Wavelength Bandwidth Research Articles

Ultra-broadband wave-absorbing metamaterials with open-hole effect

In this paper, propose the open-hole effect, which can improve the absorption effect of electromagnetic absorbers in the X- and Ku-band by regularly opening certain shaped through-holes in the dielectric material. Based on this effect, an ultra-wideband metamaterial absorber with a special open-hole structure is designed and successfully prepared by numerical simulation, and the effective wavelength bandwidth (absorption > 90 %) covers X- and Ku-band. By optimizing the dielectric material and structural parameters of the absorber, an ultra-broadband metamaterial absorber with a thickness of 2.2 mm, a maximum absorption rate of 99.35 % and an effective absorption bandwidth of 11.6 GHz was obtained. Simulations of TE and TM waves at different angles show that the absorber has excellent electromagnetic wave absorption at different angles of incidence (θ < 30°).

Flexible wavelength-, pulse-controlled mode-locked all-fiber laser based on a fiber Lyot filter.

In this paper, we report a flexible wavelength-, pulse-controlled mode-locked all-fiber laser based on a novel fiber optic Lyot filter. The wavelength, pulse duration and spectral bandwidth of passive mode-locked lasers can be tuned by controlling the polarization controller. The proposed Lyot filter was constructed by a single-mode fiber insertion between two polarization-maintaining fibers. The filter bandwidth and laser output tunability were based on the birefringence characteristics of the polarization-maintaining fibers. This all-fiber laser is simple and stable and can be used for various applications where width-tunable or wavelength-tunable pulses are necessary.

Large wavelength bandwidth Mach-Zehnder modulator based on optical intensity equalization structure

In this paper, we propose a large wavelength bandwidth Mach-Zehnder modulator based on light intensity equalization structure. The modulator is designed into a symmetric structure to increase the optical operating bandwidth. Besides, two auxiliary MZIs are connected to the respective phase shifters of the main modulator to balance the optical intensity in them. Compared with a conventional Mach-Zehnder modulator, this design has a larger optical operating bandwidth over 56.1 nm. Besides, the maximum extinction ratio of this modulator is 26.2dB, which is 12 dB higher than that of a conventional one. The dynamic extinction ratios at speed of 40Gbps are 4.10 dB in the wavelength of 1530nm and 4.02 dB in the wavelength of 1560 nm respectively. The 3 dB electro-optical bandwidth of this modulator under different voltages are almost consistent with the performance of the conventional one. All of these prove that this structural design can effectively increases the performance of Mach-Zehnder modulators.

Optimal Design and Analysis of 4.7 μm Hybrid Deep Dielectric High Efficiency Transmission Gratings

There is currently no transmission grating with good diffraction efficiency in the 4.7 μm band. Metal gratings at this wavelength are all reflective gratings which has a diffraction efficiency of lower than 90% and lower laser damage threshold. In this paper, we bring up a design of a multi-layer transmission grating with both high diffraction efficiency and wide working wavelength band. We have proved that the transmission grating made of composite materials has an average diffraction effectiveness of more than 96% throughout the whole spectral range of 200 nm. Meanwhile, the theoretically computed transmission grating has a highest first-order diffraction efficiency of more than 99.77% at 4746 nm. This multilayer dielectric film transmission grating’s optimized design may further boost spectral beam combining power, providing a practical technique for increasing SBC power and brightness.

Microstructural characteristics of sandwiched T-shaped metamaterials for three-port splitting

This paper presents a polarization-insensitive sandwiched three-port beam splitting grating at normal incidence. The grating adopts a sandwiched structure. Based on the rigorous coupled-wave analysis (RCWA) and the simulated annealing algorithm, the grating parameters are optimized to obtain the diffraction efficiencies of 32.83% at 0th order and 32.87% at ±1st orders for transverse electric polarization, and 32.63% at 0th order and 32.39% at ±1st orders for transverse magnetic polarization. Meanwhile, the calculation results of the finite element method are in general agreement with those of RCWA. In addition, the analysis results of grating period, duty cycle, and wavelength bandwidth further demonstrate the good wavelength bandwidth of the grating and its feasibility for practical production. Therefore, the grating can be widely used in actual production.

