Multiple Passbands Research Articles

A SEA BASS on the Exoplanet HD 209458b

Abstract We present here the first application of Stellar and Exoplanetary Atmospheres Bayesian Analysis Simultaneous Spectroscopy (SEA BASS) on real data sets. SEA BASS is a scheme that enables the simultaneous derivation of four-coefficient stellar limb-darkening profiles, transit depths, and orbital parameters from exoplanetary transits at multiple wavelengths. It relies on the wavelength independence of the system geometry and on the reduced limb-darkening effect in the infrared. This approach has been introduced by Morello et al. (without the SEA BASS acronym), who discuss several tests on synthetic data sets. Here, we (1) improve on the original algorithm using multiple Spitzer/InfraRed Array Camera passbands and a more effective set of geometric parameters, (2) demonstrate its ability with Hubble Space Telescope/Space Telescope Imaging Spectrograph data sets by (3) measuring the HD 209458 stellar limb-darkening profile over multiple passbands in the 290–570 nm range with sufficient precision to rule out some theoretical models that have been adopted previously in the literature, and (4) simultaneously extracting the transmission spectrum of the exoplanet atmosphere. The higher photometric precision of the next-generation instruments, such as those on board the James Webb Space Telescope, will enable modeling the star–planet systems with unprecedented detail, and increase the importance of SEA BASS for avoiding the potential biases introduced by inaccurate stellar limb-darkening models.

Spoof Surface Plasmon Polariton-Based Reconfigurable Band-Pass Filter Using Planar Ring Resonator

In this paper, we report the design, analysis, and development of spoof surface plasmon polariton (SSPP)-based reconfigurable band-pass filter using a planar ring resonator. A transition from quasi-transverse electromagnetic (QTEM) mode of microstrip to SSPP mode was implemented which has been subsequently used to develop a reconfigurable band-pass filter. Trapezoidal shape periodically corrugated metallic grooves etched on the planar metallic surface have been used in the implementation of this transition. In the designed transition, impedance and mode matching between QTEM mode and SSPP mode have been achieved using gradient grooves. The developed transition has been used in the characterization of a ring resonator corrugated with the periodical array of the trapezoidal shape grooves. This SSPP ring resonator shows multiple passbands at different frequencies within the specified frequency range. Varactor diodes have been incorporated in the SSPP ring resonator to obtain tunable passband. Three types of varactor-tuned circuits have been experimentally implemented and characterized using SMV2019-079LF diode package. These circuits will pave the path for development of other front-end circuit elements using the concept of spoof SPP.

Extended discussion of “Metamaterial composed of different cells exhibiting a negative refraction property over multiple frequency bands”

Herein, an extended discussion of the paper published in Journal of Modern Optics, whose title is “Metamaterial composed of different cells exhibiting a negative refraction property over multiple frequency bands”, is performed. In order to realize the multiple negative passbands, different cells are chosen to stack in the x and y axes to form a two-layer or a three-layer metamaterial unit. Different multiple passbands are obtained by comparing with these units coupling cells in different directions.

Alkalis atomic emission spectroscopy and flame temperature measurement of diesel impinging flames in an opposed multi-burner gasifier

Atomic emission spectroscopy can well characterize atom release properties and flame temperature. This work aims to investigate the spectroscopic characteristics of alkalis atoms and measurement method of flame temperature in diesel impinging flames, based on a bench-scale opposed multi-burner (OMB) gasifier. A fiber-optic spectrometer and a CCD camera coupled with multiple bandpass filters are used to obtain the spectral emission lines and two-dimensional emission distributions of Na∗ and K∗, respectively. The results indicate that alkalis atoms can be released and excited in impinging region and four jet regions. The emission intensities of Na∗ and K∗ under different O/C are the strongest in the impinging region, suggesting that the atom release concentration and flame temperature are the highest. Moreover, the thermal excitation degree is related to the type of atom, and Na atom is much easier to be excited than K atom. It is confirmed that alkalis atom content and flame temperature were the two main influence factors on the emission intensity, and emission intensity can be used to qualitatively characterize flame temperature under the same O/C. In addition, atomic emission spectroscopy (AES) was given to quantitatively calculate the flame temperature. It is verified that the AES method is and feasible to derive diesel flame temperature and monitor the temperature changes of OMB gasifiers in real time.

Design Method for Multiband Filters With Compact Configuration in Substrate Integrated Waveguide

In this paper, a design method for multiband bandpass filters with compact configuration in substrate integrated waveguide is proposed by combining the single-band/dual-band synthesis method and the multimode resonator theory. The designed filters could generate multiple filtering passbands without expanding their entire physical size. In addition, all the passbands could be efficiently synthesized and designed with any prescribed order in theory, which has been rarely reported in multiband filters, especially in the design of quad-band filters. As examples, one third-order quad-band filter and one third-order tri-band filter are designed, fabricated, and measured. Good agreement is attained between their simulated and measured S-parameters, and both the two sets of results have verified the feasibility of the proposed design method and attractive performances of the designed multiband filters.

