Dispersive Element Research Articles

Large Dispersion Silicon Bragg Grating for Full-Field 40-GBd QPSK Phase Retrieval Receiver

Optical devices that introduce and compensate for dispersion serve an important role in communication networks, photonic signal processing, and nonlinear optics. In this article, we demonstrate a silicon photonic Bragg grating which simultaneously achieves a large dispersion and wide bandwidth. We measure the grating to have a dispersion of −146 ps/nm over a 171 GHz bandwidth, representing the highest demonstrated grating dispersion over this wide bandwidth in a standard thickness silicon photonics process. Additionally, we show a significant reduction of group delay ripple by tuning the grating using an integrated phase shifter array to address fabrication variations. We further use the silicon grating as a dispersive element in a direct-detection phase retrieval receiver for 40 GBd quadrature phase shift keying (QPSK) signals and achieve a bit error rate (BER) below the 20% forward error correction (FEC) threshold. These results establish the potential for scalable silicon photonic circuits leveraging large dispersion for optical communication and other applications.

Computational spectropolarimetry with a tunable liquid crystal metasurface

While conventional photodetectors can only measure light intensity, the vectorial light field contains much richer information, including polarization and spectrum, that are essential for numerous applications ranging from imaging to telecommunication. However, the simultaneous measurement of multi-dimensional light field information typically requires the multiplexing of dispersive or polarization-selective elements, leading to excessive system complexity. Here, we demonstrate a near-infrared spectropolarimeter based on an electrically-tunable liquid crystal metasurface. The tunable metasurface, which acts as an encoder of the vectorial light field, is tailored to support high-quality-factor guided-mode resonances with diverse and anisotropic spectral features, thus allowing the full Stokes parameters and the spectrum of the incident light to be computationally reconstructed with high fidelity. The concept of using a tunable metasurface for multi-dimensional light field encoding may open up new horizons for developing vectorial light field sensors with minimized size, weight, cost, and complexity.

Large-aperture, widely and linearly tunable, electromagnetically actuated MEMS Fabry-Perot filtering chips for longwave infrared spectral imaging.

Longwave infrared spectral imaging (LWIR-SI) has potential in many important civilian and military fields. However, conventional LWIR-SI systems based on traditional dispersion elements always suffer the problems of high cost, large volume and complicated system structure. Micro-electro-mechanical systems Fabry-Perot filtering chips (MEMS-FPFC) give a feasible way for realizing miniaturized, low cost and customizable LWIR-SI systems. The LWIR MEMS-FPFC ever reported can't meet the demands of the next-generation LWIR-SI systems, due to the limitation of small aperture size and nonlinear actuation. In this work, we propose a large-aperture, widely and linearly tunable electromagnetically actuated MEMS-FPFC for LWIR-SI. A multi-field coupling simulation model is built and the wafer-scale bulk-micromachining process is applied to realize the design and fabrication of the proposed MEMS-FPFC. Finally, with the rational structural design and fabrication process, the filtering chip after packaging has an aperture size of 10 mm, which is the largest aperture size of LWIR MEMS-FPFC ever reported. The fabricated electromagnetically actuated MEMS-FPFC can be tuned continuously across the entire LWIR range of 8.39-12.95 µm under ±100 mA driving current with a pretty good linear response of better than 98%. The developed electromagnetically actuated MEMS-FPFC can be directly used for constructing miniaturized LWIR-SI systems, aiming for such applications as military surveillance, gas sensing, and industry monitoring.

Analysis of electron emission characteristics of triggered vacuum switch based on cold cathode materials

A trigger vacuum switch that works for a long time is subject to the stable emission of initial electrons. Cold cathode materials such as velvet and carbon fiber have the characteristics of large emission electron area, uniformity, and stability. In this paper, two cold cathode materials, namely T4 rayon velvet and T300 carbon fiber board, are attached. They were used on the surface of the vacuum switch cathode, the trigger electrode was located in the middle of the cathode, and the trigger vacuum switch was triggered by a positive polarity high-voltage pulse along the surface flashover. The breakdown voltage and dispersion were studied in the form of capacitive discharge, and the electron emission characteristics of the two materials were explored from a microscopic perspective, such as through scanning electron microscope and energy dispersive spectrometer element analysis. The results show that the triggering vacuum switch using this cold cathode material has stable triggering, wide operating voltage, and low breakdown voltage dispersion. The electron emission of the velvet has both fiber tip emission and lateral flashover mechanism, and carbon fiber is prone to surface damage; the anode metal surface is partially carbonized due to electron sputtering.

