Ultra-narrow Band Research Articles

Design of a compact ultra-narrow band dual band filter for WiMAX application

A novel narrow-band bandpass filter with two fully controllable passbands is proposed in this letter. The filter is designed through a systematic, yet simple approach, in which two independently-controllable passbands are realized using two different coupling paths. Each passband can be tuned independently only by changing one parameter of the filter. The measured and simulated results are in good agreement, showing, two passbands cantered at 3.5 and 5.8 GHz with fractional bandwidths of 0.8% and 1%, respectively. The return loss in the first and second passbands are better than 19 dB. The filter exhibits a very good out of band rejection performance, suppressing spurious bands up 16 GHz. The demonstrated filter has a compact size of 0.21λg × 0.13λg, where λg is the guided wavelength at 3.5 GHz.

Ultra-narrow band blue-emitting Ba5SiO4Cl6: Eu2+ phosphors with excellent thermal stability

The narrow band phosphors with excellent thermal stability have received growing attention from academic and industrial researchers. In this work, a novel Ba5SiO4Cl6: Eu2+ phosphor was prepared via solid phase reaction. Their crystal structure, phase composition, morphology and optical performance containing photoluminescence (PL) emission, PL excitation and temperature-dependence PL spectra were systematically analyzed. Compared with commercial BaMgAl10O17: Eu2+ blue phosphor, the as-obtained Ba5SiO4Cl6: Eu2+ phosphor displays a narrower band blue emission (λem = 440 nm) with a full width at half maximum of 32 nm under the near ultraviolet light excitation and an excellent thermal stability for 83.3% of the initial intensity at 150 °C. The quantum yield of the Ba4.98Eu0.02SiO4Cl6 phosphors was estimated to be as high as 57.2%. Finally, a LED device coupling UV-chip (400 nm) with Ba5SiO4Cl6: Eu2+, (Sr, Ba)2SiO4: Eu2+, (Sr, Ca)AlSiN3: Eu2+ phosphors display attractive optical performance with LE = 45 lm/W, CCT = 3407 K and Ra = 94. Therefore, there are good reasons for believing that the Ba5SiO4Cl6: Eu2+ phosphor will be a market prospect phosphor for the application of lighting and display.

Numerical design of a metasurface-based ultra-narrow band terahertz perfect absorber with high Q-factors

An ultra-narrow band perfect absorber based on metasurface for terahertz frequency has been designed and simulated numerically by the finite-difference time-domain method. This unit of the structure is composed of the top metallic layer, the polyimide dielectric layer and another metallic layer at the bottom. There is one cylindrical hole and two small tangential cylinders at the top layer. The absorption spectrum shows that there are tri-band and dual-band resonant peaks for two orthogonally polarized incident waves, respectively. The absorption coefficient can reach the maximum value of 99.4% at 1.79 THz. Furthermore, the full width half maximums of the resonant peaks are all about 0.005 THz. And the high Q-factor value of about 474 can be obtained. Moreover, the sensing performance of the resonant peaks under different refractive indices has been investigated. The maximum sensitivity and Figure of Merit of 190.4 GHz/RIU and 38.8 RIU−1 can be achieved, respectively.

Study of dual-coupler fiber ring and saturable absorber-based stable single-longitudinal-mode fiber laser

A configuration of single-longitudinal-mode (SLM) erbium-doped-fiber (EDF) ring laser with high stability and narrow linewidth is proposed and experimentally demonstrated. The device is composed of a dual-coupler fiber ring (DCFR) and an unpumped EDF-based saturable absorber (SA); the DCFR serves as the mode filter and facilitates the selection of the SLM while the SA produces the ultranarrow band autotracking filter effect and guarantees the SLM out. This scheme possesses the merits of being easy to fabricate, good performance, and high stability. It is easy to manufacture without strict limitations in the length of the DCFR. The output of the SLM EDF laser presents excellent performance with a linewidth of 1.52 kHz and the optical signal-to-noise ratio of 54 dB. Moreover, the proposed EDF laser exhibits remarkably good stability: the SLM operation is observed to have been stable for 3 h; the output power fluctuation and the central wavelength variation of the laser are 0.011 dB and 0.02 nm in 1 h, respectively.

