Ps Group Delay Research Articles

Moiré photonic superlattice-induced transparency at commensurate angle in a terahertz metasurface composed of triple layer square lattices

The control of the speed of terahertz waves is always a challenge since the bandgap of most optical materials is much larger beyond meV with subtle nonlinear susceptibility. Moiré metasurfaces are shown to exhibit wide tunable optical properties and extraordinary physical phenomena at specific commensurate angles. These can be achieved by a careful design of the metasurface to manipulate terahertz slow light. Herein, we demonstrate a triple layer Moiré metasurface with a distinct electromagnetically induced transparency (EIT) phenomenon at commensurate angles. The proposed metasurface is composed of an intrinsic square lattice embedded into another Moiré photonic superlattice made of twisted square lattice at commensurate angles of 10.39° and 7.63°. The coupling between adjacent meta-atoms on the combined metasurface leads to destructive interference of dual trapped lattice modes, which results in a transparency window at the terahertz band. A maximum group delay of 9.76 ps is found at the transparent window of 0.84 THz when the commensurate angle is 10.39°. When the commensurate angle reduces to 7.63°, the transparency window shifts to 0.57 THz with a 5.96 ps group delay. The coupled Lorentz oscillator model indicates that the nonlinear optical susceptibility at transparency windows is above zero. Our results create an approach to tune the EIT as well as slow light in the terahertz band. Our device can have potential applications in terahertz signal processing and storage.

The impact of contact and contactless interactions between the meta-atoms on terahertz bound states in the continuum

The excitation and manipulation of symmetry-protected bound states in the continuum (SP-BIC) is significantly valuable for metasurface-based biosensors. The interactions between adjacent meta-atoms determine the fundamental properties of SP-BIC; however, this topic has not been profoundly explored. In this work, we experimentally and numerically investigate the effects of contactless and contact interactions between adjacent dual-gap split-ring resonators (DSRRs) on the SP-BIC. We demonstrate that there is only one SP-BIC at 0.9 THz when the incident radiation polarization is parallel to the gap in both contactless and contact coupling conditions. When the polarization is vertical to the gap, the individual SP-BIC shifts the frequency to 0.8 THz under contactless coupling. Under contact coupling, the SP-BIC degrades to be an electromagnetically induced transparency (EIT) windows at 0.8 THz. We calculated a 3.6 ps group delay of slow light for EIT. Numerical simulations indicate that the combination of one magnetic dipole (MD) in the inner arm and another electric dipole in the outer arm of DSRR results in quasi-BIC at 0.9 THz and 0.8 THz under contactless coupling. Under contact coupling conditions, the formation of quasi-BIC at 0.9 THz is similar to contactless coupling. However, two MDs of opposite polarity results in the EIT windows at 0.8 THz. Our results reveal excitation and manipulation of terahertz SP-BIC via contactless and contact coupling, which is significant for the innovation of terahertz biosensors.

A Compact 1.0–12.5-GHz LNA MMIC With 1.5-dB NF Based on Multiple Resistive Feedback in 0.15-μm GaAs pHEMT Technology

In this paper, a 2-stage compact wideband low-noise amplifier (LNA) monolithic microwave integrated circuit (MMIC) with multiple resistive feedback (MRFB) is presented. From the DC point of view, the proposed MRFB functions as a self-biasing structure to bias transistors in the optimal condition, improving the noise figure (NF) and linearity. Meanwhile, by employing MRFB with source degeneration and input inductor, the proposed LNA achieves wideband flat gain at the AC side. In comparison with traditional topologies, a wide bandwidth of more than 11.5 GHz with low noise figure of less than 2.5 dB can be achieved. To verify the proposed LNA structure, a chip prototype is fabricated in a 0.15- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> GaAs E-mode pHEMT process with a compact die size of only 0.75 mm2 including all the testing pads. From the measurement results, the proposed LNA circuit features a 1.0 to 12.5 GHz 3-dB working bandwidth (172% fractional bandwidth), 23.6 peak gain, 1.51 dB minimum NF, 66.7± 15 ps group delay, and 24.3/12.6 dBm best OIP3/OP1dB, respectively. The total DC power is around 87.5 mW from a single 2.5-V power supply.

