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Refractive index of PML
Posted 2024年4月18日 GMT-4 08:34 Electromagnetics, Wave Optics Version 6.1 1 Reply
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Hi, In the mode analysis of optical fibers, the Perfectly Matched Layer (PML) is used as a boundary condition. Generally, the cladding layer of the fiber serves as the PML, and its effective refractive index is set to be the same as or slightly larger than that of the core material. This results in the effective refractive index of the designated PML being a constant real value rather than a complex-valued function of radial coordinates. For a cylindrical-shaped PML, its refractive index should ideally be a complex-valued function of radial coordinates. How should this simulation setup be understood, and how can the effectiveness of this method be explained? Your assistance is greatly appreciated.
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A PML is meant to absorb outgoing radiation without reflecting it back into the modeling domain, that is why complex highly imaginary index is applied there. The cladding layer is not meant to absorb radiation but rather confine it inside the fiber. That is why a real index is applied there. There is certainly a better and more quantitative mathematical rationale for this in the COMSOL documentation.
Cheers Edgar
-------------------Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com