Ocean Surface Roughness from Satellite Observations and Spectrum Modeling of Wind Waves

Abstract Many wind wave spectrum models provide excellent wave height prediction given the input of wind speed and wave age. Their quantification of the surface roughness, on the other hand, varies considerably. The ocean surface roughness is generally represented by the mean square slope, and its direct measurement in open ocean remains a challenging task. Microwave remote sensing from space delivers ocean surface roughness information. Satellite platforms offer global coverage in a broad range of environmental conditions. This paper presents low-pass mean square slope (LPMSS) data obtained by spaceborne microwave altimeters and reflectometers operating at L, Ku, and Ka bands (about 1.6, 14, and 36 GHz). The LPMSS data represent the spectrally integrated ocean surface roughness with 11, 95, and 250 rad m−1 upper cutoff wavenumbers, and the maximum wind speeds are 80, 29, and 25 m s−1, respectively. A better understanding of the ocean surface roughness is important to the goal of improving wind wave spectrum modeling. The analysis presented in this paper shows that over two orders of magnitude of the wavenumber range (0.3–30 rad m−1), the spectral components follow a power function relating the dimensionless spectrum and the ratio between wind friction velocity and wave phase speed. The power function exponent is about 0.38, which is considerably smaller than unity as expected from the classical equilibrium spectrum function. It may suggest that wave breaking is not only an energy sink but also a source of roughness generation covering a wideband of wavelengths about 20 m and shorter. Significance Statement This paper presents low-pass mean square slope (LPMSS) data obtained by spaceborne microwave altimeters and reflectometers operating at L, Ku, and Ka bands (about 1.6, 14, and 36 GHz). The LPMSS data represent the spectrally integrated ocean surface roughness with 11, 95, and 250 rad m−1 upper cutoff wavenumbers, and the maximum wind speeds are 80, 29, and 25 m s−1, respectively. A better understanding of the ocean surface roughness is important to the goal of improving wind wave spectrum modeling that is critical to the investigation of air–sea interaction and ocean remote sensing. The analysis presented in this paper suggests that wave breaking is not only an energy sink but also a generation source of surface roughness covering a wide band of wavelengths about 20 m and shorter.

Theoretical study on the diffraction-based generation of a 2D orthogonal lattice of optical beams: physical bases and application for a vortex beam multiplication.

A comprehensive theoretical study on the generation of a 2D orthogonal lattice of optical beams based on the near-field diffraction and Talbot effect is presented. First we investigate the near-field diffraction of an optical beam with a finite lateral extension from an infinite 2D orthogonal grating. It is shown that the resulting diffraction patterns over the Talbot planes depend on the following parameters: the period and opening ratio (OR) of the grating, wavelength and spatial spectral bandwidth of the incident beam, and the propagation distance. In terms of these parameters, we find multiplication conditions: the certain conditions under which a 2D orthogonal lattice of the Fourier transform of the incident beam is generated on the Talbot planes. Therefore, if the incident beam is Fourier-invariant and all the established multiplication conditions are fulfilled, the intensity profile of each of the individual Talbot images resembles the intensity profile of the incident beam. We consider the Laguerre-Gaussian beams having zero radial index as an important class of the vortex beams. We explicitly show that these beams are Fourier-invariant and we calculate their spatial spectral bandwidth. As a result, in the illumination of a 2D orthogonal binary grating with this kind of vortex beam, a 2D orthogonal lattice of the incident optical vortex is generated at the Talbot planes. Considering the obtained multiplication conditions, for the first time, to our knowledge, we determine a multiplication interval. This interval covers the propagation distances at which the vortex beam multiplication occurs. Moreover, we obtain the maximum possible value of the grating's OR for the realizations of the vortex multiplication. It is shown that both the multiplication interval and the maximum value of the OR depend on the topological charge (TC) of the incident beam. With the aid of some practical examples and defining a multiplication quality factor, the mentioned results are verified quantitatively. In addition to the vortex beam multiplication effect, we consider another interesting phenomenon that results from the interference of the grating's first diffraction orders. We call this phenomenon the first diffraction orders interference (FDOI) effect. We show that both the multiplication and the FDOI effects occur simultaneously but at different propagation distances. It is also shown that the multiplication and FDOI intervals separate and distance from each other by increasing the TC of the incident beam.