Implementation of broadband optical receiver amplifier with low group delay variation

Considering the ever-increasing growth of data traffic in communication systems, optical receiver amplifiers are now emerging as a key feature of various optical receivers. This article presents a broadband optical receiver amplifier for high-speed and low latency communication systems. The proposed amplifier is based on the distributed amplifier configuration, and employs the negative group delay technique to reduce the group delay variation. The experimental results of the proposed amplifier show a 15 dB average gain, 3 dB noise figure, and 8 ps group delay variation at frequency ranging from DC to 40 GHz. To the best of our knowledge, the proposed distributed amplifier (DA) demonstrates the lowest group delay variation among the reported forward optical module distributed amplifiers (DAs) for high data rates applications.

A Low Impedance Current-Reuse Path for UWB-PA to Improve Efficiency and Gain

Current-reuse circuit with a low impedance current-reuse path has been proposed to enrich high flat gain, high efficiency, and high output power across the operating band. While an inductor-capacitor (LC) interstage is employed to improve the linearity of the proposed PA. In the second stage, the shunt peaking design in a common-source circuit is employed to improve the power gain, while a network of reactance compensation is adopted at the output of the second stage to overcome the parasitic capacitance's impact on the active device. The post-layout simulation using the TSMC 65 nm CMOS process is carried out on the entire frequency range from 3.1 GHz to 10.6 GHz. The post-layout simulation achieved ±42 ps group delay variation, 32% power-added efficiency (PAE), and 32-dB power gain. Matching input and output of less than −10 dB has been achieved over the operating band, and it achieved an output power of 18.3 dBm.

A 61.2-dBΩ, 100 Gb/s Ultra-Low Noise Graphene TIA over D-Band Performance for 5G Optical Front-End Receiver

This work reports in first time a 100-Gb/s, ultra-low noise, variable gain multi-stagger tuned transimpedance amplifier (VGMST-TIA) over the D-band performance. The whole work is binding into two phases. The first phase involves the modeling and characterization of graphene field-effect transistor (GFET) with an optimized transition frequency of operation. While in the second phase, a TIA design employs a T-shaped symmetrical L-R network at the input, which mitigates the effect of photo diode capacitance and achieves a D-band of operation. The proposed work uses a VGMST to establish TIA, which realizes optimum noise performance. The high gain 3-stage VGMST-TIA effectively minimizes the white noise and illustrates a sharp out-of-band roll-off to achieve considerable noise reduction at high frequencies. The active feedback mechanism controls the transimpedance gain by tuning the control voltage which results better group delay. Besides, an L-C circuit is employed at the output to enhance bandwidth. The full TIA is implemented and fabricated using a commercial nano-manufacturing 9-nm graphene film FET on a silicon wafer using 0.065-μm process. The TIA achieves a flat transimpedance gain of 61.2 dBΩ with ± 9 ps group delay variation over the entire bandwidth. The proposed TIA measured an impedance bandwidth of 0.2 THz with ultra-low input-referred noise current density of 2.03 pA/√Hz. The TIA supports a 100-Gb/s data transmission due to large bandwidth; therefore, a bit-error-rate (BER) less than 10−12 is achieved. The chip occupies an area of 0.92 * 1.34 mm2 while consuming power of 21 mW under supply of 1.8 V.