Reactive ion plasma etched surface relief gratings for low/medium/high resolution spectroscopy in astronomy

We report the fabrication of a binary-phase proof-of-concept astronomical diffraction grating embedded in a quartz substrate via reactive ion plasma etching. This grating operates at the first diffraction order within the 450 to 750 nm wavelength band. It features 1400-nm-deep, 188-nm-wide binary grooves at a 566-nm pitch, or 1767 lines/mm groove density, over a 25.4 × 25.4 mm2 area. A high depth-to-width ratio ( ∼ 8 ∶ 1 in this case) is one of the keys to near-theoretical diffraction efficiency being attained by the fabricated grating (94% at center wavelength and 70% at band edges) over a broad bandpass (>200 nm). This performance is also attributed to high-resolution micro-lithographic electron-beam patterning and anisotropic reactive ion etching process fabrication techniques. These types of binary gratings can potentially be high-throughput alternatives to Volume-Phase Holographic Gratings (VPHGs) for general spectroscopic applications. When scaled to appropriate sizes for astronomy, such gratings can serve as main or cross dispersion elements in low-, medium-, and high-resolution spectrographs not only in ground-based telescopes but also in those subject to challenging environmental conditions such as in space observatories.

Integrated photodetectors for compact Fourier-transform waveguide spectrometers

Extreme miniaturization of infrared spectrometers is critical for their integration into next-generation consumer electronics, wearables and ultrasmall satellites. In the infrared, there is a necessary compromise between high spectral bandwidth and high spectral resolution when miniaturizing dispersive elements, narrow band-pass filters and reconstructive spectrometers. Fourier-transform spectrometers are known for their large bandwidth and high spectral resolution in the infrared; however, they have not been fully miniaturized. Waveguide-based Fourier-transform spectrometers offer a low device footprint, but rely on an external imaging sensor such as bulky and expensive InGaAs cameras. Here we demonstrate a proof-of-concept miniaturized Fourier-transform waveguide spectrometer that incorporates a subwavelength and complementary-metal–oxide–semiconductor-compatible colloidal quantum dot photodetector as a light sensor. The resulting spectrometer exhibits a large spectral bandwidth and moderate spectral resolution of 50 cm−1 at a total active spectrometer volume below 100 μm × 100 μm × 100 μm. This ultracompact spectrometer design allows the integration of optical/analytical measurement instruments into consumer electronics and space devices.

Preparation of silicone-PCL composite particles with hierarchical structure and the super-hydrophobic fabrics via directly electrostatic spraying

Herein, microspheres with a rough structure were prepared via electrostatic spraying, using a spray solution prepared by dissolving poly(ε-caprolactone) (PCL) and ladder-like fluorinated polysilsesquioxane (F-PH-LPSQ) blends in chloroform. The effects of concentration, voltage, flow rate, receiving distance and blending ratio on the morphology and particle size distribution of the microspheres were investigated. The microsphere spray coatings prepared under different blending ratios were tested: the results demonstrate that the contact angles of the coatings all exceeded 150°, the rolling angles were all smaller than 1° and the adhesion forces were all <51 μN, thus displaying excellent superhydrophobicity. The formation mechanism of the ‘roughened’ microsphere morphology was explored by analysing the energy dispersive spectroscopy results and element content of the protruding and pitted parts of the sprayed particles. The spraying and blending ratio was optimised and determined to be 1.0:0.4. Subsequently, the PCL/F-PH-LPSQ microspheres were directly sprayed and coated with the developed spray solution via electrostatic spraying. The water contact angle of the finished cotton fabric was found to be ≥160°, which provided excellent hydrophobicity and self-cleaning function. Following the sandpaper abrasion and adhesion tests, the contact angle of the fabrics coated with the microspheres remained ≥155°,indicating a good mechanical stability.

