| Recently, microring resonators have received considerable attention due to their advantages of ultra-narrow3dB bandwidth, compact structure and suitability for large-scale integration. However, the integration degree of photonic integration circuit is restrained by the fact that it is impossible to downscale the size of dielectric based microring resonators into the regime of subwavelength due to the diffraction limit. In order to overcome the diffraction limit, Surface Plasmon Polaritons (SPPs) are employed to realize the microring resonators. This is due to the fact that metal could confine the light tightly near its surface and transport the energy in the regime of subwavelength, and the size could then be reduced.In this article, we have investigated the working principles of dielectric based and SPPs based microring resonators, separately. And then the experiment procedures are given thorough introduction. The followings are the achievements of the article:1. We have investigated the working principles of microring resonators and presented the formulas for the transmission spectrum. In addition, the formulas for the performance parameters of microring resonators are presented and then the impact of the change of structural parameters on the performance is analyzed.2. We have proposed and designed a parallel microring resonators based filters, which is composed of a series of microrings and two bus waveguides. Theoretical analysis reveals that the proposed microring filters clearly exhibit the character of steep-edge and flat-top spectrum when the number of microrings is not less than six. It is demonstrated that when the number of microrings is six, the-0.5dB、-3dB、-20dB linewidth of the proposed filer is0.8nm,1.6nm,1.9nm, separately, which definitely meets the requirement of WDM system. Furthermore, a trade-off in terms of the steep-edge and flat-top character and side band is needed:the characteristics of flat-top and steep-edge is well presented with a large side band at a large coupling coefficient (e.g.0.6), while the characteristics of flat-top and steep-edge is nearly missing with a small side band at a small coupling coefficient (e.g. 0.14).3. A nanorods based SPPs waveguide is proposed. The transportation loss is reduced significantly by introducing additional interaction mechanism named conduction current exchange, which is realized by connecting the base end of each nanorod. Simulation results reveal that the transportation length of the proposed waveguide is as long as20.87μm at the wavelength of1.55μm, far larger than that of traditional nanorods based SPPs waveguides.4. A SPPs waveguide based on a core-shell structure is proposed, and then its application in microring resonators is analyzed. Simulation results reveal that for a microring resonator based on such a waveguide, the3dB line-width is1.7nm and the extinction ratio is23dB, which are both better than that of conventional SPPs microring resonators.5. A microring resonator based filter is fabricated on a SOI wafer. The radius of the microring is7μm, gap width between microring and bus waveguide is1.8μm, and the waveguide cross-section is300x250nm. The experiment results reveal that the free spectral range is18nm, extinction ratio for the transmission spectrum at drop and through is15dB and5dB, separately. |
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