Low-threshold And High-efficiency Photonic Crystal Lasing

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.