Preparation and tribological performance of MoS2 nanoparticles supported on fly ash microparticles

PurposeThis paper aims to explore the preparation and tribological performance of MoS2 nanoparticles supported on fly ash (FA) microparticles.Design/methodology/approachFA was activated by NaOH, oleic acid and HCl to obtain three modified FA samples. Nano-MoS2 was deposited on them to form MoS2/FA additives for poly-α-olefin (PAO) modification. Tribological tests were conducted on a reciprocating rig through the ball-on-disk friction manner. Using X-ray diffraction, scanning electron microscope, energy dispersive spectrometer, Raman spectrometer and element analyzers, the products and their lubrication mechanisms were characterized.FindingsAt 1.5 Wt.%, nano-MoS2 and MoS2/FA could remarkably improve the tribological properties of PAO. The nano-MoS2 deposited on the HCl-activated FA presented better lubrication performance than nano-MoS2. It could reduce friction and wear by approximately 27% and approximately 66%, respectively. The lubrication of MoS2/FA can be attributed to the formation of MoS2 and carbon containing lubricating film.Originality/valueFA was applied as a supporter to prepare MoS2/FA lubricants. The reuse of FA, a solid waste, is important for environmental protection. Moreover, MoS2/FA is more economical than nano-MoS2 as a lubricant, because it contains approximately 71% of low-cost FA.

Nonlinear Fourier transform receiver based on a time domain diffractive deep neural network

A diffractive deep neural network (D2NN) is proposed to distinguish the inverse nonlinear Fourier transform (INFT) symbols. Different from other recently proposed D2NNs, the D2NN is fiber based, and it is in the time domain rather than the spatial domain. The D2NN is composed of multiple cascaded dispersive elements and phase modulators. An all-optical back-propagation algorithm is proposed to optimize the phase. The fiber-based time domain D2NN acts as a powerful tool for signal conversion and recognition, and it is used in a receiver to recognize the INFT symbols all optically. After the symbol conversion by the D2NN, simple phase and amplitude measurement will determine the correct symbol while avoiding the time-consuming NFT. The proposed device can not only be implemented in the NFT transmission system, but also in other areas which require all optical time domain signal transformation and recognition, like sensing, signal coding and decoding, beam distortion compensation and image recognition.

Giant Dielectric Properties of W6+-Doped TiO2 Ceramics.

The effects of the sintering temperature and doping level concentration on the microstructures, dielectric response, and electrical properties of W6+-doped TiO2 (WTO) prepared via a solid-state reaction method were investigated. A highly dense microstructure, pure rutile-TiO2, and homogenously dispersed dopant elements were observed in all of the ceramic samples. The mean grain size increased as the doping concentration and sintering temperature increased. The presence of oxygen vacancies was studied. A giant dielectric permittivity (ε′ ~ 4 × 104) and low tanδ (~0.04) were obtained in the WTO ceramic sintered at 1500 °C for 5 h. The ε′ response at a low temperature was improved by increasing the doping level concentration. The giant ε′ response in WTO ceramics can be described by the interfacial polarization at the interface between the semiconducting and insulating parts, which was supported by the impedance spectroscopy.

