Flat Bandwidth Research Articles

Effects of alkali ions on the optical properties, bandwidth flatness, and gain coefficient of near-infrared emission spectra of Er3+-doped zinc silicate glass

In this paper, we investigate and report the effects of alkali ions A+ (A+ = Li+, Na+, K+) on the optical properties, bandwidth flatness (BFN), gain coefficient (G(λ)) for the near-infrared (NIR) emission spectra of Er3+-doped SiO2–ZnO–La2O3 (SZL) zinc silicate glass. With the change in the composition of A+ ions in the order from not containing any A+ ions → Li+ → Na+ → K+ → containing all three A+ ions including Li+, Na+, and K+, the direct and indirect bandgap (DBG and IBG), the absorption cross-section (σabs(λ)), the emission cross-section (σems(λ)), and the G(λ) parameters of Er3+-doped SZL glasses were determined to increase gradually. NIR emission intensities of Er3+-doped at 4I13/2 → 4I15/2 transition under excitations of both 808 and 980 nm LD all were significantly increased with the composition of A+ ions varies in order from not containing A+ ions → Li+ → Na+ → K+ → containing all three A+ ions. The reasons for the influence of A+ ions on the UC and NIR emission intensities of Er3+-doped in SZL glass are investigated and discussed. In addition, upconversion (UC) emission spectra of Er3+-doped, CIE 1931(x; y) coordinates and color region for UC emission spectra of Er3+-doped SZL glasses with different compositions of A+ ions under excitation of 980 nm laser diode (LD) are also determined.

Ultra-flat bands at large twist angles in group-V twisted bilayer materials.

Flat bands in 2D twisted materials are key to the realization of correlation-related exotic phenomena. However, a flat band often was achieved in the large system with a very small twist angle, which enormously increases the computational and experimental complexity. In this work, we proposed group-V twisted bilayer materials, including P, As, and Sb in the β phase with large twist angles. The band structure of twisted bilayer materials up to 2524 atoms has been investigated by a deep learning method DeepH, which significantly reduces the computational time. Our results show that the bandgap and the flat bandwidth of twisted bilayer β-P, β-As, and β-Sb reduce gradually with the decreasing of twist angle, and the ultra-flat band with bandwidth approaching 0eV is achieved. Interestingly, we found that a twist angle of 9.43° is sufficient to achieve the band flatness for β-As comparable to that of twist bilayer graphene at the magic angle of 1.08°. Moreover, we also find that the bandgap reduces with decreasing interlayer distance while the flat band is still preserved, which suggests interlayer distance as an effective routine to tune the bandgap of flat band systems. Our research provides a feasible platform for exploring physical phenomena related to flat bands in twisted layered 2D materials.

Realization of all-band-flat photonic lattices

Flatbands play an important role in correlated quantum matter and have promising applications in photonic lattices. Synthetic magnetic fields and destructive interference in lattices are traditionally used to obtain flatbands. However, such methods can only obtain a few flatbands with most bands remaining dispersive. Here we realize all-band-flat photonic lattices of an arbitrary size by precisely controlling the coupling strengths between lattice sites to mimic those in Fock-state lattices. This allows us to go beyond the perturbative regime of strain engineering and group all eigenmodes in flatbands, which simultaneously achieves high band flatness and large usable bandwidth. We map out the distribution of each flatband in the lattices and selectively excite the eigenmodes with different chiralities. Our method paves a way in controlling band structure and topology of photonic lattices.

