Small Group Delay Research Articles

Graphene metamaterials-based plasmon-induced terahertz modulator for high-performance multiband filtering and slow light applications.

We proposed multilayered graphene (Gr)-based surface plasmon resonance-induced high-performance terahertz (THz) modulators with tunable resonance frequencies. Previously reported Gr metamaterials-based THz plasmonic modulators had small group delay, low extinction ratio (ER), and difficult-to-tune resonant frequency without changing structural parameters in the THz range. A comprehensive investigation employing the finite-difference time-domain (FDTD) simulation technique revealed high group delay, broad tunability independent of structural parameters, and large ER for our proposed quadband and pentaband plasmonic modulators. We obtained tunable group delays with a maximum of 1.02 ps and 1.41 ps for our proposed quadband and pentaband plasmonic modulators, respectively, which are substantially greater compared to previously reported Gr-based metamaterial structures. The maximum ER of 22.3 dB was obtained, which was substantially high compared to previous reports. Our proposed modulators were sensitive to the polarization angle of incident light; therefore, the transmittance at resonant frequencies was increased while the polarization angle varied from 0° to 180°. These high-performance plasmonic modulators have emerging potential for the design of optical buffers, slow light devices, multistop band filters, integrated photonic circuits, and various optoelectronic systems.

Analytical modelling of ultra‐small group delay variation of ultra‐broadband RF power amplifier using NSGA‐II algorithm

AbstractThis paper proposes a ± 9.4 ps ultra‐small group delay (GD) variation of fully integrated 65 nm complementary metal oxide semiconductor (CMOS) power amplifier (PA) over 6.5–17 GHz broadband for wireless application. The proposed CMOS PA is realised by using broadband stage, RLC inter‐stage and power stage topologies. The non‐dominated sorting genetic algorithm (NSGA‐II) is employed for PA parameter optimisation to ensure a small GD variation of ±9.4 ps over broadband with an excellent small signal gain flatness of 23.65 ± 1.85 for 6.5–17 GHz. The small GD variation of ±9.4 ps and ± 11.05 ps are attained under two cases of DC supply voltages of 2.4/1.2 V and 1.2/1.2 V, respectively. To the best of author's knowledge, the achieved GD variations are lowest among all CMOS PAs as reported so far. In addition, an analytical modelling of GD is derived to validating the minimum GD variation using zero‐pole compensation. With supply voltages of 2.4/1.2 V at 6.5 GHz, the large signal power gain, Psat and OP1dB are 26 dB, 19.3 dBm and 17.94 dBm, respectively, while peak power added efficiency (PAE) is 38.196%. At reduced supply voltages of 1.2/1.2 V, the PA achieves maximum power gain of 17.7 dB and peak PAE of 35% at 6.5 GHz. The CMOS PA occupies an area of 0.206 mm2.

A Compact Fully-Differential Distributed Amplifier with Coupled Inductors in 0.18-µm CMOS Technology

This paper presents a compact fully-differential distributed amplifier using a coupled inductor. Differential distributed amplifiers are widely required in optical communication systems. Most of the distributed amplifiers reported in the past are single-ended or pseudo-differential topologies. In addition, the differential distributed amplifiers require many inductors, which increases the silicon cost. In this study, we use differentially coupled inductors to reduce the chip area to less than half and eliminate the difficulties in layout design. The challenge in using coupled inductors is the capacitive parasitic coupling that degrades the flatness of frequency response. To address this challenge, the odd-mode image parameters of a differential artificial transmission line are derived using a simple loss-less model. Based on the analytical results, we optimize the dimensions of the inductor with the gradient descent algorithm to achieve accurate impedance matching and phase matching. The amplifier was fabricated in 0.18-μm CMOS technology. The core area of the amplifier is 0.27 mm2, which is 57% smaller than the previous work. Besides, we demonstrated a small group delay variation of ±2.7 ps thanks to the optimization. the amplifier successfully performed 30-Gbps NRZ and PAM4 transmissions with superior jitter performance. The proposed technique will promote the high-density integration of differential traveling wave devices.