Broadband dual-channel channelizer based on a microwave photonic power tunable image rejection down-conversion.

Radiofrequency (RF) channelization has potential high frequency and wideband advantages in frequency-domain channel segmentation and down-conversion reception. In this paper, we propose a compact dual-channel channelizer that can process high-frequency wideband signals. It uses double-polarization double-sideband electro-optic modulation and Hartley structure photoelectric conversion to realize down-conversion channelization of the high-frequency wideband signal. The power matching between two polarization signals can be realized by controlling the modulator bias, so the crosstalk between the two output signals can be suppressed. The proposed channelizer has a compact structure since the electro-optic modulation is based on one single laser and one single integrated modulator. No filters are used in the structure, contributing to a very wide RF operation bandwidth and low constraints of laser wavelength. In the experiment, the single frequency signal pairs from 9 GHz to 15 GHz can achieve an inter-channel image rejection ratio of 53 dB. Furthermore, the channelizer slices multi-octave bandwidth quadrature phase shift keying (QPSK) signals up to 16 GHz with the wideband isolation higher than 10 dB and outputs them to two channels in parallel. The error vector magnitudes (EVM) of 9-17 GHz and 18-26 GHz band QPSK signals are guaranteed to be under 23.58% after channelized separation. To the best of our knowledge, the proposed channelizer provides high inter-channel interference suppression at dual-band adjacent signals with 8 GHz bandwidth for the first time. Therefore, the proposed channelizer has great application value for the reception and processing of millimeter signals in the future.

EXPANSE: A time-of-flight EXPanded Angle Neutron Spin Echo spectrometer at the Second Target Station of the Spallation Neutron Source

EXPANSE, an EXPanded Angle Neutron Spin Echo instrument, has been proposed and selected as one of the first suite of instruments to be built at the Second Target Station of the Spallation Neutron Source at the Oak Ridge National Laboratory. This instrument is designed to address scientific problems that involve high-energy resolution (neV-μeV) of dynamic processes in a wide range of materials. The wide-angle detector banks of EXPANSE provide coverage of nearly two orders of magnitude in scattering wavenumbers, and the wide wavelength band affords approximately four orders of magnitude in Fourier times. This instrument will offer unique capabilities that are not available in the currently existing neutron scattering instruments in the United States. Specifically, EXPANSE will enable direct measurements of slow dynamics in the time domain over wide Q-ranges simultaneously and will also enable time-resolved spectroscopic studies. The instrument is expected to contribute to a diverse range of science areas, including soft matter, polymers, biological materials, liquids and glasses, energy materials, unconventional magnets, and quantum materials.

Application of the novel environment-cleaned light-emitting diode devices in various test fields

Faced with the impact of extreme climate, countries have proposed carbon dioxide emission reductions, hoping to achieve carbon neutrality by 2050, and Taiwan’s industries must also face the transformation of low-carbon green energy. Light-emitting diode (LED) is a cost effective semiconductor device that produces light within a narrow bandwidth of wavelength through electroluminescence. Recently, LED technology has attention to apply in the area of food production, preservation, and safety. At present, some researches have been demonstrated that the antimicrobial LED visible light is less anti-microbial efficacy than ultraviolet (UV) light. However, the antimicrobial LED visible light has been recognized as an alternative technology to UV light since it is an environmentally friendly and safe technology for human and animals. For this reason, LED technology has recently received attention for applying in many test fields as laboratory, pig farms, computer, bio-medical industries etc. In this study, this novel clean and disinfect tool-novel environment-cleaned LED devices were tested in the various fields and obtained the positive results as the application of novel environment-cleaned LED devices on anti-fungal efficacy, and ethylene, PM2.5, and harmful gas degradations in laboratory, anti-bacterial and virus efficacy in laboratory and/or pig farms, anti-microbial notebook panel development, and anti-colorectal cancer in vitro. In the future, we wish this novel environment-cleaned LED devices will friendly used in human and animal environments to decrease the harmful matters in the environments.