Multiwavelength fiber laser based on enhanced bidirectional SOA utilizing Lyot filter

We demonstrated a multiwavelength fiber laser (MWFL) based on two bidirectional semiconductor optical amplifiers (SOAs) and a Lyot filter. The structure is enhanced by placing two -SOAs in a bidirectional region to improve the lasing performance. This resulted in a higher extinction ratio (ER) of 36.05 dB, as earlier work only achieved a maximum extinction ratio (ER) of 17 dB utilizing an SOA based on bidirectional configuration. The performance of the MWFL in unidirectional and bidirectional configurations, as well as different parameter settings of SOA current and polarization controller (PC) angle is examined. Using a unidirectional configuration decreases the amplification on one side of the SOA, hence reducing the wavelength bandwidth by 2 nm, which is equivalent to six lasing lines. According to the wavelength bandwidth of 13 nm and channel spacing of 0.22 nm, the optimal performance of MWFL employing bidirectional configuration is 56 lasing lines within 3 dB bandwidth. Consequently, we decreased each SOA's operating current, resulting in lower lasing lines. Changing the PC angle modifies the polarization degree and state, hence impacting multiwavelength flatness and wavelength bandwidth performance. When the polarizer is removed, the ER and lasing lines are decreased to 42 dB and 9 nm, respectively. The MWFL has high stability with a peak power fluctuation of 0.25 dB in 120 min.

An integrated LNA‐phase shifter in 65 nm CMOS for Ka‐band phased‐array receivers

SummaryIn this paper, a vector‐sum phase shifter (VSPS) integrated with a wideband high‐gain low‐noise amplifier (LNA) for Ka‐band phased‐array receivers is presented. The digitally controlled VSPS based on the RF phase shifting architecture consists of a modified I/Q signal generator with additional inductor resonance and a programmable variable gain amplifier (VGA) based on Four 3 × 4 transistor arrays. Besides the reduced parasitic effect of the I/Q signal generator, an Equidistant Contraction Technology (ECT) is used in the VGA, to maintain higher phase shift accuracy of the VSPS. A multistage LNA with series inductor peaking is adopted to fulfill the flat wideband gain, where LC resonance networks are used as interstage matching to compensate for gain roll‐off at a higher frequency. Based on simulations in 65 nm CMOS technology, the presented LNA‐Phase shifter has achieved an average NF of 3.24–3.66 dB, and an average gain of 13.1–23.6 dB. Moreover, an RMS phase error of 1.1–12.6°, an RMS gain error of 4.2–5.6 dB, and an RMS magnitude error of 2.1–2.8 dB are maintained across 27–40 GHz, with a 360° phase shift coverage in steps of approximately 2.8125°. The chip consumes 16.83 mW from a 1.2 V supply voltage, and the occupied area is 0.65 mm2.

Wideband High-Efficiency Transmitarray Antenna Using Compact Double-Layer Dual-Linearly Polarized Elements

In this letter, we propose a wideband high-efficiency transmitarray antenna (TAA) consisted of compact double-layer dual-linearly polarized elements. By loading L-shaped branches and four vias, these elements achieve a low transmission loss and full phase shift in a wide frequency band. Then, an optimization method for calculating the wideband average element loss is introduced, which determines the element distribution on the transmitarray aperture. For verification, a TAA prototype consist of 400 elements is fabricated and measured. The peak gain and aperture efficiency measured at 12 GHz are 27.1 dBi and 52.5%, respectively. The measured 1-dB gain bandwidth is 20.4% and the minimum aperture efficiency achieved across the 1-dB gain bandwidth is 33%. The results reveal that the proposed TAA exhibits the advantages of flat gain bandwidth, high aperture efficiency, low profile, and low cost, endowing it with the potential for conformal applications and the capability to reliably connect satellite links as a communication antenna.