A highly robust RF 65 nm CMOS power amplifier design using Quasi-Newton control algorithm for wireless system

This article reports a novel robust approach towards CMOS power amplifier (PA) using Quasi-newton (QN) control algorithm in 65 nm CMOS process which provides best performance parameters over redundant wide bandwidth ranging from 2.4 to 16.4 GHz frequency band. Each stage are designed and optimized using QN algorithm to get desired goals such as high linearity, small group delay variations and high PAE across the entire frequency band of interest. Moreover, pole-zeros compensation technique is adopted and derived to get better stability of the proposed PA. The simulation and measurement results of PA achieved a small signal power gain of 10.5–16.8 dB with input return loss of better than 10 dB over the frequency band of 2.4 GHz to 16.4 GHz. A small group delay variation of ±58 ps over full frequency band of operation is achieved by optimizing the design parametric analysis. It is also observed that within the frequency of 6.5 to 14.6 GHz, an excellent small group delay variation of only ±11 ps is achieved and this is due to stage-2 tuning compensation technique. It also demonstrates the achieved input power in 1 dB compression points are −3.1 to 4.3 dBm, leading to maximum power added efficiency of 36.3%, respectively. The proposed PA consumes a lower DC power of 20.5 mW under supply voltage of 1.5. In addition, Process, voltage and temperature (PVT) analysis is executed at different conditions in order to achieve a robustness of the proposed PA over the entire band of operation.

An asymmetric CPW‐fed modified bow tie‐shaped antenna with parasitic elements for ultra‐wideband applications

SummaryIn this paper, a modified bow tie‐shaped antenna for ultra‐wideband (UWB) communication applications is presented. The anticipated antenna consists of a CPW‐fed modified bow tie‐shaped patch and two asymmetric ground planes with dual parasitic elements. Electromagnetic computation on the antenna demonstrates that the patch and grounds are strongly linked, and the designed antenna can exhibit multiple resonances which overlap to reveal the UWB working spectrum. Experimental verification of the presented antenna shows that the antenna achieved a working band of 3.2–11.0 GHz, with a fractional bandwidth of 109.9%. The antenna also attained a peak gain of 4.32 dBi at 7.3 GHz and peak efficiency of 87.3% at 6.8 GHz and reveals excellent time‐domain behavior and omnidirectional radiation patterns throughout the operating band. A small‐size, large operating band, high gain and efficiency, high fidelity factor, omnidirectional radiation patterns, and very small group delay make the antenna ideal for portable communication devices in the UWB band.

Small Group Delay Variation and High Efficiency 3.1–10.6 GHz CMOS Power Amplifier for UWB Systems

A two-stage cascaded power amplifier (PA) employing a proposed Resistor-Capacitor (RC) interstage was provided and simulated. The current-reuse topology is employed at the first stage to lower the power consumption, while the RC interstage helps to enrich the gain flatness and the wideband matching. The shunt peaking topology in a common source configuration is adopted at the second stage to enhance the power gain. The postlayout simulation is performed using the TSMC 65 nm CMOS process operating in a frequency band of 3.1 GHz to 10.6 GHz. The postlayout simulation results indicate that a high flat gain of approximately 22.8 ± 1.2 dB, small group delay variation of ±50 ps, and good input and output matching of less than −10 dB are achieved over the desired working band. Moreover, a saturated output power of 10 dBm and maximum power-added efficiency (PAE) of 29.5% is achieved at 6 GHz. The proposed PA consumes the low power of 15.5 mW from 1.2 V supply voltage.

Synchronized multi-wavelength soliton fiber laser via intracavity group delay modulation

Locking of longitudinal modes in laser cavities is the common path to generate ultrashort pulses. In traditional multi-wavelength mode-locked lasers, the group velocities rely on lasing wavelengths due to the chromatic dispersion, yielding multiple trains of independently evolved pulses. Here, we show that mode-locked solitons at different wavelengths can be synchronized inside the cavity by engineering the intracavity group delay with a programmable pulse shaper. Frequency-resolved measurements fully retrieve the fine temporal structure of pulses, validating the direct generation of synchronized ultrafast lasers from two to five wavelengths with sub-pulse repetition-rate up to ~1.26 THz. Simulation results well reproduce and interpret the key experimental phenomena, and indicate that the saturable absorption effect automatically synchronize multi-wavelength solitons in despite of the small residual group delay difference. These results demonstrate an effective approach to create synchronized complex-structure solitons, and offer an effective platform to study the evolution dynamics of nonlinear wavepackets.

