High Group Delay Research Articles

Compact and low phase-noise dual-frequency oscillator based on dual-band filter with multiple coupling technique

This paper presents a switchable feedback dual-frequency oscillator with ultra low phase-noise based on dual-band filter for the first time. The application of multiple coupling technique in dual-band filter such as direct coupling, indirect coupling, self-coupling and source-load coupling not only reduces the circuit size significantly but also obtains high group delay that the ultra low phase-noise can be achieved. Due to the auxiliary oscillating network, two different oscillation frequencies are switched independently without inter-modulation. For demonstration, a physical prototype was fabricated and measured. The measured results show that the proposed dual-frequency oscillator can oscillate at 887 MHz or 2.446 GHz by controlling four PIN diode switches and the phase-noise keeps better than −139 dBc/Hz and −136.1 dBc/Hz at 1 MHz frequency offset. And the output power of 887 MHz and 2.446 GHz are 5.94 dBm and 5.08 dBm respectively.

Enhancing phase modulation and group delay in reflective Huygens metasurfaces via a Fabry-Perot cavity.

Huygens metasurfaces exhibit excellent optical properties such as 2π phase modulation and slow light effects. However, they face challenges including wide bandwidth and low group delay due to their high radiation losses. Here, we propose a reflective Huygens metasurface coupled with an F-P cavity. We demonstrate that F-P resonance modes can couple with magnetic-quasi-bound-state (M-QBIC) and electric-quasi-bound-state (E-QBIC) in the Huygens metasurface through constructive interference, significantly enhancing the quality factors of both QBICs. Through structural parameter optimization, our reflective Huygens metasurface achieves 4π phase modulation and a high group delay of up to 166 ps. Compared to the non-coupled Huygens metasurface with the same structural asymmetry, the group delay of the F-P coupled reflective Huygens metasurface is enhanced by up to 30 times. Our design reduces the fabrication precision requirements for Huygens metasurfaces, enabling similar group delays to be achieved in low-symmetry coupling structures as in highly symmetric non-coupling structures. Additionally, the performance of this metasurface shows robustness to changes in incident light polarization. This design highlights the potential for achieving high-quality factors, large phase modulation, and large group delay, offering new avenues for the design of highly sensitive tunable devices, efficient nonlinear optical devices, and narrowband slow light devices.

Low phase noise anti-interference differential oscillator based on balanced bandpass filter with common-mode reflectionless characteristic

In this paper, a low phase noise anti-interference differential oscillator is proposed. The balanced bandpass filter with common-mode reflectionless characteristic is proposed and adopted in the differential oscillator to simultaneously achieve high group delay peak and common-mode interference noise absorption. For demonstration, the proposed differential oscillator is designed, simulated, manufactured and measured. It demonstrates that the proposed differential oscillator has a high output power of 6.67 dBm at the center oscillating frequency of 2.48 GHz, excellent second harmonic suppression of 46.01 dB, low phase noise of − 119.96 dBc/Hz at 100 kHz offset. The verification of the anti-interference function is performed with a differential mixer and the results show that the proposed differential oscillator can absorb external common-mode interference and effectively ensure the stable output of intermediate frequency signals.

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.

Design Study High Reflectors Graded Index Mirror Dispersive Properties

This paper investigates the dispersive properties of a spectral filter—a quarter-wave (QW) mirror. The study considers the modeling with a smoothly changing refractive index of the applied material (Rugate filter) using Fourier transform analysis of a high and low refractive index. These chirped structures exhibit high reflectivity and low group delay dispersion. The introduced result in this study is in some way better than already existing ones and/or can be used to obtain a meaningful practical effect, because it adopts calculation methods that are characterized by the accuracy and reliability of data using different statistical parameters and can be adopted with all modern and old methods of preparation. These improvements can have significant implications for various applications. Moreover, we investigate different statistical parameters, such as mean, median, mode, and standard deviation (STD), and analyze their impact on the rugate filter group delay (GD) and group delay dispersion (GDD) performance.

Making entangled photons indistinguishable by a time lens

We propose an application of quantum temporal imaging to restoring the indistinguishability of the signal and the idler photons produced in type-II spontaneous parametric down-conversion with a pulsed broadband pump. It is known that in this case, the signal and the idler photons have different spectral and temporal properties. This effect deteriorates their indistinguishability and the visibility of the Hong-Ou-Mandel interference, respectively. We demonstrate that inserting a time lens in one arm of the interferometer and choosing properly its magnification factor restores perfect indistinguishability of the signal and the idler photons and provides 100% visibility of the Hong-Ou-Mandel interference in the limit of high focal group delay dispersion of the time lens.

