Minimum Insertion Loss Research Articles

Polarization-independent wavelength demultiplexer based on a single etched diffraction grating device

Polarization-compatible receivers are indispensable in transceivers used for wavelength division multiplexing optical communications, as light polarization is unpredictable after transmission through network fibers. However, the strong waveguide birefringence makes it difficult to realize a polarization-independent wavelength demultiplexer in a silicon photonic receiver. Here, we utilized the birefringence effect for simultaneously demultiplexing wavelengths and polarizations, and experimentally demonstrated a polarization-independent wavelength demultiplexer with a single device on a SiPh platform. The principle was validated on an etched diffraction grating, which successfully split the arbitrarily polarized light containing four wavelengths into eight channels with single-polarization and single-wavelength signals. Polarization-dependent losses of 0.5–1.8 dB, minimum insertion loss of 0.5 dB, and crosstalks lower than −30 dB were experimentally measured for the fabricated etched diffraction grating. Thus, a promising general solution was developed for implementing polarization-independent wavelength division multiplexing receivers and other polarization-independent devices on photonics platforms with birefringent waveguide devices.

Application of Compact Folded-Arms Square Open-Loop Resonator to Bandpass Filter Design

Folded-arms square open-loop resonator (FASOLR) is a variant of the conventional microstrip square open-loop resonator (SOLR) that facilitates further device size miniaturization by having the two arms of the conventional SOLR folded inwards. This paper highlights the benefits of this brand of compact SOLR by implementing a five-pole Chebyshev bandpass filter (BPF) using compact FASOLR. The test BPF is presented, with centre frequency of 2.2 GHz, fractional bandwidth of 10%, passband ripple of 0.04321 dB, and return loss of 20 dB. The design is implemented on a Rogers RT/Duroid 6010LM substrate with a dielectric constant of 10.7 and thickness of 1.27 mm. The filter device is manufactured and characterised, with the experimentation results being used to justify the simulation results. The presented measurement and electromagnetic (EM) simulation results demonstrate a good match. The EM simulation responses achieve a minimum insertion loss of 0.8 dB and a very good channel return loss of 22.6 dB. The measurement results, on the other hand, show a minimum insertion loss of 0.9 dB and a return loss of better than 19.2 dB. The filter component has a footprint of 36.08 mm by 6.74 mm (that is, 0.26 λg × 0.05 λg), with λg indicating the guided wavelength for the 50 Ohm microstrip line impedance at the centre frequency of the proposed fifth-order bandpass filter.

A Balanced Substrate Integrated Waveguide Phase Shifter with Wideband Common-Mode Suppression

In this paper, a slotted substrate integrated waveguide (SIW) is used to create a balanced phase shifter with wideband common-mode (CM) suppression. Differential-mode (DM) impedance matching and CM suppression are achieved by utilizing the fact that TE20 mode and TE10 (TE30) mode can only transmit DM signals and CM signals, respectively, and by increasing the bandwidth for CM suppression via slots. Furthermore, a wideband phase shift with low phase deviation can be obtained due to the phase slop counteract between the slot and the delay line. Compared with the state-of-the-art, the proposed one has the advantages of wideband CM suppression, wide phase shift range, and a simple and easy-to-make structure. Five prototypes covering the frequency of 3.5 GHz are designed with the relative operating bandwidth for 45° ± 2° (90° ± 4.5°, 135° ± 6°, and 180° ± 8°) phase shifter of 20% (20%, 20%, and 20%), with the minimum insertion loss of 0.41 dB (0.5 dB, 0.58 dB, and 0.59 dB), with the minimum return loss greater than 15 dB, and with the relative bandwidth for 15-dB CM suppression of 59% (59%, 58%, and 57%).