Silicon nitride chirped spiral Bragg grating with large group delay

As one of the most important optical filtering devices, Bragg gratings have been extensively used in various systems. A long Bragg grating is desired for many applications including frequency selection in semiconductor lasers and dispersion control for ultra-short pulses. As a prominent example, integrated spiral Bragg grating waveguides (SBGWs) have drawn much attention in the years. However, until now, the length of an integrated grating is still limited to a few milli-meters due to total waveguide loss. In this work, we propose and demonstrate a novel long chirped SBGW with waveguide loss as low as 0.05 dB/cm on a silicon nitride (Si3N4) platform. A 13.8 cm SBGW is fabricated, which is the longest on-chip waveguide grating reported so far. The SBGW’s reflection bandwidth is 9.2 nm from 1556.3 nm to 1565.5 nm, and it provides a total of 1440 ps group delay, that is, −156.5 ps/nm of dispersion. The group delay response shows great linearity and temperature stability. This integrated device holds great potential for various applications including in-line dispersion compensation, optical true delay phase array, and microwave photonics.

Coherently controllable terahertz plasmon-induced transparency using a coupled Fano-Lorentzian metasurface.

Metamaterials have been engineered to achieve electromagnetically induced transparency (EIT)-like behavior, analogous to those in quantum optical systems. These meta-devices are opening new paradigms in terahertz communication, ultra-sensitive sensing and EIT-like anti-reflection. The controlled coupling between a sub-radiant and a super-radiant particle in the unit cells of these metamaterial can enable multiple narrow plasmon induced transparency (PIT) windows over a broad band, with considerable group delay of electromagnetic field (slow light effect). Phase coherence between these PIT windows is highly desired for next-generation multichannel communication network. Herein, we numerically and experimentally validate a controllable frequency hopping mechanism between "slow light" windows in the terahertz (THz) regime. The effective media are composed of plasmonic "molecules" in which an asymmetric split-ring resonator (ASRR) or Fano resonator is displaced on the side of a cut-wire (Lorentz oscillator). Two metasurfaces where ASRR is on opposite side of the cut-wire are investigated. In these two cases, the proximity of the cut-wire to the gap on the ASRR having asymmetry is different. On one side, when the gap is nearer to the cut wire, displacing the ASRR along the cut-wire, produces only one narrow transparency window at 0.8 THz, corresponding to 20 ps group delay. When the ASRR is positioned on the opposite side, such that the gap is further, two transparency windows are observed when the ASRR is displaced along the cut-wire. That is, the transparency window hops from 0.8 THz to 1.2 THz. This corresponds to an increase from 20 to 30 ps in slow light effect. Numerical simulations suggest these single or multiple PIT windows occur if the couplings between the plasmonic modes in the different arrangements are either in-phase or out-of-phase, respectively.

Low Harmonic Distortion DFB Laser for Broadband Analog Applications

$1.35~\mu $ m AlGaInAs/InP DFB lasers with low harmonic distortion and high frequency response bandwidth have been demonstrated for broadband analog applications. By optimizing active layers and setting Bragg wavelength 10 nm blue shifted of the gain peak wavelength, the device has a threshold current of 8.5 mA, 3-dB frequency response bandwidth of 21 GHz at 60 mA and 28GHz at 90 mA, second harmonic distortion of −23 dB and 1.5 ps group delay time up to a modulation frequency of 25 GHz. These highly linear and high frequency response bandwidth DFB lasers are realized for broadband analog applications and will become the key transmitters for the future 5G millimeter wave communication systems.

Terahertz electromagnetically-induced transparency of self-complementary meta-molecules on Croatian checkerboard

A terahertz (THz) electromagnetically-induced transparency (EIT) phenomenon is observed from two types of self-complementary meta-molecules (MMs) based on rectangular shaped electric split-ring resonators (eSRR) on Croatian checkerboard. Each MM contains a couple of identical size eSRRs and a couple of structural inversed eSRRs twisted π/2 in checkerboard pattern. In the first type of MM (type-I), the gap is in the middle line of eSRR. In the second type of MM (type-II), the gap is on the two arms of eSRR. Both types of MMs exhibit EIT effect. A maximum 20 ps group delay is observed at the transparency window of 0.63 THz in type-I MM; while a maximum 6.0 ps group delay is observed at the transparent window of 0.60 THz in type-II MM. The distribution of surface currents and electrical energy reveals that only CeSRR contribute to the transparency window as well as the side-modes in type-I MM, where the current leakage via contact point contributes to the low-frequency side-mode, and the coupled local inductive-capacitive (LC) oscillation in CeSRRs contributes to the high-frequency side-mode. In type-II MM, however, the localized dipolar oscillator of CeSRR contributes to the low-frequency side-mode; while the hybridization of dipole oscillation on eSRR and LC resonance on CeSRR contributes to the high-frequency side-modes. Our experimental findings manifest a new approach to develop THz slow-light devices.