High Efficiency, Good phase linearity 0.18 µm CMOS Power Amplifier for MBAN-UWB Applications

This paper presents the design of 3.1-10.6 GHz class AB power amplifier (PA) suitable for medical body area network (MBAN) Ultra-Wide Band (UWB) applications in TSMC 0.18 µm technology. An optimization technique to simultaneously maximize power added efficiency(PAE) and minimize group delay variation is employed. Source and Load-pull contours are used to design inter and output stage matching circuits. The post-layout simulation results indicated that the designed PA has a maximum PAE of 32 % and an output 1-dB compression of 11 dBm at 4 GHz. In addition, a small group delay variation of ± 50 ps was realized over the whole required frequency band . Moreover, the proposed PA has small signal power gain (S21) of 12.5 dB with ripple less than 1.5 dB over the frequency range between 3.1 GHz to 10.6 GHz, while consuming 36 mW.

Three-line coupled-line narrowband bandstop filter with wide upper bandpass bandwidth

A three-line coupled-line narrowband bandstop filter is proposed to obtain wide upper bandpass bandwidth and avoid the tightly-coupled limitation. This structure of the proposed bandstop filter has two three-line coupled-line sections, four open-circuit stubs and one through transmission line. The main advantages of this filter include very narrow band rejection, wide upper bandpass bandwidth, high selectivity with sharp roll-off skirt, small and flat group delay performances. The measured results indicate that the stop bandwidth with 10-dB suppression at the center operating frequency of 0.97 GHz is about 4.12% and the highest frequency of the upper passband with 15-dB return loss is 6.44 GHz (the frequency ratio h is almost 6.64). The circuit size is 0.027 λg2. In addition, this proposed bandstop filter is very suitable for low-cost single-layer microstrip implementations with small size.

2.3–21 GHz broadband and high linearity distributed low noise amplifier

This paper focuses on the design of a 2.3–21 GHz Distributed Low Noise Amplifier (LNA) with low noise figure (NF), high gain (S21), and high linearity (IIP3) for broadband applications. This distributed amplifier (DA) includes S/C/X/Ku/K-band, which makes it very suitable for heterodyne receivers. The proposed DA uses a 0.18 μm GaAs pHEMT process (OMMIC ED02AH) in cascade architecture with lines adaptation and equalization of phase velocity techniques, to absorb their parasitic capacitances into the gate and drain transmission lines in order to achieve wide bandwidth and to enhance gain and linearity. The proposed broadband DA achieved an excellent gain in the flatness of 13.5 ± 0.2 dB, a low noise figure of 3.44 ± 1.12 dB, and a small group delay variation of ±19.721 ps over the range of 2.3–21 GHz. The input and output reflection coefficients S11 and S22 are less than −10 dB. The input compression point (P1dB) and input third-order intercept point (IIP3) are −1.5 dBm and 11.5 dBm, respectively at 13 GHz. The dissipated power is 282 mW and the core layout size is 2.2 × 0.8 mm2.

Ultrafast Pulse Manipulation in Dispersion-Flattened Waveguides With Four Zero-Dispersion Wavelengths

On-chip formation and manipulation of ultrashort pulses would be of great interest to ultrafast optics and integrated photonics communities. One of key issues is dispersion-assisted nonlinear interactions of broadband frequency components. In this article, we show for the first time that a bilayer waveguide for quasi-TE mode without using a slot produces a quite flat and saddle-shaped dispersion profile. Different from previously reported TE-mode waveguides with flattened dispersion, the proposed waveguide exhibits a greatly simplified structure with no need for a high-aspect-ratio slot and has quite small group delay difference in a wide spectral range with four zero-dispersion wavelengths (ZDWs). We study supercontinuum generation in hybrid dispersion regime for the first time, in which the broadened spectrum covers a bandwidth with all ZDWs. It is found that one can obtain greatly improved spectral flatness in supercontinuum generation, with a power variation as small as 3 dB over a bandwidth of >500 nm. Moreover, the proposed waveguides are particularly suitable for low-distortion pulse propagation over a long distance, which is important for on-chip ultrashort pulse delivery.