A 17.7–19.2-GHz Receiver Front End With an Adaptive Analog Temperature- Compensation Scheme

This article presents an eight-element 17.7–19.2-GHz receiver front end with 1–2 concurrent beams in a 65-nm CMOS technology. Each output beam utilizes a temperature-compensation variable-gain amplifier (TC-VGA) to minimize the temperature-induced gain variation. The concept of the proposed TC-VGA and the realization of corresponding adaptive analog control are introduced in detail. The front-end architecture and circuit-level design to enable a flat wideband gain response, precise phase and amplitude control, low power consumption, and adaptive analog temperature compensation are presented. Wafer probing is conducted to measure the performance of the receiver front end. The measured gain-temperature coefficient is ±0.005 dB/°C from −15°C to 85 °C at 17.7–19.2 GHz, while the counterpart without temperature compensation is −0.1 dB/°C. The chip demonstrates a 28-dB power gain, a 26% 3-dB fractional bandwidth, a 3.2–4.1-dB noise figure (NF), and a −27.4-dBm input 1-dB gain compression point (IP <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathrm {1\,dB}}$ </tex-math></inline-formula> ) for each element. In addition, each channel provides 7-bit phase-shifting resolution and 6-bit attenuation for a 15.75-dB gain range with a <1.5° root-mean-square (rms) phase error, and a < 0.22-dB rms amplitude error. The chip occupies <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4.65\times2.77$ </tex-math></inline-formula> mm2 area with pads, equivalent to 1.61 mm2 per element (for two beams), and consumes 37.2 mW per element per beam. To the best of our knowledge, the receiver front end demonstrates the minimum gain variation with temperature among silicon RF-beamforming front ends.

Two-Dimensional Elliptical Microresonator Arrays for Wide Flat Bandwidth and Boxlike Filter Response

Based on two-dimensional elliptical microresonator arrays, we designed and fabricated a compact filter on the silicon-on-insulator platform with potential applications for on-chip optical interconnects. The fabricated optical filter exhibits a wide flat bandwidth of 951 GHz with the shape factor of 0.57 at the through port for the 3×20 arrays. The out-of-band rejection is as high as 50 dB. The crosstalk is also very low (−46 dB). The spectral shows a boxlike response. Although there are sixty rings used in the array, the insertion loss is still very small (≤1.36 dB).

Design and simulation of high modulation efficiency, low group velocity dispersion lithium niobate slow-wave electro-optic modulator based on a fishbone-like grating

Thin-film lithium niobate (LN) has emerged as an excellent platform for electro-optic modulators (EOMs) owing to its strong electro-optic (Pockels) effect. However, it remains an open challenge to achieve high modulation efficiency in chip-scale EOMs, primarily due to the limitation of light-matter interaction. Here, we propose an on-chip slow-wave LN EOM with a length of 3.4 mm with high modulation efficiency by using a fishbone-like grating. By assembling the fishbone-like grating, the Pockels effect is significantly enhanced as a result of the compression of the local density of states. Benefiting from this effect, the modulation efficiency of the modulator can be improved to 4.6 times of the original. In addition, a 3 mm matched micro-structure electrode is designed to realize the low group velocity of the microwave modulation signal. The simulation results show that the modulation efficiency of this slow-wave EOM is 1.42 V·cm. The slow-light effect is realized theoretically with a flat optical operating bandwidth of about 21 nm, group velocity dispersion < 2 ps2/mm, and low loss < 0.33 dB. Additionally, a 3 dB modulation bandwidth of 80 GHz is verified by simulation by virtue of the proposed micro-structure electrode.

Numerical analysis of a three-wave-mixing Josephson traveling-wave parametric amplifier with engineered dispersion loadings

The recently proposed Josephson traveling-wave parametric amplifier (JTWPA) based on a ladder transmission line consisting of radio-frequency superconducting quantum interference devices and exploiting three-wave mixing has great potential in achieving both a gain of 20 dB and a flat bandwidth of at least 4 GHz. To realize this concept in practical amplifiers, we model the advanced JTWPA circuit with periodic modulation of the circuit parameters (engineered dispersion loadings), which allow the basic mixing process, i.e., ωs=ωp−ωi, where ωs, ωp, and ωi are the signal, the pump, and the idler frequencies, respectively, and efficiently suppress propagation of unwanted higher tones, including ω2p=2ωp, ωp+s=ωp+ωs, ωp+i=ωp+ωi, etc. The engineered dispersion loadings allow achieving a sufficiently wide 3 dB-bandwidth from 3 to 9 GHz combined with a reasonably small ripple (±2 dB) in the gain-vs-frequency dependence.

