Single Passband Research Articles

A Method for Designing Multi-Band Rasorbers for Wideband Applications

Rasorbers with a single passband (narrow or wide) or multiple narrow passbands have been reported for stealth applications over the past few years. In this work, a method of designing the multi-band rasorber with wide passband(s) is proposed for the stealth of wideband antennas. Firstly, the method of designing multi-band FSS is proposed based on the theory of N-band resonator, in which all the passbands exhibit second-order response. Secondly, a parallel resonator combining spiral inductor and interdigital capacitor is proposed to satisfy wide passband requirements at lower frequency of the operating band. Finally, to verify the proposed method, a dual-band rasorber consisting of FSS and resistive layer is fabricated and measured. The measured results illustrate two passbands within 4.9-6 GHz (20.0%) and 8.6-9 GHz (6.3%), respectively. Three absorption bands with 48.4%, 25.7%, and 22.0% fractional bandwidths are also achieved.

Cascaded Microwave Photonic Filters for Side Mode Suppression in a Tunable Optoelectronic Oscillator applied to THz Signal Generation & Transmission

We demonstrate experimentally an optoelectronic oscillator (OEO) in which high side-mode suppression is achieved by cascading a phase modulator-based single passband tunable microwave photonic (MWP) filter with an optoelectronic feedback loop-based infinite impulse response (IIR) MWP filter. The OEO provides an RF oscillation that can be tuned from 6.5 GHz to 17.8 GHz with a phase noise lower than -103 dBc/Hz. Experimental results show that inclusion of the IIR section leads to a 20 dB reduction of phase noise close to the carrier and an increase of 10 dB in side mode suppression, compared to the equivalent OEO without an IIR section. The OEO was used to drive an optical frequency comb generator to generate a THz signal at 242.6 GHz by optical heterodyning; inclusion of the IIR section increases suppression of the side modes neighboring the THz carrier. A radio over fiber link was then implemented at a 242.6 GHz carrier frequency, with transmission of a 24 Gbps signal over 40 km of fiber and a 30 cm wireless path at a bit error rate below the forward error correction limit. The proposed system may be applied to frequency reconfigurable THz links and radars.

MEMS-SOA Spectrum-Sliced Auto-Equalized Source Enabling Uniformly Tunable Microwave Photonic Filter

In this work, we report a Micro-Electro-Mechanical System (MEMS)-Semiconductor Optical Amplifier (SOA) active interferometer as a low cost and miniaturized tunable broadband sliced source and optical loss auto-equalizer for single pass band microwave photonic filter (MPF). A low finesse Fabry-Perot MEMS interferometer is formed from a movable deeply etched micro-mirror in front of a cleaved fiber facet. The interferometer slices the amplified spontaneous emission (ASE) output of the SOA, while the output is feedback to the SOA again for amplification and optical loss auto-equalization through the SOA gain saturation effect. This configuration improved the uniformity of the MPF passband attenuation along the tuning range down to 3.72 dB only. The filter center frequency can be finely tuned electrically for ±241.6 MHz with a MEMS electrostatic comb actuator driving the mirror. The center frequency is controlled by the distance between fiber facet and micro-mirror. The operation of the proposed MEMS-SOA based MPF is experimentally verified as a proof of concept from 1.2 to 4.5 GHz and can be easily extended to higher frequencies. A tuning resolution of 6.04 MHz/ $\mu \text{m}$ is achieved with stopband attenuation larger than 20 dB and 3-dB bandwidth mean value of 141 MHz.

8fJ/Step Bandpass ADC With Digitally Assisted NTF Re-Configuration

In this work we propose a single channel band-pass (BP) SAR ADC with dynamic noise transfer function (NTF) re-configuration. The proposed ADC employs a low-power two-stage architecture. After the SAR finishes quantization, the residue is extracted by firing the comparator multiple times. An estimate of the residue is obtained by employing a maximum likelihood based estimator (MLE). The output of the ADC is obtained by subtracting a delayed version of the estimated residue from the SAR output thus generating a complex NTF with multiple notches in the spectrum. A 65nm ADC prototype achieves 74.1/78dB SNDR/DR over a 101.2kHz bandwidth while consuming $17~\mu \text{W}$ from a 1V supply at 2.43MS/s. The ADC core occupies an area of 0.12mm2. The ADC achieves 8fJ/c-step bandpass FoM which is $85\times $ better than state-of-the-art BP ADCs with similar bandwidth and $8.7\times $ better than all reported state-of-the-art BP ADCs.