Tunable group delay in a doubly resonant metasurface composed of two dissimilar split-ring resonators

We develop a method to control the group delay of electromagnetic waves continuously using a doubly resonant metasurface. The method is based on the dependences of i) the group velocity in a medium featuring two resonance lines on the resonance linewidths and ii) the resonance linewidth of a metasurface composed of split-ring resonators on an incidence angle of electromagnetic wave. To verify this method for group-delay control, we design a terahertz metasurface composed of two split-ring resonators with different resonance frequencies and numerically analyze the transmission characteristic of the metasurface. Double resonance lines are observed for oblique incidence and the resonance transmission dips become deeper and broader with increasing the incidence angle. The group delay at around the center frequency of the double resonance lines is found to vary in the range about from 0s to 20 times the period of the incident wave with the incidence angle. In contrast with a previously reported method for variable control of group delay using electromagnetically-induced-transparency-like metamaterials, a high transmittance is achieved for a small group delay condition.

Optimizing the spectro-temporal properties of photon pairs from Bragg-reflection waveguides

Bragg-reflection waveguides (BRWs) fabricated from AlGaAs provide an interesting nonlinear optical platform for photon-pair generation via parametric down-conversion (PDC). In contrast to many conventional PDC sources, BRWs are made of high refractive index materials and their characteristics are very sensitive to the underlying layer structure. First, we show that the design parameters like the phase matching wavelength and the group refractive indices of the interacting modes can be reliably controlled even in the presence of fabrication tolerances. We then investigate how these characteristics can be taken advantage of when designing quantum photonic applications with BRWs. We especially concentrate on achieving a small differential group delay between the generated photons of a pair and then explore the performance of our design when realizing a Hong–Ou–Mandel interference experiment or generating spectrally multi-band polarization entangled states. Our results show that the versatility provided by engineering the dispersion in BRWs is important for employing them in different quantum optics tasks.

High Efficiency and Small Group Delay Variations 0.18-$\mu$ m CMOS UWB Power Amplifier

A new staggered tuning technique, by optimizing the inter-stage matching circuit, is proposed to realize a power amplifier (PA) with small group delay (GD) variations and excellent gain flatness across the full bandwidth of ultra-wideband (UWB) system. The proposed PA consists of two stages where the first stage is constructed by a current-reuse with shunt RC feedback topology to realize gain flatness and low power consumption. The design is implemented in 0.18 ${\mu }\text{m}$ commentary metal-oxide semiconductor (CMOS) technology, fabricated, and tested. The proposed PA has a measured power gain ( ${|{\mathrm{ S}}_{21}|}$ ) of 11.5 ± 0.7 dB, maximum power-added efficiency (PAE) of 26% and an output 1-dB compression point of 9 dBm, respectively, and this is the maximum PAE among CMOS PAs that cover the full bandwidth of UWB system. Besides, the PA has a small GD variations of ± 68 ps which is the lowest till date.

A compact UWB‐BPF based on microstrip‐to‐CPW transition with multiple transmission zeros

AbstractA hybrid microstrip‐to‐coplanar waveguide (CPW) based broadside coupled ultra‐wideband (UWB) bandpass filter (BPF) of compact nature with multiple transmission zeros (TZ) is proposed. The CPW in ground consists of a short circuited multiple mode resonator (MMR), which is in conjugation with two microstrip lines on the top, arranged in back‐to‐back manner. Initially, the impedance ratio of the MMR is adjusted to place its resonant modes quasi‐equally within the UWB passband and later the dimensions of microstrip lines are optimized to enhance the broadside coupling. The setup generates a passband with reduced insertion loss, small group delay and multiple TZ. The presence of TZs provide sharp roll‐offs at either passband edges and a wide stopband. The experimental BPF is fabricated and its measured data validated against simulation results. The proposed structure measures 14.6 × 9.6 mm2.

