Ph.D. Oral Exam Announcement: Onur Can Akkaya

Onur Can Akkaya ocakkaya at
Tue Mar 20 15:05:17 PDT 2012

Stanford University Ph.D. Oral Examination – Department of Electrical Engineering 

Title: High-Sensitivity Thermally Stable Interferometric Acoustic Sensors and Optical Sensor Networks for Remote Sensing Applications 

Speaker: Onur Can Akkaya 
Dissertation Advisor: Prof. Olav Solgaard 
Co-Advisor: Prof. Michel J. F. Digonnet 

Date: Wednesday , March 21, 2012 
Time: 3:00 pm (refreshments at 2:45 pm) 
Location: Allen-X Auditorium (formerly CIS-X Auditorium) - Room 101 


Optical sensors have been the key devices in a number of applications, including remote sensing, underwater acoustic communications, oil exploration, surveillance and structural health monitoring for massive aerospace and wind-energy structures. These applications impose critical specifications both on device level and systems level. 

In the first part of my talk, I will introduce a high-sensitivity, thermally stable, compact optical acoustic sensor with a large bandwidth and high dynamic range. The device is based on a photonic-crystal fabricated on a compliant single-crystal silicon membrane, which is placed near the metalized end of a single-mode fiber to form a Fabry-Perot (FP) cavity. We demonstrated high reproducibility in operating wavelength (±1 nm) and fabricated ten FP sensors with measured displacement sensitivities within ±0.3 dB. The response was shown to be polarization independent and thermally stable. We showed that ~130 °C change in temperature can be tolerated before the FP resonance shifts by only 1 nm. The FP interferometer enabled experimental detection of 4.5x10 -14 m/√Hz membrane displacement. An experimental sensor was shown to measure acoustic pressures down to a record low of 5.6 µPa/√Hz with a flat-band response greater than 8 kHz and a sensitivity extending down to at least 100 Hz. The dynamic range in pressure was greater than 100 dB. I will present an electromechanical model of the device as a tool for designing and optimizing this micro-physical structure. This analytical model enabled the analysis of the coupled parameters of the design on the device response and noise. Results are shown to be in very good agreement with the experimentally measured quantities. 

In the second part, I will present the design of a time-division-multiplexed optical sensor network architecture employing multiple low-gain erbium-doped fiber amplifiers. Using this architecture, I will demonstrate an experimental system with ten acoustic sensors multiplexed and interrogated with a single laser source at a single wavelength. The signal-to-noise-ratio for each sensor response was measured to be within ±0.95 dB of the nominal value. I will also present the system performance in terms of cross-talk and polarization dependence. Finally, I will introduce a model identifying the noise contributions in this complex system, which predicts that up to 350 sensors can be multiplexed with this new multiplexing architecture. 

Onur Can Akkaya 
Ph.D. Candidate, Dept. of Electrical Engineering 
Center for Nanoscale Science and Engineering 
Stanford University, CA 

Email: ocakkaya at 

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