Journal of Physics D: Applied Physics

Cui, Ying; Wang, Xiaosai; Jiang, Huan; Jiang, Yongyuan

doi: 10.1088/1361-6463/ac4450pmid: N/A

Circular dichroism (CD) response is extremely important for dynamic polarization control, chiral molecular sensing and imaging, etc. Here, we numerically demonstrated high-efficiency and tunable CD using a symmetry broken graphene-dielectric-metal composite microstructure. By introducing slot patterns in graphene ribbons, the metasurface exhibits giant polarization-selective absorption for circularly polarized (CP) wave excitations. The maximum CD reaches 0.87 at 2.78 THz, which originates from the localized surface plasmon resonances in patterned graphene. Besides, the operating frequency and magnitude of CD are dynamically manipulated by gating graphene’s Fermi energies. The proposed chiral graphene metasurface with high-efficiency and tunable capability paves a way to the design of active CD metasurfaces.

Bhowmik, Tanmay; Sikdar, Debabrata

doi: 10.1088/1361-6463/ac4455pmid: N/A

Electro-optical modulation, where a radio frequency signal can be encoded in an optical field, is crucial to decide the overall performance of an integrated photonics system. Due to the growing internet penetration rate worldwide, polarization-division-multiplexing (PDM) technique has emerged to increase the link capacity, where polarization-independent modulators are desirable to reduce system complexity. In this study, we propose a novel parallel directional coupler based dual-polarization electro-absorption modulator based on epsilon-near-zero (ENZ) material. The proposed design is capable of independent and synchronized modulation of two fundamental modes viz. transverse magnetic (TM) and transverse electric (TE) mode of a standard silicon (Si) rib waveguide. Indium-tin-oxide (ITO)–Si based two parallel hybrid plasmonic waveguides (HPW1 and HPW2) are placed such that fundamental TM (TE) mode of the input bus waveguide can be coupled to HPW1 (HPW2). The ENZ-state of ITO, acquired upon two independent electrical gating, enables large modulation depth by utilizing enhancement of electric field at the absorptive carrier accumulation layer. With a 27 μm active length, the extinction ratio (ER) of the proposed design is 10.11 dB (9.66 dB) for TM (TE) modulation at 1550 nm wavelength. This results in a 0.45 dB ER-discrepancy and indicates the polarization-insensitive nature of the modulator. The insertion losses and modulation bandwidths of our design are less than 1 dB and more than 100 GHz, respectively, for both polarizations over the entire C-band of wavelength. The proposed design can find potential applications in the PDM-enabled integrated photonics systems and high speed optical interconnections at data center networks.

Ding, Ye; Li, Qiang; Li, Jingyi; Wang, Lianfu; Yang, Lijun

doi: 10.1088/1361-6463/ac4295pmid: N/A

Graphene oxide (GO) has emerged as a unique and multifaceted novel material with a wide range of applications in electrochemistry and optoelectronic engineering. In these applications, the GO surface is characterized with different functional structures in the micro-nano scale, while the femtosecond laser is a promising and versatile tool for manufacturing these structures comparing with conventional approaches. However, the comprehensive surface responses and corresponding regimes of GO surface under femtosecond laser irradiation are not yet identified, which creates obstacles to the further application of femtosecond lasers in programming GO surfaces with specific nanopatterns. Herein, theoretical models characterizing the electrical response, i.e. the transient spatial and temporal distribution of infrared femtosecond laser-excited free electron density at the GO surface layers are established. The numerical simulations are carried out using the discontinuous Galerkin finite element algorithm with a 5 fs time step. The relationship between the laser polarized electric field and free electron density is revealed. On this basis, the surface plasma distribution is characterized, the accuracy of which is verified through the comparison of experimental ablation morphology. Thermal, morphological and chemical responses of the GO surface using different parameters are analyzed correspondingly, from which the formation and evolution mechanisms of surface nanopatterns with different features are explained. This work offers a new insight into the fundamental regimes and feasibility of ultrafast patterning of GO for the application of multifunctional device engineering.

