| Distributed Feedback (DFB) dye lasers possess many advantages, such as mirrorless,low threshold,narrow linewidth,easily tunable and integratable, et al. These all make them have broad application prospects in optical devices, integrated optics, optical communications, and ultrafast material analysis, et al. Conventional DFB dye lasers acheive tuning output usually through changing the pump angle between the two coherent light, the tuning means is relatively simple. Based on the physical and chemical characteristics of nematic liquid crystal (NLC) molecules that is sensitive to electric field, the author injected LC and dyes into the special LC cell and the designed grooves, and achieved conveniently tuning through applying voltage on the cell or the grooves.This paper firstly derived the coupled wave equations of refractive index or gain periodic distribution medium using the coupled wave theory. According to the equations, the author obtained oscillation condition and oscillation frequency,mode spectrum,transmission and reflection power gain of the DFB lasers, the study showed that the resonator of DFB lasers provided by internal periodic perturbation in medium, and DFB lasers have strict wavelength selectivity, low threshold and narrow linewidth.Experiments have been carried out to study the output characteristics of gain distributed feedback dye laser. The author obtained the tuning output through holographic pumping the LC cell respectively injected dye PM567,PM597 and P0616A using Nd: YAG (532nm,10ns,1Hz), the tuning ranges were respectively 550nm~587nm and 565nm~590nm when the pump half-angles between two coherent light changed from 46o to 50o and from 45.5o to 47.5o, the thresholds were respectively 33.5μJ and 36.7μJ, and the linewidth were all less than 0.1nm. The half-angle was fixed to be 50o, the author obtained tuning output from 553nm to 563nm when applying square-wave voltage (3.4V~4.2V, 10kHz) on the cell. When the angleΦbetween the polarization of two coherent light increasing, the output laser energy gradually decreased, whenΦis about 90o (the experiment value was about 86o), the laser quenched, then, when the pump energy increased to the original 1.6 times, the laser re-appeared.The author designed one-dimensional refractive index DFB lasers filled with LC, and determined the size of the grooves (slot pitch is 920nm, groove width is 460nm, the depth is about 1μm.) according to fluorescence spectrum of dyes in laboratory. FDTD method was used to simulate electromagnetic wave propagation process in the designed grooves structure, the results showed that: the center wavelength of forbidden band assumed hypsochromic shift when the value of the refractive index difference between LC and groove material declined, and the difference value was larger, the band gap was wider and deeper, and groove periods were more, the band gap were deeper and steeper, and the linewidth of laser locating at the band edge would be narrower. The author also calculated the gain of laser at the band edge and found that it was 17 times to the gains of other laser wavelengths, the laser at the band edge was easy to win the mode competition, and thus emitted narrow linewidth laser. After applying voltage on the grooves, the band edge moved, and the wavelength of laser output also changed, that was the reason for the voltage tuning. |
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