Dual terahertz slow light plateaus in bilayer asymmetric metasurfaces

This work theoretically proposed dual terahertz (THz) slow light plateaus by tuning the destructive interference between a toroidal magnetic momentum and magnetic dipole momentum. The metasurfaces are in a sandwich structure. A metallic cut-wire is patterned on one side of polyimide thin-film, and a rectangular split-ring resonator (SRR) on the other side with asymmetric layout. By translating the SRR along the cut-wire from the top terminal to the bottom terminal of the cut-wire, dual slow light plateaus are found in the transparency window at a certain range of displacement. A maximum of 40.4 ps group delay is achieved as the displacement achieves 9 μm. The numerical mapping of electromagnetic field indicates that the electrical dipole on metallic cut-wire results in a localized toroidal magnetic momentum, while the inductive-capacitor oscillation of SRR results in a magnetic dipole momentum. These two momentums have opposite directions, which will repel each other at certain displacement, creating the transparency windows. Furthermore, an electrical coupling takes place in between the bilayer metasurface so that the slow light achieves a maximum, with the aforementioned two mechanisms working in coincidence.

Electrical Control of Electromagnetically Induced Transparency by Terahertz Metamaterial Funneling

AbstractElectromagnetically induced transparency (EIT) analogs using metamaterials have diverse applications, including nonlinear optics, telecommunications, and biochemical sensors. These EIT analogs can be actively controlled by embedding semiconducting materials into metamaterial structures, but most active EIT metamaterials require complex optical setups and complicated fabrication processes. Graphene‐based EIT metamaterials are some of the most promising active EIT systems because of their simple controllability by electrical bias, but related researches have so far been limited to theoretical or numerical studies. Here, experimentally verified graphene EIT metamaterials are provided by controlling the terahertz funneling of the unique metaatom structures. The proposed active EIT metamaterials are fabricated on flexible and ultrathin polyimide films to acquire the lowest substrate insertion losses and achieve a 1 ps group delay change at the transmission peak of the EIT analog. Moreover, because the proposed metamaterials exhibit resonance properties that vary depending on the polarization direction, the phase delay can be controlled up to 80° from the proposed metamaterials by rotating the incident polarization to the orthogonal direction. Overall, by controlling the group and phase delay of incident waves in a single metamaterial device simultaneously, a multifunctional active tuning system can be realized in the terahertz range.

Maximization of terahertz slow light by tuning the spoof localized surface plasmon induced transparency

This work numerically investigates a localized terahertz (THz) slow light phenomenon by tuning the spoof localized surface plasmon-induced transparency (PIT). A binary meta-molecule supports the interaction of the spoof localized surface plasmon (spoof-LSP), which is composed of a metallic arc and a textured circular cavity of periodic grooves. By tuning the central angle θ of the arc from 90 degrees to 170 degrees, a slow light plateau is found in the transparency window at certain frequency range. A maximum of 46 ps group delay is achieved at the θ of 135. The numerical mapping of the electromagnetic field indicates a new-born dipolar spoof-LSP that appears at the transparency windows on the circular cavity with opposite polarity to the spoof-LSP on the metallic arc. These two spoof-LSPs of opposite direction lead to a fake quadrupole, which will repel each other in magnetic dipole momentum. The slow light achieves maximum with the induced spoof-LSP and is the same as the origin spoof-LSP on the metallic arc in oscillation strength. This work paves a new way for the maximization of THz slow light.

