Experimental implementation for near-field displaying application of bound states in continuum supported by terahertz metasurfaces.

Optical bound states in continuum (BICs) are the special lossless electromagnetic resonance modes found in optical transmission media. Optical BICs supported by metasurfaces can bring a series of image-based applications, which can be classified into far-field image-based applications and near-field image-based applications according to imaging distance. The far field image-based applications of optical BICs supported by metasurfaces have been proved theoretically and experimentally. However, the near-field image-based applications are still in the stage of theoretical demonstration, and its practical feasibility is still questioned. In this letter, we have experimentally demonstrated the feasibility of near-field image-based applications of optical BICs. An all-silicon terahertz metasurface that supports near-field displaying based on quasi-BIC is designed. Its unit cell is based on the classic asymmetric elliptical strip structure, and one unit cell of the metasurface corresponds to one display pixel. By observing the electric field distribution of the metasurface in the near-field region, the display of the given image is successfully constructed. The near-field image-based application of BICs may be beneficial for the information encryption, the hidden item detection, matter analysis, etc.

Perfect linear polarization wave generator based on quasi-bound states in the continuum.

Quasi-bound states in the continuum (q-BICs) in optical metasurfaces have been found to carry special radiation polarization properties. Herein, we have studied the relationship between the radiation polarization state of a q-BIC and the polarization state of the output wave, and theoretically proposed a perfect linear polarization wave generator controlled by the q-BIC. The proposed q-BIC has an x-polarized radiation state, and the y co-polarized output wave is completely eliminated by introducing additional resonance at the q-BIC frequency. Finally, a perfect x-polarized transmission wave with very low background scattering is obtained, and the transmission polarization state is not limited by the incident polarization state. The device can be used to efficiently obtain narrowband linearly polarized waves from non-polarized waves, and can also be used for polarization-sensitive high-performance spatial filtering.

Locatable-body temperature monitoring based on semi-active UHF RFID tags.

This paper presents the use of radio-frequency identification (RFID) technology for the real-time remote monitoring of body temperature, while an associated program can determine the location of the body carrying the respective sensor. The RFID chip's internal integrated temperature sensor is used for both the human-body temperature detection and as a measurement device, while using radio-frequency communication to broadcast the temperature information. The adopted RFID location technology makes use of reference tags together with a nearest neighbor localization algorithm and a multiple-antenna time-division multiplexing location system. A graphical user interface (GUI) was developed for collecting temperature and location data for the data fusion by using RFID protocols. With a puppy as test object, temperature detection and localization experiments were carried out. The measured results show that the applied method, when using a mercury thermometer for comparison in terms of measuring the temperature of the dog, has a good consistency, with an average temperature error of 0.283 °C. When using the associated program over the area of 12.25 m2, the average location error is of 0.461 m, which verifies the feasibility of the sensor-carrier location by using the proposed program.

Theoretical Study on All-Dielectric Elliptic Cross Metasurface Sensor Governed by Bound States in the Continuum.

The appearance of all-dielectric micro-nano photonic devices constructed from high refractive index dielectric materials offers a low-loss platform for the manipulation of electromagnetic waves. The manipulation of electromagnetic waves by all-dielectric metasurfaces reveals unprecedented potential, such as focusing electromagnetic waves and generating structured light. Recent advances in dielectric metasurfaces are associated with bound states in the continuum, which can be described as non-radiative eigen modes above the light cone supported by metasurfaces. Here, we propose an all-dielectric metasurface composed of elliptic cross pillars arranged periodically and verify that the displacement distance of a single elliptic pillar can control the strength of the light-matter interaction. Specifically, when the elliptic cross pillar is C4 symmetric, the quality factor of the metasurface at the Γ point is infinite, also called the bound states in the continuum. Once the C4 symmetry is broken by moving a single elliptic pillar, the corresponding metasurface engenders mode leakage; however, the large quality factor still exists, which is called the quasi-bound states in the continuum. Then, it is verified by simulation that the designed metasurface is sensitive to the refractive index change of the surrounding medium, indicating that it can be applied for refractive index sensing. Moreover, combined with the specific frequency and the refractive index variation of the medium around the metasurface, the information encryption transmission can be realized effectively. Therefore, we envisage that the designed all-dielectric elliptic cross metasurface can promote the development of miniaturized photon sensors and information encoders due to its sensitivity.

A low noise transimpedance amplifier for optical receiver.

In this paper, a regulated cascode (RGC) structure and a shunt-feedback transimpedance amplifier are cascaded. By analyzing the average input-referred noise current, this paper used the method of adjusting the metal-oxide-semiconductor size and increasing the transimpedance gain to optimize the circuit noise characteristics without introducing redundant structures and noise sources. The measured results demonstrated that when the photodetector capacitance is 300 pF and the supply voltage is 1.8 V, the fabricated transimpedance amplifier has a transimpedance gain of 59.5 dBΩ and a -3 dB bandwidth of 4 GHz. Simultaneously, the average input-referred noise current spectral density is less than 7 pA/√Hz, and the data rate is as high as 5 Gb/s. The circuit takes advantage of the traditional shunt-feedback transimpedance amplifier and introduces a RGC structure between it and the input terminal as a current buffer structure. A π-type matching network was formed by adding an inductor between the shunt-feedback amplifier and the introduced RGC. All these structures can effectively improve the gain-bandwidth product of the designed amplifier.