新一代计算机光互连普遍采用的垂直腔面发射激光器（VCSEL），是波长为850 nm的多模激光器。为了更好地与其匹配，需要开发截面大小与其输出面大小接近的脊形波导。在成功制备了最小截面积70 μm×50 μm，直线长度21 cm聚硅氧烷脊形波导的基础上，对其损耗机制进行了理论分析。利用微扰理论分析可知吸收损耗可以忽略不计，主要损耗由上下表面和侧面粗糙度引起的表面散射损耗决定。利用变分原理和有限元方法分析了气泡、缺陷和杂质对场分布的影响，得出了基模和1阶模受到肉眼可辨的影响和发生跃变时气泡、缺陷或杂质的具体量值。利用CCD摄像法测量传输损耗，实验结果与理论结果基本相符。

Vertical cavity surface emitting laser (VCSEL) is widely used in the interconnection of new-generation computer, which is a multi-mode laser with the wavelength at 850 nm. A rib waveguide with section area similar to the output plane needs to be developed to fit VCSEL better. Based on the successful preparation of polysiloxane rib waveguide, which has the smallest area of 70 μm×50 μm and straight length of 21 cm, theoretical analysis of its loss mechanism is processed. By using perturbation theory, it is concluded that the absorption of material can be neglected and the main loss of scattering comes from the loss of surface scattering induced by the roughness of top surface, bottom surface and side surface. By using variational principle and finite element method, the field distribution influenced by bubble, defect and impurity is analyzed. Concrete measured value of bubble, defect and impurity at saltus, visible influence of basic mode and first-order mode is gotten. Transmission loss measured by CCD photography shows that experimental results fit the theoretical results well.