High-Resolution Sensing System Based on Fiber Bragg Grating Fabry–Perot Interferometer and Frequency-Domain Demodulation

A high-resolution sensing system is proposed and demonstrated. The sensor head is a Fabry–Perot interferometer formed by two cascaded uniform fiber Bragg grating sensors, and the microwave scanning demodulation system consists of a frequency-stabilized laser, a microwave generator, an electro-optic modulator, a photodetector, and a data acquisition unit. Owing to the ultra-narrow transmission bands of the sensor head and the small resolution of the microwave scanning demodulation system (at the order of kHz), the system can realize a high resolution for strain, curvature, and lateral force sensing, up to $\text{n}\varepsilon $ , 10−3 m−1, and $\mu \text{g}$ , respectively, with sensitivities of −9.696 MHz/ $\mu \varepsilon $ , −4346.97 MHz/m−1, and −120.02 MHz/g, respectively. Because of the fast frequency shifts of the microwave generator, the system proposed in this paper has high potential for dynamic signal sensing.

Anti-Multipath Performance Improvement of an M-ary Position Phase Shift Keying Modulation System.

Low-Power Wide-Area Network (LPWAN) is the technology that the Internet-of-Things (IoT) uses in long-distance, wide-coverage scenarios. As one of the ultra-narrowband (UNB) modulation techniques, M-ary position phase shift keying (MPPSK) modulation can provide high coverage and high reliability for LPWAN. This paper proposes a multipath separation method based on MPPSK modulation, which aims to eliminate the influence of multipath on the main path without increasing the spectrum overhead and system complexity. Specifically, the modulation parameter of the system is adjusted according to the delay value, so that the phase jump of the multipath signal falls outside the phase jump of the main path symbol to achieve separation of the multipath from the main path. Moreover, a normalized symbol joint decision method is proposed in order to reduce the introduced noise while using multipath information for decisions. The simulation results indicate that the multipath separation conditions given in this paper can meet the requirements of multipath separation of MPPSK signals. Compared with the existing mainstream decision scheme, the normalized symbol joint decision improves the demodulation performance of the system.

Monodisperse Gold Nanorods for High-Pressure Refractive Index Sensing.

The effects of hydrostatic pressure on the surface plasmon resonances (SPRs) of aqueous dispersions of monodisperse gold nanorods (AuNRs)were determined up to 9 GPa. The ultranarrow longitudinal SPR band of monodisperse AuNRs allows us to monitor a gradual red shift with pressure, which shows abrupt jumps at the liquid to ice phase VI and ice phase VII transitions. Despite solidifying at low pressure (∼1.8 GPa), water displays a regime of quasi-hydrostaticity in said phases VI and VII, up to ca. 5 GPa. Above this pressure, nonhydrostatic effects manifest themselves through broadening of the SPR bands, but barely any effect is observed on the position of the surface plasmon mode. The variation in the SPR peak wavelength with pressure allowed us to determine the pressure dependence of the refractive index of water. Unlike Brillouin scattering or interferometric techniques, this plasmon-spectroscopy-based method leads to a more direct determination of the refractive index, which is well described empirically by Murnaghan-type equations in the three explored phases. We report herein the obtained analytical functions providing the pressure dependence of refractive index in the liquid, ice VI, and ice VII phases of water.

Ultra-narrow band perfect metamaterial absorber based on dielectric-metal periodic configuration

The ultra-narrow band perfect metamaterial absorber (PMA) based on dielectric-metal periodic configuration for near infrared spectral region is proposed. The PMA consists of a dielectric resonant structure and a metal substrate. Two design examples show that the proposed PMAs are able to exhibit nonpolarizing absorption peaks at normal and oblique incidences respectively. Moreover, the absorption spectra of the PMA for oblique incidence are insensitive to the incident angle under TE polarized light illumination. But this PMA exhibits a large spectral shift by rotating the angle of incidence under TM polarized light illumination. Then a PMA sample for oblique incidence is fabricated through thin-film deposition and electron beam lithography patterning. Finally, the reflection spectra of the fabricated PMA sample are measured. The absorption spectra obtained by subtracting the measured reflection spectra from incident spectra are consistent with the theory. Thus the novel characteristics of the ultra-narrow band PMA based on dielectric-metal periodic configuration are experimentally demonstrated.