A New Varactor-Tuned 5.8 GHz Dielectric Resonator Band-Stop Filter for ITS and C-V2X Coexistence with Vehicular DSRC

In this paper, we introduce an electronically tuneable band-stop filter based on a dielectric resonator, along with its design principles and equivalent circuit model aimed at the coexistence of intelligent transport systems (ITS) and cellular vehicle-to-everything (C-V2X) communications operating at 5.9 GHz, with the widely spread vehicular dedicated short range communications (DSRC) at 5.8 GHz. The proposed architecture involves a dielectric resonator coupled via a microstrip transmission line to a planar ring resonator. The resonance is electronically tuned by varying the bias voltage of a varactor diode placed in the ring. This design is analyzed theoretically and experimentally. For validation, a filter operating at 5.8 GHz was designed. The prototype is capable of enhancing coexistence exhibiting to features. First, when inserted into the ITS transmitter chain, it reduces unwanted transmitter emissions in the out-of-band spectrum occupied by the DSRC carriers in the 5.8 GHz frequency band of at least 25 dB, with a minimal insertion loss at 5. 9 GHz of 1.6 dB; secondly, when inserted in the ITS receiver chain, it exhibits high linearity that prevents the generation of intermodulation products falling into the filter pass band. The prototype features more than 21 dBm of third-order input intercept points, and a tuning range of 26 MHz while maintaining a minimal loaded Q factor of 93. The prototype is discussed regarding the detailed equivalent circuit parameter extraction and their dependency upon the control voltage.

Optical switch of low-insertion-loss based on the Brewster angle effect

Optical switches are critical components for optical communication devices, and currently, they are now bottlenecking the development of optical telecommunications. In this study, we propose an innovative all-optical Kerr switch based on the Brewster angle effect, which exhibits a graphene/SiO2/graphene/SiO2 structure and an insertion loss (IL) that can be minimized by tuning the Fermi level of the graphene layers. A novel Brewster’s angle effect is achieved, resulting in a change in the incidence angle under nonlinear conditions as well as on–off switching of the phase change. The proposed switch has perfect absorption at an incident angle of 63 deg, where the phase of the reflected light is shifted from − π to 0. Furthermore, the Brewster angle of the switch was successfully shifted from 63 deg to 80 deg with an incident frequency of 0.8 THz. It was observed that an increase in Fermi level continuously shrank the nonlinear region of the switch. The minimum IL of the proposed optical switch was only 2 dB, which is indicative of excellent energy efficiency. The results of this study can aid in the development of key devices for broadband communications and electromagnetic sensing.

A compact 5G band N77 bandpass filter with multiple zeros based on GaAs integrated passive device process

AbstractIn this paper, a compact 5G band N77 bandpass filter (BPF) with multiple zeros is designed based on GaAs integrated passive device (IPD) process. The BPF consists of lumped capacitors and inductors. Hybrid resonator technology which consists of a combination of shunt and series resonant tanks are proposed to produce six transmission zeros in the stopband and significantly improve the filter selectivity. In addition, a series resonator at the output port of the filter was introduced to produce another transmission zero at the upper stopband and further improve the stopband suppression. Meanwhile, to reduce the area and insertion loss of the filter, a stacked inductor is designed by using IPD technology, which can greatly reduce the area and size of the filter. The minimum insertion loss is 1.782 dB. The size of the entire BPF is 1.3 mm × 0.7 mm.

Design of Nonreciprocal Multifunctional Reflectionless Bandpass Filters by Using Circulators

In this brief, the method of using nonreciprocal circulator networks to construct multifunctional components is proposed. A nonreciprocal single-ended bandpass filter based on two circulators is proposed. Because the circulator has a characteristic of nonreciprocal structure, the filter has different responses in the forward and reverse signal paths. And a nonreciprocal balanced bandpass filter is also introduced. This brief shows that signal transmission states in circulator networks are different when they terminate in different loads. Therefore, when different ports are used as input ports, the nonreciprocal balanced bandpass filter can be viewed as a filter or a power divider. A nonreciprocal single-ended bandpass filter working at 3.44 GHz and 3.21 GHz and a nonreciprocal balanced bandpass filter with 3-dB bandwidth from 2.80 GHz to 3.66 GHz and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\vert{S} _{\mathrm{ ccBA}}~\vert$ </tex-math></inline-formula> below −16.74 dB are realized. When the nonreciprocal balanced bandpass filter is used as a power divider, its minimum insertion loss is 1.07 dB and the amplitude difference is only 0.15 dB at the center frequency.