Localized terahertz electromagnetically-induced transparency-like phenomenon in a conductively coupled trimer metamolecule.

We experimentally investigate the terahertz (THz) electromagnetically-induced transparency (EIT)-like phenomenon in a metamolecule (MM) of three-body system. This system involves a couple of geometrically identical split-ring resonators (SRRs) in orthogonal layout conductively coupled by a cut-wire resonator. Such a three-body system exhibits two frequency response properties upon to the polarization of incident THz beam: One is the dark-bright-bright layout to the horizontally polarized THz beam, where there is no EIT-like effect; the other is bright-dark-dark layout to the vertically polarized THz beam, where an EIT-like effect is observable. The transparency window can be tuned from 0.71 THz to 0.74 THz by the displacement of cut-wire inside the trimer MM. A maximum of 7.5 ps group delay of THz wave is found at the transparent window of 0.74 THz. When the cut-wire moved to the mid-point of lateral-side of SRR, the EIT-like phenomenon disappears, this leads to a localized THz slow-light effect. The distribution of surface currents and electric energy reveals that the excited inductive-capacitive (LC) oscillation of bright-SRR dominates the high frequency side-mode, which is isolated to the displacement of cut-wire resonator. However, the low frequency side-mode originates from the constructive hybridization of LC resonance in dark-SRR coupled with a localized S-shaped dipole oscillator, which is tunable by the displacement of cut-wire. As a consequence, the group delay as well as the spectral configuration of transparency window can be manipulated by tuning one side-mode while fixing the other. Such an experimental finding reveal the EIT-like effect in a conductively coupled three-body system and manifests a novel approach to achieve tunable THz slow-light device.

Localized slow light phenomenon in symmetry broken terahertz metamolecule made of conductively coupled dark resonators

We demonstrate a localized slow light phenomenon in a symmetry broken metamolecule (MM) of conductively coupled dark resonators at a terahertz band. Under a dark-mode excitation condition, the single mode resonance becomes dual modes by breaking the uniaxial symmetry of MM. Thus, a transparency window exists in between dual modes. An interaction of V-shaped plasmonic antenna-type (VA) resonances results in a plasmon-induced transparency (PIT) when the asymmetric deviation is below 13 μm. A maximum 25.9 ps group-delay of incident THz pulse is observed at the transparency window. When the asymmetric deviation is beyond 13 μm, one excitation pathway switches from VA resonance to the inductor-capacitor (LC) resonance, which dominates the high-frequency side-mode. Then, the PIT effect transfers to the PIT-like behavior and the slow light phenomenon vanishes. The aforementioned discovery allows for a speed modulation of slow light via symmetry breaking in MM.

Plasmonic-Induced Absorption and Transparency Based on a Compact Ring-Groove Joint MIM Waveguide Structure

Through adding a groove to an end-coupled perfect ring (PR) resonator, a ring-groove (RG) joint metal–insulator–metal (MIM) structure is proposed. Destructive interference for the expected surface plasmon mode will occur due to the phase differences between two optical paths, leading to the plasmonic-induced absorption response with abnormal dispersion, which is analogous to the electromagnetically induced absorption in the three-level atomic system. A transmission dip is achieved at the former-peak wavelength of the PR resonator, while two transmission peaks arise around the window. The proposed structure, which benefits from –0.3 ps group delay time, will be preferred in the ultrafast-light applications. Due to the same interference effect, plasmonic-induced transparency response with slow-light characteristic is also investigated by arranging the RG joint resonator to be a side-coupled configuration. Therefore, a new approach for on-chip light-speed control can be developed by using the proposed structures, whose performances are investigated by the finite-difference time-domain (FDTD) method and the coupled mode theory.

