Tao Zhi-Yong, Fan Ya-Xian
1] Key Lab of In-fiber Integrated Optics, Ministry Education of China, Harbin Engineering University, Harbin 150001, People's Republic of China [2] Photonics Research Center, College of Science, Harbin Engineering University, Harbin 150001, People's Republic of China.
Sci Rep. 2014 Nov 18;4:7092. doi: 10.1038/srep07092.
Orthogonality plays a fundamental role in various mathematical theorems and in physics. The orthogonal eigenfunctions that represent the intrinsic motions of various physical systems can also be regarded as transverse wave modes in a straight waveguide. Because of their orthogonality, these modes propagate independently, without mutual interference. When the wall separation fluctuates, the former mode orthogonality is destroyed because of the change in the Euclidean space of the system. Here, we experimentally demonstrate the extraordinary single-mode transparency that arises as a result of the intense mode interference induced by orthogonality breaking in a waveguide with a varying cross section. A mode diagram is also introduced to illuminate these mode interactions. In particular, measurements of the transverse field distributions indicate that a three-mode interaction leads to a single high-order mode that penetrates through the lower-mode bandgaps when the wall period is carefully selected. The observation of Bessel-like transverse distributions is promising for applications in wave-control engineering.
正交性在各种数学定理和物理学中都起着基础性作用。表示各种物理系统固有运动的正交本征函数也可被视为直波导中的横向波模式。由于它们的正交性，这些模式独立传播，互不干扰。当壁间距波动时，由于系统欧几里得空间的变化，先前的模式正交性被破坏。在此，我们通过实验证明了在具有变化横截面的波导中，由正交性破坏引起的强烈模式干涉所产生的非凡单模透明度。还引入了一个模式图来阐明这些模式相互作用。特别地，横向场分布的测量表明，当仔细选择壁周期时，三模相互作用会导致一个高阶单模穿透低阶模带隙。观察到的类贝塞尔横向分布在波控工程应用中很有前景。
