Super Broadband Research Articles

Broadband and extremely low frequency sound isolation by a programmable shunted electromechanical diaphragm with force dipole effect

Broadband sound isolation in low frequencies by a partition with a small dynamic mass is a challenge to the mass law. We review the conventional sound isolation panels and membrane-type acoustic metamaterials and find that the former is equivalent to a monopole identical to a single path control system and the latter is similar to a dipole equivalent to a feed-forward system with zero time delay. Neither is likely to enhance sound isolation in a broad bandwidth and at low frequencies. Here, we introduce a “force dipole” effect, which is a passive feedback force countering the incident sound. The device is based on a passively shunted electromechanical diaphragm (SEMD), consisting of a moving-coil attached diaphragm, a permanent magnet generating a DC magnetic field, and a programmable analog circuit shunting the coil. It isolates sound in a super broad bandwidth down to the infrasound region. In reaction to an incident sound, a Lorentz force is exerted on the moving-coil opposing the incident pressure force, forming a near-perfect dipole. The net residual force is greatly reduced and so is the sound wave transmission. The force dipole effect is determined by the shunt circuit and our experiments in an impedance tube show that the spectrum of transmission loss (TL) of the SEMD can be programed by a smart circuit; it is maintained at 20 dB or above from 15 Hz to 772 Hz. The mass and stiffness laws are broken over 5.7 octaves. The lumped-parameter theoretical model is verified by experiment, and further analysis predicts that a superconducting circuit will achieve a super broadband band gap.

Tailoring of communication band luminescence for super broadband optical amplifier based on [formula omitted] co-doped nanoporous silica glass

We report on a series of Er3+/Yb3+/P5+ co-doped silica glass from nanoporous silica glass based on glass phase separation technology. The optical properties of the Er3+/Yb3+/P5+ co-doped glasses were investigated. Measurements showed that phosphorus can promote energy transfer from Yb3+ ions to Er3+ ions while suppressing the energy transfer from Er3+ ions to Yb3+ ions and efficiently suppressing the amplified spontaneous emission (ASE) from Yb3+ ions at 1030 nm. Additionally, the luminescence of Er3+ (I413/2→I415/2) was greatly extended under 976 nm laser excitation, and the full width at half maximum (FWHM) of Er3+ (I413/2→I415/2) was measured to be up to 72 nm and enables the luminescence peak redshifted. The emission cross section of Er3+ (I413/2→I415/2) was calculated to be 1.6*10−20cm2, one order higher than that of other silica glasses. It is suggested that the Er3+/Yb3+/P5+ co-doped silica glasses based on nanoporous silica glass present great potential for broadband amplification.

Improving the light absorption efficiency in thin-film plasmonic tandem solar cell

Recently, thin-film solar cells have received much attention due to low production cost. However, such cells suffer from low efficiency due to which they cannot be used for practical applications. To cater this problem, we have numerically investigated thin-film tandem solar cells comprising of double active layers made of amorphous silicon (a-Si) and crystalline silicon (c-Si) of different energy bandgaps. The tandem cell is found to absorb large amount of solar photons compared to a single a-Si and c-Si solar cells. To further improve the absorption efficiency, we efficiently utilized the surface plasmon resonance (SPR) effect of plasmonic nanoparticles, which are deposited in the form of a square lattice in the top a-Si active layer. The absorption characteristics of the cell are enhanced and tuned by optimizing the material and size of the nanoparticles. Moreover, periodic disorders are incorporated, which allow mixing of plasmonic modes having different angular momenta, resulting in a super broadband light absorption from 300 to 1100 nm and yielding a short circuit current density of 33.917 mA/cm2 in the active layers. The proposed plasmonic tandem cell can be advantageous for most of the photovoltaic applications.

A dual-excited and dual near-infrared emission phosphor Mg14Ge5O24:Cr3+,Cr4+ with a super broad band for biological detection