On the feasibility of using a laser guide star adaptive optics system in the daytime

We investigate the use of ultra-narrow band interference filters to enable daytime use of sodium laser guide star (LGS) adaptive optics systems. Filter performance is explored using theoretical and vendor supplied filter transmission profiles, a modeled daylight sky background, broadband measurements of the daytime sky brightness on Maunakea, and an assumed photon return from the sodium LGS and read noise for the wavefront sensor (WFS) detector. The critical parameters are the bandpass of the filter, the out-of-band rejection, and the peak throughput at the wavelength of the LGS light. Importantly, a systematic trade between these parameters leads to potentially simple solutions enabling daytime observations. Finally, we simulated the Mid-Infrared Adaptive Optics (MIRAO) system planned for the Thirty Meter Telescope with an end-to-end simulation, folding in daytime sky counts. We find that MIRAO with five sodium LGSs, commercial off-the-shelf filters to suppress the sky background in the LGS WFSs, and a near-infrared natural guide star (K ≤ 13) tip/tilt/focus WFS can attain daytime Strehl ratio values comparable to those at night.

A single-longitudinal-mode narrow-linewidth dual-wavelength fiber laser using a microfiber knot resonator

A stable narrow-linewidth dual-wavelength single-longitudinal-mode (SLM) erbium-doped fiber laser is demonstrated using a microfiber knot resonator (MKR). A MKR made by the microfiber knotting method exhibits the characteristics of flexibility, high quality factor and broad free spectral range and can be used as a comb-like ultra-narrow band pass filter. SLM operation of the fiber laser can be generated as a function of the Vernier effect by cascading a 650 m diameter MKR in the ring cavity. In combination with a common fiber Bragg grating, narrow linewidths (0.016 nm and 0.019 nm) of dual wavelength are generated. Finally, a SLM ring laser with narrow linewidth and low-frequency noise is achieved. Simultaneous generation of first- and second-order optical vortex beams in the dual-wavelength fiber laser using different mode-selective couplers is demonstrated.

Packet collision analysis when heterogeneous unlicensed IoT technologies coexist

This study deals with the impact of unlicensed Internet of Things (IoT) network coexistence in terms of packet collision. The classical packet collision studies based on the Poisson distributed process generally assume homogeneous networks with packets of equal lengths. The authors propose a new approach which can be applied to a more general context including heterogeneous networks and different packet lengths. The proposed approach is based on modelling the vulnerable period and the packet length as uniform random variables. Then, the two main IoT networks considered in unlicensed spectrum, LoRa and Sigfox, are being investigated in more detail. For these two networks, closed-form analytical formulas for the intra-and inter-network probability of packet collisions between nodes are provided and confirmed by simulations results. For this context, it is also shown that the ultra-narrow band feature of Sigfox is rather a drawback than an advantage from the collision point of view. To enhance the probability of collision, some possible evolutions of the Sigfox physical layer are finally suggested.

Probability of false alarm based interference suppression methods in Internet of Things (IoT) systems

There is going to be significant growth of connected devices, such as smart phones, tablets, and sensors. It has been predicted that by 2020, there are more than 50 billion connected devices in the world. Most of common home IoT devices require little interaction and produce minimal data. Or some healthcare or factory automation sensors need or want to measure and send data to and from the Internet regularly. These are not massive consumers of bandwidth. These can be called narrowband (NB) or ultra-narrowband (UNB) signals. Even if this saves both spectrum resources and power consumption, its drawback is that in the consequence of the IoT headway, the amount of devices and, thus, the amount of NB signaling as well as radio frequency (RF) noise are significantly growing. Thus, interference suppression (IS) is indispensable. In this paper, three probability of false alarm (PFA) based methods, namely Neyman–Pearson (NP) criterion, forward consecutive mean excision (FCME), and localization algorithm based on double-thresholding (LAD) are applied for a wireless NB-IoT network, especially, in the last 100 m region, i.e., from devices to an access point (AP). Besides the traditional fixed threshold approach, an adaptive threshold setting is also proposed to enhance the performances in frequency selective fading channels. The simulation results show that the proposed methods excellently work even in a dense NB-IoT network, where contains a large number of devices.

