A broadband thermo-optic $2\times 2$ Mach–Zehnder switch that can control two spatial modes simultaneously on a silicon chip is demonstrated in this Letter. A broadband multimode 3 dB coupler is first realized based on symmetrically coupled waveguides with a sub-wavelength structure. The length of the coupler is only 24.2 μm. By employing such a multimode 3 dB coupler together with symmetrical delay arms, an optical switching functionality is realized experimentally with excess losses less than 1.3 dB and crosstalks less than $-15\mathrm{dB}$ over a 60 nm bandwidth for the two spatial modes. An arbitrary splitting ratio at two output ports for the two modes simultaneously is also demonstrated when applying different currents on the heater.

中文翻译：

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基于硅密堆积波导阵列的用于多种空间模式的宽带光开关

宽带热光 $\mathrm{2个}\times \mathrm{2个}$这封信演示了可同时控制硅芯片上两个空间模式的马赫曾德尔开关。首先基于具有亚波长结构的对称耦合波导实现宽带多模3 dB耦合器。耦合器的长度仅为24.2μm。通过将这种多模3 dB耦合器与对称延迟臂一起使用，可以以小于1.3 dB的过量损耗和小于1.3 dB的串扰通过实验实现光开关功能$-15\mathrm{D\; b}$两种空间模式在60 nm带宽上的带宽。当在加热器上施加不同的电流时，还将展示两种模式同时在两个输出端口上的任意分配比。