提出了一种基于大芯径塑料包层光纤的嵌入式微结构光纤器件，该结构的锥区末端具有均匀的折射率分布与光场分布。理论分析结果表明，耦合系数随着锥区直径的减小呈现指数形式增大，增大锥区的长度可以使器件的损耗减小。实验上采用固定式加热方法和移动式加热方法分别制作了这种器件，使用移动大热区拉锥系统可以使锥区的长度增大近5倍。利用波长632.8 nm的He-Ne激光，测试了该器件不同长度锥区的损耗，锥区长度为0.7 cm时损耗约为2.63 dB，而锥区长度为3.4 cm时损耗约为1.06 dB，锥区长度对器件损耗的影响与理论分析一致，可以通过改进器件的结构实现低损耗传输。

An embedded microstructure fiber device with large-core plastic cladding fibers inserted is presented. The refractive index profile of the taper end is uniform, and so is the power distribution. On the basis of the theoretical analysis, the coupling coefficient of the nearest-neighboring fibers is exponentially decreased with the decreasing diameter of the taper. The transmission loss of the device is lower when the length of the taper is longer. This kind of devices are fabricated by the fixed flame method and the movable flame method, respectively. The taper is elongated nearly five times by the movable large-hot-zone fiber-tapering system. The transmission loss of the two devices from one inserted fiber to the taper end is measured with He-Ne laser at about 632.8 nm wavelength. The loss values are about 2.63 dB with the taper length of 0.7 cm and 1.06 dB with the taper length of 3.4 cm. The influence of the taper length agrees with the theoretical analysis, and low-loss device can be achieved by improving the structure.