talbot effect of an optical grating is studied both theoretically and experimentally. A structure of grating-mirror combination, fabricated by the micro-nano processing method, is used for out-of-plane structure detection. The detection of a weak Coriolis force is realized by using the highly sensitive displacement characteristic of Talbot imaging of near-field diffraction with a mirror mass block and single-layer grating. The experimental results show that, the micro-displacement detection sensitivity can reach up to 0.09%/nm, and the MOEMS gyroscope can be moved in the driven direction, with a resonant frequency of 7048 Hz and a quality factor of 700, which indicates great potential of the Talbot effect in developing novel high-performance micro-gyroscopes.

Single-detecting-path high-resolution displacement sensor based onself-interference effect of a single submicrometer grating.

On the basis of the self-interference effect between ±1 st-order diffraction beams from a single optical submicrometer grating, we demonstrate a single-detecting-path optical displacement sensor with high resolution. Using a quadrant optoelectronic detector, a single-detecting-path system without any wave plates is realized experimentally. Combined with an interpolation circuit, we demonstrate the system for displacement measurement within a range of 200 µm. The results indicate a detecting sensitivity of 905.4°/µm and an accuracy of ±1.9µm. It is worth mentioning that, considering a maximum subdividing factor of 9674 used in experiment, the resolution goes down to 41.1 pm in principle. We demonstrate a compact optical sensor with high resolution, which is promising in developing miniaturized displacement systems.

High-precision microdisplacement sensor based on zeroth-order diffraction using a single-layer optical grating.

A high-precision microdisplacement sensor based on zeroth-order diffraction of a single-layer optical grating is reported. Laser grating interference occurs when part of the laser is reflected diffraction by the grating and another part is vertically reflected back by a mirror and diffracted again by the grating, thus generating optical interferometric detection. For the purpose of obtaining the optimal contrast of the optical interferometric detection, the duty cycle of the grating and the orders of diffraction were optimized by the diffraction scalar theory. The microdisplacement sensor demonstrates a sensitivity of 0.40%/nm, a resolution of 0.6 nm, and a full-scale range of up to 100 µm. This work enables a high-performance displacement sensor, and provides a theoretical and technical basis for the design of a displacement sensor with an ultracompact structure.

Large-scale range diffraction grating displacement sensor based on polarization phase-shifting.

A method is proposed and demonstrated to improve a diffraction grating displacement sensor to simultaneously achieve nanometer-level resolution and an extended range of operation. The method exploits the polarization phase-shifting optical path to extract two sinusoidal signals with a quadrature phase shift. The interpolation circuit is applied to nonlinearly convert two sinusoidal signals into a standard incremental AB quadrature digital signal, implementing an extended operation range with the magnitude of a laser coherence length. This work enables displacement measurement operated at large-scale range, and provides a significant guide for the design of a high performance micro-displacement sensor.

Spectropolarimetric measurement based on a fast-axis-adjustable photoelastic modulator.

A fast-axis-adjustable photoelastic modulator (Faa-PEM) is developed and studied, and a spectropolarimetric imaging method using the Faa-PEM and an acousto-optic tunable filter is presented. The Faa-PEM modulation retardation amplitude and fast-axis direction of the Faa-PEM can be adjusted by adjusting the two drives with no mechanical rotation. The I, Q, and U of the Stokes parameters of the incident light can be obtained by adjusting the retardation amplitude and fast-axis direction of the Faa-PEM. This measurement method does not require high-frequency components, and thus a general area array detector can realize the measurement. Theoretical simulation analyses show that the relative errors ΔI/I, ΔQ/Q, ΔU/U, and ΔDoLP/DoLP are less than 5.6% and that the deviation error ΔAoLP is less than 0.2° (at I=1.00, Q=0.707, U=0.707, V=0.0, -0.1°≤Δθ0≤0.1°, and -0.05 rad≤Δδ0≤0.05 rad). A prototype was developed and tested. The test results show that the average absolute relative error of the degree of linear polarization is 0.36%, and the average absolute deviation error of the angle of linear polarization is 0.048°. The method has potential application value in spectropolarimetric imaging technology.