Upgrade of the OSIRIS primary spectrometer

A proposed upgrade is presented for the primary part of the indirect time-of-flight near-backscattering spectrometer OSIRIS at the ISIS Facility. This upgrade comprises a new supermirror guide with non-linear defocusing and focusing sections, a new wavelength bandwidth chopper system and a flexible slit system to adjust the divergence. The new neutron guide has an elliptical defocusing section, a curved section and an elliptical focusing section. The estimated gain factor in intensity is wavelength dependent between 4 and 7 at the sample position with a homogeneous divergence distribution on a smaller beam spot. The divergence will increase by up to a factor 3 compared to the present guide, but can be reduced by up to a factor 5 through the slit system. The increased guide cross section requires a system of two counter-rotating disc choppers with larger disc diameters than the present ones for the selection of the wavelength bandwidth. Estimates for the performance indicate that the proposed upgrade will keep the OSIRIS spectrometer competitive in the years to come.

Reflected Spectroscopy of Small Exoplanets II: Characterization of Terrestrial Exoplanets

A space telescope capable of high-contrast imaging has been recognized as the avenue toward finding terrestrial planets around nearby Sun-like stars and characterizing their potential habitability. It is thus essential to quantify the capability of reflected light spectroscopy obtained through direct imaging for terrestrial exoplanets, and existing work focused on planetary analogs of modern Earth. Here we go beyond Earth analogs and use a Bayesian retrieval algorithm, ExoReL , to determine what we could learn about terrestrial exoplanets from their reflected light spectra. Recognizing the potential diversity of terrestrial exoplanets, our focus is to distinguish atmospheric scenarios without any a priori knowledge of the dominant gas. We find that, while a moderate-resolution spectrum in the optical band (0.4−1.0 μm) may sufficiently characterize a modern Earth analog, it would likely result in incorrect interpretation for planets similar to Archean Earth or having CO2-dominated atmospheres. Including observations in the near-infrared bands (1.0−1.8 μm) can prevent this error, determine the main component (N2, O2, or CO2), and quantify trace gases (H2O, O3, and CH4) of the atmosphere. These results are useful to define the science requirements and design the wavelength bandwidth and observation plans of exoplanet direct imaging missions in the future.

Colloidal Quantum Dot Light Emitting Diodes at Telecom Wavelength with 18% Quantum Efficiency and Over 1MHz Bandwidth.

Developing high performance, low‐cost solid‐state light emitters in the telecom wavelength bandwidth is of paramount importance for infrared light‐based communications. Colloidal quantum dot (CQD) based light emitting diodes (LEDs) have shown tremendous advances in recent times through improvement in synthesis chemistry, surface property, and device structures. Despite the tremendous advancements of CQD based LEDs in the visible range with efficiency reaching theoretical limits, their short‐wave infrared (SWIR) counterparts mainly based on lead chalcogenide CQDs, have shown lower performance (≈8%). Here the authors report on highly efficient SWIR CQD LEDs with a recorded EQE of 11.8% enabled by the use of a binary CQD matrix comprising QD populations of different bandgaps at the emission wavelength of 1550 nm. By further optimizing the optical out‐coupling via the use of a hemispherical lens to reduce optical waveguide loss, the EQE of the LED increased to 18.6%. The CQD LED has an electrical bandwidth of 2 MHz, which motivated them to demonstrate its use in the first SWIR free‐space optical transmission link based entirely on CQD technology (photodetector and light emitter) opening a new window of applications for CQD optoelectronics.

