Whispering gallery (WG) microcavities have been applied for a variety of optoelectronic devices due to their extraordinary characteristics of high quality factor ( Q ) and small mode volume, crucial to accurately tune the quality factor for realizing the high-speed optical modulation and short pulse laser. In this paper, we propose and theoretically analyze a hybrid, graphene-coupled silica microtoroid device and realize optical polarization control and electro-optic modulation due to the polarization-dependent absorption of graphene on the different cavity WG modes. By changing the gap distance between graphene and the microtoroid, the influence of graphene absorption on the different polarization modes is diverse due to the different electric field distributions of modes in the microtoroid, therefore demonstrating the different resonant wavelength shifts and quality factor variations. The transmission depth variation of the second-order transverse electric mode upon changing the gap distance between graphene and microtoroid is 4.5 dB more than that of the second-order transverse magnetic mode, verifying that the polarization control is because of the polarization-dependent absorption of graphene. Furthermore, by applying the voltage on the graphene flakes, electro-optic modulation with a high contrast of 21.7 dB is demonstrated based on this hybrid graphene-coupled silica microtoroid.

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Large strain with submicro resolution is essential for steel structural monitoring; however, the fiber base sensors are limited by the glass extension to be less than 1%. Here, we propose a U-shape core-offset fiber sensor including four fiber segments to realize a large strain sensor. Four fiber segments with slight length differences in between are core-offset fused together to achieve U-shape spring-like microstructure fiber for large transverse bending radius. The reflected high-order modes at three silica/air interfaces interfere to give a broad spectrum due to unequal segment length, which enables continuous strain detection over 35 mɛ. The air and glass hybrid structure of the device enables the large bending, and hence compression and tension measurement can be achieved simultaneously. The strain sensitivity is up to 20.75 pm/µɛ with the strain accuracy of 0.5 µɛ. This novel, to the best of our knowledge, core-offset fiber has high strain sensitivity and large strain range for compression and tension strain measurement. Furthermore, the proposed strain sensor can be fabricated easily for practical applications where large strain with high strain accuracy is needed.

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