Recently, near-infrared phosphors that can be applied in many fields such as night vision, agriculture, and bio-applications have attracted considerable interest in the research field worldwide. Herein, a multi-functional and dual-excited near-infrared phosphor Mg14Ge5O24:Cr3+,Cr4+ which provides two emission bands ranging from 700 nm to 1100 nm and 1100 nm to 1700 nm has been obtained via the traditional high-temperature solid state reaction. The presence of six and four coordination ions in the olivine structure of Mg14Ge5O24 provides a favorable environment for the coexistence of Cr3+ and Cr4+. Under blue light excitation, a super broad emission band ranging from 650 nm to 1100 nm with a full-width at half maximum (FWHM) of 266 nm is assigned to the spin-allowed 4T2 (4F) →4A2 transition of Cr3+ in a weak crystal-field environment. With the increase in the concentration of Cr ions, more and more Cr4+ preferentially occupies four coordinated Ge4+ sites, and the other broad emission band ranging from 1100 nm to 1600 nm with a FWHM of 256 nm that comes from the 3T2→3A2 transition of Cr4+ is observed. The phenomenon of NIR I region excitation and NIR II region emission appears. The transmission experiment of a biological tissue proves that the Mg14Ge5O24:Cr3+,Cr4+ phosphor has potential applications in the field of near-infrared light-emitting diodes for biological detection.

Highly dispersed Eu2+ activated Ca10(PO4)6Cl2 phosphor with enhanced blue emitting through deposition-precipitation process

Abstract A series of Eu2+ activated Ca10(PO4)6Cl2 phosphors (ClAp: Eu2+) with enhanced blue emission have been prepared by the deposition precipitation (DP) process. The XRD patterns indicate that Eu2+ ions are incorporated into Ca10(PO4)6Cl2 lattice during the DP process. The ClAp: xEu2+-DP phosphor exhibits an super broad excitation band of 250 nm–420 nm consisting of three distinct peaks at 276 nm, 343 nm and 365 nm, ascribed to the 4f6 → 4f75 d1 transition of Eu2+ ions in 4f and 6 h sites. Under 350 nm excitation, ClAp: xEu2+-DP phosphors show the intense blue emission at 453 nm and the maximum intensity is obtained when x = 0.3. Notably, an enhanced blue emission intensity of ~2.1 times can be found for ClAp:0.3Eu2+-DP phosphor compared with the sample prepared by traditional solid state reaction (SSR) method. Further, the EDX elemental mapping of the phosphor demonstrates that DP process can effectively promote the uniform distribution of Eu2+ ions on the surface of ClAp crystal and avoid the aggregating problem of activators in SSR method, which can greatly improves the photoluminescence property. It can be concluded from HRTEM images and decay curves that ClAp:0.3Eu2+-DP phosphor exhibits characteristic lattice fringes similar to those of ClAp:0.3Eu2+-SSR phosphor, but a longer average decay lifetime (392 ns). In addition, the presence of trivalent europium ions on the surface of ClAp: 0.3Eu2+-SSR and ClAp: 0.3Eu2+-DP phosphors can be identified by XPS analysis. All the results reveal that DP process is an efficient way to prepare highly dispersed Eu2+ activators in Ca10(PO4)6Cl2 host and the ClAp: Eu2+-DP phosphors can be the promising candidate for blue emission in white LEDs.

Super broadband acoustic impedance matching by MUT‐type acoustic metamaterial

AbstractWe show the structure and matching theory of MUT‐type acoustic matching device. A simulation model of the finite element method was constructed and the following evaluations were made: (1) analysis of the stress distribution inside the proposed device in order to find the mechanism of ultrasound propagation, (2) comparison of the performance as an acoustic matching device with the conventional matching layer method in ultrasound frequency, and (3) dependence of acoustic matching performance on design parameters. The MUT‐type acoustic matching device based on the proposed design guidance showed higher acoustic transmittance and wider bandwidth than the conventional 1/4 wavelength acoustic matching system.

Efficient Super Broadband NIR Ca2LuZr2Al3O12:Cr3+,Yb3+ Garnet Phosphor for pc‐LED Light Source toward NIR Spectroscopy Applications

AbstractSuper broadband near‐infrared (NIR) phosphor converted light‐emitting diodes (pc‐LEDs) are future light sources in NIR spectroscopy applications such as food testing. At present, a few blue LED excitable super broadband NIR phosphors (bandwidth > 300 nm) have been developed producing the NIR output powers below 26 mW at 100 mA input current after LED packaging. Here, an efficient super broadband NIR phosphor achieved by doping Yb3+ is reported in the NIR Ca2LuZr2Al3O12:Cr3+ (CLZA:Cr3+) garnet phosphor developed previously. Benefited from the superposition of Cr3+ emission and highly efficient Yb3+ emission excited by energy transfer from Cr3+, the codoped CLZA:Cr3+,Yb3+ phosphor shows a bandwidth of 320 nm and an internal quantum efficiency of 77.2% both higher than that (150 nm and 69.1%) of singly doped CLZA:Cr3+ phosphor. The codoped phosphor converts LED produced 41.8 mW NIR output at 100 mA input current. The pc‐LED as a light source is also well applied to the NIR transmission spectra measurement of water. The results indicate the great potential of CLZA:Cr3+,Yb3+ phosphor in super broadband NIR pc‐LED applications.

