| Recently, group velocity control of light by microring resonators has been one of hot research areas in photonics field. Resonance can be enhanced in microring resonators through structure design, and large dispersion and significant group velocity can be realized. However, using lossy microring resonators to realize fast or slow light often suffers serious attenuation and great distortion near the critical point. As the EIT effect in atomic vapor, EIT-like effect referred to as coupled-resonator-induced transparency (CRIT) exists in coupled double-ring resonators (CDRRs), which is often accompanied by greater dispersion than single microring resonators and can realize obvious slow and fast light.In this dissertation, taking the group velocity control of light as the main application goal and introducing gain as an assistant means to improve the effect of the group velocity control, we researched the characteristics of transmission and dispersion in coupled double-ring resonators with loss or gain comprehensively. In summary, major research contents and achievements are as the following:1. The transmission characteristics of single and coupled double-ring resonators were studied. Based on the transfer functions of the single and coupled double-ring resonators, the major characteristics of their effective phase shifts at different conditions were provided. For the CDRRs, we pointed out that the classification of the transmittance response can be distinguished according to the number of its extreme points, and the equation satisfied by the extreme points was given.2. The transmission characteristics of CDRRs including those with gain are investigated systematically. The lasing thresholds of gain structures were provided. For the first time, based on the symmetry between the transmission characteristics of two coupled double-ring resonators with symmetrical loss and gain, the transmittance and dispersion characteristics of CDRRs with gain are analyzed systematically. We pointed out that their transmittance spectra may appear as specific inversed CRIT (ICRIT) and CRIA (ICRIA) and criteria for different transmittance spectrum types were given. According to the relative relation between the transmittances at resonance and at the split modes, the corresponding relation between parameter conditions and types of transmission spectra was analyzed comprehensively. According to expression of group delay under different loss or gain, the conditions of slow and fast light in various situations were analyzed. Combining the conditions for different types of the transmittance spectra, conditions for types of the transmittance spectra and slow/fast light were provided completely.3. The influence of structure parameters on CDRR group delay and transmittance were investigated systematically. Through finding derivatives of CDRR group delay and transmittance with respect to the coupling coefficients and amplitude transmission factors, the effect of these parameters on group delay and transmittance at different conditions were found. Combing the parameter conditions for fast or slow light when mode splitting appears, comprehensive performance-parameter relations for group velocity control are provided. We showed for a specific design goal how to use these performance-parameter relations to carry out design and optimization. Moreover, the working bandwidth of group velocity control realized by a CDRR was defined and the factors affecting the working bandwidth were analyzed.4. The effects of higher order dispersion on output pulse in single and coupled double-ring resonators were analyzed. Through calculating the pulse response of microring resonators without loss/gain to incident pulses at the extreme value point of the second-and third-order dispersion respectively, the effect of the second-and third-order dispersion on output pulse were revealed. We found that as the pulse center wavelength of the incident pulse departing from the resonant wavelength, the splitting bottom of the output pulse became shallow gradually until disappeared. In addition, for slow light the splitting occurs at front part of the pulse, and for fast light it appears at the back part.5. An experimental system for transmittance spectrum measuring was developed. The transmittance spectra of single and coupled double-ring fiber resonators were measured. The CRIT effect spectra in coupled double-ring fiber resonators were realized.In this dissertation the transmittance and dispersion characteristics of CDRRs were demonstrated. The influence of the structure parameters on the transmission characteristics of CDRR, and the effect of higher order dispersion on output pulse in microring resonators were analyzed systematically. Work in this dissertation provides a solid theory foundation and design basis for applications of CDRRs on group velocity control and others based on its transmittance and dispersion performance. |
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