Blind image quality assessment in multiple bandpass and redundancy domains

Blind image quality assessment (BIQA) aims to automatically evaluate image quality without any prior knowledge of reference images and distortion types. Most of existing BIQA methods use certain probability distribution models to capture the natural scene statistics features of images in bandpass domains which can be viewed as a process of removing redundancy. There also exist methods which apply NSS features in redundancy domain. In this paper, we propose a novel method that employs both bandpass and redundancy domains to acquire the complementary features in multiple color spaces. Furthermore, hierarchical feature extraction strategy is adopted to make the image representation more powerful. Then we stack them as a multi-channel feature maps group, and use Gaussian mixture model to fit them. Finally, Fisher Vectors are used to encode them and a support vector regression model is trained as the quality predictor. Extensive experiments on four commonly evaluated image quality assessment benchmark databases show the proposed method is very competitive against other BIQA methods and has good generalization ability.

Photonic analog-to-digital conversion using a red frequency chirp in a semiconductor optical amplifier.

A photonic analog-to-digital conversion (PADC) based on intensity-to-frequency conversion using a frequency chirp in a semiconductor optical amplifier (SOA) is proposed. The presented PADC has a simple scheme whereby optical quantization is achieved using a single SOA with multiple rectangular bandpass filters placed in parallel. In this Letter, we successfully achieve 10 GSamples/s, eight-level optical quantization using a quantum-dot SOA. The PADC also has much lower input signal pulse power requirements for optical quantization, compared with conventional PADCs.

Reconfigurable RF Multiband Filter With Widely Tunable Passbands Based on Cascaded Optical Interferometric Filters

Despite the increasing importance and critical needs, reconfigurable radio frequency (RF) multiband filters are currently underdeveloped even both RF electronics and photonics technologies are being explored. Although RF multiband filters with large numbers of simultaneous passbands and wide frequency tuning range are extremely desired, achieving such functionality is extremely challenging. In this paper, a photonics-based highly tunable and reconfigurable RF multiband filter is proposed through the combination of a special designed tunable Mach–Zehnder interferometer and a reconfigurable Lyot loop filter. Both the passband frequencies and the number of simultaneous passbands are adjustable, that one or multiple passbands are continuously tuned over a 20 GHz frequency range, and the number of simultaneous passbands is reconfigurable from zero to seven. As a result, the proposed RF multiband filter can be configured with various passband combinations through the same setup, providing exceptional operation flexibility. Furthermore, broadband operation and excellent filter selectivity are obtained, with sharp passband profiles and over 35-dB sidelobe suppression.

Compact Multiband Bandpass Filter Using Low-Pass Filter Combined With Open Stub-Loaded Shorted Stub

This paper presents a new method for designing multiband bandpass filters (BPFs). The filter consists of low-pass filter and two open stub-loaded shorted stubs. Multiple transmission zeros (TZs) are produced by the open stub-loaded shorted stub, and multiple passbands can be realized. For the first time, different numbers of open stubs are used to realize multiband BPFs with two to seven passbands. The center frequencies and the last passband bandwidth can be tuned in a certain range by adjusting the TZs and transmission poles. First, a wideband BPF is presented to introduce the design concept. Theoretical analysis is done to illustrate the design principle. Then, a wide single-band BPF and a dual-band BPF are designed to demonstrate the design method. The design procedure is summarized to guide the design process. Finally, tri-/quad-/quint-/sext-/sept-band BPFs are designed according to the design principle. All the BPFs are manufactured. Measured results show good agreement with simulated ones.

Design and implementation of reconfigurable filter bank structure for low complexity hearing aids using 2-level sound wave decomposition

Abstract This paper proposes a reconfigurable digital filter bank structure, which is suitable for designing hearing aids for most types of hearing losses. The proposed structure exploits the fractional interpolation and symmetry property of linear phase filters. The structure has two stages; the first one is called masking stage and the second one is called multiple passbands generation stage. The second stage i.e., multiple passband generation stage has 2 levels. By adjusting a 7-bit control signal, different sub-bands generated by the two stages can be obtained for audiogram matching. The number of sub-bands can be increased by increasing the number of fractional interpolated filters in level 2 of the multiple passbands generation block. Using the proposed structure, various types of audiograms can be matched with acceptable delay and matching error. The merits of the proposed structure are low hardware complexity and good audiogram matching with tolerable matching error and acceptable delay, when compared to the state of the art techniques for audiogram matching. Moreover, it is a reconfigurable structure. FPGA implementation of the proposed structure is also done to supplement the theoretical claim for low hardware complexity and power.

