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Sep. 2021, Volume 14 Issue 3

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A lithium (Li)-ion exchange method is reported to fabricate functional inks containing well-dispersed two-dimensional (2D) materials. The Li-ion-exchanged Na2W4O13 (LixNa2−xW4O13) nanosheets show highly stable dispersity in water due to the high affinity of Li ions with respect to water. Moreover, the aqueous ink can be sprayed on various substrates to obtain a uniform LixNa2−xW4O13 nanosheet film, exhibiting an excellent electrochromic performance. This study breaks the limitation that the majority 2D materials can disperse well only in organic solvents or in surfactant-assisted water solutions, paving a new methodology to prepare other 2D ion-intercalated materials based on aqueous inks by appropriately selecting ion species. This cover is dedicated to the memory of Prof. Jun Zhou.
For more details, please refer to the article entitled “LixNa2−xW4O13 nanosheet for scalable electrochromic device“ by Yucheng LU et al., Front. Optoelectron., 2021, 14(3): 298−310.

Jun. 2021, Volume 14 Issue 2

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Optical metasurfaces, composed of planar arrays of sub-wavelength dielectric or metallic structures that collectively mimic the operation of conventional bulk optical elements, have revolutionized the field of optics by their potential in constructing high-efficiency and multi-functional optoelectronic systems with compact form factor. By engineering the geometry, placement, and alignment of its constituent elements, an optical metasurface arbitrarily controls the magnitude, polarization, phase, angular momentum, or dispersion of an incident light.
This special issue (Recent Advances in Optical Metasurfaces (Guest Editors: Cheng Zhang, Din-Ping Tsai)) features some recent advances of optical metasurfaces, covering various topics ranging from metasurface design to practical applications.
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Mar. 2021, Volume 14 Issue 1

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Terahertz time-domain spectroscopy (THz-TDS) has proven to be an invaluable tool for the study of elementary and collective excitations in condensed matter systems. Adding a high magnetic field to THz-TDS can lead to further insight into microscopic physics behind complex many-body behaviors of solids and allow one to access new exotic states of matter. Here, we review recent progress in combining THz-TDS and strong magnetic fields in condensed matter spectroscopy. After discussing the advantages and disadvantages of different types of high-field magnets and THz radiation detection schemes, we describe some of the new physical phenomena that were enabled by this unique “marriage” of the two methods.
For more details, please refer to the article entitled “Time-domain terahertz spectroscopy in high magnetic fields” by Andrey BAYDIN et al., Front. Optoelectron., 2021, 14(1): 110−129.
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Dec. 2020, Volume 13 Issue 4

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A stochastic optical reconstruction microscopy (STORM) super-resolution probe was developed to selectively label the intercellular tunnel nanotubes (TNTs), which can be photoblinking illuminated with a single laser beam under low power density. The TNTs was precisely localized using the photo-blinking of the probe molecules to achieve live cell STORM imaging. The ultra-fine structures of TNTs were clearly observed under STORM microscopy, of which the typical diameter was evaluated to be 133.5 ± 1.5 nm and the dynamics of a ring-like structure during the cleavage was acquired to provide the insights into the biological significance. All these results demonstrated the potential applicability of the STORM probe in the disclosure of ultra-fine structural variations beyond optical diffraction limit, which play essential roles in different biological events like cell-cell communications, signalling or mass exchanges and so on.
For more details, please refer to the article entitled “Super-resolution imaging of the dynamic cleavage of intercellular tunneling nanotubes” by Wanjun GONG et al., Front. Optoelectron., 2020, 13(4): 318−326

Sep. 2020, Volume 13 Issue 3

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Halide perovskites are very promising for display applications because of their excellent luminescence yield, tunable color in the visible spectrum, high color purity, and low material cost. In recent years, perovskite-based light-emitting diodes (PeLEDs) have obtained significant progress in terms of luminance, external quantum efficiency, and stability. Now the device metrics of best-performing blue, green, and red PeLEDs are summarized and compared, in a hope to bring researchers in this field an overview of state-of-art of PeLEDs’ performance.
For more details, please refer to the article entitled “Focus on performance of perovskite light-emitting diodes” by Peipei DU et al., Front. Optoelectron., 2020, 13(3): 235−245

Jun. 2020, Volume 13 Issue 2

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All-optical modulators to process optical signals without electro-optical conversion play an essential role in the next generation ultrafast, ultralow-power-consumption optical information processing. Graphene, with high nonlinearity and ultrashort relaxation time, is an emerging material for high-performance all-optical modulation. The switching time of graphene-based all-optical modulators ranges from milliseconds to femtoseconds. The modulation mechanisms utilized could be concluded into four types: opto-thermal effect, optical induced carrier effect, optical Kerr effect, and saturable absorption effect. To enhance light-matter interaction and boost the modulation depth while decreasing the switching threshold, graphene has been integrated with fibers, waveguides and micro/nano-cavities.
For more details, please refer to the article entitled “Graphene-based all-optical modulators” by Chuyu Zhong et al., Front. Optoelectron., 2020, 13(2): 114−128