A 0.13-&lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;$\mu $ &lt;/tex-math&gt;&lt;/inline-formula&gt;m CMOS Current-Mode All-Pass Filter for Multi-GHz Operation

A CMOS wide-bandwidth first-order current-mode all-pass filter (APF) is discussed. The circuit consists of one transistor, a resistor, a grounded inductor, and a load. When used with a current mirror as the load, the current-mode filter exhibits a high output impedance, which is advantageous from an integration point of view and enables this configuration to be cascaded with current-mode circuits. The operation of the proposed circuit is experimentally validated. The APF implemented in IBM $0.13-\mu {\textrm {m}}$ CMOS was measured to have the pole-zero pair located at 8.32 GHz and to achieve a 55 ps group delay while consuming 19 mW from a 1.5-V supply. This paper experimentally demonstrates a CMOS APF that operates at multi-GHz frequencies and achieves the highest delay-bandwidth products of the published CMOS first-order APFs known to the authors.

DESIGN OF BESSEL LOW PASS FILTER USING DGS WITH IMPROVED CHARACTERISTICS FOR RF/MICROWAVE APPLICATIONS

We report a synthesis process to design the defected ground structure (DGS)-based Bessel lowpass filter (LPF). For 5-pole LPF at fc = 2.5 GHz, its selectivity is 10.6 dB/GHz and for the DGS-based Butterworth LPF it is 12.6 dB/GHz. For the lumped elements Bessel LPF, it is only 4.84 dB/GHz. Its 20 dB rejection bandwidth is 13.1 GHz and impedance matching BW is 76%, as against 88.8% for Butterworth LPF. At fc = 7.5 GHz, the 5-pole DGS Bessel LPF has selectivity 7 dB/GHz, 20 dB rejection BW is 13 GHz and 10 dB return loss (RL) BW in passband is 4.86 GHz (64.8%) with less than 7.9 pS group delay (GD) variation. In case of a bulky mixed microstrip-waveguide (MMW) 5-pole Bessel LPF at 7.5 GHz [W. Menzel and F. Boigelsack, 29th European Microwave Conference, Munich (1999), pp. 191–194.], reported results are: sharpness of cut-off 1.48 dB/GHz, 10 dB RL BW and GD variation are 48% and 4 pS, respectively. The improved performance the DGS-based Bessel LPF can find applications in high speed data communication, front-end of a wideband communication system and in a power amplifier, by improving the selectivity, suppression of harmonics and linear distortion.

5–11 GHz CMOS PA with 158.9 ± 41 ps group delay and low power using current-reused technique

This paper proposes the design of a low group delay and low power ultra-wideband (UWB) power amplifier (PA) in 0.18μm CMOS technology. The PA design employs two stages cascade with inductive peaking technique to provide broad bandwidth characteristic and higher gain while gain flatness can be achieved by connecting inter-stage circuit. A common gate current-reused technique is adopted at the first stage amplifier to achieve good input matching, low group delay and low power. The simulation results show that the proposed PA design has an average gain of 11.5dB with flatness of ±0.4dB from 5–11GHz, while maintaining bandwidth of 4.2–12.3GHz. An input return loss (S11) less than −10.4dB and output return loss (S22) less than −9.5dB, respectively are obtained. The PA design achieves excellent phase linearity (i.e., group delay variation) of ±41ps and only consuming 17mW power from 1.2V supply voltage. A good output 1-dB compression point OP1dB of 3.7dBm is obtained. By using this method, the proposed design has low group delay variation and lowest power among the recently reported UWB CMOS PAs applications.

Cascaded passive silicon microrings for large bandwidth slow light device

Slow light devices have important applications in the areas of data buffering, signal processing, and phased array antenna. Cascaded microring resonators structure can obtain large delay and also enhance the bandwidth, which was considered as a potential approach for future on-chip optical buffer. In this paper, we demonstrated a large bandwidth slow light device using cascaded Silicon-on-insulator (SOI) based microring resonators. With carefully designed the gap between the bus and the ring waveguides and the distances between the adjacent rings, a 57 ps group delay was observed and 83 Gbps maximum allowable bit rate is suggested according the measured 3 dB spectral bandwidth in the 8-stage cascaded microrings.