Tunable multiband metasurfaces based on plasmonic core–shell nanoparticles

Metasurfaces, which can act as wavelength-selective surfaces with multiple passbands or stopbands, have numerous applications, including modulating electromagnetic radiation, and transmitarray or reflectarray antennas. In this paper, the feasibility of such metasurfaces, using plasmonic core–shell nanoparticles, has been studied. By analyzing the polarizability of such particles, it is shown that they are capable of possessing two plasmonic resonances that can be tuned to specific wavelengths by adjusting their design parameters and the constitutive media. In addition, a passband exists in between these two bands. The surface susceptibilities of the metasurface are determined using “sparse approximation formulas.” Analytical scattering coefficients were compared and found to agree with numerical results obtained using full-wave simulation.

Chip-based arbitrary radio-frequency photonic filter with algorithm-driven reconfigurable resolution.

All programmable microwave photonic filters to date have been limited by the trade-off between the resolution and the operation bandwidth to construct arbitrary filter shapes. Here, we propose a new approach to synthesize a radio-frequency photonic filter with an arbitrary response and reconfigurable resolution through phase-only tailoring, which is implemented in a low-loss photonic chip. Based on an algorithm, incorporating the target transfer function of the filter optimum resolution can be intelligently chosen by tuning the coupling coefficients and the round-trip phase of cascaded ring resonators. We achieved filtering with tunable resolution from 300MHz to 25GHz along with various filtering shapes and multiple passbands.

Theoretical analysis of adaptive harmonic window and its application in frequency extraction of vibration signal

The goal of this paper is to find an excellent adaptive window function for extracting the weak vibration signal and high frequency vibration signal under strong noise. The relationship between windowing transform and filtering is analyzed first in the paper. The advantage of adjustable time-frequency window of wavelet transform is introduced. Secondly the relationship between harmonic wavelet and multiple analytic band-pass filter is analyzed. The coherence of the multiple analytic band-pass filter and harmonic wavelet base function is discussed, and the characteristic that multiple analytic band-pass filter included in the harmonic wavelet transform is founded. Thirdly, by extending the harmonic wavelet transform, the concept of the adaptive harmonic window and its theoretical equation without decomposition are put forward in this paper. Then comparing with the Hanning window, the good performance of restraining side-lobe leakage possessed by adaptive harmonic window is shown, and the adaptive characteristics of window width changing and analytical center moving of the adaptive harmonic window are presented. Finally, the proposed adaptive harmonic window is applied to weak signal extraction and high frequency orbit extraction of high speed rotor under strong noise, and the satisfactory results are achieved. The application results show that the adaptive harmonic window function can be successfully applied to the actual engineering signal processing.

A Hybrid Algorithm for Period Analysis from Multiband Data with Sparse and Irregular Sampling for Arbitrary Light-curve Shapes

Abstract Ongoing and future surveys with repeat imaging in multiple bands are producing (or will produce) time-spaced measurements of brightness, resulting in the identification of large numbers of variable sources in the sky. A large fraction of these are periodic variables: compilations of these are of scientific interest for a variety of purposes. Unavoidably, the data sets from many such surveys not only have sparse sampling, but also have embedded frequencies in the observing cadence that beat against the natural periodicities of any object under investigation. Such limitations can make period determination ambiguous and uncertain. For multiband data sets with asynchronous measurements in multiple passbands, we wish to maximally use the information on periodicity in a manner that is agnostic of differences in the light-curve shapes across the different channels. Given large volumes of data, computational efficiency is also at a premium. This paper develops and presents a computationally economic method for determining periodicity that combines the results from two different classes of period-determination algorithms. The underlying principles are illustrated through examples. The effectiveness of this approach for combining asynchronously sampled measurements in multiple observables that share an underlying fundamental frequency is also demonstrated.

Investigations of CH∗ chemiluminescence and blackbody radiation in opposed impinging coal-water slurry flames based on an entrained-flow gasifier