Ultralow-Phase-Noise Microstrip Oscillator Based on Quasi-Bandpass Frequency Selection Network With Multiple Transmission Zeros

This article proposes a microstrip feedback-type oscillator incorporating a novel quasi-bandpass frequency selection network (FSN) for low phase noise (PN) operation. Through introducing direct source/load coupling between two coupled quarter-wavelength resonators, the FSN can theoretically realize a canonical second-order general Chebyshev bandpass response with two transmission zeros. Furthermore, the feedlines with short-circuited ends are specifically designed to generate more transmission zeros. Accordingly, this FSN is featured by quasi- bandpass response with multiple transmission zeros, so that high group delay and good out-of-band performance are achieved. Such feature plays an important role in the oscillator performance. As demonstration, one oscillator example was fabricated and measured. Its operating frequency is 1.98 GHz, the PN is −129.85 dBc/Hz at 100 kHz, the output power is 9.61 dBm, and the second harmonic suppression (SHS) reaches 48.21 dBc. All these indexes outperform those of all the other oscillators, and our reported PN is the lowest one in S-band up to now.

An iterative reassignment based energy-concentrated TFA post-processing tool and application to bearing fault diagnosis

Among the time frequency (TF) analysis (TFA) post-processing methods, limited by the accuracy of the estimated group delay (GD), the time-reassigned synchrosqueezing transform (TSST) and the second-order TSST (STSST) cannot provide a satisfied TFA performance for analyzing the signal with strong GD modulation. To settle this downside, the high order TSST (HTSST) is proposed. However, due to the truth that HTSST is sensitive to the plus-noise signal, the TF representation is not concentrated than the STSST. For further improving the TF resolution, a new TFA post-processing tool is proposed in this study, which named as local maximum high order time iterative synchrosqueezing (LHTIS) method. The basic idea of this technique can be divided as two steps. First, according to an iterative procedure, the TF coefficients of the high order frequency-varying signal are reassigned onto the estimated high order GD trajectory along time direction. Second, via maximizing the local TF coefficients after iterative reassignment in the first step, we rebuild a GD estimation operator to squeeze the obtained TF results. Numerical simulations are adopted to demonstrate the TF aggregation and the anti-noise property of LHTIS methodology. Via dealing with the fault signals of rolling bearings, the effectiveness of LHTIS is verified.

Polarization and incidence insensitive analogue of electromagnetically induced reflection metamaterial with high group delay.

In this work, we demonstrate an analogue of electromagnetically induced reflection (EIR) effect with hybrid structure consisting of a silica (SiO2) square array layer embedded in graphene-dielectric-Au film constructed F-P cavity. It is shown that the SiO2 square array and F-P cavity create transverse waveguide with high quality factor (Q-factor) and longitudinal F-P modes, and their destructive interference effectively forms the EIR-like effect, which benefits for obtaining high group delay. In addition, the C4 symmetric structure ensures the polarization-independent for this EIR-like effect. With high Q-factor at the reflection window, the ultra-high group delay as high as 245 ps can be obtained. This structure will be useful to develop the EIT-like devices with excellent performance such as high group delay, polarization and incident insensitivity, and environmental stability.

Design of Broadband Plasmon‐Induced Transparency Hybrid Metamaterial Based on the Interaction of the Metal and Dielectric Resonances

AbstractIn this paper, a broadband plasmon‐induced transparency (PIT) hybrid metamaterial system (HMS) is realized and numerically demonstrated via the interference between different resonance modes of metal and dielectric resonators. The employed PIT HMS supports a strong near‐fired coupling between unit cells consisting of eight TiO2 nested split rings (dark plasmonic resonators) surrounded by four metal cut wires (bright plasmonic resonators) embedded in the intermediate dielectric layer, and a broad transparency window which is higher than 0.9 is obtained from 0.61 to 0.76 THz with a relative bandwidth of 21.9%. In the transparent window, the drastic change of phase leads to high group delay, and the remarkable slow light phenomenon can be clearly observed. The maximum of the group delay and group index can reach 528 ps and 2880, respectively. The localization distributions of the electromagnetic field intuitively exhibit the generation and action process of destructive interference. The theoretical investigation of the two‐oscillator model further confirms the effectiveness and consistency of the simulation results. In addition, the fourfold symmetric of the proposed PIT HMS supports the liberation from the dependence of incident polarization form. Such an implementation opens a new path for the designing of filtering, switching, and data storing devices.

