Graduation Year

2015

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Electrical Engineering

Major Professor

Scott Samson, Ph.D.

Co-Major Professor

Sanjukta Bhanja, Ph.D.

Committee Member

Shekhar Bhansali, Ph.D.

Committee Member

Paris H. Wiley, Ph.D.

Committee Member

Wilfrido A. Moreno, Ph.D.

Keywords

electrostatic actuators, evanescent waves, Michelson interferometry, packaged MEMS chip, scattering microstructures, unattended sensors

Abstract

This dissertation presents a free-space, long-range, passive optical communication system that uses electrostatically modulated microelectromechanical systems (MEMS) structures coupled with a glass total internal reflection (TIR)-type corner cube retroreflector (CCR) as a non-emitting data transmitter. A CCR consists of three mirrors orthogonal to each other, so that the incident beam is reflected back to the incident beam, source. The operational concept is to have a MEMS modulator fusion with TIR CCR, such that the modulators are working periodically to disrupt the evanescent waves at the air interface of one of the three back glass faces of a TIR CCR. The MEMS chip has two primary components: (1) an array of movable light scattering silicon structures with nano roughness and (2) a glass lid with a transparent conductive indium tin oxide (ITO) film. The MEMS structures are bonded to a glass lid using flip-chip bonding. Once bonded, the MEMS structures can be modulated either toward or away from the glass lid, thus disrupting evanescent energy delivered from a probing laser beam. The MEMS structure is precisely bonded to the TIR CCR with an accuracy of 10-30 arc-seconds using a Michelson interferometry feedback system. This is a novel step by which an existing passive commercial CCR can be converted into a modulating active CCR. This CCR-MEMS unit acts as the key element of the transmitter. To illustrate the concept of a low-power, unattended, sensor-monitoring system, we developed a sensor board containing temperature, humidity, and magnetic sensors along with a microprocessor and other electronics. The sensor board and CCR board are packed together and act as the transmitter unit. We developed a benchtop system and an improved portable receiver system. The receiver system contains the laser (as source), a collimating lens (to collect retroreflected signal), an optical, narrow band pass filter, and a detector. The detector signal was amplified and filtered and sent either to the oscilloscope, a lock-in-amplifier, or a laptop to display the sensor data. Using the receiver system, a sensor-CCR-based transmitter unit, and receiver with 635 nm as source, we achieved retroreflective communication over a distance of 300 m.

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