Event

Ph.D. Dissertation Defense: Pape M. Sylla

Thursday, December 4, 2008
2:00 p.m.
Room 2460, AVW Building
Maria Hoo
301 405 3681
mch@umd.edu

ANNOUNCEMENT: Ph.D. Dissertation Defense

NAME: Pape M. Sylla

COMMITTEE: Prof. Julius Goldhar, Chair

Prof. Christopher C. Davis

Prof. Thomas E. Murphy

Dr. Marshall Saylor

Prof. Wendell T. Hill III (Dean’s Representative)

DATE/TIME: Thursday, December 4, 2008 at 2:00pm

LOCATION: Room 2460, A.V. Williams building

TITLE: Quantum Noise in Optical Parametric Amplifier Based on Lossy Nonlinear Interferometer

ABSTRACT:

Optical Parametric Amplifier (OPA) has been of wide interest the past decades due to their potential for low noise amplification and to generate squeezed light. However, the existing OPA for fiber optics application are based on Kerr medium and require kilometers of fiber to be effective.

In this thesis, using classical physics, we derive the gain of a lossless Kerr medium based nonlinear Mach-Zehnder Interferometer (NMZI OPA). Using Quantum optics, we derive the noise of a Kerr medium based OPA with lossless Kerr medium and show that the noise figure is roughly 0.

However, since in real life Kerr medium are lossy, using quantum optics, we derive the dynamic evolution of a wave inside a lossy Kerr Medium. The derivation shows the parametric amplification that takes place in the Kerr Medium and the noise that is generated as a result of loss. We then integrate that result in the analysis of a Kerr medium based OPA to get the parametric gain, the noise and the noise figure. We show that the noise figure has a simple expression as a function of loss coefficient and length of the Kerr Medium and that an early expression by a different research group is not accurate.

To simplify the procedure, we derive an estimate for Noise figure for OPAs in high gain regime. We then derive the dynamic evolution of a wave inside Kerr Medium with gain. From this and with the help of our estimate, we derive the parametric gain and the noise figure for a Kerr medium based NMZI OPA with gain. We show that the noise figure is also a very simple expression based on gain coefficient and length.

Given the length of fiber needed for a Kerr medium based NMZI OPA, we substitute it with a different nonlinear medium, namely a Saturable Absorber (SA). We could have used a Semiconductor Optical Amplifier (SOA). However, research from a different group has shown that the device is prohibitively noisy . Using a quantum mechanical atomic 3 level system model and the Heisenberg evolution equation, we derive the dynamic evolution in time for a single mode coherent wave in a saturable absorber. From this we get the differential equations describing the time evolution of the wave and the time evolution of the absorption coefficient. We then solve the differential equation to find the average absorption coefficient of the SA, the and the amplitude noise as well as the phase noise of the wave after being through the saturable absorber. The results are then used to get the noise figure of the SA based NMZI OPA.

Audience: Graduate  Faculty