Latest Performance Improvement Strategies and Techniques Used in 5G Antenna Designing Technology, a Comprehensive Study.

In the recent era, fifth-generation technology (5G) has not been fully implemented in the realm of wireless communication. To have excellent accessible bandwidth feasibility, and in order to achieve the aims of 5G standards, such as higher data rates and ultrahigh-definition video streaming, the millimeter wave (mmWave) band must be employed. Services with minimal latency and many other features are feasible only in the mmWave spectrum. To avoid numerous communication complexities such as high connection losses, short wavelength, and restricted bandwidth, as well as path-loss challenges in the mmWave range, an antenna with wide bandwidth, high gain, narrow steerable beam, high isolation, low side-lobe levels, and multiband features is required to alleviate these difficulties and meet 5G communication standards. To overcome these challenges, specific strategies and techniques should be employed in the traditional antenna designing procedure to excellently improve the performance of the antenna in terms of bandwidth, gain, and efficiency and to reduce the mutual coupling effect between the closely colocated antenna elements in MIMOs and arrays. The researchers reported on a variety of bandwidth and gain improvement approaches. To gain broader coverage, traditional antenna design techniques must be modified. In this study, the latest state-of-the-art work is reviewed, such as the role of the metamaterials (MMTs), parasitic patches, hybrid feeding, EBG structure, impact of the slots with different geometrical shapes in the radiator to achieve the goal of wide bandwidth, boosted gain, reduced side-lobes level, as well as stable radiation properties. Mutual coupling reduction techniques are also briefly reported. The role of reconfigurability is focused on in this study, and at the end, the future challenges in the field of antenna design and possible remedies to such issues are reviewed.

Impact of Broad-Spectrum Lighting on Recall Behaviour in a Pair of Captive Blue-Throated Macaws (Ara glaucogularis)

Many birds, including macaws, are highly visual animals able to detect a wide band of light wavelengths ranging into ultraviolet A, but in captivity, full-spectrum lighting is not universally employed. Where purpose-made bird lighting is used, this is typically made with the provision of ultraviolet B radiation and vitamin D3 synthesis in mind. Limited research in this field suggests behavioural and physiological benefits of broad-spectrum lighting provision, but more work is needed to broaden the taxonomic scope and to investigate its impacts on understudied areas of husbandry, including behavioural management. We compared the duration of time a bonded pair of blue-throated macaws at ZSL London Zoo opted to remain in an inside den after being recalled from an outdoors flight aviary, with and without the presence of artificial lighting in the form of High Output T5 Fluorescent lamps, which are rich in UVA and UVB wavelengths as well as those visible to humans. We hypothesized that the birds would remain inside for longer when T5 lighting was on, as they would be more visually comfortable. Using randomization analyses, we show that, over 54 trials split between winter and spring, the mean duration spent inside after recall increased from 81.04 to 515.13 s with the presence of the lighting unit, which was highly statistically significant. Our results are likely to be explained by much higher visibility of indoor surroundings creating a more hospitable indoor environment for the birds and will have implications for captive macaw management.

Hybrid Q-switched Tm:YAG ceramic laser with acousto-optic modulator and Cr:ZnSe crystal

We report on a hybrid Q-switched Tm:YAG ceramic laser emitting near 2 µm with an acousto-optic modulator (AOM) and a Cr:ZnSe crystal. Stable laser pulse could be achieved for 0.1–1 kHz repetition frequency. The narrowest pulse duration of 67.6 ns was yielded at a repetition frequency of 0.1 kHz with the maximum single pulse peak power of 27.7 kW. Maximum average output power of 517 mW was obtained at 1 kHz. The laser wavelength was located at 2013.6 nm with the wavelength bandwidth of ~ 0.1 nm. The good laser beam quality was achieved with M2 < 1.2 in both x and y axes.