Hybrid Microfluxgate and Current Transformer Sensor

In this work, we develop the hybrid current sensor comprising a microfluxgate and a current transformer (CT) for wide-bandwidth current measurement. The microfluxgate consists of two microcoil chips 3.5 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times1.75$ </tex-math></inline-formula> mm in dimension made by using the standard Complementary Metal-Oxide Semiconductor MicroElectroMechanical Systems (CMOS-MEMS) <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.35 ~\mu \text{m}$ </tex-math></inline-formula> process. The aluminum wire-bonding technique is used to construct the top excitation coil surrounding the amorphous soft magnetic core patterned by photolithography and wet etching techniques. Under the optimal excitation condition, the response of the microfluxgate current sensor becomes linear with a maximized sensitivity. The in-house made CT is combined with the microfluxgate driving system to form the hybrid current sensor by using a summing amplifier. The hybrid current sensor has a spectral current noise of 0.4 mA/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\surd $ </tex-math></inline-formula> Hz at 1 Hz. The maximum sensing range is ±10 A, and the non-linearity is less than 2% within the ±4.6 A range, corresponding to a linear dynamic range of 60 dB in a 10 Hz bandwidth. The hybrid microfluxgate-and-CT sensor has a flat bandwidth from dc to 100 kHz. It has the potential to become a practical miniature device featuring a high-dynamic range, wide bandwidth, and low-temperature drift.

Multi-Band Operation of Flat-Top Supercontinuum Laser Sources With Programmable Repetition Rate up to 50 GHz

We present ultra-broadband flat-topped supercontinuum laser sources with programmable repetition rate, spectral bandwidth, and wavelength regime. Supercontinuum sources with multiband coverage can be achieved by merging high-repetition-rate electro-optic frequency comb techniques with optical line-by-line pulse shaping. Because nonlinear broadening in the optical wave-breaking regime does not provide the required flatness and spectral bandwidth to the comb-based sources, we iteratively manipulate the spectral amplitude and phase of the optical pulse shaper. We implemented here a smooth flat-topped supercontinuum with a 97 nm bandwidth at 10 dB and programmable repetition rate up to 50 GHz by applying a bandwidth-limited quasi-super-Gaussian apodised pulse train to a highly nonlinear medium with programmable super-Gaussian and phase coefficients. This work opens new possibilities for generating robust and coherent multiple optical carriers with further C-bands in optical networks. We believe that the supercontinuum sources based on electro-optic frequency comb and pulse shaping techniques enable the provision of coherent flat-topped optical sources, at least from the L- to S-band with a programmable repetition rate and spectral bandwidth.

Renormalization group for open quantum systems using environment temperature as flow parameter

We present the T-flow renormalization group method, which computes the memory kernel for the density-operator evolution of an open quantum system by lowering the physical temperature T of its environment. This has the key advantage that it can be formulated directly in real time, making it particularly suitable for transient dynamics, while automatically accumulating the full temperature dependence of transport quantities. We solve the T-flow equations numerically for the example of the single impurity Anderson model. We benchmark in the stationary limit, readily accessible in real-time for voltages on the order of the coupling or larger using results obtained by the functional renormalization group, density-matrix renormalization group and the quantum Monte Carlo method. Here we find quantitative agreement even in the worst case of strong interactions and low temperatures, indicating the reliability of the method. For transient charge currents we find good agreement with results obtained by the 2PI Green's function approach. Furthermore, we analytically show that the short-time dynamics of both local and non-local observables follow a "universal" temperature-independent behaviour when the metallic reservoirs have a flat wide band.

Wideband chaotic tri-mode microlasers with optical feedback.

