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1

Tunable terahertz all-dielectric linear-to-circular polarization conversion metasurface

Ju Xiacao, Wang Weiguang, Liu Bingchao, Hou Yanzhao, Wen Huashun, Yang Daquan

Optica Applicata

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2022

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Vol. 52, nr 4

551--563

EN

Terahertz (THz) linear-to-circular (LTC) polarization conversion plays a crucial role in imaging and 6G wireless communication. This paper will give an account of a thermally tunable THz LTC polarization converter by using the active all-dielectric metasurface. It consists of zirconium oxide (ZrO2) microsphere resonators, active strontium titanate (STO) cladding, and flexible polyimide substrate. Through numerical simulation, the amplitude of the ellipticity of the proposed polarization converter at 0.265 THz is –1, indicating that perfect right-hand circular polarization (RHCP) wave is achieved. Meanwhile, the amplitude of the ellipticity is less than –0.8 between 0.247 and 0.278 THz (relative bandwidth is 12%). In addition, with the temperature changes of 180 K (from 200 to 380 K), the operating frequency of the converter can be tuned from 0.220 to 0.291 THz, a sensitivity about 39 GHz/100 K is achieved. Besides, the modulation depth of the ellipticity amplitude can achieve 92% at 0.220 THz, which demonstrates that the converter can output terahertz wave with different polarization states, and the device can be fabricated on a large scale. These perfect conversion performances show that the converter has potential applications in high-speed communication and imaging.

2

Single air-mode resonance photonic crystal nanofiber cavity for ultra-high sensitivity refractive index sensing

Zhang Yanni, Yang Jiaxi, Song Meiqi, Zhang Xuan, Yang Daquan

Optica Applicata

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2020

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Vol. 50, nr 2

199--207

EN

We propose a design of series-connected one-dimensional photonic crystal nanofiber cavity sensor (1-D PC-NCS) and one-dimensional photonic crystal nanofiber bandgap filter (1-D PC-NBF). The proposed structure can get a single air mode for refractive index sensing with its extinction ratio of 58.64 dB. It filters out the high order mode and reduces the interaction between signals. By 3D FDTD, the calculated sensitivity is 848.18 nm/RIU (RIU – refractive index unit). Compared with general silicon on-chip nanobeam cavity, the sensitivity is increased by eight times. The additional 1-D PC-NBF will not change the sensitivity and the position of the resonance wavelength. Therefore, the new design we propose addresses the issue of crosstalk, and can be applied to ultra-high sensitivity index-based gas sensing and biosensing without the need for complicated coupling systems.

3

Nanoslotted microring resonator for high figure of merit refractive index sensing

Yang Daquan, Duan Bing, Zhang Xuan, Lu Hui

Optica Applicata

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2020

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Vol. 50, nr 1

37--47

EN

A nanoslotted microring resonator (NSMR) with enhanced light-matter interaction has been designed, which can be used for high sensitive refractive index sensing. The performance of the device is investigated theoretically based on a three-dimensional finite-difference time-domain (3D-FDTD) method. In order to achieve high figure of merit sensing, the nanoslot geometry is exploited to make the optical field strongly localized inside the low index region and overlap sufficiently with the analytes. By using the 3D-FDTD method, the proposed NSMR sensor device achieves a high Q-factor (Q > 105) and sensitivity ~100 nm/RIU (RIU – refractive index unit). Moreover, the strong light confinement introduced by the nanoslot in NSMR results in the sensor figure of merit as high as 6.73 × 103. Thus, the design we proposed is a promising platform for refractive index-based biochemical sensing and lab-on-a-chip applications.