Broadband Solar Energy Absorption in Plasmonic Thin-Film Amorphous Silicon Solar Cell

Improving the light absorption in thin-film solar cell is essential for enhancing efficiency and reducing cost. Here, we propose an ultra-broadband amorphous silicon solar cell based on a periodic array of titanium ring-shaped metasurfaces, which achieves more than 90% absorptance in the visible range of the solar spectrum. The surface plasmon resonance supported by the nanoparticles together with the resonance induced by the metal–insulator–metal Fabry–Perot cavity leads to this broadband absorption. The impact of various materials of functional layers and the geometric structure of the nanoparticle on absorption performance is discussed in detail, and super broadband resonance is achieved after optimization. Moreover, the optimized solar cell is tested for different solar incidence angles and it is found that the structure exhibits high absorption efficiency even at large angles. Thus, the proposed solar cell design may be beneficial for most of the photovoltaic applications.

Super Broadband Acoustic Impedance Matching by MUT-type Acoustic Metamaterial

Super Broadband Acoustic Impedance Matching by MUT-type Acoustic Metamaterial

Low-Noise Closed-Loop FOG Driven by Two Broadband Sources

We propose and demonstrate experimentally a low-noise closed-loop fiber optic gyroscope (FOG) driven by two broadband sources simultaneously. The basic characteristic of built-up super broadband light source (SBLS) consisting of two superluminescent diodes (SLDs) with different wavelengths was designed and analyzed. The dispersion characteristic of half-wave voltage of multifunction integrated optical circuit (MIOC) was investigated theoretically and experimentally. The tested results agree well with the theoretical model and confirm that the customized MIOC can operate well over a large spectral bandwidth. An experimental FOG driven by the SBLS was built with a solid-core polarization maintaining photonic crystal fiber coil and the closed-loop operation was realized well. Its bias drift and scale factor were tested preliminarily, and high performance is achieved compared with the FOGs with a single SLD source.

Nonlinear optical microscopy with achromatic lenses extending from the visible to the mid-infrared

With the advent of near-infrared broadband sources stretching into the mid-infrared (MIR) region, there is a growing demand for optical components with utility over an increasingly broad spectral range. For refractive lenses, color correction over such broad bandwidths can be a challenge. In this work, we discuss and demonstrate a two-element lens design with achromaticity spanning the visible to the mid-infrared. The air-spaced doublet designed from commercially available materials shows a significant reduction in spot size and chromatic shift compared to single lens alternatives. We have tested these new broad bandwidth achromats for the purpose of laser-scanning sum-frequency generation microscopy, confirming their improved performance for nonlinear optical imaging applications. The super broadband achromatic lenses represent an attractive alternative to reflective components in ultrabroadband applications, as they enable compact transmission-based optical designs and good focusing performance at off-axis field angles.

Design of a low‐cost broadband loaded dipole antenna for VHF/UHF frequency range

This study describes the concept and design of a low-cost super broadband dipole antenna with a passive matching network. The proposed dipole antenna is designed in three steps. First, a simple planar dipole antenna with six different loads and a balanced to unbalanced (Balun) transformer is designed by the genetic algorithm optimisation. The position and value of the loads are optimised to achieve an acceptable radiation pattern and voltage standing wave ratio (VSWR) over the desired frequency bandwidth. In the next step, the shape of the printed strip dipole antenna is optimised to improve the frequency response of the designed antenna. Finally, an LC network is added to the antenna feed point to reduce the antenna VSWR at low frequencies. The final dipole antenna has a length of 1.7 m and can operate over 30-1200 MHz with VSWR -10 dBi. The proposed antenna can easily be fabricated at a low cost via the printed circuit board technology. An industrial prototype of the proposed antenna is fabricated and measured. A good agreement between measurement and simulation results is observed.