A Low Phase-Noise Dual-Frequency Oscillator Based on Filter Switching Technique

This letter presents a parallel-feedback dual-frequency oscillator (DFO) with low phase noise. It is achieved based on the filter switching technique. By using four switches to control two oscillator loops with a common active device, the oscillation frequency of the proposed DFO can be switched from one to another. Due to the high isolation level of the employed switches, the two oscillator loops almost operate independently. Thus, there is no intermodulation (IM) spurs generated in the output spectrum of the proposed DFO. In the meantime, to improve the phase noise performance of the DFO, each oscillator loop utilizes a high frequency-selectivity bandpass filter with high group delay (GD) as a frequency selective element. In this way, the low phase-noise DFO is developed. For demonstration, the DFO is designed, fabricated, and tested. As seen from the measurement results, the oscillator can oscillate at 2.04 or 3.092 GHz by controlling the four switches. At 100 kHz and 1 MHz frequency offset from the carrier frequency, the phase noises are −108.5 and −129.7 dBc/Hz for 2.04 GHz, while −112.7 and −135.7 dBc/Hz for 3.092 GHz.

A terahertz graphene metamaterial based on polarization-insensitive plasmon-induced transparency for sensing application

A graphene metamaterial based on polarization-insensitive plasmon-induced transparency (PIT) in the terahertz region is theoretically presented. The graphene metamaterial comprises a cross-shaped and four other identical graphene strips, and a distinct narrow PIT window resulted from the bright-bright coupling is obtained when the electric field is along both x and y polarization directions. Surface current distributions and the two-particle model are used to elucidate the physical mechanism of the PIT effect, where the theoretical results of the two-particle model agree well with the simulation transmission spectra. In addition, the amplitude and resonant frequency of the PIT window can be modulated by tuning the Fermi level of graphene without varying the geometric parameters. Moreover, a high group delay of 1.545 ps can be achieved at the fixed Fermi level of 1 eV. As a function of the terahertz (THz) sensor, the PIT structure exhibits excellent sensing performances with the maximum sensitivity of 0.8 THz per refractive index unit (RIU) and figure of merit (FOM) of 17.28 RIU−1. Therefore, these features indicate that this work paves the way for designing polarization-insensitive and high-performance PIT sensors in the THz region.

Low phase noise microwave oscillator with greater than 60 dB second‐harmonic suppression

This study presents a microwave oscillator in which an innovative hybrid microstrip and substrate integrated waveguide filter is proposed for phase noise reduction. By virtue of equivalent circuit, the specific topology of this filter is clearly revealed and verified by both the simulation and the experiment. It can realize a third-order elliptic bandpass response with two transmission zeros near the passband. Specific phase response can be formed, in which a high group delay can be achieved within a narrow frequency range around the centre frequency. This feature makes the filter performance very flexible for its application in microwave oscillator, and then reduces its phase noise. For demonstration, an oscillator example at 9.0 GHz was deigned, fabricated and measured. The measured phase noise at 100 kHz away from the oscillation frequency is as low as −120.06 dBc/Hz. Furthermore, the proposed oscillator is featured by greater than 60 dB second-harmonic suppression and at least the third harmonic is suppressed.

Substrate-Suspended Air Cavity Resonator and Its Application in Low Phase Noise Oscillator

In this paper, we present a substrate-suspended air cavity resonator featuring high-Q, consisting of five separate layers for confining electromagnetic energy. Its field distribution is analyzed in depth. By appropriately coupling the two resonators, a second-order Chebyshev bandpass frequency selection network is obtained, and design procedure is described. It forms a specific group delay response, in which high values can be achieved within a narrow frequency range around the center frequency. The frequency selection network has great flexibility in adjusting its magnitude and phase responses so that low insertion loss and high group delay are achieved simultaneously. This feature plays an important role in reducing phase noise when it is applied in a microwave oscillator. For demonstration, an X-band oscillator example was designed and fabricated. As the measured results show, it works at 11.16 GHz, and the phase noise at 100 KHz away from the oscillation frequency is as low as −120.68 dBc/Hz.

Substrate integrated waveguide dispersive delay structure based on wave trapping

A dispersive delay structure (DDS) is a device that creates a specified group delay function over frequency bandwidth. In this paper, the idea of trapping the electromagnetic waves in a feedback loop is proposed to achieve higher group delay swing. The proposed structure includes two transmission lines and two junctions that act as power divider/combiner. The transmission lines can be either dispersive or non-dispersive. The group delay in the proposed configuration is proportional to the injected power into the feedback loop. So, an increase in the group delay swing can be done by improving the junctions or by adding more feedback loops to the structure. Based on this configuration, a novel DDS, using the substrate integrated waveguide (SIW) transmission line, is introduced. According to the experimental results, the proposed device with a relatively compact size creates high group delay swings (9 ns), and its insertion loss is about 7 dB.

Design, fabrication and measurement of highly-dispersive mirrors with total internal reflection.