Application of dual-structure grating for equal three-channel splitting in reflection

A new three-channel beam splitter with dual-structure is described in this paper. Through numerical calculation by finite element method (FEM), with an incident wavelength of 1550 nm, such the dual-structure grating can be obtained with diffraction efficiencies of more than 32% in the ± 1st and 0th order for transverse magnetic (TM) polarization and more than 31% for transverse electric (TE) polarization. The effect of period, duty cycle, incident angle and wavelength on the diffraction efficiency are also presented in this paper. Compared with other three-channel gratings, the proposed grating has wider incident wavelength bandwidth and satisfying performance.

Polarization Raman lidar for atmospheric correction during remote sensing satellite calibration: instrument and test measurements.

A compact polarization Raman lidar has been designed and constructed for using it for atmospheric correction measurements during satellite optical sensor calibration in areas with high altitude and extremely low aerosol loading. The parameters of this lidar, such as laser wavelength, telescope diameter and interference filter bandwidth, were simulated and optimized for the best observation performance. The instrument has low weight, is small in size, and requires air cooling instead of commonly used water-cooling of the laser. Thus, the instrument is suitable for autonomous operation in remote sites. The lidar prototype was installed in Lijiang (26°43' N, 100°01' E), China, a potential observation site for calibrations of optical sensors of satellites. This observation site has been shown to be an appropriate place for remote sensing and satellite calibration activities with low aerosol loading, thin air and a comparably high proportion of cloud-free days. A field campaign carried out between November 2019 and April 2020 allowed for thoroughly testing the instruments. The results of test observations show that complete overlap between emitted laser beam and field-of-view of the receiver unit is achieved at relatively low heights above ground. The measurement accuracy is comparably high. Thus, this instrument is suitable for operating in areas with relatively clean atmospheric conditions.

Nano-cylindrical hole metamaterials for high-efficiency ultra-bandwidth two-dimensional diffraction

Two-dimensional (2D) grating as the core component of the 2D grating displacement measurement system has a more demanding performance in recent years. In this paper, a 2D metal grating with an array of nano-cylindrical holes is proposed, which can achieve a high diffraction efficiency (DE) output of 2 × 2 at a wavelength of 780 nm, where the DEs of (0, ±1) and (±1, 0) orders are over 23% with a nonuniformity of 0.23%. Meanwhile, the results of the finite-difference time-domain method are in good agreement with those of the finite element method. Notably, the proposed grating has a wavelength bandwidth of 44 nm and a large angular bandwidth of 12° when the DE of all main diffraction orders is chosen to be above 20% as the target condition. This angular bandwidth is a significant improvement relative to previous reports. Moreover, the results show that the proposed grating has good manufacturing tolerances while ensuring high performance, demonstrating its feasibility in practical manufacturing. Therefore, this grating has significant potential in the field of 2D grating displacement measurement due to its simplicity, high efficiency, good uniformity, wide bandwidth and good process tolerance.

Holographic Waveguide Display With Large Field of View and High Light Efficiency Based on Polarized Volume Holographic Grating

We propose a polarization multiplexing structure based on multilayer reflective polarized volume holographic gratings(PVGs) to improve the field of view and brightness of the augmented reality waveguide display. The multilayer structure forms the splicing of different response bandwidths by stacking PVGs with different periodic components, and realizes the expansion of the wavelength (angle) bandwidth. The polarization multiplexing structure controls the polarization of the diffracted light by controlling the rotation direction of the liquid crystal pitch in the liquid crystal material, so that both left-hand and right-hand circularly polarized light are diffracted to enhance efficiency. Based on these two structures, the wavelength bandwidth of PVG is increased by 40 nm, the angular bandwidth is increased by 10° and the diffraction efficiency is nearly doubled. In order to verify the feasibility of these two structures, we use the holographic waveguide display with OLED as the image source. The demonstrated waveguide prototype shows a complete display with a diagonal field of view of 55°. The brightness of virtual image was measured as high as 1100 cd/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> with a transparency of 72% for ambient light.