Coaxial Low-Pass Filter Design and Manufacture

In this study, a low-pass filter with coaxial transmission lines is designed and produced. The objective for designing a coaxial low-pass filter was to utilize both low loss transmission and high breakdown voltage capability for high power microwave applications to enable the suppression of the second harmonic of the 4.4-6 GHz C-Band ( C-Band was selected as a proof of concept ) signals with minimal insertion loss. Microwave and 3D electromagnetic simulators were used in the filter design. The design was started by establishing an 11 th order Chebyshev low-pass filter prototype giving 0.05 dB ripple. Based on this prototype, a filter circuit consisting of capacitors and inductors as lumped elements was designed. The low and high impedances to be selected for the stepped impedance method, which is the basis of the transition to coaxial transmission lines, were decided and the most suitable impedances for manufacturing was determined. The filter using these impedances and designed with stepped impedance lines was transformed into the filter in which coaxial transmission lines are used. Coaxial transmission lines in the low-pass filter circuit consist of conductors with an insulating material in between. While the insulating material is selected as air in the high impedance sections of the transmission lines, it is PTFE (Polytetrafluoroethylene) with an insulating constant of 2.1 in the low impedance sections. The designed filter was manufactured. The basic properties of the manufactured filter were characterized by using RF measuring devices and compared with the designed filter. The measurements results prove that the frequency responses of the designed filter and the produced filter are very close to each other. Namely, a low-pass filter with a cutoff frequency of 6 GHz, a sharp suppression of about 45 dB at the stopband of 9 GHz and a return loss of 20 dB was designed and produced by using coaxial transmission lines. The novelty in our work can be stated that the power handling capability is increased by two techniques. The first one is that the highest transmission line radius preventing the higher order mode excitations is used to decrease the conductor loss. Teflon is covered around the low impedance lines to enhance the dielectric breakdown capability. Teflon inclusion is also used to decrease the practical low impedance level that improves the filter characteristics.

A Compact Bandpass Filter Manifold With Ultrawide Frequency and Bandwidth Tuning

This paper reports a comprehensive design methodology and a compact multilayer integration concept for a fully-reconfigurable bandpass filtering (BPF) manifold with simultaneous ultrawide center frequency and bandwidth (BW) tuning. The manifold is based on two RF-switched tune-all BPFs whose transfer function is shaped by three-poles and two transmission zeros (TZs) (i.e., three-pole/two-TZs). Tunability can be achieved by solely reconfiguring the resonant frequency of its constituent resonators (i.e., tuning-coupling less approach). A multi-layer PCB-based vertical integration scheme is proposed for size miniaturization leading to 43% smaller area than a conventional single layer implementation approach. For practical validation purposes, a BPF manifold was designed, built and measured. It exhibited ultrawide continuous center frequency tuning between 1.8 and 3.85 GHz (2.2:1) and continuous BW tuning between 2.5-3:1 (e.g 132-410 MHz at 2 GHz). For all of the aforementioned tuning states, the minimum passband insertion loss (IL) was measured between 2-9 dB and its IIP3 between 12.3-30 dBm.

