Diffractive optical lens design and fabrication for integrated monitoring of microelectromechanical lateral comb resonators

Abstract

Analysis of fault characteristics and control of microelectromechanical systems (MEMS) is becoming increasingly important as these devices are incorporated into safety critical systems. Mechanically decoupled monitoring techniques are needed to ensure that accurate, low-noise positional information is gathered from these devices during operation. Optical monitoring has been shown by various groups to be capable of achieving this goal. However, Integrated Optical Monitoring (IOM) must be achieved in order to enable incorporation with the MEMS die in a single package for effective lifetime system monitoring. This research addresses the design, fabrication and testing of diffractive optical elements (DOEs) for achieving IOM.. DOEs for on and off-axis single and multiple beam generation are modeled based on a linear optical system model paraxial gaussian beam theory. The DOEs are generated using a MATLAB tool that was completed as part of this work to calculate the desired input wave, output wave, and transfer function. This data is then used to generate a phase lens profile with an etch depth that is dependent on the material that will be used for lens fabrication. DOEs are fabricated on a borosilicate substrate and testing of the lenses is performed using a beam profiler to determine the number, shape and power of the probe beams for comparison with the results from the simulated lenses. Experimental DOE test results compare well with those obtained from the modeling tool validating the use of the DOE design tool and the fabrication process for subsequent research implementing IOM architectures.

Characterization of diffractive optical lenses for use in MEMS integrated optical monitoring

“…Previous work [1,2,3] in our group has dealt with MEMS devices, particularly lateral comb resonators. These devices are 300um long, 100um wide, and oscillate laterally when excited with an alternating current.…”

“…The inner fingers move side to side because of the voltage difference produced by the AC current on the outer fingers. Current and previous work within our group is concentrated on control, fault detection, and integrated optical monitoring of these MEMS devices [1,2,3]. All of those efforts were intended to increase reliability and robustness of theses systems.…”

“…Previous research [1,2,3] in the area of integrated diffractive lenses by our group has lead to the modeling, design, and fabrication of Fresnel diffractive optical elements. Below is an image of the proposed on-axis lens scheme [1].…”

“…Previous research [1,2,3] in the area of integrated diffractive lenses by our group has lead to the modeling, design, and fabrication of Fresnel diffractive optical elements. Below is an image of the proposed on-axis lens scheme [1]. The on-axis lenses are 800 um 2 and designed to focus a 5 um laser spot to and from the sample, have focal ranges from 1 to 5 mm, be fabricated using photolithography techniques, and operate at the 633nm wavelength of the vibrometer system.…”

Diagnosis of operational changes in microelectromechanical systems via fault detection

“…Proposed optical/electrical test package[75] From the illustration it can be seen that the package consists of an optical substrate to which a MEMS can be attached.The Diffractive Optical Elements (DOEs) are fabricated on the bottom of the substrate while the gold electrical connections are fabricated on the top side. The design and fabrication of the integrated lenses is published in the Master's Thesis of William McCormick [75].…”