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Slow Light Effect Of Femtosecond Surface Plasmon Pulse And Group Velocity Control

Posted on:2014-08-24Degree:DoctorType:Dissertation
Country:ChinaCandidate:C L LiFull Text:PDF
GTID:1260330392472581Subject:Optics
Abstract/Summary:PDF Full Text Request
Surface plasmons (SPs), existing in interface of metal and insulator, are specialelectromagnetic field. Owing to the breakthrough of the light diffraction limit, SPsare considered to be potential information carrier of the next generation integratedphotonic circuit. Slow light, that group velocity is far less than light speed invacuum, is potentially applied in delay line, optical storage, improving sensitivity ofinterferometer, and so on. Due to characteristics of SPs and slow light, slow lighteffect of SPs has attracted wide attention. Owing to the strong dispersion ofwaveguide for SPs slow light effects, femtosecond SPs pulse propagating in thewaveguide will distort, which affects the transmission rate and transmission distance.Based on these reasons, we discussed effects of dispersion on the femtosecond SPspulse, slow light effect of SPs and control of group velocity for femtosecond SPspulse. Several methods of controlling group velocity are proposed. The specificworks in this thesis are summarized as follows:First of all, the transmission characteristics of the femtosecond SPs pulse areresearched. Through analyzing effects of loss dispersion on frequency spectrum offemtosecond SPs pulse, the conditions of pulse broadening or narrowing induced byloss dispersion are obtained. Exploiting the one-order Bragg condition, asuperlattice with loss peak at loss dispersion curve is designed to reach the balancebetween pulse broadening induced by group velocity dispersion and pulse narrowinginduced by loss dispersion. This work provides theoretical basis for analyzingbroadening of femtosecond SPs pulse.Secondly, the group velocity control by input pulse width is realized in thesuperlattice containing a defect layer. According to Kramers-Kronig dispersionrelation, waveguide presents a strong normal dispersion effect near the frequencycorresponding to transmission peak, which just meets the condition for SPs slowlight effect. A defect layer is placed into the superlattice, the length of the defectlayer is determined, which makes the frequency corresponding to the superlatticetransmission peak to be193.5THz. The slow group velocity of SPs propagatingthrough the superlattice is confirmed using the transmission matrix theory based on the characteristic impedance method. Due to group velocity difference of SPs withdifferent frequency and frequency spectrum change with pulse width, the groupvelocity control by input pulse width is realized. The results, calculated by themethod of finite-difference time-domain (FDTD), show that group velocitydecreases from0.51c to0.13c with the increasing of input pulse width. In addition,the physical mechanism of pulse broadening is analyzed using the theory of lossdispersion, group velocity dispersion and high-order dispersion.Again, the method of wide range tunable group velocity is proposed to overcomelarge pulse broadening and range limit in method of group velocity control by inputpulse width. Exploiting the FDTD method, the normalized delay bandwidth productis calculated at different period N of Bragg reflector. The value of N is determined toobtain the largest normalized delay bandwidth product, which reduces largelybroadening of SPs pulse propagating in superlattice. The physical mechanism isgiven. Replacing the linear medium with Kerr nonlinear medium, according toFabry-PĂ©rot cavity resonance condition and Kramers-Kronig dispersion relation, theincreasing of SPs electric field intensity leads to wide range change of groupvelocity of SPs pulse with center frequency193.5THz. Changing peak intensity ofinput pulse, the wide range adjustment of group velocity is realized. The resultcalculated by FDTD method shows that group velocity increases from0.24c to0.9cwith the increasing of peak intensity of input pulse.Finally, fine adjustment of SPs pulse group velocity is realized in Kerr nonlinearmedium/metal waveguide. Near to the SPs frequency, Kerr nonlinear medium/metalwaveguide with strong normal dispersion effect leads to group velocity offemtosecond SPs pulse slowing down. Due to group velocity of femtosecond SPspulse changing with relative dielectric constant of Kerr nonlinear medium, thecontrol of group velocity for femtosecond pulse by peak intensity of input pulse isrealized in Kerr nonlinear medium/metal waveguide. Using FDTD method, thechange of group velocity for femtosecond SPs pulse with peak intensity of inputpulse is calculated, which confirms the method. In addition, effects of groupvelocity dispersion and self-phase modulation on pulse width are analyzed.
Keywords/Search Tags:surface plasmons, femtosecond pulse, control of group velocity, superlattice, Kerr nonlinear, pulse deformation
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