DSP-Based Physical Layer Security for Coherent Optical Communication Systems

A novel digital signal processing (DSP)-based scheme for physical layer security in coherent optical communication systems is proposed and numerically investigated. The optical layer signal encryption is accomplished by two dispersive elements and one phase modulator (PM) driven by a DSP-generated encryption key, whilst signal decryption uses similar components but with inverted dispersion values and security keys. A critical aspect of the DSP-based physical layer security is that the security keys, driving the PMs to hide/recover the data signals, must be highly unpredictable and noise-like, thus orthogonal frequency division multiplexing (OFDM) signals are employed as they possess these characteristics, they can also be easily generated and cover a suitably wide range of unique keys. Numerical simulations are conducted to determine optimum system parameters for achieving a high level of security, the key parameters requiring optimization are the dispersion of the dispersive elements and the bandwidth of the security keys. Using these determined optimum parameters, in-depth investigations are undertaken of encryption/decryption induced transmission performance penalties, sensitives to various parameter offsets and operation over various transmission distances. To observe any data signal dependencies, various performance metrics are investigated for different combinations of modulation formats (DQPSK and 16QAM) and baud rates (40 Gbaud and 100 Gbaud) for the transmitted data signals. The proposed DSP-based physical layer security scheme is shown to have the potential to achieve, in a low-cost and highly effective manner, a high level of physical layer security with acceptable performance penalties for existing coherent optical communication systems.

The Influence of Discharge Mode on Morphology of Al–Ni Nanoparticles Prepared by Underwater Electrical Wire Explosion

We report the results of experiments investigating the influence of discharge mode on morphology of Al–Ni bimetallic nanoparticles prepared by underwater electrical explosion (UEE) of intertwined Al/Ni wire. The experiments were conducted using a pulsed power generator with the stored energy of [Formula: see text][Formula: see text]J (underheat mode) and [Formula: see text][Formula: see text]J (overheat mode), delivering to the intertwined Al/Ni wire a [Formula: see text][Formula: see text]kA current rising during [Formula: see text]s. By analyzing electrical signals, we conclude that there exists a competitive process between Al wire and Ni wire, and the latter always lags behind the former in various stages, duo to the difference of electrical resistivity. Using transmission electron microscope (TEM) and energy dispersive spectroscopy (EDS), the morphology and element composition of nanopowders obtained at underheat mode and overheat mode were studied. The results reveal that core-shell structured Al–Ni nanoparticles can be easily obtained at underheat mode, due to the mismatched specific surface energy and matching lattice type between aluminum and nickel. Besides, the Al–Ni powder prepared by underwater electrical wire explosion (UEWE) has a smaller particle size (less than 100[Formula: see text]nm) and more consistent particle size distribution compared with traditional preparation methods. These results show that UEWE is very attractive for the preparation of Al–Ni nanopowders, which is helpful in improving the specific surface area of Raney–Ni catalyst.

Design Simulation and Data Analysis of an Optical Spectrometer

Spectrometers have a wide range of applications ranging from optical to non-optical spectroscopy. The need for compact, portable, and user-friendly spectrometers has been a focus of attention from small laboratories to the industrial scale. Here, the Czerny Turner configuration-based optical spectrometer simulation design was carried out using ZEMAX OpticStudio. A compact and low-cost optical spectrometer in the visible range was developed by using diffraction grating as a dispersive element and a USB-type webcam CCD (charge-coupled device) as a detector instead of an expensive commercial diffraction grating and detector. Using National Instruments LabVIEW, data acquisition, processing, and display techniques were made possible. We employed different virtual images in LabVIEW programs to collect the pixel-to-pixel information and wavelength-intensity information from the image captured using the webcam CCD. Finally, we demonstrated that the OpticStudio-based spectrometer and experimental measurements with the developed spectrometer were in good agreement.

Nonlinear wave transmission in a two-dimensional nonlinear electric transmission network with dissipative elements

A two-dimensional nonlinear discrete electric transmission network made of several well-known anharmonic modified Noguchi lines coupled transversely to one another with a linear inductor is considered and the dynamics of modulated waves are investigated. The linear analysis shows that increasing either the dispersive elements of the network, the coupling elements of the network, or the transverse wavenumber increases the propagating frequencies. Employing the reductive perturbation method, we establish that the dynamics of modulated waves in the network system are governed by a two-dimensional dissipative nonlinear Schrödinger (NLS) equation having, depending on both the longitudinal and transverse wavenumbers as well as on the network parameters, either the hyperbolic or the elliptic character. Through the derived dissipative NLS equation, the phenomenon of the baseband modulational instability (MI) of the electric system under consideration is investigated and the analytical expression for the baseband MI growth rate is presented. We show that the dispersive elements of the network system softens the baseband MI and enhances the baseband MI domain. Under the condition of the baseband MI, we find approximate modulated wave solutions of the governing equations which are then used for analytical investigation of the transmission of super rogue wave voltage, Peregrine soliton voltage, and bright solitary wave signals through the network system under consideration. The effects of the network and solution parameters such as the dispersive, coupling parameters, the carrier wavenumber, and the wavenumbers in both the longitudinal and transverse directions on the dissipative wave signals are presented.

