Abstract
High refractive index (RI) thin films are capable of pulling waveguide mode profiles towards themselves. In this study, it is shown that by applying high RI coatings with specific thicknesses on the side of optical waveguides, significantly different mode profiles for orthogonal polarizations can be achieved. This phenomenon, that we call it polarization-selective mode shaping, can be extensively used in the enhancement of polarization-dependent integrated optical devices. As an illustrating application, a tri-layer structure consisting of poly(methyl methacrylate)/graphene/chalcogenide on a side-polished fiber is designed to realize an extremely high extinction ratio polarizer. This structure changes the mode profiles in a way that the attenuation of TE mode is maximized, while the power carried by the TM mode remains relatively constant. Simulations and experimental characterizations confirm that polarization-selective mode shaping coordinates four loss mechanisms to maximize the extinction ratio and minimize the insertion loss of the polarizer. The fabricated polarizer is examined in the O, C, and L telecommunication frequency bands. This configuration achieves the high extinction ratio of 51.3 dB and its maximum insertion loss in the tested wavelengths is 1.79 dB. The proposed polarizer has been compared with other state-of-the-art polarizers in the conclusion section which shows its superiority.
Highlights
The interaction of light in waveguides with the surrounding media depends mainly on the penetration of the evanescent field in that media, which depends on the mode profile
In addition to these simulations, an analytical study of 2D counterpart of this waveguide is presented in the Supplementary Information, which proves that formation of different mode profiles for different polarizations is a direct consequence of Maxwell’s equations
The full width at half maximum (FWHM) of the 2D Raman band was monitored in a scan over the polished surface of the fiber which confirmed the presence of a single-layer graphene on the fiber (Fig. 4b)[44]
Summary
The interaction of light in waveguides with the surrounding media depends mainly on the penetration of the evanescent field in that media, which depends on the mode profile. The capability of high RI thin films to induce contrast in orthogonal mode profiles is investigated numerically To confirm these results experimentally and illustrate the potential applications of PSMS, a graphene-based in-line fiber polarizer (GILFP) is designed, fabricated, and characterized. This polarizer benefits from poly(methyl methacrylate) (PMMA)/graphene/As2S3 (chalcogenide) tri-layer coating on the top of a side-polished fiber (SPF). This structure reduces the power carried by the TE mode more than that by the TM mode through four loss mechanisms. Owing to the uniform optical response of graphene in a broad spectral range, this method can be used to realize polarizers for other wavelengths with appropriate fibers and coatings
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