Design of Metal Insulator Metal based Square Ring Resonator Plasmonic Filter using Silica Slits for Dual Band Applications

In this paper, Metal-Insulator-Metal (MIM) based dual-band plasmonic bandpass filters (BPF) with single and dual silica slits design and analysis is presented. The Square Ring Resonator (SRR) is coupled using Coupled feed line for dual-band operations. The coupled feed line is used for dual-band operating wavelengths, 1300 nm (230.6 THz) and 1600 nm (187.37 THz). Design and simulations are performed using complex electromagnetic simulatorknown as computer simulation technology (CST) microwave tool. The proposed filters are used for plasmonic single and dual-band bandpass filter (BPF) applications in photonic integrated circuits (PIC’s).

Tripole type wideband bandpass frequency selective surface for X‐band applications

The study presents a novel single dielectric layer wideband bandpass frequency selective surface (FSS) topology. The structure is designed using a kind of the tripole type FSS which has been analysed for its behaviour. Next, the operating bandwidth has been increased by using the meander lines in the middle of the unit-cell. The proposed FSS structure covers the X-band (45.03% fractional bandwidth) of the electromagnetic (EM) spectrum with a −3 dB transmission bandwidth. Its −1 dB bandwidth extends from 7.93 to 11.93 GHz. The wide operating bandwidth with a single dielectric layered structure makes it suitable for the hybrid radome applications. For the normally incident EM wave, adjacent to the lower and upper cut-off frequencies, the structure offers better than 18 dB attenuation which increases the out of the band rejection. Finally, the proposed structure is fabricated and experimentally verified for the dual polarisation and angle stability up to 45°. Eventually, to prove the novelty in terms of the operating bandwidth and the fabrication simplicity, an exhaustive state-of-the-art comparison is also presented.

Compact Single- and Dual-Band Filtering 180° Hybrid Couplers on Circular Patch Resonator

In this article, an effective approach is proposed to design of compact single and dual-band patch filtering 180° hybrid couplers based on circular patch resonator. Without an additional circuit, the prescribed in-phase and out-of-phase specifications of the coupler are achieved by elaborately studying and utilizing the electric field distributions of the degenerate resonant modes in the unslotted/slotted patch resonators. Meanwhile, the desired single-/dual-band filtering responses are attained by virtue of the coupling extent between the two designed patch resonators in the back-to-back form. In our design, a pair of TM11-modes at first makeup a single passband for single-band operation, and a pair of TM11-like modes and a pair of TM12-like modes then construct the two separate passbands for dual-band operation, respectively. After the working principle is explained, the design procedure based on the coupling matrix is provided. For demonstration, two prototypes for single- and dual-band patch filtering 180° hybrid couplers are implemented, respectively. Measured results coincide well with simulated ones, verifying the proposed design concept.

Synoptic Measurements of Electron Temperature and Speed in the Solar Corona with Next Generation White-Light Coronagraph

Current white-light coronagraphs measure polarized brightness (pB) of the solar corona using a single bandpass filter to measure the density of electrons. However, future coronagraphs can be modified to take pB images through four bandpass filters to measure density, temperature and speed of electrons. In this article, we use a spherical three dimensional coronal model of the Bastille Day coronal mass ejection to synthetically measure pB through four bandpass filters along lines of sight originating from two observers located diametrically in front (1 AU, 0, 0) and behind (-1 AU, 0, 0) the plane of the sky on the xy-ecliptic plane. The lines of sight pass through 81 positions on a straight line parallel to the solar north–south z-direction in the yz-plane and this line intersects the ecliptic at (0, $1.25~\mbox{R}_{\odot}$ , 0) from Sun center. The 81 data points are separated in intervals of $0.05~\mbox{R}_{\odot}$ and points extend from (0, $1.25~\mbox{R}_{\odot}$ , - $2.0~\mbox{R}_{\odot}$ ) to (0, $1.25~\mbox{R}_{\odot}$ , $2.0~\mbox{R}_{\odot}$ ). The measured pB ratios are used to measure temperature and speed, then we compare with true temperature and speed in the plane of the sky, and quantify the difference, which is a systematic error associated with using modeled pB ratios, based on a symmetric corona, to compare with measured pB ratios, on an asymmetric corona. This understanding is reached by allowing the coronal model to rotate a full circle in intervals of $1^{\circ}$ and illuminating the lines of sight with both symmetric and asymmetric coronal atmospheres about the plane of the sky.