Synergistic Reducing Effect for Synthesis of Well-Defined Au Nanooctopods With Ultra-Narrow Plasmon Band Width and High Photothermal Conversion Efficiency.

Branched Au nanoparticles have attracted intense interest owing to their remarkable properties and a wide variety of potential applications in surface-enhanced Raman spectroscopy (SERS), photothermal therapy, photoacoustic imaging, and biomedicines. The morphology and spatial arrangement of branches play the most crucial role in the determination of their properties and applications. However, it is still a synthetic challenge to control the exact arm numbers of branches with specific spatial arrangements. Here we report a facile method for the kinetically controlled growth of Au nanooctopods (NOPs) with a high yield (81%), monodispersity, and reproducibility by using the synergistic reducing effect of ascorbic acid and 1-methylpyrrolidine. The NOPs have eight arms elongated along <111> directions with uniform arm lengths. Due to their well-defined size and shape, NOPs show ultra-narrow surface plasmon band width with a full width at half maximum of only 76 nm (0.20 eV). Upon irradiation with laser, the NOPs possessed excellent photothermal conversion efficiencies up to 83.0% and photoacoustic imaging properties. This work highlights the future prospects of using NOPs with desired physicochemical properties for biomedical applications.

Learning from a Mineral Structure toward an Ultra-Narrow-Band Blue-Emitting Silicate Phosphor RbNa3 (Li3 SiO4 )4 :Eu2.

Learning from natural mineral structures is an efficient way to develop potential host lattices for applications in phosphor converted (pc)LEDs. A narrow-band blue-emitting silicate phosphor, RbNa3 (Li3 SiO4 )4 :Eu2+ (RNLSO:Eu2+ ), was derived from the UCr4 C4 -type mineral model. The broad excitation spectrum (320-440 nm) indicates this phosphor can be well matched with the near ultraviolet (n-UV) LED chip. Owing to the UCr4 C4 -type highly condensed and rigid framework, RNLSO:Eu2+ exhibits an extremely small Stokes shift and an unprecedented ultra-narrow (full-width at half-maximum, FWHM=22.4 nm) blue emission band (λem =471 nm) as well as excellent thermal stability (96 %@150 °C of the initial integrated intensity at 25 °C). The color gamut of the as-fabricated (pc)LEDs is 75 % NTSC for the application in liquid crystal displays from the prototype design of an n-UV LED chip and the narrow-band RNLSO:Eu2+ (blue), β-SiAlON:Eu2+ (green), and K2 SiF6 :Mn4+ (red) components as RGB emitters.

Ultra-Narrow-Band Blue-Emitting Oxoberyllates AELi2 [Be4 O6 ]:Eu2+ (AE=Sr,Ba) Paving the Way to Efficient RGB pc-LEDs.

Highly efficient phosphor-converted light-emitting diodes (pc-LEDs) are popular in lighting and high-tech electronics applications. The main goals of present LED research are increasing light quality, preserving color point stability and reducing energy consumption. For those purposes excellent phosphors in all spectral regions are required. Here, we report on ultra-narrow band blue emitting oxoberyllates AELi2 [Be4 O6 ]:Eu2+ (AE=Sr,Ba) exhibiting a rigid covalent network isotypic to the nitridoalumosilicate BaLi2 [(Al2 Si2 )N6 ]:Eu2+ . The oxoberyllates' extremely small Stokes shift and unprecedented ultra-narrow band blue emission with fwhm ≈25 nm (≈1200 cm-1 ) at λem =454-456 nm result from its rigid, highly condensed tetrahedra network. AELi2 [Be4 O6 ]:Eu2+ allows for using short-wavelength blue LEDs (λem <440 nm) for efficient excitation of the ultra-narrow band blue phosphor, for application in violet pumped white RGB phosphor LEDs with improved color point stability, excellent color rendering, and high energy efficiency.

