Modeling and Design of Diffraction Gratings for Optically-Read Vibration Sensors

Friday, September 23, 2016
4:00 p.m. in ETC 4.150


Randall P. Williams, PE

Department of Mechanical Engineering, and
Microelectronics Research Center
The University of Texas at Austin
http://www.mrc.utexas.edu

Displacement detection using optical interferometric techniques allows for high sensitivity and low sensor self-noise which are unmatched by other displacement measurement methods. However, diffraction gratings commonly used in such applications can generate zeroth-order reflected beams which result in reduced sensor performance and packaging limitations. A new grating concept has been designed, fabricated, and tested at the UT Microelectronics Research Center which has a reduced zeroth-order reflected beam, opening the doors for new sensor integration approaches. The design criteria for zeroth-order beam elimination is illustrated using a simple model based on phasor arithmetic, and Fourier propagation techniques are used to model the optical field for realistic grating geometries and incident beam profiles. Important insight into the behavior of the sensor is gained for a range of different operating conditions, which commonly used grating models often fail to capture. Finally, comparisons between the models and experimental measurements on prototypes gratings will be presented and discussed.