Reconfigurable-Bandwidth DWB BPF With Fixed Operation Frequency and Controllable Stopband

In this brief, a novel planar topology is presented for the design of reconfigurable-bandwidth dual-wideband bandpass filters with fixed operation frequency and controllable stopband. The proposed design is started from a three-mode passive filtering structure with five transmission zeros, whose second and third passband edges can be independently allocated. Then, two PIN diodes are used as the tuning elements. With the help of these PIN diodes, three bandwidth states can be achieved. In contrast to the previous works with only independently tunable single passband edges, the first and fourth passband edges of the proposed filter can be reconfigurable in same absolute ranges, while the rest two ones are unaltered. For validation, a reconfigurable prototype is designed and measured. The measured results agree well with the theoretical analysis, verifying a simple design approach of DWB BPFs with new reconfigurable-bandwidth property.

Recipes for bolometric corrections and Gaia luminosities of B-type stars: application to an asteroseismic sample

ABSTRACT We provide three statistical model prescriptions for the bolometric corrections appropriate for B-type stars as a function of (i) Teff, (ii) Teff and log g, and (iii)Teff, log g and [M/H]. These statistical models have been calculated for 27 different filters, including those of the Gaia space mission, and were derived based on two different grids of bolometric corrections assuming LTE and LTE+NLTE, respectively. Previous such work has mainly been limited to a single photometric passband without taking into account non-local thermodynamic equilibrium (NLTE) effects on the bolometric corrections. Using these statistical models, we calculate the luminosities of 34 slowly pulsating B-type (SPB) stars with available spectroscopic parameters, to place them in the Hertzsprung–Russell diagram and to compare their position to the theoretical SPB instability strip. We find that excluding NLTE effects has no significant effect on the derived luminosities for the temperature range 11 500–21 000 K. We conclude that spectroscopic parameters are needed in order to achieve meaningful luminosities of B-type stars. The three prescriptions for the bolometric corrections are valid for any galactic B-type star with effective temperatures and surface gravities in the ranges 10 000–30 000 K and 2.5–4.5 dex, respectively, covering regimes below the Eddington limit.

RETRACTED ARTICLE: Optical spectroscopic analysis of bandpass filter used for laser protection based on cobalt phosphate glass

A protection glass against laser beam was fabricated from a cobalt oxide-doped copper phosphate glass with series of 40P2O5–(20−x) Na2O–38ZnO– xCo3O4–1CuO in the molar ratio with x = 1, 2, 3, 4 and 5 using a conventional glass casting and quenching technique. The density was measured by Archimedes method, and the molar volume was calculated. Increasing the heavy element, cobalt oxide in a glass composition causes an unusual phenomenon between the density and molar volume that they have the same trend. The XRD technique has been used to investigate the glass systems and prove the complete glass state of the systems. Optical spectroscopic analysis from the transmittance data of the glass filter showed that these filters had a single band pass with a double band stop in the UV, visible and IR, which covers the region that is used in some laser protection glass like organic dye lasers, polymer lasers, solid-state dye lasers, excimer, quadrupled Nd:YAG laser and quintupled Nd:YAG laser. This can be used for a glass laser safety protection.

Temperature-insensitive relative humidity sensing based on a carrier-suppression-effect-free tunable optoelectronic oscillator using a non-coherent broadband optical source

A relative humidity (RH) sensing scheme with high resolution and high interrogation speed based on an optoelectronic oscillator (OEO) is proposed and experimentally demonstrated. A carrier-suppression-effect-free single bandpass microwave photonic filter (MPF) with no baseband response is employed in the OEO to select the oscillating frequency, which is consisted of a non-coherent broadband optical source, a Mach-Zehnder interferometer (MZI) with one arm embedded a phase modulator, a dispersion compensation fiber and a photodetector. In one arm of the MZI, a section of optical fiber is coated with a polyvinyl alcohol (PVA) film acting as sensing probe, in which the PVA film can convert the RH variation to the strain on the fiber. When the RH changes, the arm-length difference and free spectral range of the MZI is changed, leading to a frequency change of the MPF as well as the oscillating signal of the OEO. By simply monitoring the frequency shift of the oscillating signal in the electrical domain, a high resolution and high interrogation speed RH measurement can be achieved. The temperature cross-sensitivity can be almost eliminated by adding a section of fiber without PVA film coating in the other arm of the MZI. An experiment is performed, and a high RH sensitivity of 2.016 MHz/%RH with a high resolution of 0.17 % is achieved.