Mar. 2020, Volume 13 Issue 1

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Graded photonic super-crystals have been fabricated through holographic lithography. A phase pattern was generated through pixel-by-pixel phase engineering. A 532 nm laser was incident onto the phase pattern displayed in a spatial light modulator. A diffraction pattern was generated and imaged through a 4f system. A Fourier filter was placed to let pass four outer beams and eight inner beams. These twelve beams were overlapped to form an interference pattern. A photoresist mixture received the exposure of the interference pattern. After the photoresist development, graded photonic super-crystals were obtained as confirmed by the scanning electron microscope (SEM). The graded photonic super-crystals have eight gradient lattice clusters surrounding the central non-gradient lattices. For more details, please refer to the article entitled “Holographic fabrication of octagon graded photonic super-crystal and potential applications in topological photonics” by Oliver Sale et al., Front. Optoelectron. 2020, 13(1): 12-17.

Dec. 2019, Volume 12 Issue 4

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The triple-mesoscopic perovskite solar cells are fabricated by a screen-printing technique based process, which is fast and compatible with commercial production lines. By optimizing the compositions of the pastes and the printing parameters, TiO2, ZrO2 and Carbon films with desired dimensions can be effectively deposited on transparent conducting substrates. After infiltrating the perovskite absorber in the mesoporous scaffold, the fabrication of triple-mesoscopic perovskite solar cells is completed. Since no expensive hole transporting material or noble metal is required, triple-mesoscopic perovskite solar cells own the advantages of low material cost and simple fabrication process, and offer promising prospects for commercialization.For more details, please refer to the article “Screen printing process control for coating high throughput titanium dioxide films toward printable mesoscopic perovskite solar cells”.

Sep. 2019, Volume 12 Issue 3

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Vortex beam with low spatial coherence is called partially coherent vortex (PCV) beam. In contrast with a coherent vortex (CV) beam whose intensity distribution maintains a doughnut profile during propagation in free space, the intensity of a PCV beam evolves gradually from a doughnut profile to a Gaussian profile upon propagation. The most exciting property of a PCV beam is that its spectral degree of coherence (SCD) displays ring dislocations (i.e., coherence singularities) in the far field, and the topical charge information can be inferred from the ring dislocations. Thus the use of PCV beam for information transfer and recovery is very promising, particularly in adverse environment (e.g., random media and turbulence), which will degrade the spatial coherence of light beam on propagation. For more details, please refer to the article “Review on partially coherent vortex beams”.

Jun. 2019, Volume 12 Issue 2

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Terahertz (THz) spectroscopy has drawn a significant amount of attention in the fields ranging from homeland security to environmental monitoring, because of its capability of non-invasive, non-destructive measurement. However, advanced THz remote sensing techniques are obstructed by strong absorption by water vapor in the ambient air, as well as the difficulties in generating intense broadband coherent THz radiation and effective detection from remote distance. The THz wave generation scheme shown in the image provides a possible solution of THz source for remote sensing applications, where a laser pulse becomes a ring-Airy beam after a phase mask, then the ring-structured optical beam collapses at focus with a parabolic caustic and creates plasma which generates THz wave. The THz generation performance can be improved through tailoring the generation media, i.e., the air-plasma. This idea can be also applied to THz wave detection based on THz-radiation-enhanced-emission-of-fluorescence (THz-REEF). For more details, please refer to the article “Terahertz wave generation from ring-Airy beam induced plasmas and remote detection by terahertz-radiation enhanced-emission-of-fluorescence: a review” by Kang LIU, Pingjie HUANG and Xi-Cheng ZHANG, Front. Optoelectron. 2019, 12 (2): 117-147. [Photo credits: Yiwen E]

Mar. 2019, Volume 12 Issue 1

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Optical vortices, also known as orbital angular momentum (OAM) beams, have been studied for decades. In various optical vortices enabled applications such as optical communications, optical sensing and optical measurement, the generation of multiple optical vortices is of great importance. It is highly desirable to develop methods for generating a large number of optical vortices with less optical elements. Here we focus on the methods of multiple optical vortices generation and its applications. We present the methods for generating multiple optical vortices in three cases, i.e., 1-to-N collinear OAM modes, 1-to-N OAM mode array, and N-to-N collinear OAM modes. Diverse applications of multiple OAM modes in optical communications and non-communication areas are reported. We also discuss future trends, perspectives and opportunities of multiple optical vortices generation. For more details, please refer to the article “A review of multiple optical vortices generation: methods and applications” by Long ZHU and Jian WANG, Front. Optoelectron. 2019, 12 (1): 52-68.