提出了一种基于热光调节的可调光衰减器结构。该衰减器通过腐蚀光纤包层到一定厚度和长度后,在表面涂覆较大热光系数的聚合物材料得到。从模场变化角度分析了传输光束的衰减与涂覆材料折射率的关系,并从实验上测试了使用不同涂覆材料时的衰减。理论分析与实验结果均表明在涂覆材料折射率略大于原光纤包层材料折射率时,涂覆材料折射率微小的变化将引起传播光束衰减的大幅度变化,并且光纤被腐蚀的长度越长或包层材料剩余厚度越小,衰减越大。因此,由热光系数大、折射率略大于光纤包层的聚合物材料所组成的可调光纤衰减器,具有衰减调节范围大且功耗小、插入损耗小、成本低、低偏振特性、易于与其它光纤器件耦合或集成等特点。

A fiber-type variable optical attenuator (VOA) based on thermo-optic effect is proposed. The VOA is fabricated by etching down a certain depth and length of the cladding of optical fiber and covering with polymer with large thermo-optic coefficient. The relationship of the attenuation and the refractive index of the substitute is theoretically analyzed in terms of the mode field distribution (MFD) of the fiber. The attenuation of the VOA is measured in different substitutes of cladding. It is shown theoretically and experimentally that the attenuation varies significantly when the refractive index of the substitute has a little change, as long as the refractive index is slightly larger than that of the cladding. Moreover, the longer the etched fiber or the thinner the cladding is, the larger the attenuation of the VOA is. Therefore, this fiber-type VOA, which is substituted by a polymer with large thermo-optic coefficient and refractive index slightly higher than that of the cladding, is of large dynamic range, low insertion loss, low polarization-dependent loss, low power consumption and easily coupled or integrated with other fiber-optic components.