The characteristics of excited CH radical (CH∗) chemiluminescence and blackbody radiation in opposed impinging coal-water slurry (CWS) flames were investigated in this paper based on a bench-scale opposed multi-burner (OMB) gasifier. CH∗ chemiluminescence is a significant radical species in flame spectral diagnostics, and blackbody radiation can reflect the spatial distribution of solid particles produced in flame. A fiber-optic spectrometer and a CCD camera coupled with multiple bandpass filters are used to obtain the spectral emission lines and two-dimensional spectral distributions, respectively. The results show that CH∗ emission peak at 431 nm and continuous blackbody radiation can be detected in CWS flames. The differences of spectral distributions between diesel and CWS impinging flame are analyzed. Impinging zone is the core chemical reaction region, and solid particles are also concentrated in impinging zone, indicating that four-burner impinging can well restrict the reactants and flames in the impinging zone, thereby greatly reduce the damage to the refractory walls. Moreover, according to the time-averaged distributions, the intensity and area of CH∗ emission and blackbody radiation are enhanced with the increase of oxygen and carbon molar ratio (O/C), demonstrating that improving O2 velocity promotes the chemical reactions, and flame temperature plays more dominant role than solid particle quantity in blackbody radiation. The time-dependent blackbody radiation evolution presents periodical change. Besides, it is found that O/C or syngas concentration can be feasibly estimated using CH∗ chemiluminescence in OMB gasifier.

Multiwavelength mode-locked cylindrical vector beam fiber laser based on mode selective coupler

We propose and demonstrate a multiwavelength mode-locked fiber laser with cylindrical vector beam generation for the first time, to the best of our knowledge. The mode-locking mechanism is based on a nonlinear polarization rotation effect in fiber, and the multiwavelength operation is contributed to by an in-line birefringence fiber filter with periodic multiple passbands, formed by incorporating a section of polarization maintaining fiber into the laser cavity with a fiber polarizer. Furthermore, by using a home-made mode selective coupler, which acts as both a mode converter from fundamental mode to higher-order mode and an output coupler, multiwavelength mode-locked cylindrical vector beams have been obtained. This may have potential applications in mode-division multiplexing optical fiber communication and material processing.

Multi-band optical bandpass filter with picometer bandwidth in visible spectrum formed by prism pair coupled planar optical waveguide.

An optical bandpass filter structure of multiple bands in the visible spectrum with bandwidths in picometer scale (full width at half maximum, FWHM) is theoretically analyzed. The filter is in a form of prism pair coupled planar optical waveguide. For each individual guided mode, multiple pass-bands are obtainable in violet, green, and red regions of the visible spectrum, respectively. High efficiencies and symmetric band shape with flat null sideband can be obtained with practical material dispersion and loss taken into account. The central wavelength of each band can also be angularly tuned within a certain range with little influence on the efficiency or bandwidth. This kind of ultra-narrow bandpass optical filter can be used in high resolution spectroscopies, laser technologies, optical communications, and optical sensing.

Novel programmable microwave photonic filter with arbitrary filtering shape and linear phase.

We propose and demonstrate a novel optical frequency comb (OFC) based microwave photonic filter which is able to realize arbitrary filtering shape with linear phase response. The shape of filter response is software programmable using finite impulse response (FIR) filter design method. By shaping the OFC spectrum using a programmable waveshaper, we can realize designed amplitude of FIR taps. Positive and negative sign of FIR taps are achieved by balanced photo-detection. The double sideband (DSB) modulation and symmetric distribution of filter taps are used to maintain the linear phase condition. In the experiment, we realize a fully programmable filter in the range from DC to 13.88 GHz. Four basic types of filters (lowpass, highpass, bandpass and bandstop) with different bandwidths, cut-off frequencies and central frequencies are generated. Also a triple-passband filter is realized in our experiment. To the best of our knowledge, it is the first demonstration of a programmable multiple passband MPF with linear phase response. The experiment shows good agreement with the theoretical result.

Tunable and Selectable Multipassband Microwave Photonic Filter Utilizing Reflective and Cascaded Fiber Mach–Zehnder Interferometers

In this paper, we have proposed and experimentally demonstrated a new approach to implement microwave photonic filter with tunable and selectable multiple passbands by using reflective and cascaded fiber Mach–Zehnder interferometers and dispersive medium. By employing the proposed structure, microwave photonic filter (MPF) with more aperiodic passbands compared with previous methods have been achieved. The proposed MPF exhibits advantages such as simple structure, easy implementation, good tunability, and passband selection performances.

Tunable Single-Passband Microwave Photonic Filter Based on Sagnac Loop and Fabry–Perot Laser Diode**Supported by the National Natural Science Foundation of China under Grant Nos 61302026, 61275067 and 61575034, and the Jiangsu Natural Science Foundation under Grant No BK2012432.

A tunable single-passband microwave photonic filter is proposed and demonstrated, based on a laser diode (LD) array with multiple optical carriers and a Fabry–Perot (F-P) laser diode. Multiple optical carriers in conjunction with the F-P LD will realize a filter with multiple passbands. By adjusting the wavelengths of the multiple optical carriers, multiple passbands are merged into a single passband with a broadened bandwidth. By varying the number of the optical carrier, the bandwidth can be adjusted. The central frequency can be tuned by adjusting the wavelength of the multiple optical carriers simultaneously. A single-passband filter implemented by two optical carriers is experimentally demonstrated.