Kumar, Ashok; Khan, Mustaque A; Kumar, Mahesh

doi: 10.1088/1361-6463/ac33d7pmid: N/A

Since the discovery of graphene there has been a strong interest in two-dimensional (2D) materials among the scientific community due to their extraordinary properties. Although ultraviolet (UV) photodetectors based on bulk wide bandgap semiconductors exhibit a good response, their photodetection performance significantly diminishes as their thickness is reduced to atomic scale, due to poor absorption and surface dangling bonds. 2D layered materials are free of dangling bonds and have a layer-dependent tunable bandgap and optoelectronic properties. Even an atomically thin layer of a 2D material shows high absorption due to strong light–matter interaction. 2D materials are attracting a lot of attention due to their compatibility with flexible, wearable devices and the ease of making van der Waals heterostructures. Although graphene and transition metal dichalcogenides have shorter band gaps, these materials can be easily integrated with other wide bandgap materials for UV detection, and such integration has often produced extraordinary device performance. Also, low bandgap, strong UV-absorbing 2D materials can be utilised for UV detection by using an optical bandpass filter. Recently, wide-bandgap 2D materials such as gallium sulphide (GaS), hexagonal boron nitride (hBN), and bismuth oxychlorides (BiOCls) have been explored for application in UV photodetection. Many of these wide bandgap materials show extraordinary UV photodetection performance.

Gudovskikh, A S; Baranov, A I; Uvarov, A V; Kudryashov, D A; Kleider, J-P

doi: 10.1088/1361-6463/ac41fapmid: N/A

Microcrystalline gallium phosphide (GaP)/Si multilayer structures grown on GaP substrates using combination of plasma enhanced atomic layer deposition (PE-ALD) for GaP and plasma-enhanced chemical vapor deposition for Si layers deposition are studied by three main space charge capacitance techniques: capacitance versus voltage (C-V) profiling, admittance spectroscopy (AS) and deep level transient spectroscopy (DLTS), which have been used on Schottky barriers formed on the GaP/Si multilayer structures. C-V profiling qualitatively demonstrates an electron accumulation in the Si/GaP wells. However, quantitative determination of the concentration and spatial position of its maximum is limited by the strong frequency dependence of the capacitance caused by electron capture/emission processes in/from the Si/GaP wells. These processes lead to signatures in AS and DLTS with activation energies equal to 0.39 ± 0.05 and 0.28 ± 0.05 eV, respectively, that are linked to the energy barrier at the GaP/Si interface. It is shown that the value obtained by AS (0.39 ± 0.05 eV) is related to the response from Si/GaP wells located in the quasi-neutral region of the Schottky barrier, and it corresponds to the conduction band offset at the GaP/Si interface, while DLTS rather probes wells located in the space charge region closer to the Schottky interface where the internal electric field yields to a lowering of the effective barrier in the Si/GaP wells. Two additional signatures were detected by DLTS, which are identified as defect levels in GaP. The first one is associated to the SiGa + VP complex, while the second was already detected in single microcrystalline GaP layers grown by PE-ALD.

Fan, Zhiqiang; Sun, Jun; Cao, Yibing; Song, Zhimin; Shi, Yanchao; Hua, Ye; Wu, Ping

doi: 10.1088/1361-6463/ac453bpmid: N/A

A novel self-injection relativistic backward wave oscillator (RBWO) has been proposed. By introducing a self-injection path into the RBWO, a small portion of the energy in the reflector can be coupled to the upstream of the reflector, and then the formed electric field in the self-injection path region can pre-modulate the passing electron beam, to promote a frequency-locking oscillation of the electron beam. The pre-modulated electron beam can be expected to enhance the beam-wave interaction and suppress parasitic mode oscillation, which is beneficial for maintaining the dominant role of the operating mode. The proposed self-injection RBWO shows great potential for improving the conversion efficiency and pulse duration time. Through particle-in-cell simulation, a microwave with a power of 10.6 GW is obtained, when the beam voltage is 1.08 MeV, and the beam current is 18.6 kA. The conversion efficiency is 53%.

