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Title:Non-linear optical properties of semiconductor nano-structures for slow light and wavelength conversion
Author(s):Nielsen, David C.
Director of Research:Chuang, Shun-Lien
Doctoral Committee Chair(s):Kwiat, Paul G.
Doctoral Committee Member(s):Chuang, Shun-Lien; Eckstein, James N.; Hubler, Alfred W.
Department / Program:Physics
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):quantum dots
four-wave mixing
slow light
fast light
wavelength conversion
Abstract:The use of semiconductor nanostructures for all-optical signal processing is investigated. We first examine theoretically the utilization of quantum dots for wavelength conversion via four-wave mixing. Our results show that quantum dots with only a single bound state are more efficient than both quantum wells and quantum dots with a large number of excited states. We compare experimentally quantum dots and quantum wells with results which are consistent with our theoretical analysis. We measure the small-signal conversion of both single and multiple optical channels, and compare the results to cross-gain modulation in the same device. Our results show that four-wave mixing provides efficient, high-speed wavelength conversion in up to four, independent channels, and at speeds up to 40 GHz. Using a pulsed laser, we also examine the signal-to-noise ratio for the converted signal with our measurements showing an excellent signal to noise ratio and no patterning effect for a 25 ps pulse. To examine the theoretical limit of four-wave mixing for short pulses, we perform numerical calculations using the finite-difference beam propagation method in both a quantum dot and quantum well semiconductor optical amplifier. These calculations indicate that the quantum dot device performs better at the powers and speeds of relevance to telecommunications, but that the faster spectral hole relaxation rate of quantum wells allows for more efficient conversion of pulses less than 1 ps. We then examine how the cross-gain modulation response of the device can be increased and demonstrate that an additional pump field can create a cavity mode in the device which suppresses carrier oscillations and extends the XGM bandwidth from 1 GHz to greater than 25 GHz. Finally, we look at using a cavity mode for the purpose of slow- and fast-light and theoretically demonstrate that a fast- to slow-light transition occurs at the lasing threshold. These results compare well with previous measurements, and we present our own experimental investigations utilizing both a distributed-feedback laser and a ring laser. Utilizing a ring laser, we are able to achieve a delay bandwidth product of 10 for a 10 ps pulse in a single semiconductor device.
Issue Date:2010-05-19
Rights Information:Copyright 2010 David Nielsen
Date Available in IDEALS:2010-05-19
Date Deposited:May 2010

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