Thermally Stable Optical Filtering Using Silicon-Based Comb-Like Asymmetric Grating for Sensing Applications

A silicon-based compact comb-like asymmetric grating is proposed as a thermally stable optical filter for label-free sensing applications. The device is designed and fabricated with a cavity section introduced between the two grating regions which are partially etched in the lateral direction to ensure the nonzero coupling of the fundamental and first-order modes in the propagation and counter-propagation direction. To demonstrate refractive index sensing, resonance shift in the device is measured with sodium chloride (NaCl) dissolved in DI water. In contrast to conventional Bragg grating where stopband lies in the transmission spectrum, the proposed device allows a single narrow passband transmission peak with a large Free Spectral Range (FSR) attributed to the engineered photonic bandgap of two modes present in the waveguide region. The device is deliberately designed such that slightly wide resonance peak is obtained that makes device operation thermally stable for a large temperature variation of ±15 K. A higher-order leaky mode with strong light-analyte interaction (due to long corrugation width) in the gratings governs high sensitivity of ≈352 nm/RIU for different concentrations of NaCl from 0% to 10% in the Deionized (DI) water with a small footprint area of $18~{\mu } {m}^{\textsf {2}}$ only. Proposed filter characteristics are well suited for multifunctional applications in integrated photonic devices.

Asymmetric CPW-fed electrically small metamaterial- inspired wideband antenna for 3.3/3.5/5.5 GHz WiMAX and 5.2/5.8 GHz WLAN applications

In this work, a new concept is introduced to enhance the bandwidth of metamaterial (MTM) inspired antenna. The MTM inspired antenna mainly comprises a single split-ring resonator and a hexagonal-shaped closed ring resonator with asymmetric coplanar waveguide feed, which leads to antenna compactness. The physical dimension of the intended antenna is 17 mm × 20 mm × 1.6 mm. Due to MTM loading, the antenna achieves more compactness with ka = 0.87 < 1 resulting in a smaller electrical dimension of 0.18λ0 × 0.21λ0 × 0.017λ0 at 3.24 GHz. The intended antenna provides a wider bandwidth ranges from 3.06 GHz to 5.89 GHz with a percentage impedance bandwidth of 63.24% due to the merging of two resonating modes into a single passband. The proposed antenna provides a gain greater than 2 dBi for the entire working band with a maximal gain of 3.65 dBi at 5.2 GHz and radiation efficiency greater than 85% for the complete working band. Also, the antenna shows a consistent radiation pattern throughout the working band and hence the intended antenna is appropriate for 5.2/5.8 GHz WLAN IEEE 802.11 a/h/j/y, and 3.3/3.5/5.5 GHz WiMAX IEEE 802.16e applications.

Closed-loop ring resonator topology for bandpass filter applications

&lt;p class="Pa41"&gt;This paper presents a single mode pseudo-elliptic bandpass resonator based on closed-loop ring topology. The resonator is built from six quarter wavelength transmission lines to form a square closed-loop ring structure. This structure creates transmission zeros at the lower and upper sidebands so that high selectivity bandpass filter response is achieved. The advantage of this topology is that the design is less complex since no perturbation is needed on the ring lines for creation of transmission zeros. Higher-order filters can be constructed by introducing quarter-wavelength coupled-lines, coupled at both input and output of the closed-loop ring resonator. For proof of concept, the filters are designed at 10 GHz up to 3&lt;sup&gt;rd&lt;/sup&gt; order, simulated using full-wave electromagnetic simulator on microstrip substrate, &lt;em&gt;FR-4&lt;/em&gt; with characteristics given as &lt;em&gt;Ԑr &lt;/em&gt;= 4.70, &lt;em&gt;h &lt;/em&gt;= 1.499 mm and &lt;em&gt;tan δ &lt;/em&gt;= 0.012. The filters are simulated and responses are found to be agreeable with the proposed idea.&lt;/p&gt;

High-precision strain-insensitive temperature sensor based on an optoelectronic oscillator.

