Kejian Chen

A Study of FSS in Terahertz Range for Polarization Modulation Purpose

A polarization sensitive frequency selective surface (FSS) composed of connected electric LC resonators is proposed as the terahertz wave filter. The experimental results match the simulation results well and show that the FSS has good capability of polarization control and wavelength selection. The tunability of FSS is also studied by investigating the relation between the conductivity of the joint area of bent-lines and the resonant peak position/strength. Such a device can be applied as a flexible polarization modulator.

Location-dependent metamaterials in terahertz range for reconfiguration purposes

We propose and demonstrate a multifunctional location-dependent metamaterial in the terahertz (THz) range in which the unit cell consists of two pairs of coupled resonators. Experimental and simulation results of our devices reveal that both pairs of the coupled resonators will keep their individual resonance modes when they join together. Thus, the overall transmission spectrum is a combination of frequency response spectra of its corresponding constituent parts. While changing the locations of the inner resonators in our structure, controllable width of transmission window and changeable number of transmission dips can be realized. Our design provides a feasible structure for multifunctional microelectromechanical devices.

Differences in the evolution of surface-microstructured silicon fabricated by femtosecond laser pulses with different wavelength.

We experimentally investigate the differences in the evolution of surface-microstructured silicon fabricated by femtosecond laser pulses with different wavelength as a function of irradiated laser energy. The results show that when laser energy absorbed by the silicon material is the same, laser pulses with a shorter wavelength can form the surface-microstructured silicon with less laser energy, while the corresponding spike height is much lower than that of laser pulses with a longer wavelength. This is because the penetration depth of the laser pulses increases exponentially at the increase of the laser wavelength. Additionally, for two laser pulses with the certain wavelength and the certain absorption efficiency of silicon, the proportional relations between their formed spike height and irradiated laser energy should be determined. In particular, the average spike height is 3 times with 8 times corresponding energy for 800 nm laser pulses than that of 400 nm. These results are a benefit for the fast and optimum-morphology preparation of microstructured silicon.

A review of 3D-printed sensors

ABSTRACT Nowadays, sensors play an important role in human life. Among the many manufacturing methods used in the fabrication of sensors, three-dimensional (3D) printing has gradually shown its advantages, particularly with commercial products. Physical sensors, biosensors, and chemical sensors can all be fabricated via 3D printing technology, through either directly printing sensing components, printing molds for casting sensors, or printing platforms to be integrated with commercial sensors. In this article, the varieties of features and applications of 3D printing technologies used in the fabrication of sensors are reviewed. Several types of 3D printing technologies are compared for better understanding of the tools. With the development of new or hybrid manufacturing methods and materials used in the 3D printing technology, this technology will show its great advantages and potential in the fabrication of highly sensitive nanosensors or compound sensors with 3D intricate structures.

An electrically tunable terahertz metamaterial modulator with two independent channels

An electrically tunable terahertz modulator with two independent channels employing a hybrid metamaterial is established. The implemented Schottky structures consist of metallic squares with tips and crosses, which form two types of Schottky structures on an n-doped gallium arsenide (GaAs). By selecting one or both types of Schottky structures to connect to the Ohmic contact, under a bias voltage, a depletion zone can be generated and the semiconductor conductivity can be actively controlled to modulate the transmission of a corresponding channel band or both the channels. Such an electrically controlled modulator with two independent channel bands paves the way to achieving terahertz communication and is more conducive to practical applications.

Dual-Focuses Metalens for Copolarized and Cross-Polarized Transmission Waves

Metasurfaces can reshape the wavefront in the desired manner by manipulating the phase profile and amplitude of the incident wave. In this paper, we demonstrate an ultrathin terahertz metalens based on our designed resonator structure, where the polarization state can be converted to the orthogonal direction and the parabolic phase profile is designed covering a 2π phase region. Many functional metalenses are also engineered to meet the demand of focusing, dual-polarization confocal, and dual focuses for orthogonal polarization in the frequency range from 0.65 to 0.8 THz. The presented metalenses can provide potential applications in terahertz communications and imaging systems.

Publisher’s Note: Effect on cross-polarization conversion by the end shape of eSRR in a multilayer metamaterial device

This PDF file contains the errata for “OE Vol. 55 Issue 04 Paper OE-2016-0328-ERR” for OE Vol. 55 Issue 04

The effect on cross-polarization conversion by the end shape of electric split-ring resonators in a multilayer metamaterial device

Abstract. Several types of multilayer metamaterial devices are studied to achieve cross-polarization conversion as well as subwavelength transmission enhancement. The surface current of three metamaterial layers reveals that the induced current around the apertures of the middle metal layer is the key to the physical mechanism. Furthermore, the simulated results show that the proposed devices have good performance on both the polarization conversion ratio and transmission rate. Lastly, a tunable cross-polarization conversion design is proposed and researched. These results can help to facilitate the development of high-sensitivity sensors and terahertz technology.

A method of monitoring the temperature of the photoconductive antenna

Photoconductive antenna (PCA), as the most widely used emitter (or detector) in Terahertz time-domain spectroscopy (TDS) system, virtually acts as a semiconductor switch, whose electrical conductivity controlled by pump light. At the same time, the heat caused by the pump light and the electrical bias will be stacked in a tiny area. Inevitably, the thermal effects, which may reduce the performance of PCA and the operational lifetime of device, need to be considered, especially for that generated by a compact package fiber-pigtailed photoconductive antenna. Nonetheless, there still lacks of relevant reports about real-time temperature monitoring for PCA. This paper proposes a method to obtain the temperature information by observing the temperature dependent frequency drifting of radiation spectroscopy. In other words, it converts the temperature information via analyzing the radiation spectrum of the conventional TDS system. In this work, we simulate a design of meta-atom-loaded PCA with indium antimonide (InSb). As a kind of temperature-dependent permittivity of the semiconductor, InSb is stuffed into the gap of split-ring resonator (SRR). When the temperature increases from 300K to 380 K, the resonance frequency shifts from 0.582THz to 0.678THz (a shift more than 16%), calculated by the commercial software-CST. The significant blue shift is caused by the SRR loading temperature sensitive materials, well analyzed by the LC resonant circuit model. Then, one can clearly obtain the actual antenna temperature from the radiation spectrum through the relationship between temperature and resonance frequency. Always, this simply method could be applied to shift the peak frequency of spectrum for various applications.

A study of trapped mode resonances in asymmetric X-shape resonator for frequency selective surface

FSS is a two-dimensional periodic array of resonating metallic-dielectric structures, When FSS device steps into Terahertz range from microwave range, it is studied as THz functional components (such as Terahertz filter, Terahertz biochemical sensor, etc.) to promote the functionality of the THz spectroscopy/imaging system. When the device requires a narrow band transmission window for frequency selecting or a high electric field concentration in certain area to improve its sensitivity for sensing, normally, a high quality (Q) resonant structure can give helps. Recently, high-Q resonance induced by trapped mode resonance i studied widely in FSS research areas. To induce trapped mode resonance, one can simply break the symmetric of the unit structure of FSS. In this paper, several asymmetric X-shaped resonators for FSS working in terahertz range have been studied numerically. To compare the behaviour of X-shape resonator under different conditions (with additional part: Heart lines, Shoulder lines, Wrap or Shoes squares), a common platform (θ=60, θis angle of X shape) which is suitable for most of cases was used to make the study more meaningful. As the field enhancement behaviour is related to the trapped mode introduced by the asymmetric structure, we propose such kind of device to be used as a high quality filter or as a sensing element for biochemical samples.