Graduate Theses, Dissertations, and Problem Reports 2006 Characterization of diffractive optical lenses for use in MEMS integrated optical monitoring Christopher W. Hollandsworth West Virginia University Follow this and additional works at: https://researchrepository.wvu.edu/etd Recommended Citation Hollandsworth, Christopher W., "Characterization of diffractive optical lenses for use in MEMS integrated optical monitoring" (2006). Graduate Theses, Dissertations, and Problem Reports. 1705. https://researchrepository.wvu.edu/etd/1705 This Thesis is protected by copyright and/or related rights. It has been brought to you by the The Research Repository @ WVU with permission from the rights-holder(s). You are free to use this Thesis in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you must obtain permission from the rights-holder(s) directly, unless additional rights are indicated by a Creative Commons license in the record and/ or on the work itself. This Thesis has been accepted for inclusion in WVU Graduate Theses, Dissertations, and Problem Reports collection by an authorized administrator of The Research Repository @ WVU. For more information, please contact [email protected]. CHARACTERIZATION OF DIFFRACTIVE OPTICAL LENSES FOR USE IN MEMS INTEGRATED OPTICAL MONITORING Christopher W. Hollandsworth Thesis submitted to the College of Engineering and Mineral Resources at West Virginia University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE in ELECTRICAL ENGINEERING Dr. Lawrence Hornak, Ph.D., Chair Dr.Parviz Famouri, Ph.D. Dr. Dimitris Korakakis, Ph.D. Lane Department of Computer Science and Electrical Engineering West Virginia University Morgantown, West Virginia 2006 Keywords: MEMS, Optical Monitoring, DOE, Fresnel Lens ABSTRACT THEORY AND CHARACTEREIZATION OF DIFFRACTIVE OPTICAL LENSES FOR USE IN MEMS INTEGRATED OPTICAL MONITORING CHRISTOPHER W. HOLLANDSWORTH Micro Electro Mechanical Machines (MEMS) are finding use in an increasing number of applications. Many of these applications, especially safety critical ones, require continuous knowledge of the operational status of the MEMS device over its lifetime. In-situ monitoring of the operational status of these devices is better suited to optical methods which provide a non-invasive way of continuously determining device position as a function of time. This data is central to determining the MEMS state and operational condition. Whether the optical source is internal to the MEMS package or external to the package and introduced via optical fiber, lenses will be required within the package to focus the MEMS optical probe beam to and from the test device. The need for hybrid co-integration with the MEMS die within its package results in physical dimension and focal length constraints on the lenses used and points toward the applicability of diffractive optical lenses to realize the goal of MEMS in- situ integrated optical monitoring. The spot diameter must be of a width comparable to any lateral displacement that must be measured so that acceptable resolution of the motion can be observed. Diffractive lenses are capable of meeting all of these requirements. Previous work designed and fabricated Fresnel binary phase diffractive lenses in borofloat glass substrates as a means to achieve the required lens function for either a visible (632 nm wavelength) or near IR (1310 nm) probe beam. This work undertakes the full optical characterization of these previously fabricated lenses, compares their performance (spot size, focal length, efficiency) to that expected from theory, and determines if they meet the original lens design criteria, These results enable an initial assessment of these lenses for use in MEMS in-situ lifetime optical monitoring. ACKNOWLEDGMENTS I would like to thank my committee chair Dr. Larry Hornak for his invaluable help and guidance, without which this may not have been possible. I want to thank my committee members Dr. Dimitris Korakakis and Dr. Parviz Famouri. I also want to thank Dr. Kolin Brown for his assistance in the laboratory. My thanks go to the following MEMS group members for their assistance through my work: Afshin Izadian, Deepasree Konduparthi, John Harmon, William McCormick, and Divya Pisharoty. I want to thank my family for their support through this time, especially my fiancé Kelly Showalter for her love, encouragement, and patience. iii Contents Abstract ii Acknowledgements iii Contents iv List of Figures vi List of Tables xi 1 Introduction............................................................................................................................1 1.1 MEMS and Device Monitoring Needs .......................................................................1 1.2 Prior MEMS Work......................................................................................................2 1.3 Previous Integrated Optical Monitoring Work ........................................................3 1.4 Direction and Organization of Thesis ........................................................................7 2 Neutral Density Filter Characterization..............................................................................8 2.1 Test Setup...................................................................................................................8 2.2 Measured Neutral Density Filter Transmission Percentages................................9 2.4 Transmission Through Neutral Density Filters for Non-Normal Incidence .....17 2.5 Point Distortions from Particulate Matter on Filters ..........................................19 3 HeNe Laser Characterization.............................................................................................20 3.1 Gaussian Beam Theory and Gas Lasers..................................................................20 3.1.1 Expression for Gaussian Beam........................................................................21 3.1.2 Beam Intensity ..................................................................................................22 3.1.3 Beam Power.......................................................................................................23 3.1.4 Beam Radius, Divergence, and Depth of Focus .............................................23 3.1.5 Gas Lasers .........................................................................................................25 iv 3.2 Spectral Output .......................................................................................................26 3.3 Waist Location, Waist Size, and Angular Divergence .........................................28 3.4 Pointing Stability.....................................................................................................35 3.5 Power Dissipation Over Distance...........................................................................37 3.6 In-Plane Power Distribution and Beam Shape.....................................................38 4 Borofloat Characterization .................................................................................................44 5 Objective Characterization.................................................................................................48 6 Electromagnetic Propagation and Optical Lens Theory..................................................52 6.1 Ray Theory .................................................................................................................53 6.1.1 Snell’s Law and Law of Reflection..................................................................54 6.2 Wave Theory ..............................................................................................................54 6.3 Interference and Diffraction Theory........................................................................54 6.3.1 Huygens-Fresnel Principle...............................................................................56 6.3.2 Fresnel Zone Plate ............................................................................................58 6.3.2.1 Zone Plate Description ............................................................................58 6.3.2.2 Material Selection and Fabrication Techniques ...................................59 7 DOE Lens Modeling and Design ........................................................................................61 8 Lens Characterization .........................................................................................................62 8.1 Test Setup and Lens Description ...........................................................................62 8.2 Diameter...................................................................................................................66 8.3 Partial Incidence of Laser on Lens ........................................................................67 8.4 Focal Point and Focal Range..................................................................................70 8.5 Multiple Peaks .........................................................................................................72 8.6 Pointing Stability.....................................................................................................73 8.7 Power Loss, Efficiency, and SNR...........................................................................74 v 8.8 In-Plane Power Distribution and Beam Shape.....................................................77 8.9 Visual Inspection