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Research On Mechanisms Of Control Of Light Speed And Their Applications In Optical Devices

Posted on:2013-08-20Degree:DoctorType:Dissertation
Country:ChinaCandidate:P LiaoFull Text:PDF
GTID:1228330374499571Subject:Electromagnetic field and microwave technology
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The optical packet switching network is the necessary tendency of the future high-speed optical network, which not only can completely overcome the electronic bottleneck, but also has a lot of advantages such as ultra-high speed, transparency, flexibility and large capacity. All-optical buffer and all-optical switch, which have dominant effect on the performance of the switching and routing, have been considered as key components for the optical packet switching network. Slow light effect can control the group velocity of light and enhance the nonlinear interaction, which can be used to realize optical devices such as all-optical buffer, switching and routing. So far, it has attracted widespread attention in the area of optical commutation networks, optical computation, and microwave technology. We theoretically investigate the phenomenon of slow and fast light based on electromagnetically induced transparency and coherent population oscillations, as well as some all-optical devices based on slow light. The major contributions of this paper can be summarized as follows:1) The effect of the relative phase on the group velocity of light in a close-loop two-level system with coherent population oscillation and four wave mixing effects is investigated theoretically. It is found that the phase can be used to modify the absorption-dispersion characteristic of the system. This striking behavior is the result of coherence interference between two contributions of coherent population oscillation and four wave mixing effects. In addition, the control role of the relative phase on the group index is investigated. It is shown that by modifying the value of the phase, the group velocity of light can be adjusted and the transition from subluminal propagation to superluminal propagation can also be achieved. Furthermore, the effect of the parameters such as the coupling field and the propagation length on the group velocity is analyzed. This phase-dependent slow and fast light can provide a new mechanism to realize tunable optical buffer and all-optical switch.2) We theoretically propose a scheme of phase-controlled all-optical switching due to the effect of degenerate four-wave mixing (FWM) and coherent population oscillation (CPO) in a two-level system driven by a strong coupling light and two weak symmetrically detuned lights. The analytical results show that the phase of the FWM light can be utilized to switch between constructive and destructive interference, which can lead to the transmission or attenuation of the probe light and thus switch the light on or off. The simulation results also verify the feasibility of this scheme and analyze the performance of the switching quantitatively. In addition, effect of inhomogeneous broadening on the switching is studied in detail. The results show that inhomogeneous broadening can’t wash out the switching effects. Therefore, due to the quick response in semiconductor systems, a fast all-optical switching can be realized at low light level. Finally, a possible experiment is presented.3) We theoretically propose a scheme of polarization selective tunable photonic bandgap based on electromagnetically induced transparency, in the first case, a tripod-type system driven by a weak linearly polarized probe light and a π-polarized standing-wave control light is studied. The results show that double photonic bandgaps can be obtained at two different frequencies due to Zeeman splitting induced by an external magnetic field. This allows us to selectively manipulate the components of the probe light, which exhibits polarization selective features. In the second case, the atom is initially prepared in the superposition of two degenerate ground states. This atomic coherence makes the medium exhibit linear birefringence phenomenon. Similarly, a linear polarization selective photonic bandgap can be obtained. Owing to the tunable bandgaps, these peculiar features can be employed to devise schemes for a polarization beam splitter, polarization selective routing and signal extraction.4) We theoretically propose a scheme of a phase grating based on coherent population trapping in a tripod-type system. Due to atomic coherence and quantum interference, the system shows a high refractive index without absorption and a dark state. With a intensity mask in one of the driving optical fields, the refractive index of the medium is periodically modulated with vanishing absorption. Thus, a perfect phase grating can be obtained, which can effectively diffract light into the high-order direction. In addition, atomic coherence can cause the amplification of the probe light. In this region, a hybrid grating can be created with diffraction efficiency enhanced. This grating is simple, tunable and has high diffraction efficiency, which has potential application in all-optical communication.
Keywords/Search Tags:control of light speed, slow and fast light, electromagnetically induced transparency, coherent populationoscillations, all-optical buffer, all-optical switch, electromagneticallyinduced photonic bandgap, electromagnetically induced grating
PDF Full Text Request
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