Mei Yu

Surface plasmon resonance sensors relying on conventional metals such as gold and silver are plagued by problems including low hardness, vulnerability to defects, and high costs. In this research, a Kretschmann-configuration long-range surface plasmon resonance sensor is ingeniously designed by leveraging black phosphorus (BP). As a two-dimensional material, BP possesses a thickness-tunable direct bandgap, which facilitates efficient excitation of surface plasmon polaritons. The sensor architecture comprises a prism, a coupling dielectric layer, a BP film, and a sensing medium. Through meticulous optimization of parameters like the BP layer number (set to 7), the thickness of the coupling dielectric layer (optimized to 850 nm), and the refractive index, the sensor achieves an impressive sensitivity of 63.71 °/RIU and a figure of merit of 303.38 /RIU when an N-BK7 prism is utilized. In comparison to sensors based on materials such as graphene, Ag, and Au, this BP-based sensor demonstrates a superior equilibrium between sensitivity and the sharpness of the resonance spectrum. This superiority is corroborated by the analysis of the electric field distribution.

Future far-infrared space observatories equipped with cryogenic telescopes require ultra-sensitive detectors to enable measurements limited only by the sky background. We present the design, fabrication, and characterization of a superconducting kinetic inductance detector (KID) at 4.3 THz. The lumped-element KID comprises a tantalum interdigitated capacitor and a 100-nm-wide aluminum-line inductor connected in parallel. The inductor acts also as a low-volume absorber. We achieved photon-noise-limited performance with a noise equivalent power of 1.9 × 10−19 W/Hz referenced to absorbed blackbody power at a modulation frequency of 300 Hz. Under optical loading above 1.83 fW, the detector remains stable with white-noise spectra extending down to ∼100 mHz.

Transition metal diselenides, as a new class of two-dimensional semiconductor materials, have higher thermal stability, stronger optoelectronic properties and higher carrier mobility than sulfides, and perform better in optoelectronic devices. Among them, two-dimensional niobium diselenide (NbSe ₂ ) nanocrystals have excellent flexibility, fast optical response properties, outstanding chemical stability and light absorption properties, and thus have potential applications in the field of optical sensors. Here we present for the first time an optical biosensor based on multilayer NbSe ₂ , which can achieve high sensitivity and high FOM response to the refractive index of the medium by precise tuning of the optical and structural parameters of the sensor. The results of the theoretical study show that the multilayer NbSe ₂ at the nanoscale is capable of producing extremely strong Fano resonance effects in the proposed sensor structure in this paper. Compared with the conventional Au thin-film surface plasmon resonance (SPR)-based sensor, the figure of merit (FOM) of the NbSe ₂ @Ti ₃ C ₂ -MXene Fano-SPR-based sensor proposed in this study is substantially improved by a factor of 28. Our theoretical study demonstrates that NbSe ₂ is a surface plasmonic material with excellent Fano effect, which provides a theoretical reference for its experimental study in the field of biosensors.

In this study, a functional segmentation method for the design of adiabatic devices is presented. This method can be applied to calculate the compact adiabatic waveguide shapes for adiabatic taper waveguides and adiabatic mode converters. We introduce two algorithms, namely the quadratic function segmentation design for the adiabatic taper waveguide and the cubic function segmentation design for the adiabatic mode coupler. The design shows that for each segment, there is no need for separate simulations to obtain the length of each segment, and only the length of each segment can be determined by equations. This approach is much less cumbersome than other numerical design methods for adiabatic devices. The proposed functional segmentation design requires only a device length of 36 μm to achieve 95% power transfer efficiency, while a traditional linear-shape connection requires a device length of 54 μm to achieve the same power transfer efficiency. Therefore, the device designed by the function segmentation method has better compactness compared to the conventional linear-shape connection design of adiabatic devices.

Few-layer transition metal disulfides have attracted much attention in the field of optoelectronic devices due to their unique optical and electronic properties. Among them, two-dimensional tantalum diselenide (TaSe ₂ ) nanocrystals have excellent flexibility, fast optical response properties, outstanding chemical stability, and light absorption properties and thus have potential applications in the field of optical sensors. Here we present for the first time an optical biosensor based on multilayer 2H-phase TaSe ₂ /graphene, which can respond to subtle refractive index changes of the sensing medium by precise tuning of the optical and structural parameters of the sensor. The results of theoretical scientific studies show that multilayer TaSe ₂ /graphene films at the nano-scale can produce extremely strong long-range surface plasmon resonance (LRSPR) in the sensor structure proposed in this paper. Compared with the conventional Au nanofilm surface plasmon resonance (SPR) sensor, the figure of merit (fOm) of the proposed TaSe ₂ SPR-based sensor improved by a factor of 9.6. Our theoretical study demonstrates that TaSe ₂ is a surface plasmonic material with excellent performance and provides a theoretical reference for its experimental study in the field of biosensors.

