M.Sc Thesis


M.Sc StudentVolodarsky Oleg
SubjectHigh Power Pulse Interferometry for Low-Noise Optical
Detectors of Ultrasound
DepartmentDepartment of Electrical and Computer Engineering
Supervisor ASSOCIATE PROF. Amir Rosenthal
Full Thesis textFull thesis text - English Version


Abstract

Optical detectors of ultrasound are an enabling technology in the field of optoacoustic imaging, which can achieve levels of miniaturization beyond those of conventional piezoelectric detectors. Nonetheless, the sensitivity of optical detectors still falls short of their piezoelectric counterparts in most practical scenarios and their scale-up to multi-element arrays is challenging. This research is dedicated to the development of an interferometric technique for lownoise detection of ultrasound, called pulse interferometry (PI), which can potentially enable both low-noise operation and scalability. Two PI systems have been developed: In the first, two modifications were introduced to PI scheme, a pulse stretcher for reducing nonlinear effects and noise reduction was demonstrated by using a custommade free-space Fabry-Perot cavity to filter out amplified spontaneous emission from source, leading to shot-noise-limited detection for a spectral band of 80 nm and for optical powers up to 5 mW. In the second, burst-mode capabilities were added in order to further increase the optical power to compensate for the expected power loss per channel in when interrogating multiple sensing element simultaneously. Acoustic sensitivity measurements were conducted in scenarios emulating the interrogation of 20 to 200 elements, achieving up to 25-fold increase in sensitivity in the burst-mode operation and noise levels down to 50 Pa, sufficient for many optoacoustic imaging applications.