Compact CEBG Filter for High-Frequency Applications With Low Insertion Loss

A compact configurable electromagnetic bandgap (CEBG) filter and a low-loss low-temperature cofired ceramics (LTCCs)-based electromagnetic bandgap (EBG) filter have been proposed. To the best of the authors’ knowledge, this is the minimum size configurable bandpass filter (BPF) ever reported using EBG material. The proposed circuits successfully integrate an integrated passive device (IPD) technique-based high- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula> capacitors and LTCC-based built-in capacitors with EBG substrates. The frequencies of the filters can be easily adjusted by controlling the capacitors. For proof-of-concept demonstration purposes, CEBG filters and LTCC-based EBG filters were designed and experimentally validated from the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$C$ </tex-math></inline-formula> -band to the Ku-band. The measurement results demonstrated the filters’ compact size, wide stopband, and reduced insertion loss (IL) as working frequency increases. Four LTCC EBG filters are implemented and fabricated with the highest working frequency of 17 GHz, a minimum IL of 1.91 dB, and a 3-dB fractional bandwidth (FBW) of 3%. The CEBG filter demonstrated a compact size of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.6\times1.35$ </tex-math></inline-formula> mm, a configurable frequency from 6.88 to 13.5 GHz with an almost constant FBW. Insertion losses of the EBG filters reduce as their working frequencies increase which shows an excellent high-frequency application capability of the filters.

Design of miniaturized single and dual-band bandpass filters using diamond-shaped coupled line resonator for next-generation wireless systems

AbstractThis paper presents a multi-mode resonator (MMR) for next-generation wireless systems that achieves single and dual-band bandpass filter (BPF) responses using a split-ring dual-path structure. The proposed BPF design is realized by employing two pairs of parallel couple lines and two symmetrical step-impedance open-circuited stubs (SIOCS). SIOCS are used to improve selectivity and increase the number of transmission zeros/poles. The proposed single-band BPF exhibits an ultra-wideband (UWB) response having a center frequency of 7.5 GHz, a minimum insertion loss of less than 0.48 dB, and a maximum return loss of 25.35 dB. The proposed UWB BPF has a stopband suppression of 39.34 dB up to 18 GHz and a 3 dB fractional bandwidth of 48.23%. Moreover, a dual-band BPF has been accomplished by utilizing the same architecture while slightly changing the MMR structure and adding more coupling. The center frequency (bandwidth) of the dual broadband BPF is 7.40 GHz (2.40 GHz) and 14.15 GHz (1.7 GHz), respectively. The measured minimum insertion loss is less than 0.23 dB and a return loss of less than 16.8 dB with 3 dB FBWs of 32.4 and 12.1%. Finally, two prototypes are fabricated to validate the proposed characteristics. The BPF's simulated and measured results are in good agreement.

All-Fiber Waveplate Made of Helically Wound Spun Highly Birefringent Optical Fiber

Waveplates are elements that are widely used in the optical system for polarization transformation. In the fiber optical system, it is highly desired to utilize waveplates in the all-fiber form with minimum insertion loss and stable performance. In this paper, we propose an all-fiber waveplate that is made of the helically wound spun highly birefringent (SHB) optical fiber. To function as waveplates, the torsion of the helix should be equal to the inherent polarization rotation of the SHB fiber so that the geometric rotation can match the inherent polarization rotation. Therefore, the phase difference between two orthogonal components of the incident polarized light can increase almost linearly with the fiber length. Because the SHB fiber is insensitive to external perturbations, the proposed waveplate can provide a definite and stable polarization transformation. We develop a model based on the perturbation theory to characterize the polarization evolution of the helically wound SHB fiber. Simulations and experiments have demonstrated the excellent performance of our all-fiber waveplates.