In this study, a numerical method for designing efficient adiabatic devices with multiple structural parameter variations (NAMSP) is developed. This method can be applied to a wide range of devices based on adiabatic mode evolution structures. The numerical design complexity of multiple structural parameter variations will be greatly improved compared to the case of a single parameter variation. Therefore, an efficient domain decomposition scheme was originally introduced into the NAMSP method. The proposed method can help compute compact adiabatic guided-wave shapes for these adiabatic devices with multiple structural parameter variations. Adiabatic devices with multiple structural parameter variations are used to connect different complex waveguides, which are often difficult to design using analytical methods. The design involves tapering the width of the two or more core layers at one time; however, this change in the width typically affects the mode both vertically and horizontally. Our numerical method allows the shape of the width variation for each layer that facilitates compact adiabatic mode transformation to be obtained. The efficiency of the adiabatic device that was designed using the NAMSP method considerably exceeds that obtained using a linear-shaped device. Moreover, our designed adiabatic device enables an ultra-wide operating bandwidth (spans in the wavelength from 1050 nm to 4780 nm).

MXenes-based van der Waals heterojunction materials with excellent chemical stability and bioaffinity have been widely used in biosensing in recent years. We propose a new MoSe ₂ @Zr ₂ CO ₂ heterostructure as a long-range surface plasmon resonance (LRSPR) sensor based on the Kretschmann configuration from simulation and optimize the structure parameters algorithmically. Firstly, we investigate the effect of different layers of MoSe ₂ @Zr ₂ CO ₂ heterojunction on the LRSPR wave. The results show that the optimal number of layers for heterogeneous layers is 18. Secondly, the effects of dielectric thickness and refractive index on sensitivity are investigated in depth, and optimized structural parameters are obtained. Finally, the effect of prisms with different refractive coefficients on the sensor performance is also discussed, and it is shown that prisms with lower refractive coefficients can effectively improve the sensitivity performance of the sensor. The sensor response performance to biomolecules is greatly enhanced due to the gain of light absorption and surface plasmon resonance. Compared with the conventional precious metal Au-based (50 nm) thin-film SPR sensor, the figure of merit (FOM) of the sensor is improved by a factor of 8.16, and higher sensitivity (92.48°/RIU) and quality factor (319.63 RIU ^-1 ) are obtained in the visible range.

Ordinary mixers can hardly meet the requirements in terahertz (THz) communications due to the low-power and expensive THz sources. Sensitive harmonic mixers have been widely studied to avoid this problem, owing to the fact that the higher the number of harmonics, the lower the local oscillator (LO) frequency, and the lower the cost. High-T_c superconducting (HTS) Josephson junction (JJ) mixers are performing candidates for THz receiver frontends because of the advantages of excellent sensitivity, wide bandwidth, high harmonic number and low LO power requirement. However, the normal-state resistance of HTS JJ is so low that traditional antennas are difficult to match it. In other words, it is quite a challenge to match the input impedance to a low input impedance for traditional antennas, especially for antennas fed by coplanar striplines (CPSs). In this work, based on the structure of bowtie, two types of stub tuners were integrated to decrease the impedance of the bowtie antenna so as to improve the coupling efficiency between the traditional bowtie antenna and the JJ. Furthermore, HTS YBa₂Cu₃O_7-δ (YBCO) JJ harmonic mixers coupled with the proposed structures and fed by CPSs are fabricated and measured. The measurements show that the JJ mixer coupled with a pair of open-end stubs of the bowtie antenna achieves up to 88 harmonics, with a conversion efficiency of −69.6 dB. In contrast, the JJ mixer coupled with a pair of lumped-element stubs of the bowtie antenna only attains to 30 harmonics, with a conversion efficiency of −73.4 dB. Additional numerical simulations indicate that the coupling efficiency is enhanced when the complex impedance of the antenna is explicitly considered. Compared with other coupled traditional antennas, the JJ mixer with bowtie antenna has the largest harmonic number. This work paves the way for the future application of low-frequency and low-cost LO for THz communications.

We experimentally present a tunable electromagnetically induced transparency (EIT)-like response in bright-bright mode resonators. In contrast to previous studies, we used NbN film and a gold film composite structure metamaterial. A significant slow-light effect could be observed at the transmission window, and the maximum group index could reach 100. As a variation in temperature alters the intrinsic ohmic loss of superconducting NbN film, a temperature-dependent transmittance and slow-light effect were observed. To better illustrate the physical mechanism of the two modes, a hybrid coupling model was introduced to fit the experimental transmission spectra and extract the characteristic parameters of sub-resonators. We found excellent agreement with experimental results. Our results provide deeper insight into the metamaterial analogs of an EIT-like response and offer an alternative approach for engineering slow-light devices, bandpass filters, and switches/modulators at terahertz frequencies.