A tri-mode micro-square laser under optical feedback is proposed and demonstrated to generate chaos with the broadband flat microwave spectrum. By adjusting lasing mode intensities, frequency intervals, and optical feedback strength, we can enhance the chaotic bandwidth significantly. The existence of two mode-beating peaks makes the flat bandwidth much larger than the relaxation oscillation frequency. Effective bandwidth of 35.3 GHz is experimentally achieved with the flatness of 8.3 dB from the chaotic output spectrum of the tri-mode mode laser under optical feedback.

Integrated Stacked Parallel Plate Shunt Capacitor for Millimeter-Wave Systems in Low-Cost Highly Integrated CMOS Technologies

This letter presents a stacked parallel plate (SPP) shunt capacitor (SC) that benefits from metal stack increment with process nodes advancement. It demonstrated high quality (Q) factor and high self-resonance frequency (SRF), promoting the design of analog integrated circuits (IC) in low-cost highly-integrated CMOS technologies at millimeter-wave (mm-wave) frequency range. As a proof-of-concept, an analytical-equation based design method is also proposed and three ac-grounded capacitors: 300-fF, 600-fF and 900-fF, are implemented in STMicroelectronics (STM) 55-nm process. Characterization is performed up to 100 GHz. An effective capacitance density of 0.8 fF/μm2 is obtained. Measurements show Q-values reaching up to 14.7 at 100 GHz and equivalent input series resistances with flat wide band behavior reaching at most an average of 0.55 Ω. SRFs of 140 GHz for the 900-fF SPP-SC up to 368 GHz for the 300-fF SPP-SC are also determined from measurements: the highest SRFs for such large capacitances to the authors’ knowledge.

Two-pump parametric amplification in the presence of fiber dispersion fluctuations: a comparative study.

Fiber optical parametric amplifiers (FOPAs) operating based on four-wave mixing (FWM) are versatile devices with increasing applications in optical communication systems. In this paper, the effects of dispersion fluctuations on the performance of bandwidth, ripple, parametric gain, and saturation power of a two-pump FOPA based on four-wave and six-wave models are studied and compared. Coupled-amplitude equations representing the non-degenerate FWM process in optical fiber are solved numerically to compute the parametric gain over the communication wavelengths. The behaviors of the performance parameters are critically analyzed and compared with different types of fluctuation strengths (or amplitudes) specified by the combinations of correlation length (Lc) and fluctuation amplitude (σ). Based on the results, it was found that the flat gain bandwidth for the four-wave model remains unchanged and is insensitive to the strengths of fluctuations. The gain ripples, however, get higher as the fluctuation strengths increase. On the other hand, the flat gain bandwidths of the six-wave model are hardly identified due to the tremendous and continuous ripples within the pump wavelengths. In addition, the minimum parametric gain values for both four-wave and six-wave models reduce as the fluctuation strengths increase. Also, the lowest value of parametric gain leads to the highest saturation power and vice versa. The dispersion fluctuations affect the FWM process's efficiency and deteriorate the overall amplifier performance, particularly for the six-wave model. The numerical analysis obtained via the six-wave model is especially useful since this model closely matches with practical circumstances.

An efficient wide flatness gain bandwidth with parallel hybrid fiber amplifier

AbstractIn this article, we experimentally propose an efficient wide flat gain bandwidth with a parallel hybrid fiber amplifier. The setup includes parallel amplifier branches. In the first branch, serial erbium‐doped and Raman fiber amplifiers are used. In the second branch, only a Raman fiber amplifier is used. Three Raman pump power units (i.e., 1410, 1480, and 1495 nm) are used to achieve Raman gain at different optical communication bands. At optimum pump powers and at a small‐signal power of −30 dBm, an average gain of 18.5 dB with a maximum gain variation of 3 dB and a gain flatness bandwidth of 83 nm, that is, from 1527 to 1610 nm, is achieved. This gain flatness is expanded to 92 nm (1525–1617 nm) at a large input signal power of −5 dBm with an average gain level of 13 dB. In our proposed amplifier, the Raman amplification peaks (1510 and 1595 nm) are chosen to be far from the erbium amplification peak (1530–1570 nm) in order to avoid the overlapping and the saturation in the first amplifier branch. Therefore, due to such wavelength optimization in addition to the recycling the residual Raman pump power, a wide flatness gain bandwidth is achieved for both of low and large input signal powers.