Spectrum dispersion element based on the metasurface with parabolic phase.

New kinds of dispersion elements are required for the minimization of the spectrometers. Metasurfaces offer new methods for a novel type of spectrometers due to their ultra-thin property and great ability to manipulate the electromagnetic field. Here, we propose and demonstrate a spectral modulated metasurface as a miniaturized dispersion element that possesses parabolic phase profile. Different wavelengths of the incident light can be dispersed to different spatial positions due to the accumulation of the dynamic phase varies with the wavelengths from metasurface. Detailed theoretical spectrum dispersion ability is analyzed and experimental demonstration is achieved. The polarization conversion efficiency is high, which is promising to be used in practical applications. Such metasurface provides a new and simple way to design dispersion devices and has the potential to be used in spectrometers, variable filters, spectrum tomography, etc.

A High-Resolution MIR Echelle Grating Spectrometer with a Three-Mirror Anastigmatic System

With the emergence of high-performance infrared detectors and the latest progress in grating manufacturing technology, high-resolution and high-sensitivity infrared spectrometers provide new methods for application to many fields, including astronomy and remote sensing detection. Spectral detection has attracted considerable attention due to its advantages of noncontact and stability. To obtain the detailed features of the missile’s tail flame spectrum, traditional plane reflection gratings are used as the main dispersive element; however, the instrument’s volume will increase with increasing resolution, which is not conducive to remote sensing detection from airborne platforms. Such spectrometers cannot meet high-resolution spectroscopy requirements. To address this problem, this paper proposes an immersion echelle spectrometer combined with a three-mirror astigmatism optical system. High resolution and compact size were achieved. In this paper, a small high-resolution infrared echelle spectrometer optical system was created by combining an off-axis three-mirror anti-astigmatism system, a Littrow structure, and a concave grating Wadsworth imaging device. The optical system operated in the 3.7–4.8 μm band; the echelle grating worked under quasi-Littrow conditions, while the concave grating was used for auxiliary dispersion to separate overlapping orders. The resolution of the optical system in the entire working band was 23,000–45,000. The optical plane size of the spectrometer was around 360 mm × 165 mm. The results show that the Mid-IR echelle spectrometer achieved high spectral resolution, better than 0.25 cm−1, meeting missile tail flame detection requirements. This device has the potential for real-time long-range target detection when warheads are destroyed. While this study focuses on the mid-wave infrared band, its approach can also be extended to other infrared bands.

Calibration of image plate and back illuminated charge coupled device detectors at the thermal emission band of high Z target laser produced plasmas (80–800 eV)

We present a systematic method to absolutely calibrate detector efficiency vs photon energy using a laser produced plasma broadband x-ray source, a gold standard calibrated detector, and transmission gratings (TGs) as dispersive elements. Calibration uses one calibrated TG and a calibrated gold standard detector on one channel and a second calibrated TG and a detector to be calibrated on the other channel. Both channels simultaneously view the laser-produced plasma x-ray source from the same angle with respect to the laser beam and the planar target normal. Image plate detectors are calibrated for the first time at photon energies below 700 eV. Single shot simultaneous calibration of several detectors is possible, making this method an efficient and practical way to periodically calibrate detectors, using in-house capabilities of laser laboratories.

Private correlated random bit generation based on synchronized wideband physical entropy sources with hybrid electro-optic nonlinear transformation.

