Abstract:In general， all known applications of high-power microwaves directly use energy to interact with matter. In recent years， with the development of powerful millimeter-wave radiation sources， microwave technology has gradually shifted towards the millimeter-wave frequency band. Due to the wavelength of radiation， millimeter waves have several unique characteristics， which allow for both the active development of existing technologies and the creation of new ones that require high power or radiation energy. This article provides an overview of research on the application of millimeter waves to solve problems in physics， material science， biomedicine， and others， including heating and diagnostics of thermonuclear plasma， processing and analysis of materials， biological effects， etc. The main difficulties arising in the implementation of the described tasks are presented， and the future development is also prospected.

Abstract:This paper discusses the influence of Sb/In ratio on the transport properties and crystal quality of the 200 nm InAsxSb1-x thin film. The Sb content of InAsxSb1-x thin film in all samples was verified by HRXRD of the symmetrical 004 reflections and asymmetrical 115 reflections. The calculation results show that the Sb component was 0.6 in the InAsxSb1-x thin film grown under the conditions of Sb/In ratio of 6 and As/In ratio of 3, which has the highest electron mobility (28560 cm2/V·s) at 300 K. At the same time, the influence of V/III ratio on the transport properties and crystal quality of Al0.2In0.8Sb/InAsxSb1-x quantum well heterostructures also has been investigated. As a result, the Al0.2In0.8Sb/InAs0.4Sb0.6 quantum well heterostructure with a channel thickness of 30 nm grown under the conditions of Sb/In ratio of 6 and As/In ratio of 3 has a maximum electron mobility of 28300 cm2/V·s and a minimum RMS roughness of 0.68 nm. Through optimizing the growth conditions, our samples have higher electron mobility and smoother surface morphology.

Abstract:Terahertz （THz） technology is undergoing a rapid development in biomedical applications. Researchers have made a series of important achievements in the study of biological samples on various levels such as biomolecules， cells， tissues， and individual organisms， which provide new insights and innovative approaches for biological research and biomedical diagnosis. In this review， the progress of applying THz technology in biomedical studies has been summarized， including three key aspects， namely， spectroscopic detection， imaging， and biological effects. The challenges encountered in THz biomedical applications have been discussed， and the future development directions have also been envisioned.

Abstract:Photoreflectance （PR） has been widely used for the characterization of various semiconductors as well as their surface and interface properties due to its non-destructive and high sensitivity virtues. From the viewpoint of the employment of monochromator， the experimental setup may be classified into front and backside （or dark and bright） configurations， which were applied to characterize the heterostructure of InP/In_0.52Ga_0.48As/InP grown by molecular beam epitaxy. It reveals that the front configuration well separates the luminescence from the modulation signal while the backside configuration benefits the extraction of weak modulation signals with the employment of high excitation power. Based on the backside configuration， we also observed a below band-gap excitation phenomenon， i.e. that the modulation signal of InP exhibits under the excitation of energetically low modulation light （1064 nm laser）. The result demonstrates that the backside configuration may be employed as a contactless electro-modulation technique for the characterization of wide band gap semiconductor heterostructures.

Abstract:Variable optical attenuator （VOA） arrays can be widely applied in optical communication and optoelectronic systems， but few VOA arrays are reported. Here a liquid-stop based microfluidic VOA array is proposed. It uses a spiral orbit to achieve different degrees of synchronous energy attenuation of multiple beams， or uses an annular orbit to achieve a same degree of synchronous energy attenuations， where the clear aperture of liquid stop is regulated by the electrowetting-on-dielectric effect. It has a compact structure， small volume， simple operation and low cost. Meanwhile， the attenuation ratio of beams can be flexibly adjusted to achieve the power equalization. The research results indicate that the VOA array has a wide attenuation range （0-100% attenuation） and very small insertion loss （0.26 dB） over general VOA arrays. The response time is 0.1 ms， and it is insensitive to the polarization. It can also act as an optical switch array. The proposed VOA array demonstrates the potential of integration and high performance， and it can provide a cost-effective way for applications.