We have proposed and experimentally demonstrated a high-precision and strain-insensitive temperature sensor based on an optoelectronic oscillator (OEO). The oscillation frequency of the OEO is determined by the single passband microwave photonic filter (MPF) by using stimulated Brillouin scattering (SBS). The sensing fiber, which acts as the SBS gain medium, is exposed to temperature variations. The Brillouin frequency shift (BFS) changes along with the temperature. Since the central frequency of the MPF is a function of the BFS, the oscillation frequency of the OEO is varied. Besides, due to the mode competition in the OEO, the influence of the strain is eliminated. Thus, the temperature variations can be estimated through measuring the oscillation frequency. We carry out a proof-to-concept experiment. Temperature sensing with a high sensitivity of 1.00745 MHz/°C is achieved. The maximum measurement error of temperature obtained is within ± 0.5 °C. The proposed scheme has merits of simplicity and compact configuration. In addition, the proposed temperature sensor can realize quasi-distributed measurement by utilizing wavelength division multiplexing (WDM).

Reconfigurable flat-top narrow bandpass filter in prism pair coupled planar optical waveguide

A reconfigurable optical bandpass filter with flat-top transmission line shape and narrow bandwidth in nanometer scale is designed and theoretically analyzed. The filter is composed of two coupling prisms and a sandwiched planar optical waveguide (POW) which is comprised of 5 layers of uniform materials with an air gap in the center. Numerical simulations demonstrate that a single passband in the visible spectrum with flat top and completely null sideband can be obtained. The central wavelength of the passband can be tuned by about ±14 nm via a ±1.78° change of the incident angle while the high transmittance and flatness of the band top can always be maintained by almost linearly adjusting the thickness of the central air layer in the POW at the same time. During the adjustment process, the bandwidth changes from 0.92 to 2.43 nm. The simple structure and flexibility of the filter could facilitate its applications in various optical fields.

A tunable microwave photonic filter based on gain-switched optical pulses

A novel approach to realize a microwave photonic filter (MPF) based on gain-switched optical pulses is proposed and demonstrated. The proposed MPF using directly modulation-based optical source is more flexible and simple than using an external modulation-based optical frequency comb source. A theoretical model describing the principle of the proposed MPF is derived, which is confirmed by experimental results. Under different modulation and injection parameters, we present a numerical simulation of the frequency response of the proposed MPF. With no discernible tones, the proposed MPF is demonstrated by a proof-of-concept experiment. A single passband is achieved, which can be continuously tuned from 1 to 30 GHz. Further, self-phase modulation is explored in the optical domain to broaden the spectrum of gain-switched optical pulses and narrow down the bandwidth of the MPF passband.

Wideband tunable single passband microwave photonic filter based on optical injection

Optical injection is an effective way to generate a tuned microwave photonic filter (MPF). However, the tuning range of the optical injection-based MPF is limited by the nonlinear dynamics and the nonideal roll-off optical filter. To enlarge the tuning range of the MPF, a polarization modulated optical signal injection distributed feedback semiconductor laser is employed. The method is free from the nonlinear dynamics and the nonideal roll-off optical filter. The experimental result shows that the proposed MPF can be tuned from 0 to 40 GHz by directly tuning the center wavelength of the optical carrier. The tuning range can be increased if polarization modulator and photodetector with larger bandwidth are exploited. To the best of our knowledge, this is the largest frequency tuning range of optical injection-based MPF.

Single passband microwave photonic filter with widely tuning range based on optical injected distributed feedback semiconductor laser

A novel widely tunable single passband microwave photonic filter (MPF) is proposed and experimentally demonstrated, which is based on a carrier-suppressed double sidebands (CS-DSB) optical signal injected into an distributed feedback (DFB) laser. A polarization modulator (PolM) and a polarization beam splitter (PBS) are exploited to generate the CS-DSB optical signal. When the CS-DSB optical signal is injected into the DFB laser, due to the frequency selective gain feature of optical injected DFB laser, one sideband of the CS-DSB optical signal is selected and amplified. Beating the amplified sideband with the optical carrier, the gain spectrum of the DFB laser is mapped to the frequency response of the MPF. The MPF can be tuned by adjusting the wavelength of the DFB laser. Experiment results show that the MPF can be tuned from 0 to 40 GHz by changing the working temperature of the DFB laser.