We propose and experimentally demonstrate a novel, to the best of our knowledge, private correlated random bit generation (CRBG) scheme based on commonly driven induced synchronization of two wideband physical entropy sources, which employs an open-loop distributed feedback laser followed by a hybrid electro-optic nonlinear transformation hardware module for effective bandwidth expansion and privacy enhancement. A Mach-Zehnder interferometer followed by an electro-optic self-feedback phase modulation loop as well as a dispersion element are constructed as a private hardware module to perform post-processing and nonlinear transformation of the synchronized signal. A record high rate of 5.2-Gb/s CRBG is successfully achieved between two synchronized wideband physical entropy sources with an enhanced entropy source rate and hardware key space. The demonstrated scheme may provide a new way for CRBG in future high speed secure communication systems.

Ultrastructure reveals ancestral vertebrate pharyngeal skeleton in yunnanozoans.

Pharyngeal arches are a key innovation that likely contributed to the evolution of the jaws and braincase of vertebrates. It has long been hypothesized that the pharyngeal (branchial) arch evolved from an unjointed cartilaginous rod in vertebrate ancestors such as that in the nonvertebrate chordate amphioxus, but whether such ancestral anatomy existed remains unknown. The pharyngeal skeleton of controversial Cambrian animals called yunnanozoans may contain the oldest fossil evidence constraining the early evolution of the arches, yet its correlation with that of vertebrates is still disputed. By examining additional specimens in previously unexplored techniques (for example, x-ray microtomography, scanning and transmission electron microscopy, and energy dispersive spectrometry element mapping), we found evidence that yunnanozoan branchial arches consist of cellular cartilage with an extracellular matrix dominated by microfibrils, a feature hitherto considered specific to vertebrates. Our phylogenetic analysis provides further support that yunnanozoans are stem vertebrates.

Low-Temperature Calcination of Metal-Organic Frameworks(MOFs) to Derive the High Entropy Stabilized Oxide for High Performance Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) battery owing to high energy density and theoretical capacity is anticipated as a high-performance rechargeable power source for flexible electronic devices and electric vehicles. However, the rapid capacity fade, low Coulombic efficiency, and significant self-discharge capacity loss due to the polysulfides shuttling are the major constraints of its real-world applications. To conquer these challenges, despite the physical encapsulation of polysulfides, chemical interactions between shuttle effect-suppressive sulfur host materials and soluble lithium polysulfides have recently been emphasized. Herein, a novel approach to synthesize the high entropic stabilized oxide (HEO) at low temperature is developed from the self-sacrificing template of metal-organic frameworks (MOFs) to chemically anchor the lithium polysulfides. As-synthesized HEO850 at 850 ºC (transition temperature) exhibited a single-phase rocksalt crystalline structure with homogenous dispersion of Ni, Mg, Cu, Co, and Zn and reversible entropic phase stabilization in the certain temperature range (750-850 ºC). When employed as a chemical anchor to lithium polysulfides (LIPSs) and compared the electrochemical performance of Li-S cells with medium configurational entropic oxide (MEOs) (HEOs-one metal cation), low entropy oxide (LEOs) (HEOs-three metal cations), and routine sulfur ketjen black (S/KB) cells, it revealed a competitive reversible capacity, excellent cycling stability and a low capacity decay rate by immobilizing the LIPSs and facilitating the redox reaction in the cathode. The cells with HEO850/KB/S cathode delivered a higher initial specific discharge capacity of 1244.1 mAh g-1 than those of MEO850/S/KB (979.625 mAh g-1), LEO850/S/KB (908 mAh g-1), and S/KB (966 mAh g-1). After 800 cycles of continuous charging and discharging at 0.5 C, the capacity of 784.1 mAh g-1 with outstanding Coulombic efficiency of 99.66 % is still retained demonstrating excellent cycling stability with a negligible capacity fade rate of 0.04% per cycle. This outstanding performance could be attributed to the synergistic contribution and exposure of numerous active sites of randomly dispersed elements in the HEO850. This study not only highlights the extraordinary electrochemical performance of Li-S battery with efficient immobilization of LIPSs but also provide a novel strategy for the synthesis of HEOs at lower calcination temperature for various energy conversion and storage applications. After getting confidence with these prilimary results, Ti-based HEOs owing to both high ionic and electric conductivities will be investigated at coin and pouch cell level as future research direction.