A light beam can be split such that one beam travels a longer distance than the other. When these split beams are recombined, the light interferes – creating either constructive or destructive interference, depending on the difference in path length. This principle of optical interferometry can be used to measure extremely small displacements or motions of a vibrating surface; in fact, interference of light waves has long been the most sensitive way to measure small displacements in nature.
At Silicon Audio, we harness the sensitivity and fidelity of optical sensing in a robust package using novel, microscale architectures free of critical alignment tolerances. We combine semiconductor light sources, diffractive optical elements, and photo-detection electronics to realize readout systems with sub-angstrom displacement detection resolution. In microphone applications, the displacement of a membrane is measured as it deforms under sound pressure. In seismic applications, the displacement is that of a proof mass responding to small vibrations of the earth’s surface. In all cases, the result is a sensor with unprecedented detection fidelity.
Our core competency in building an optical interferometer calls upon expertise in low-noise, low-power analog electronics, closed-loop control systems, and advanced optical modeling routed in both scalar and full vector wave models.
Silicon Audio reworked the reliable, traditional geophone to include an optical interferometer, resulting in a scientific-grade seismometer that can withstand the demands of exploration deployment.
By integrating an optical interferometer in a MEMS microphone, Silicon Audio achieved superior SNR in an ultra-miniature size.
B. Bicen, S. Jolly, K. Jeelani, C. T. Garcia, N. A. Hall, F. L. Degertekin, S. Quang, C. Weili, and R. N. Miles, "Integrated Optical Displacement Detection and Electrostatic Actuation for Directional Optical Microphones with Micromachined Biomimetic Diaphragms," IEEE Sensors Journal, vol. 9(12), pp. 1933-1941, December 2009.
R. N. Miles, Q. Su, W. Cui, M. Shetye, F. L. Degertekin, B. Bicen, C. Garcia, S. Jones, and N. Hall, "A Low-Noise Differential Microphone Inspired by the Ears of the Parasitoid Fly Ormia Ochracea," The Journal of the Acoustical Society of America, vol. 125(4), pp. 2013-2026, April 2009.
N. A. Hall, M. Okandan, R. Littrell, D. K. Serkland, G. A. Keeler, K. Peterson, B. Bicen, C. T. Garcia, and F. L. Degertekin, "Micromachined Accelerometers with Optical Interferometric Read-Out and Integrated Electrostatic Actuation," Journal of Microelectromechanical Systems, vol. 17(1), pp. 37-44, February 2008.
R. Littrell, N. A. Hall, M. Okandan, R. Olsson, and D. Serkland, "Impact of Relative Intensity Noise of Vertical-Cavity Surface-Emitting Lasers on Optics-Based Micromachined Audio and Seismic Sensors," Applied Optics, vol. 46(28), pp. 6907-6911, October 2007.
F. L. Degertekin, A. G. Onaran, M. Balantekin, W. Lee, N. A. Hall, and C. F. Quate, "Sensor for Direct Measurement of Interaction Forces in Probe Microscopy," Applied Physics Letters, vol. 87(21), p. 213109, November 2005.
W. Lee, N. A. Hall, and F. L. Degertekin, "A Grating-Assisted Resonant-Cavity-Enhanced Optical Displacement Detection Method for Micromachined Sensors," Applied Physics Letters, vol. 85(15), pp. 3032-3034, October 2004.
W. Lee, N. A. Hall, Z. Zhou, and F. L. Degertekin, "Fabrication and Characterization of a Micromachined Acoustic Sensor with Integrated Optical Readout," IEEE Journal of Selected Topics in Quantum Electronics, vol. 10(3), pp. 643-651, May-June 2004. – Invited paper.
N. A. Hall, W. Lee, and F. L. Degertekin, "Capacitive Micromachined Ultrasonic Transducers with Diffraction-Based Integrated Optical Displacement Detection," IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, vol. 50(11), pp. 1570-1580, November 2003.
N. A. Hall and F. L. Degertekin, "Integrated Optical Interferometric Detection Method for Micromachined Capacitive Acoustic Transducers," Applied Physics Letters, vol. 80(20), pp. 3859-3861, May 2002.
W. Cui, B. Bicen, N. Hall, S. A. Jones, F. Degertekin, and R. N. Miles, "Optical Sensing In a Directional Memsmicrophone Inspired by the Ears of the Parasitoid Fly, Ormia Ochracea," in 19th IEEE International Conference on Micro Electro Mechanical Systems, Istanbul, Turkey, 2006, pp. 614-617.
N. A. Hall, R. O. Guldiken, J. McLean, and F. L. Degertekin, "Modeling and Design of CMUTs using Higher Order Vibration Modes [Capacitive Micromachined Ultrasonic Transducers]," in 2004 IEEE Ultrasonics Symposium, Montreal, Canada, 2004, vol. 1, pp. 260-263.
W. Lee, N. Hall, and F. L. Degertekin, "Micromachined Acoustic Sensor Array with Diffraction-Based Optical Interferometric Detection," in MOEMS Display and Imaging Systems, San Jose, CA, 2003, vol. 4985, pp. 140-151.
N. A. Hall, W. Lee, J. Dervan, and F. L. Degertekin, "Micromachined Capacitive Transducers with Improved Optical Detection for Ultrasound Applications in Air," in 2002 IEEE Ultrasonics Symposium, Munich, Germany, 2002, vol. 2, pp. 1027-1030.
F. L. Degertekin, N. A. Hall, and W. Lee, "Capacitive Micromachined Ultrasonic Transducers with Integrated Optoelectronic Readout," in 2001 IEEE Ultrasonics Symposium, Atlanta, GA, 2001, vol. 2, pp. 875-881. – Invited Paper.
F. L. Degertekin and N. Hall, "Micromachined Microphone with Optical Interferometric Readout," in 2001 IEEE International Symposium on Circuits and Systems, Sydney, NSW, Australia, 2001, vol. 2, pp. 177-180.
N. A. Hall, and F. L. Degertekin, "Self-Calibrating Micromachined Microphones with Integrated Optical Displacement Detection," in TRANSDUCERS '01. EUROSENSORS XV. 11th International Conference on Solid-State Sensors and Actuators. Digest of Technical Papers, Munich, Germany, 2001, pp. 118-121.
N. Hall and F. L. Degertekin, "An Integrated Optical Detection Method for Capacitive Micromachined Ultrasonic Transducers," in 2000 IEEE Ultrasonics Symposium, San Juan, Puerto Rico, 2000, vol. 1, pp. 951-954.