A Compact On-Chip Pad Structure With an Embedded Capacitor for Broadband Millimeter-Wave Bond-Wire Interconnection

This article presents a compact on-chip pad structure with an embedded capacitor for millimeter-wave bond-wire interconnection, which is realized by 65-nm complementary metal–oxide–semiconductor (CMOS) process and able to compensate the parasitic inductance introduced by bonding wires. The proposed pad structure implemented by metal stacking is equivalent to an on-chip series capacitor. Moreover, a deep N-well structure is loaded at the bottom of the pad to reduce the parasitic pad-to-ground capacitance. This pad structure has been applied to the chip-to-chip interconnection with a measured minimum insertion loss (IL) of 2.179 dB and a measured 3-dB bandwidth of 11.9 GHz from 35.6 to 47.5 GHz. In addition, it has been applied to the chip-to-printed circuit board (PCB) interconnect ion with a measured one-sided loss of 1.7475 dB and a measured 3-dB bandwidth of 12 GHz from 22.7 to 34.7 GHz. Both applications using bond-wire interconnections prove that the proposed pad structure can compensate bond-wire inductance and realize broadband low-loss impedance matching.

High-power UTC-photodiodes for an optically pumped subharmonic terahertz receiver.

In this work, we present an optically subharmonic pumped WR3-mixer for enabling photonic coherent frequency-domain terahertz (THz) imaging and spectroscopy systems in the future. The studied mixer operates within the upper range of the WR3-band from 270 GHz to 320 GHz. High-power uni-travelling carrier photodiodes (UTC-PDs) are developed for providing the subharmonic local oscillator (LO) signal within the corresponding WR6-band in the range between 135 GHz and 160 GHz. The proposed THz mixer module consists of a gallium arsenide (GaAs)-based low barrier Schottky diodes (LBSDs) chip and an indium phosphide (InP)-based UTC-PD chip. For integrating the UTC-PD with the WR6 at the mixer's LO input, an E-plane transition and a stepped-impedance microstrip line low pass filter (MSL-LPF) are developed and monolithically integrated with the UTC-PD chip on a 100 µm thick InP substrate. The E-plane transition converts the quasi-TEM mode of the grounded coplanar waveguide (GCPW) to the dominant TE10 mode of the WR6 and matches the GCPW's impedance with the WR6's impedance. According to full-wave EM simulations, the transition exhibits a 1 dB bandwidth (BW) of more than 30 GHz (138.8-172.1 GHz) with a corresponding return loss (RL) better than 10 dB, whereas the minimum insertion loss (IL) is 0.65 dB at a frequency of 150 GHz. Experimentally, the 1 dB BW of the fabricated transition is found to be between 140 GHz and 170 GHz, which confirms the numerical results. The minimum measured IL is 2.94 dB, i.e., about 2 dB larger than the simulated value. In order to achieve the required LO power for successfully pumping the mixer in a direct approach (i.e., without an additional LO amplifier), the design of the epitaxial system of the UTC-PD is optimized to provide a high output power within the WR6-band (110-170 GHz). Experimentally, at 150 GHz, the output power of the fabricated UTC-PD chip is measured to be +3.38 dBm at a photocurrent of 21 mA. To our knowledge, this is the highest output power ever achieved from a UTC-PD at 150 GHz. Finally, the developed high-power UTC-PDs are used as LO source to pump the subharmonic WR3-mixer. Experimentally, the conversion loss (CL) is determined in dependency of the LO power levels within the RF frequency range between 271 GHz and 321 GHz for a fixed IF at 1 GHz. The achieved results have revealed an inverse relation between the CL and LO power level, where the average minimum CL of 16.8 dB is achieved at the highest applied LO power level, corresponding to a photocurrent of 10 mA. This CL figure is promising and is expected to reach the CL of electronically pumped and commercially available THz mixers (∼12 dB) after packaging the LO source with the mixer. Furthermore, an average CL of 17.2 dB is measured at a fixed LO frequency of 150 GHz and a tuned RF frequency between 301 GHz and 310 GHz, i.e., IF between 1 GHz and 10 GHz.

