脊形聚合物光波导制备及理论分析

Fabrication and Theoretical Analysis of Ridge Optical Waveguide of Polymer

报道了利用铝膜作掩模 ,通过紫外光照射制备键合型聚合物DANS PMMA脊形光波导的新方法。所制备的聚合物脊形光波导 ,其形状与通常的脊形波导相同 ,但内部折射率又与矩形波导类似。从理论上推导出该脊形波导的模式本征值方程 ,并给出相应的归一化通用曲线 ,可以供相应波导设计和制备作为参考。

Polymers that contain nonlinear optical moieties are considered to be most promising for the development of electro optic devices. There are a number of different ways to make polymer channel waveguides , such as photobleaching, reactive ion etching, and laser ablation. The photobleaching technique for forming polymer channel waveguides in a planar geometry offers compatibility with existing electronic processing technologies. Because UV light can induce a series of chemical reactions when a polymer film is exposed under it, and can also make a remarkable decrease for both thickness and refractive indexes of polymer film. Using these characteristics, we fabricated ridge polymer waveguides with DANS PMMA side chain polymer films. The fabricating process is as follows. The DANS PMMA is dissolved in 1,2 Dich loroethane. Then the solution is filtered through 0 5μm sieve and spread onto fused silica substrate by spin coating. After 24 hours curing at 60℃. Al layer is evaporated onto the DANS PMMA film and a 6μm wide of Al strip is constructed by photolithography. Then the sample is exposed to UV light through Al strip mask for 10 minutes. The measured light power on the sample surface is 40mW/cm 2, and sample temperature is 80℃. After photobleaching, a 6μm wide of DANS polymer strip waveguide is formed when Al mask is removed. The microscope view show that the surface and side wall of this waveguide are very smooth. This kind of waveguide is similar in shape to that of normal ridge waveguide, but it's refractive index distribution is similar to that of rectangular waveguide . Therefore ridge polymer waveguide can supply better restrict for transmitting light. In practical devices, the ridge polymer waveguide is sandwiched between upper and lower cladding layers. The eigenvalue functions and propagation constants are deduced for this kind of waveguide using the analysis method of slab waveguide. The normalized curves are plotted for guide index b as a function of normalized frequency V for E y nm and E x nm mode.