Broadband emission of single-phase Ca3Sc2Si3O12:Cr3+/Ln3+ (Ln = Nd, Yb, Ce) phosphors for novel solid-state light sources with visible to near-infrared light output

Abstract Novel single-component phosphors Ca3Sc2Si3O12:Cr3+/Ln3+ (CSS:Cr3+/Ln3+, Ln = Nd, Yb, Ce) with broadband near-infrared (NIR) emissions are synthesized. Their phase structure, photoluminescence properties and energy transfer between Cr3+ and Ln3+ ions are investigated. In the CSS host, Cr3+ ions occupy Sc3+ sites with low-field octahedral coordination, and thus show a broadband emission in 700–900 nm under the blue light excitation. Nd3+, Yb3+ and Ce3+ ions substitute Ca2+ sites in CSS, where Nd3+ and Yb3+ ions emit the NIR light in 900–1100 nm and their excitation efficiencies at ∼450 nm are greatly enhanced by utilizing the energy transfer from Cr3+ to Nd3+/Yb3+ ions. Ce3+ ions can further enhance the absorption of CSS:Cr3+/Ln3+ phosphors to the blue light, and at the same time contribute to the visible emission in 480–650 nm. Furthermore, CSS:Cr3+/Ln3+ phosphors show good thermal stability, and approximately 79% of the initial emission intensity is sustained at 150 °C. A phosphor-converted LED (pc-LED) prototype is fabricated by integrating the as-prepared phosphor CSS:Cr3+/Ln3+ and the commercial phosphor CaAlSiN3:Eu2+ with the blue LED chip, showing a super broadband emission ranging from 450 to 1100 nm. This finding shows the potential application of CSS:Cr3+/Ln3+ phosphors in broadband NIR pc-LEDs or super broadband LED sources with visible to NIR light output.

Characterization of Nucleobases in Broadband Terahertz Spectra from 0.5 to 10 THz with the Air-Biased-Coherent-Detection Technique.

Terahertz time-domain spectroscopy (THz-TDS) is an effective coherent detection technique for deeply understanding the structures and functions of biomolecules. However, generally not full information in the whole THz range can be obtained due to the limited detection bandwidth (usually less than 5 THz) of the traditional THz-TDS systems. In this paper, effective THz absorption spectra in 0.5–10 THz range of five typical nucleobases of DNA/RNA are characterized with a super broadband THz detection technique, called the air-biased- coherent-detection (THz-ABCD) technique. Few unexpected characteristic absorption peaks appeared in the low-frequency region and meanwhile a series of anticipated characteristic absorption peaks are found in the high-frequency region. The fingerprint spectra of these nucleobases are helpful for further analysis on the vibration and twisting behavior of hydrogen bonds, van der Waals and electrostatic forces etc. between and within DNA/RNA biomolecules.

Super Broadband-Sensitive Upconversion in Tm and Ni Codoped Perovskites

We investigated broadband-sensitive upconversion (UC) processes in a series of Tm- and Ni-sensitized ABO3 (A = Ca/Sr/Ba and B = Ti/Zr/Hf) perovskites. We have designed combinations of the sensitizers and host cations such that super broad solar radiation ranging from 900 nm to nearly 2000 nm can be efficiently upconverted to 800 nm and shorter wavelengths. The Ni2+ ions located at the center of O2− octahedra absorbed photons in the 900–1500 nm range and transferred those energies to the nearby Tm3+ ions. The Tm3+ ions upconverted those energies at 800 nm, along with the energies absorbed by themselves in the 1100–1250 and 1550–2000 nm ranges, exhibiting super broadband sensitivity. Among the ABO3:Tm, Ni (A = Ca/Sr/Ba and B = Ti/Zr/Hf) upconverters, CaTiO3:Tm, Ni exhibited the best performance due to its most distorted crystal structure, which intensified the emission and absorption extents by increasing the optical transition probabilities of Tm3+ and Ni2+ ions. Introduction of alkali ions at the Ca2+ sites and Nb5+ ions at the Ti4+ sites intensified the UC emission by many folds, mainly due to a charge balance mechanism. At the same time, bigger and smaller codoped alkali ions created an asymmetric crystal field around the active ions and further enhanced the UC emission. Importantly, the upconverted photons are within the absorption edges of GaAs, Cu2ZnSnS4, and dye-sensitized solar cells making wider applications of these upconverters besides crystalline Si solar cells.

A flat-field soft X-ray spectrometer for X-ray absorption spectroscopy measurement of warm dense matter

A flat-field soft X-ray spectrometer operating in the spectral range of 250–1240 eV was designed and built for warm dense matter and high-energy density plasma physics. It employs a grazing incidence toroidal mirror as a focusing optic, an aberration-corrected varied line-spacing concave grating with 2400 lines/mm as a dispersive element, and a charge coupled device as an X-ray detector. The dispersion and energy resolution are calibrated with a high-power laser-produced plasma and X-ray free electron laser sources. A resolving power over 370 was achieved over the entire spectral range. A super broadband spectrum in the range of 250–1000 eV was measured from the laser-produced bismuth plasma. The signal-to-noise ratio of 130 was obtained with an average of 10 pulses. These results demonstrate the capability of the spectrometer for single laser shot based experiments for warm dense matter and high energy density plasma research.