High group delay dispersion (GDD) is often required for ultrafast laser applications. To achieve GDD level higher than -10000 fs2 in a single mirror setting is difficult due to the high sensitivity to unavoidable production inaccuracies. To overcome the problem, total internal reflection (TIR) based dispersive mirrors have been proposed in theory. In this paper, we report our continuous effort to further design, fabricate and measure TIR based dispersive mirrors.

Ultra‐low phase noise oscillator employing mixed electric and magnetic coupling resonator

AbstractIn this article, a pair of stub‐loaded interdigital hairpin resonators‐based filter with high group delay and improved stopband suppression is used to design an S‐band ultra‐low phase noise single‐ended oscillator. A transmission zero closed to the edge of passband in the filter is generated by introducing strong electric and magnetic coupling, which can improve the phase noise performance of the proposed oscillator. A low phase noise figure‐of‐merit (FOM) that considers both insertion loss and group delay of the feedback loop is used to evaluate the overall phase noise performance of the proposed oscillator. In order to verify the concept, the proposed oscillator is designed and fabricated. The measured results show that the oscillation frequency is 2.037 GHz with the output power of 8.92 dBm while the second harmonic suppression level is about 35.66 dB. The phase noise and the FOM of the proposed oscillator at 100 kHz frequency offset are −127.95 and −199.31 dBc/Hz, respectively. According to the open literature, this is one of the best phase noise performances of the single‐ended hybrid integrated oscillators oscillating at the similar frequency range.

Low phase noise L‐band oscillators based on novel general Chebyshev bandpass filters

SUMMARYOscillators act as signal sources for wireless communication systems, radars, wireless charging, and other industrial applications, whose phase noises directly determine system performance. In this paper, two low‐phase noise microwave oscillators based on novel microstrip second‐order band‐pass filters are presented. These filters are characterized by good frequency selectivity owing to two transmission zeros near to the passbands. As a result, relatively high group delay can be achieved at center frequencies, which is vital to the phase noise performance of the oscillators to be designed. Simultaneously, the bandwidths can be made narrow enough so that actual oscillating frequency is very close to the designed one. In addition, the introduction of stepped impedance makes these filters capable of harmonic suppression, which efficiently suppresses the harmonics in the output such as the second harmonic. These filters are compact and also of easy design. Finally, two microwave oscillators at 2.0 GHz are designed on these microstrip filters. As the measured results show, their output frequencies are 2.002 GHz. The phase noises are −127.21 and −127.03 dBc/Hz@100 kHz, respectively. The second harmonic suppressions are as great as 30.45 and 39.21 dBc, respectively.

Ultralow Phase-Noise Differential Oscillator Using Quarter Stepped-Impedance Resonator

In this letter, an ultralow phase-noise differential oscillator is proposed using a balanced feedback filter based on quarter stepped-impedance resonators (QSIRs). Phase-noise performance of the designed oscillators can be significantly improved by taking advantage of high peak group delay, improved stopband suppression, and differential configuration of the proposed feedback filter. To verify the hypothesis and compare the phase-noise performance among single-ended and differential oscillators, both the prototypes are designed, fabricated, and measured. The measured results show that the designed single-ended and differential oscillators are operating at 1.953 GHz. The differential oscillator shows not only a good balanced output power of 8.29 dBm with a measured high suppression of 40.07 dB on the second harmonic but also a superior low phase-noise performance of −130.19 dBc/Hz at a frequency offset of 100 kHz. To the best of our knowledge, this is the best phase-noise performance among the state-of-the-art works designed on planar hybrid integrated circuits at a similar frequency range.

Bandwidth Enhancement of a Wide Slot Antenna Using Fractal Geometry for UWB Application with Multiple Notched Bands

In this paper a combination of rectangular and elliptical fractal geometry is applied on a regular hexagonal wide slot antenna fabricated using a FR4 substrate to obtain ultra wide band (UWB) operation. The bandwidth enhancement of the wide slot antenna due to this fractal curve is studied in a step by step manner and the corresponding mathematical analysis is also presented. The comparison of the proposed fractal geometry with the existing fractal geometries is also exhibited. Multiple input multiple output performance of the proposed UWB antenna is also analysed. Two pairs of L-shaped slots are etched on the ground plane and a metallic ring is inserted inside the slot to produce triple band notch characteristics at 3.98 GHz, 5.56 GHz and 7.94 GHz. These three notch bands can avoid interference with existing WIMAX, downlink of C-band satellite communication, WLAN and uplink of X band satellite communication. The proposed band notched UWB antenna exhibits acceptable radiation characteristics with satisfactory gain, high radiation efficiency and constant group delay in the operation band.