Sub-Wavelength Grating Enhanced Ultra-Narrow Graphene Perfect Absorber

A sub-wavelength grating has been elaborately designed to enhance the absorption of the monolayer graphene at λ = 1.55 μm based on the coupled leaky mode theory (CLMT). The results indicate that the absorption can reach 99.8% at the resonant wavelength, and the absorption peak is ultra-narrow due to the excitation of TM31 mode in the grating structure. Taking advantages of the tunable chemical potential of graphene which is bias voltage controllable, the proposed structure can function as an adjustable absorber. The high figure of merit up to 1329 and sensitivity with the value of 66 are achieved. With the ultra-narrow absorption band and tunable peak positions, the graphene perfect absorber holds great potential application in sensing and biology.

Ultra-narrow bandgap non-fullerene organic solar cells with low voltage losses and a large photocurrent

Based on nonfullerene IEICO-4F, ITCC and PC71BM acceptors, photo-carrier losses via bi-molecular recombination in organic solar cells (OSCs) with an ultra-narrow band gap are comparatively investigated with mid-gap OSCs.

Backscatter Communications for Wireless Powered Sensor Networks With Collision Resolution

Wireless powered backscatter communications is an attractive technology for next-generation low-powered sensor networks such as the Internet of Things. However, backscattering suffers from collisions due to multiple simultaneous transmissions and a dyadic backscatter channel, which greatly attenuate the received signal at the reader. This letter deals with backscatter communications in sensor networks from a large-scale point-of-view and considers various collision resolution techniques: directional antennas, ultra-narrow band transmissions, and successive interference cancellation. We derive analytical expressions for the decoding probability and our results show the significant gains, which can be achieved from the aforementioned techniques.

Localization in Low Power Wide Area Networks Using Wi-Fi Fingerprints

Supply chain management requires regular updates of the location of assets, which can be enabled by low power wide area networks, such as Sigfox. While it is useful to localize a device simply by its communication signals, this is very difficult to do with Sigfox because of wide area and ultra narrowband nature. On the other hand, installing a satellite localization element on the device greatly increases its power consumption. We investigated using information about nearby Wi-Fi access points as a way to localize the asset over the Sigfox network, so without connecting to those Wi-Fi networks. This paper reports the location error that can be achieved by this type of outdoor localization. By using a combination of two databases, we could localize the device on all 36 test locations with a median location error of 39 m . This shows that the localization accuracy of this method is promising enough to warrant further study, most specifically the minimal power consumption.

Ultra-narrow band perfect absorbers based on Fano resonance in MIM metamaterials

Metallic nanostructures have attracted numerous attentions in the past decades due to their attractive plasmonic properties. Resonant plasmonic perfect absorbers have promising applications in a wide range of technologies including photothermal therapy, thermophotovoltaics, heat-assisted magnetic recording and biosensing. However, it remains to be a great challenge to achieve ultra-narrow band in near-infrared band with plasmonic materials due to the large optical losses in metals. In this letter, we introduced Fano resonance in MIM metamaterials composed of an asymmetry double elliptic cylinders (ADEC), which can achieve ultra-narrow band perfect absorbers. In theoretical calculations, we observed an ultranarrow band resonant absorption peak with the full width at half maximum (FWHM) of 8 nm and absorption amplitude exceeding 99% at 930 nm. Moreover, we demonstrate that the absorption increases with the increase of asymmetry and the absorption resonant wavelength can be tuned by changing the size and arrangement of the unit cell. The asymmetry metallic nanostructure also exhibit a higher refractive sensitivity as large as 503 nm/RIU with high figure of merit of 63, which is promising for high sensitive sensors. Results of this work are desirable for various potential applications in micro-technological structures such as biological sensors, narrowband emission, photodetectors and solar thermophotovoltaic (STPV) cells.