非线性一维光子晶体波导光双稳

利用非线性折射率系数较大且非线性时间响应较快的CdS_xSe_1-x玻璃为材料,设计并制备了非线性一维光子晶体波导光双稳器件,该器件的折射率空间分布呈正弦形式。实验测得双稳开关的阈值功率密度为1.60×10⁵W/cm²,开关时间为63ps。采用时域有限差分方法讨论了光子晶体带隙随入射光强变化而移动的情况,随着入射光功率密度的增加,光子晶体的带隙中心向短波方向移动。同时计算了该器件的双稳特性,理论计算得到双稳开关的阈值功率密度为1.40×10⁵W/cm²,开关时间约为50ps。获得了理论与实验基本一致的结果。

Characteristics of Optical Bistability of Nonlinear One-dimensional Photonic Crystal Waveguide

We designed and manufactured an optical bistability waveguide device based on nonlinear one-dimensional photonic crystal used CdS_xSe_1-x doped glass. This kind of semiconductor doped glass has large nonlinear refractive index and nonlinear fast response time. The distribution of refractive index of the nonlinear one-dimensional photonic crystal waveguide satisfies sine function. We obtained the nonlinear photonic crystal waveguide by exposure holography and etching techniques. Length of the photonic crystal waveguide is about 3 mm. The height of the peak-groove of the waveguide is 0.1 μm. According to our design, the center of bandgap of the one-dimensional photonic crystal lies at 514.5 nm while the power density of the incident light, the incident light was reflected by the photonic crystal. When the power density of the incident light increasing, the bandgap is shifting to the direc-tion of short wavelength due to the decreasing of the refractive index with the increasing of the incident power density, so more incident light is transmitted. In experiment, we used an active mode-locking pulse of Ar ion laser as the light source which wavelength is 514.5 nm, repeating frequency is 82 MH z and pulse width is 200 ps. The light beam was coupled into the device by prism with a laser average power of 1.28 W (in the case of nonlinear saturation operation, optimum coupling efficiency is about 6%). Pulse wave forms of incident light and transmitted from sample were recorded in turn by 7904 oscilloscope. The optical bistability curve of input power density and output one is fitted by computer. We obtained the threshold power density of bistable switch to be 1.60×10⁵ W/cm² (it is equivalent to average power of 77 mW) and both the rise and fall time are 63 ps. We used the Finite Difference Time Domain Method to obtain the characteristics of the bandgap shift with the incident power density increasing of the nonlinear photonic crystal and calculate the optical bistability curve of this device. In theory, the threshold power density of bistable switch is about 1.40×10⁵ W/cm² and the switch time is about 50 ps. The theoretical results agree well with the experimental ones. This device is a new and feasible one for optical information process and optical computing in the future.