A Compact Ultrawideband Reflector Antenna: Using a Wide-Band Omnidirectional Antenna with a Mechanically Steerable Endfire Beam to Illuminate a Half-Cut Paraboloid Reflector

An ultrawideband, compact, paraboloid reflector antenna with a mechanically steerable endfire beam is presented, with its performance evaluated in frequency, time, and power domains. A fixed, omnidirectional monocone feed, engineered to maintain the same illumination of the reflector during its rotation, is used to facilitate scanning. Moreover, the omnidirectional mode of the antenna system can be enabled by recessing the reflector. A monocone feed is designed using the spherical mode expansion (SME) technique to achieve consistent monopole-like patterns over a wide bandwidth. To achieve the small group delay variation at a reduced size, the reflector is placed close to the monocone. The nearfield paraboloid can still produce a planar wavefront without destructive interference despite this proximity; therefore, the destructive interference is avoided. The reflector is designed based on a multidimensional parametric study to accomplish a reduced size and reasonable performance in both frequency and time domains.

Design and analysis of wideband low‐power LNA for improved RF performance with compact chip area

Here, a wideband low-noise amplifier (LNA) based on the two-stage cascade configuration is presented to improve the radiofrequency (RF) performance. With the common gate (CG) input stage, the proposed LNA provides wideband input matching, while the wideband gain response was achieved using the peaking inductors inserted at the drain terminals of each stage. With a standard CMOS process, the chip area of the proposed wideband LNA is only 0.116 mm2. However, it consumes a 5.4 mW power from a supply voltage of . From the post-layout simulation results, it achieves maximum power gain of 11.13 dB at 8.5 GHz, input return loss below −9.44 dB, reverse isolation less than −60 dB, and small group delay variation of ±97 ps across 8.5–20 GHz frequency range. Moreover, noise figure (NF) lies in the range of 2.19–3.23 dB, whereas the NF minimum () varies in the range of 1.55–2.91 dB for 8.5–20 GHz frequency range. Apart from this, the proposed LNA achieves an IIP3 of 0.96 dBm, when a two-tone test is performed with a frequency spacing of 50 MHz.

Compact circular-patch-based bandpass filter for ultra-wideband wireless communication systems

Ultra-wideband (UWB) is a radio technology that enables low-power-level, short-range, and wide-bandwidth communication, and it has been widely applied in personal area networks, precision geolocation, medical, surveillance, and vehicular radar systems. Since Federal Communications Commission released the unlicensed use of the UWB range (3.1–10.6GHz), a significant attention has been paid to the development of UWB devices, particularly UWB bandpass filters. In this paper, we propose a novel UWB bandpass filter based on circular patch resonator that is grounded by via and perturbed by slits and defected ground structures. The resonator’s behaviour is analysed in detail and it is shown that its specific configuration allows a flexible control of the three lowest resonant modes, which are used to form UWB passband. To demonstrate the potential of the resonator, a UWB filter has been designed, fabricated, and measured. The filter is characterized by the insertion loss lower than 1dB and return loss higher than 17dB within the passband, as well as by very small group delay variation of only 0.07ns. Also, the filter exhibits suppression higher than 19dB up to 30GHz, and very small overall dimensions of only 0.31λg×0.31λg, and thus it outperforms other published UWB filters.

Lowpass filters approximation based on modified Jacobi polynomials

The orthogonal Jacobi polynomials are not suitable for the characteristic function in the continuous- and discrete-time filter designs because they are not fulfilling the basic conditions: to be pure odd or to be pure even. A simple modification of Jacobi polynomials, proposed in this Letter, is performed to obtain a new filter approximating function. Magnitude frequency responses of obtained filters exhibit more general behaviour compared to that of classical Gegenbauer (ultraspherical) filters, due to one additional parameter available in the Jacobi polynomials. This parameter can be used to obtain magnitude response with smaller passband ripple values (nearly monotonic behaviour), smaller group delay variations or sharper cutoff slope. The proposed modified Jacobi polynomials are not orthogonal; however, many known orthogonal polynomials can be obtained as theirs special cases.

Numerical modelling of multimode fibre-optic communication lines

The results of numerical modelling of nonlinear propagation of an optical signal in multimode fibres with a small differential group delay are presented. It is found that the dependence of the error vector magnitude (EVM) on the differential group delay can be reduced by increasing the number of ADC samples per symbol in the numerical implementation of the differential group delay compensation algorithm in the receiver. The possibility of using multimode fibres with a small differential group delay for data transmission in modern digital communication systems is demonstrated. It is shown that with increasing number of modes the strong coupling regime provides a lower EVM level than the weak coupling one.