Karmakar, Subhajit; Varshney, Ravi; Roy Chowdhury, Dibakar

doi: 10.1088/1361-6463/ac42f7pmid: N/A

Optically thin metasurfaces operating at sub-skin depth thicknesses are intriguing because of their associated low plasmonic losses (compared to optically thick, beyond skin-depth metasurfaces). However, their applicability is restricted largely because of reduced free space coupling with incident radiations resulting in limited electromagnetic responses. To overcome such limitations, we propose enhancement of effective responses (resonances) in sub-skin depth metasurfaces through incorporation of a magneto-transport (giant magneto resistance) concept. Here, we experimentally demonstrate dynamic magnetic modulation of structurally asymmetric metasurfaces (consisting of superlattice arrangement of thin (∼10 nm each) magnetic (Ni)/nonmagnetic (Al) layers) operating in the terahertz (THz) domain. With increasing magnetic field (applied from 0 to 30 mT approximately, implies increasing superlattice conductivity), we observe stronger confinement of electromagnetic energy at the resonances (both in dipole and Fano modes). Therefore, this study introduces a unique magnetically reconfigurable ability in Fano resonant THz metamaterials, which directly improves their performances operating in the sub-skin depth regime. Our study can be explained by spin-dependent THz magneto-transport phenomena in metals and can stimulate the paradigm for on-chip spin-based photonic technology enabling dynamic magnetic control over compact, sub-wavelength, sub-skin depth metadevices.

Pal, Arnab; Feng, Zhenjie; Wu, Hao; Wang, Ke; Si, Jingying; Chen, Jiafeng; Chen, Yanhong; Zhang, Yifeng; Chen, Fei; Ge, Jun-Yi; Cao, Shixun; Zhang, Jincang

doi: 10.1088/1361-6463/ac44c3

Yun, Xiaofan; Lin, Wenkui; Hu, Rui; Wang, Xiaoyi; Zeng, Zhongming; Zhang, Xinping; Zhang, Baoshun

doi: 10.1088/1361-6463/ac4452pmid: N/A

With the increasing application of personal navigation systems in consumer electronics, the demand for multi-axis magnetic sensors based on MEMS is growing. We report a biaxial MEMS DC magnetic sensor consisting of an Mo/AlN/Fe80Ga20 film bulk acoustic resonator, with anisotropy ΔE effect-based sensing principle. Different from the previously reported 1D magnetic sensor based on the ΔE effect, the anisotropic ΔE effect was used to realize in-plane and out-of-plane 2D magnetic field responses on a discrete sensor, and the sensor had two readout methods: resonant frequency f and return loss S11. The magnetic sensor realized the resonant frequency f shifted by 1.03 MHz and 0.2 MHz in the 567 Oe in-plane magnetic field and 720 Oe out-of-plane magnetic field, respectively, and the S11 changes by −30.2 dB and −0.92 dB. As the applied magnetic field increases, the −3 dB bandwidth quality factor Q3dB of the S11 curve gradually increases, and its maximum values in the in-plane and out-of-plane magnetic fields are 77 143 and 1828, respectively, which reduces the detection limit of the magnetic sensor. The resonant magnetic sensor has stable high linear temperature and frequency drift characteristics, and its temperature frequency coefficient is −48.7 ppm °C−1.

Ling, Xiaohui; Zhang, Zan; Chen, Shizhen; Zhou, Xinxing; Luo, Hailu

doi: 10.1088/1361-6463/ac3456pmid: N/A

Optical beam shifts, which mainly refer to the Goos–Hänchen shift and spin-Hall shift, widely exist in basic optical processes such as interface reflection and refraction. They are very sensitive to changes in the parameters of the materials that constitute the interface and therefore show great potential for applications in precision metrology and sensing. The interaction between light and two-dimensional (2D) atomic crystals is very weak, and beam shifts provide an alternative approach to explore and characterize 2D atomic crystals. In this paper, we first present a full-wave theory of beam shifts and introduce the experimental measurement of beam displacements with quantum weak measurement technology, and then review their applications in characterizing 2D atomic crystals, such as determining the layer number and measuring the optical conductivity of few-layer graphene. Finally, we discuss the beam displacements in twisted bilayer 2D atomic crystals and 2D atomic crystals under applied electric or magnetic fields.