A Design Fiber Performance Monitoring Tool (FPMT) for Online Remote Fiber Line Performance Detection

A new technique for fiber faults events detection and monitoring in optical communication network systems is proposed. The fiber performance monitoring tool is a new proposed technique designed to detect, locate, and estimate the fiber faults without interrupting the data flow with efficient costs and to improve the availability and reliability of optical networks as it detects fiber faults remotely in real time. Instead of the traditional old method, the new proposed FPMT uses an optical time domain reflectometer to detect multiple types of fiber failures, e.g., fiber breaks, fiber end face contamination, fiber end face burning, large insertion losses on the connector and interconnection, or mismatches between two different types of fiber cables. The proposed technique methodology to detect the fiber failures depends on analyzing the feedback of the reflected signal and the pattern shape of the reflected signal over network fiber lines, supports a higher range of distance testing and performance monitoring, and can be performed inside an optical network in real time and remotely by integrating with an OSC board. The proposed technique detects fiber faults with an average accuracy of measurement up to 99.8%, the maximum distance to detect fiber line faults is up to 150 km, and it can improve the system power budget with a minimal insertion loss of 0.4 dB. The superiority of the suggested technique over real networks was verified with success by the Huawei labs’ infrastructure nodes in the simulation experiment results.

Surface-Acoustic-Wave Devices Based on Lithium Niobate and Amorphous Silicon Thin Films on a Silicon Substrate

This work presents an acoustic platform using solidly mounted thin-oriented lithium niobate (LiNbO3) film on silicon (Si). A thin layer of amorphous Si eliminates a conductive layer generated in the thin-film bonding processes and contributes to acoustic energy confinement and thermal frequency stability. The gigahertz operating frequency is achieved by resorting to the guided acoustic wave shear-horizontal wave (SH0) in a 400-nm-thick X-cut LiNbO3 thin film. Due to the elimination of the parasitic surface conduction (PSC) effect, the electromechanical coupling of the guide acoustic wave is maximized in the Si-based heterogeneous wafer. Due to the minimized acoustic impedance mismatch between surface material and substrate, longitudinal and higher order spurious modes are suppressed. Due to the stiff substrate with a small temperature expansion coefficient (TEC), the solidly mounted structure features a reduced temperature coefficient of frequency (TCF) and improved power handling. The fabricated resonator shows an extracted electromechanical coupling coefficient of 22.8%, a high loaded <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula> of 1208 at 1.6 GHz, and a TCF of −36 p/min/K. The compressed filter is demonstrated with a minimum insertion loss (IL) of 0.6 dB, a fractional bandwidth (FBW) of 8%, an out-of-band rejection of 30 dB, a TCF of −38.5 p/min/K at roll-off, and a miniaturized footprint of 0.4 mm2. The performance has shown the strong potential of the LiNbO3–Si platform for front-end applications in 5G.

Large-Range Spurious Mode Elimination for Wideband SAW Filters on LiNbO₃/SiO₂/Si Platform by LiNbO₃ Cut Angle Modulation.

A LiNbO3 (LN)/SiO2/Si multilayered structure was recently reported as a new platform for achieving wideband radio frequency (RF) filters. However, the in-band ripples in filters resulting from the spurious Rayleigh mode lead to deteriorated performance, and thus, a wide Rayleigh elimination window (REW) is highly desired for realizing spurious-free wideband surface acoustic wave (SAW) filters with a wide design space and good process tolerance. Here, we investigated the spurious mode suppression on the LN/SiO2/Si platform theoretically and experimentally through modulating the cut angle ( θ ) of LN. The K2 dispersion characteristics of the main mode (shear-horizontal wave) and spurious mode (Rayleigh wave) on LN/SiO2/Si substrates were systematically analyzed by the finite-element method (FEM), along with bulk LN for comparison. It is found that the REW is wider on LN/SiO2/Si than bulk LN, as Rayleigh wave can be totally eliminated with Cu electrode normalized thickness ( [Formula: see text]) ranging from 0.1 to 0.19 when θ is between 19° and 22° on the LN/SiO2/Si platform, in contrast to the quite narrow REW on bulk LN restricted to some specific [Formula: see text]. To verify the simulation results, resonators were prepared on 15°YX-LN/SiO2/Si, 20°YX-LN/SiO2/Si, bulk 15°YX-LN, and bulk 20°YX-LN. In addition, the typical spurious-free wideband SAW filter with [Formula: see text] nm based on the 20°YX-LN/SiO2/Si platform demonstrates high performance with a center frequency ( [Formula: see text]) of 1.27 GHz, a minimum insertion loss (ILmin) of 0.7 dB, and a 3-dB fractional bandwidth (FBW) of ~20.1%. This work provides a workable solution in fabricating spurious-free wideband and low-loss SAW filters for fifth-generation (5G) applications.