Analysis and design of diode physical limit bandwidth efficient rectification circuit for maximum flat efficiency, wide impedance, and efficiency bandwidths

Generally, a conventional voltage doubler circuit possesses a large variation of its input impedance over the bandwidth, which results in limited bandwidth and low RF-dc conversion efficiency. A basic aspect for designing wideband voltage doubler rectifiers is the use of complex matching circuits to achieve decade and octave impedance and RF-dc conversion efficiency bandwidths. Still, the reported techniques till now have been accompanied by a large fluctuation of the RF-dc conversion efficiency over the operating bandwidth. In this paper, we propose a novel rectification circuit with minimal inter-stage matching that consists of a single short-circuit stub and a virtual battery, which contributes negligible losses and overcomes these existing problems. Consequently, the proposed rectifier circuit achieves a diode physical-limit-bandwidth efficient rectification. In other words, the rectification bandwidth, as well as the peak efficiency, are controlled by the length of the stub and the physical limitation of the diodes.

Design and Study of a Wide-Band Printed Circuit Board Near-Field Probe

Magnetic near-field probes (NFP) represent a suitable tool to measure the magnetic field level from a small electromagnetic interference (EMI) source. This kind of antenna is useful as a magnetic field probe for pre-compliance EMC measurements or debugging tasks since the user can scan a printed circuit board (PCB) looking for locations with strong magnetic fields. When a strong H-field point is found, the designer should check the PCB layout and components placement in that area to detect if this could result in an EMI source. This contribution focuses on analyzing the performance of an easy to build and low-cost H-field NFP designed and manufactured using a standard PCB stack-up. Thereby, the frequency range and sensitivity of the NFP-PCB are analyzed through a Finite Element Method (FEM) simulation model that makes it possible to evaluate its sensibility and effective frequency range. The numerical results obtained with the FEM models are validated against measurements to verify the design and performance of our NFP. The FEM model reproduces the experimental procedure, which is used to evaluate the performance of the NFP in terms of sensitivity by means of the simulated near-field distribution. The NFP-PCB has almost a flat response from 180 MHz to 6 GHz, with an almost perfect concordance between numerical and experimental S21 results. The numerical results show an average transmission loss of −27.9 dB by considering the flat response bandwidth, whereas the experimental one is −29.7 dB. Finally, the designed NFP is compared to two high-quality commercial probes in order to analyze its performance.

Homogenized electromechanical coefficients and effective parameters of 1–3 piezocomposites for ultrasound imaging transducers

Analytical models can be useful tools to develop efficient transducers dedicated to a specific application field. This work proposes a homogenization technique for establishing the effective coefficients and parameters of 1-3 piezocomposite whose both phases are piezoelectrically active. Such piezocomposite materials may have homogenized electromechanical properties resulting from positive hybrid effect. A numerical simulation of the effective parameters resulting from a PZT-5A / PVDF-TrFE composition shows that, volume fraction influences significantly on the properties of the piezocomposite and consequently on its behaviour in service. As an end-user application for ultrasound imaging, those piezocomposite materials are effectively integrated in a piezocomposite transducer, coupled with a dedicated backing. The resulting characteristics in terms of impulse response and associated electroacoustic echo are compared and discussed for typical configurations. A method for the optimization of the design of such piezocomposite transducer is presented. Specific estimators based on the bandwidth flatness BWF and bandwidth amplitude product BWA are proposed as stable and smooth criteria for an optimization procedure.