【作者】 应翠凤；

【导师】 田建国；

【作者基本信息】 南开大学 ， 光子学与光子技术， 2013， 博士

【摘要】 光子晶体低阈值激射在高灵敏荧光检测和全光通信中具有重要的应用前景。在众多研究中,实现低阈值、高效率光子晶体激射仍然是现阶段科学研究的重要目标。本论文通过设计特殊色散能带的一维双周期光子晶体结构来实现低阈值、高效率光子晶体激射,并从实验和理论上研究在双周期光子晶体激射新现象和新机制。主要内容包括：1.研究激发条件对光子晶体激射阈值和激发效率的影响。首先基于重铬酸盐明胶(DCG)和全息方法制备了一维(1D)光子晶体结构,并对其掺杂荧光染料若丹明6G(Rh6G),实现光泵浦光子晶体带边激射。通过改变泵浦光的激发角度来调整激发条件,我们发现光子晶体带边激射的激射阈值和激发效率对泵浦光的激发角度十分敏感。我们还从理论上采用传输矩阵法(TMM)计算了在不同激发角度下光子晶体的有效增益,与实验结果吻合较好。2.设计并制备一维双周期光子晶体,在光子禁带中引入具有平坦色散的子能带,并证实子能带激射效应明显优于带边和缺陷模式。我们介绍两种1D双周期光子晶体的全息制备方法：四束光干涉法和二次曝光法。实验和数值结果表明子能带具有低群速度、低二阶色散和长距离电场增强。通过计算电场在单周期和Moire双周期光子晶体中的空间分布,我们得到子能带模式的电场强度是带边的3倍。由于双周期光子晶体子能带具有低群速度、高光子态密度,长距离电场增强等优异性能,在荧光增强和低闽值激射等方面具有潜在的重要研究价值。3.在掺杂Rh6G的1D Moire双周期光子晶体结构中实现了低阈值、高效率的子能带激射,激射强度达到裸眼可视。双周期光子晶体子能带具有平坦色散和长距离电场局域增强,可产生较高的光子转换效率。相比与未曝光的明胶薄膜,双周期光子晶体实现了荧光增强达660倍以上。与单周期带边激射相比,双周期子能带的阈值降低到了1/6,激发效率提高了8倍。4.从实验和理论两个方面研究了在一维双周期光子晶体中观察到的新颖的彩色多环锥形激射现象。根据实验结果,我们提出了能带耦合模型,从理论上解释锥形激射的产生机制,获得了与实验结果相符的理论分析结果。我们从理论上论证了光子晶体中杂质引起的散射可以使两个平坦色散能带在特定的角度产生耦合。接着通过分析锥形激射不同角度的荧光光谱,我们证实了能带耦合的存在。根据样品的透射光谱和能带耦合模型,我们数值计算了双周期彩色多环锥形激射波长和对应的激射角度,理论结果与实验数据相符。由此可知锥形激射的激射光斑由光子晶体的能带结构决定,直接反映出光子晶体能带的重要特征。综上,我们制备了一维双周期光子晶体,获得了具有优异平坦色散子能带,并进一步实现子能带激射,证实了子能带激射在多个方面明显优于光子晶体带边激射和缺陷激射。我们还在一维双周期光子晶体中观察到新颖的彩色多环锥形激射现象,并据此提出能带耦合模型解释锥形激射的产生机制,获得了与实验结果相符的理论分析结果。更多还原

【Abstract】 Low-threshold photonic crystal (PC) lasing has been widely studied for its application in all-optical communication and high sensitive fluorescence detection. Among the studies of PC lasing, reduction of the lasing threshold and improvement of the lasing efficiency are of special interest. In this dissertation, we focus on realization of low-threshold and high-efficiency PC lasing by designing a one-dimensional (ID) dual-periodic PC. We also study the novel lasing emission from dual-periodic PC both experimentally and theoretically. The details are descripted as follows:1. We demonstrated the influences of excitation conditions on the PC lasing threshold and excitation efficiency were studied. Optically pumped band edge lasing was obtained from Rhodamine6G (Rh6G)-doped1D PC fabricated by holography in dichromated gelatin (DCG). Results show that the lasing threshold and excitation efficiency are sensitive to the excitation condition, which can be altered by tuning the pump angle. Numerical calculation of effective gain in the PC with different excitation angles were performed by transfer matrix method (TMM), which matched well with experimental results.2. Extremely flat minibands were induced in the stop band by dual periodicity in a1D PC. Two holographic fabrication methods of1D dual-periodic PC were proposed:four-beam interference holography and double-exposure holography. The experimental and numerical results show that the minibands have slow group velocity, weak second order dispersion and large spatial region for electric field enhancement. We also calculated the electric field distribution at miniband mode, whose intensity is about3times of that at band edge mode. Since the minibands have low group velocity, high density of optical states and large spatial region for light-matter interaction, they have potential applications in fluorescence enhancement and low-threshold lasing.3. Low-threshold and high-efficiency miniband lasing was achieved in Rh6G-doped1D Moire dual-periodic PC. The lasing intensity was strong enough to be naked-eye observable. Compared with the dye-doped film in un-exposed region, an enhancement of fluorescence emission by a factor of up to660was achieved in Moire dual-periodic PC. We also presented that the lasing efficiency was dramatically enhanced about eight times and meanwhile the threshold was decreased to about1/6of that of the band-edge lasing in the single-periodic PC. This high optical conversion efficiency can be attributed to the extremely flat dispersion and large mode volume of the miniband induced by dual-periodicity. This finding provides potential applications in ultra-sensitive fluorescence detection and PC laser system.4. The multiple and colorful cone-shaped lasing emission from a1D dual-periodic PC was investigated both experimentally and theoretically. Based on the experimental results, we proposed a band-coupling model, which well explained the mechanism of cone-shaped lasing. We demonstrated that the unavoidable scattering of imperfect structure and the Bragg diffraction of periodic structure would lead to a coupling effect between flat bands along a special direction. This was verified by the angular fluorescence spectra from a dye-doped1D PC. We also perform a numerical simulation based on the band-coupling model to estimate lasing wavelengths and emission-cone angles from dual-periodic PC, which match well with those from experimental results. This result indicated that the lasing pattern, which is determined by the photonic band structure, may give a direct visualization of the PC band structure.In summary, we have realized extremely flat dispersion minibands in a1D dual-periodic photonic crystal and have obtained low-threshold and high-efficiency miniband lasing. We also observed a novel multiple and colorful cone-shaped lasing was in a1D dual-periodic PC. A band-coupling model was proposed to explain the mechanism of cone-shaped lasing, which well matched with experimental data.更多还原