Narrow waveguide after input section can effectively filter out the high modes which cause the ununiformity of Y-branches and has little influence on the length and excess loss of the device.

• 在输入波导后添加一段起模式过滤作用的窄波导结构,可以在对器件长度及损耗影响很小的情况下,有效滤除高阶模,减小干涉效应,改善器件输出的均匀性。