基于夹层结构的偏振无关1×2定向耦合型解复用器的设计

Design of polarization-insensitive 1×2 directional coupler demultiplexer based on sandwiched structure

提出一种基于夹层结构的偏振无关1×2定向耦合型解复用器,用于分离1310 nm和1550 nm两个波长.通过合理选择夹层结构芯区的折射率及波导间隙,可以调节同一波长两个正交偏振模的耦合长度相等,实现偏振无关;通过合理选择夹层结构波导宽度,可以使两个波长分别从不同输出波导端口输出,实现解复用功能.运用三维有限时域差分法进行建模仿真,对结构参数进行优化,并对器件性能进行了分析.结果表明:该器件定向耦合波导的长度为23μm,插入损耗低至0.1 dB,输出波导间的串扰低至–26.23 dB,3 dB带宽可达290 nm和200 nm.另外,本文提出的器件采用Si3N4/SiO2平台,可有效减小波导尺寸,提高集成度,不仅实现了偏振无关,而且结构紧凑、损耗低,在未来的集成光路中具有潜在的应用价值.

An ultra-compact 1×2 demultiplexer based on directional coupler(DC)waveguide is proposed to separate the 1310 nm wavelength from 1550 nm wavelength,in which a new Si3N4/SiNx/Si3N4 sandwiched structure is used to realize polarization insensitivity.Firstly,the new sandwiched structure is designed to be polarizationindependent.The coupling lengths of two orthogonal polarization modes at the same wavelength versus the gap between two parallel SiNx waveguides g1 are calculated with several groups of structure parameters of the demultiplexer.The result shows that the coupling lengths for the two orthogonal polarization modes at the same wavelength can be identical by choosing the proper g1.Then,how to realize the function of wavelength separation is studied.When one wavelength propagates at even multiple of coupling length and the other wavelength propagates at odd multiple of coupling length,and vice versa,the two working wavelengths will output from different output ports,thereby the two wavelengths are successfully separated.Under the premise of satisfying such conditions,a comparison of size and performance among the devices with different groups of structure parameters is given to find the best one.The demultiplexer based on Si3N4/SiO2 platform has a compact structure,easy integration and good tolerance.Three-dimensional(3D)finite-difference time-domain method is used for simulation,and the results show that the length of the DC waveguide is only 23μm;the insertion loss and crosstalk are as low as 0.1 dB and–26.23 dB respectively;a broad 3-dB bandwidth of 200 nm is achieved.To demonstrate the transmission characteristics of the demultiplexer,the evolution of the excited fundamental mode in the demultiplexer is also given.The novel demultiplexer is polarization-independent and can work at 1310 nm and 1550 nm wavelengths simultaneously.It has a potential application value in future integrated optical circuits.