Polarization-independent and super broadband flat lens composed of graded index annular photonic crystals

Abstract In this paper, we propose two types of all-dielectric polarization-independent graded index annular flat lens with a wide operating frequency range. The lenses are composed of two-dimensional triangular and square lattice photonic crystals with circular silica ( S i O 2 ) rods in the air. We assume in both square and triangular structures, the lenses are obtained by making air holes within each dielectric rod and we consider that the outer radius of the created annular rods is maintained constant while the size of the inner air holes varies along the transverse direction whose the air holes variation follow two types of linear and parabolic function. The graded structures are made in such a way that the modulus of the refractive index is biggest at the centre and decreases towards the edges. The optical properties and the physical background of the polarization-independent focusing mechanism are studied in frequency and spatial domains, using plane wave expansion and finite-difference time-domain methods. Our numerical results show that, through an appropriate set of design, the designed lenses are able to focus the light regardless of polarization for a wide frequency range into approximately same focal length in which difference between the focal distance of TE and TM polarization modes stays below λ 4 . Compared to previously polarization-independent designed photonic crystal based lenses, our proposed structures work under much wider frequency range. Also, in contrast with most of the graded structures, our graded lens are made without altering the lattice constant along the optical axis or transverse to the optical axis. Moreover, the design approach is restricted to the use of silica and non-use of more complicate materials such as liquid crystals, plasma, and the like. Thus, the designed systems can be constructed easier relative to the previously designed lenses.

Super Broadband Near-Infrared Phosphors with High Radiant Flux as Future Light Sources for Spectroscopy Applications

The near-infrared (NIR) light source is desirable for real-time nondestructive examination applications, which include the analysis of foodstuffs, health monitoring, iris recognition, and infrared cameras. The emission spectra of such an infrared light source should also be as broad as possible for effective performance, in view of the fact that the broad absorption and reflection of light by the organic elements present in foodstuffs and human health fall in the blue and NIR regions of the electromagnetic spectrum, respectively. In this letter, a blue light-emitting diode (LED) excitable super broadband NIR phosphor light source is developed with a high fwhm of 330 nm and radiant flux of 18.2 mW for the first time. The observation of super-broad-band luminescence from two distinct luminescence centers is studied and evidenced by electron paramagnetic resonance, X-ray absorption near-edge structure, steady-state luminescence, and time-resolved luminescence at ambient and high-pressure environments. Finall...

Broadband near-infrared emission and energy transfer in Nd-Bi co-doped transparent silicate glass-ceramics for optical amplifiers

The Bi+-doped, Nd3+-doped, and Nd3+-Bi+ co-doped in SiO2–Al2O3–BaF2–LaF3–TiO2 transparent silicate glass-ceramics were fabricated by conventional melting-quenching technique. The super broadband near-infrared luminescence, decay time spectra in Nd3+-Bi+ co-doped transparent silicate glass-ceramics under 808 nm excitation were investigated. The interesting in this paper is due to energy transfer between Bi+ and Nd3+ ions already exists lead to super broadband NIR emission extending from 1050 to 1550 nm with a full-width at half-maximum (FWHM) of 480 nm which covered the whole O, E and S bands were observed in the Nd3+-Bi+ co-doped transparent silicate glass ceramics. In addition, based on the decay time spectra, mechanism of energy transfer processes between Bi+ and Nd3+ ions were also discussed and proposed.

Super broadband near-infrared emission and energy transfer in Nd–Bi–Er co-doped transparent silicate glass-ceramics

Super broadband NIR (near-infrared) emission and energy transfer of Nd–Bi–Er co-doped transparent silicate glass-ceramics under excitation 808 nm laser diode were investigated. Super broadband NIR emission in Nd–Bi–Er co-doped extending from 1000 to 1600 nm with a full-width at half-maximum (FWHM) of 600 nm were observed. This result is due to the overlapping NIR emission band centered at 1275 nm (ES1 → GS) of Bi-related and NIR emission band centered at 1063 nm (4F3/2 → 4I11/2) of Nd3+ as well as NIR emission spectral band centered at 1546 nm (4I13/2 → 4I15/2) of Er3+. At the same time, the energy transfer processes between Bi-related, Nd3+ and Er3+ were also discussed and proposed.