An 11–40-GHz High-Power Switch With Miniaturized High-Order Topology Using 100-nm GaN-on-Si HEMTs

This article proposes an ultrawideband switch with miniaturized high-order topology. A 100-nm gate-length GaN-on-Si process is used for high-power capability, and the modeling of the GaN high-electron-mobility transistors (HEMTs) is given to analyze its parasitic values. For wideband or high isolation, the high-order switch is one solution, whose die area is naturally large. To address this issue, a miniaturized coupled-resonator switch topology was proposed using inverter transformation, where two parallel LC tanks and four inverters are replaced by two series LC tanks. Furthermore, a miniaturized coupling structure is introduced using a common inductor to replace three individual ones, contributing to an 86% size reduction. For demonstration, one 11–40.5-GHz single-pole single-throw (SPST) switch with four transmission poles (TPs) has been designed and fabricated. A small chip size of 0.32 mm2, low ON-state minimum insertion loss (IL) of 0.55 dB, and a high-power capability of 1.3 W are achieved.

Multi-frequency switch and excellent slow light based on tunable triple plasmon-induced transparency in bilayer graphene metamaterial ∗ ∗Project supported by National Natural Science Foundation of China (NSFC) (61605018, 11904032, 61841503).

We propose a novel bilayer graphene terahertz metamaterial composed of double graphene ribbons and double graphene rings to excite a dynamically adjustable triple plasma-induced transparency (PIT) effect. The coupled mode theory (CMT) is used to explain the PIT phenomenon, and the results of the CMT and the finite-difference time-domain simulation show high matching degree. By adjusting the Fermi levels of graphene, we have realized a penta-frequency asynchronous optical switch. The performance of this switch, which is mainly manifested in the maximum modulation depth (MD = 99.97%) and the minimum insertion loss (IL = 0.33 dB), is excellent. In addition, we have studied the slow-light effect of this triple-PIT and found that when the Fermi level of graphene reaches 1.2 eV, the time delay can reach 0.848 ps. Therefore, this metamaterial provides a foundation for the research of multi-frequency optical switches and excellent slow-light devices in the terahertz band.

Design Guidelines for a Tunable SOI Based Optical Isolator in a Partially Time-Modulated Ring Resonator

In this paper, we present the design guidelines for a tunable optical isolator in an SOI-based ring resonator with two small time-modulated regions. By considering a physical model, the proper geometrical and modulation parameters are designed, based on a standard CMOS foundry process. The effect of the variation of the key parameters on the performance of the isolator is explained by two counter-acting mechanisms, namely the separation between the resonance frequencies of counter-rotating modes and energy transfer to the side harmonic. We show that there is a trade-off between these parameters to obtain maximum isolation. Consequently, by applying the quadrature phase difference one can obtain the maximum separation between the resonance frequencies and hence the minimum insertion loss, while the maximum isolation is obtained at the modulation phase difference of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$-0.78\pi$</tex-math></inline-formula> , which leads to a higher insertion loss. Robustness of the design is investigated through a sensitivity analysis for the fabrication variations in the distance and width of the modulated regions. We demonstrate that there is a trade-off between isolation and insertion loss, and by varying the modulation parameters, we can achieve isolation of 18 (5) dB with 7 (1.8) dB insertion loss.