Abstract:Optical coherence tomography （OCT） technology has the advantages of non-invasive， high-resolution， and real-time imaging， which is widely used in various fields such as biomedicine， material science and infrared sensing. In this paper， a ridge suspended optical waveguide based on silicon nitride （Si₃N₄） is proposed. The structural parameters of the designed waveguide were optimized by using finite difference time domain （FDTD） method. The characteristics of the supercontinuum spectrum generated in the optimized waveguide were investigated The simulation results show that for the optimized optical waveguide structure with ridge width of 750nm， ridge height of 700nm， plate thickness of 200nm， and upper layer height of 150nm， when a pump light with wavelength of 1.3μm， peak power of 2kW and pulse width of 50fs was injected into the waveguide， a broadband supercontinuum spectrum with wavelength covering the visible to the mid-infrared region （703~4014nm） can be generated. This work plays an important role in promoting the application of on-chip integrated broadband light source in biomedical imaging and related fields.

Abstract:The effects of calcium fluoride （CaF₂） doping on the optical and physical and chemical properties of Ytterbium fluoride （YbF₃） materials were studied. Pure YbF₃ thin films and YbF₃ thin films doped with different proportions of CaF₂ were deposited by electron beam and thermal evaporation， respectively. The characteristics of single layer were measured by spectrometer， stress measurement system， X-ray Diffraction （XRD）， Atomic Force Microscope （AFM） and other measuring devices. The optical constants were fitted by the classical Lorentz oscillator model. The results show that the single-layer film with better optical and physical and chemical properties is obtained by electron beam deposition， in the condition of 1% CaF₂ doping. A long-wave infrared anti-reflection multi-layer sample was designed and fabricated and its spectrum and reliability test were carried out. The results show that its transmittance in the long-wave infrared region is as high as 99%， and the reliability meets the requirements of space application.

Abstract:To meet the high-speed and high-capacity demands of communication, a 300GHz electronic wireless transmission system for terahertz frequencies is proposed, which incorporates Probability Shaping (PS), Discrete Multi-tone Modulation (DMT) and DFT-Spread (DFT-S) techniques. PS increases the Euclidean distance between constellation points, thereby enhancing the receiver sensitivity. In the system at most 55% bit error rate is decreased, enabling to extend transmission range. DFT-S technique reduces 1.68 dB peak-to-average power ratio of Orthogonal Frequency Division Multiplexing (OFDM) signals in the system, thus improving their resistance to nonlinear effects. By integrating these advanced digital signal processing techniques, 12GBaud PS-16QAM OFDM-DMT signals and 10GBaud PS-64QAM DFT-S-OFDM-DMT signals were successfully implemented in 1 m wireless transmission. Finally, the performance advantages of these digital signal processing techniques were compared.

Abstract:Metasurfaces in the long wave infrared （LWIR） spectrum hold great potential for applications in thermal imaging， atmospheric remote sensing， and target identification， among others. In this study， we designed and experimentally demonstrated a 4 mm size， all-silicon metasurface metalens with large depth of focus operational across a broadband range from 9 μm to 11.5 μm. The experimental results confirm effective focusing and imaging capabilities of the metalens in LWIR region， thus paving the way for practical LWIR applications of metalens technology.

Abstract:The development of InGaAs/InP single-photon avalanche photodiodes （SPADs） necessitates the utilization of a two-element diffusion technique to achieve accurate manipulation of the multiplication width and the distribution of its electric field. Regarding the issue of accurately predicting the depth of diffusion in InGaAs/InP SPAD， simulation analysis and device development were carried out， focusing on the dual diffusion behavior of zinc atoms. A formula of to quantitatively predict the diffusion depth is obtained by fitting the simulated twice-diffusion depths based on a two-dimensional （2D） model. The 2D impurity morphologies and the one-dimensional impurity profiles for the dual-diffused region are characterized by using scanning electron microscopy and secondary ion mass spectrometry as a function of the diffusion depth， respectively. InGaAs/InP SPAD devices with different dual-diffusion conditions are also fabricated， which show breakdown behaviors well consistent with the simulated results under the same junction geometries. The dark count rate （DCR） of the device decreased as the multiplication width increased， as indicated by the results. DCRs of 210⁶， 110⁵， 410⁴， and 210⁴ were achieved at temperatures of 300K， 273K， 263K， and 253K， respectively， with a bias voltage of 3V， when the multiplication width was 1.5 μm. These results demonstrate an effective prediction route for accurately controlling the dual-diffused zinc junction geometry in InP-based planar device processing.