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We proposed an effective approach to enlarge the slow light bandwidth and normalized-delay-bandwidth product in an optimized moiré lattice-based photonic crystal waveguide that exhibits intrinsic mid-band characteristics. A flatband corresponding to a nearly constant group index of 34 over a wide bandwidth of 82 nm centered at 1550 nm with near-zero group velocity dispersion was achieved. A large normalized-delay-bandwidth product of 0.5712 with a relative dispersion of 0.114%/µm was obtained, which is a significant improvement if compared with previous results. Our results indicate that the photonic moiré lattice waveguide could advance slow light applications.

We present a single-layer, transmissive metalens for focusing the orthogonal polarization components of incident light to two independent focal spots without affecting the initial orthogonal polarization states. To produce the required phase profile, the cross-shaped nanorod, as the unit cell of the metalens, is developed to support arbitrary combinations of two independent phase shifts (0- $2\pi$ ) of transverse electric and transverse magnetic polarized light. A deep neural network is trained to generate the design parameters of each unit cell efficiently and accurately. The metalens is simulated with finite-difference time-domain method and good agreements are observed comparing with theoretical prediction. This work provides a new solution to multi-foci metalens and polarization beam splitter and may find potential applications in deep sensing, holography, information encryption and display.

Modified near-ballistic uni-traveling-carrier photodiodes with improved overall performances were studied theoretically and experimentally. A bandwidth up to 0.2 THz with a 3 dB bandwidth of 136 GHz and large output power of 8.22 dBm (99 GHz) under the −2V bias voltage were obtained. The device exhibits good linearity in the photocurrent-optical power curve even at large input optical power, with a responsivity of 0.206 A/W. Physical explanations for the improved performances have been made in detail. The absorption layer and the collector layer were optimized to retain a high built-in electric field around the interface, which not only ensures the smoothness of the band structure but also facilitates the near-ballistic transmission of uni-traveling carriers. The obtained results may find potential applications in future high-speed optical communication chips and high-performance terahertz sources.

We systematically investigated graphene-based slot and multi-slot waveguides. A tri-slot waveguide which significantly enhances the light-graphene interaction was experimentally demonstrated with low insertion loss. By integrating a dual-layer graphene h-BN heterostructure on the tri-slot waveguide, a high efficiency modulator is designed, which combines the advantages of high modulation efficiency (0.376 dB/μm), low insertion loss (0.01 dB/μm), large modulation bandwidth (∼0.13 THz) and low power consumption (∼0.128 pJ/bit). Our work may promote the development of future high efficient graphene-based optical devices.

This paper proposes flat bands and quasi-bound states in the continuum (Q-BIC) in a moiré lattice. In addition to the inter-layer coupling and small rotation angle, we show that the inter-node coupling in a single-layer moiré lattice can be controlled to obtain moiré flat bands. Unlike any flat bands reported in lattices such as kagome, rhombus, Lieb, and stub, we show that the moiré lattice exhibits both singular and non-singular flat bands simultaneously. We investigate the flat band’s eigenmodes to confirm their flatness and assess their singularity. The robustness of the flat bands to variation of background permittivity ε b is studied. Moreover, by further engineering the inter-node distance, the moiré flat band states change to a quasi-bound state at a non-zero wave vector. The Q-BIC exhibit an ultra-high quality factor (Q-factor) of 2.7142 × 10 6 , ultra-low mode volume of 0.214318 µ m 3 , and very narrow linewidth centred at 350.54 THz. We demonstrate the capability of the Q-BIC for lasing and nanocavity applications. Our results show that a single-layer photonic moiré lattice provides a suitable platform to explore fundamental phenomena related to flat band systems.

Electromagnetically induced transparency like effect, which can form a sharp transmission window within a broad spectrum, has been widely studied due to its potential in many optical devices. In this work, unlike traditional couple-ring resonator structure, we propose a new scheme to achieve electromagnetically induced transparency using only one hole-ring resonator. Thus, the proposed scheme can greatly miniaturize the device. At the wavelength of about 1550 nm, the structure can form multiple transparency windows and can behave as a refractive index sensor with high resolution, the figure of merit can reach larger than 530. The proposed scheme can pave the way for many practical applications such as optical sensors, optical switches and slow light devices.

We report a highly efficient graphene-based modulator by using an edge plasmonic effect in this paper. The modulation efficiency of the proposed modulator can be as large as 1.58 dB/μm, which is several times larger than that of previous reported modulators. By enhancing the gap plasmon mode and the edge plasmonic effect in a well-designed diagonal waveguide, a wedge-to-wedge SPP mode is strongly confined in both horizontal and vertical directions in terms of a small mode area (Aef /A0

This paper presents an L-2L de-embedding method for characterizing the electromagnetic properties of through-silicon-vias (TSVs) in 3-D ICs. To the best of our knowledge, this is the first paper that discusses the use of de-embedding method for multiport TSVs. The L-2L de-embedding structure and the analysis algorithm are first introduced. Then, the techniques for meeting two crucial requirements in accurately applying the method on multiport TSVs are proposed. To meet these two requirements, the de-embedding structure is designed to enhance the symmetry and the shielding TSVs are used to decrease the mutual admittance. The simulation results show that with the appropriate design, the shielding TSVs are able to greatly reduce the mutual admittance with little impact on TSVs and RDLs. Finally, the performance of the designed structures with and without shielding TSVs is examined via both full-wave simulation and the measurements. With the full-wave simulation results of TSVs as reference, it turns out that the de-embedding accuracy is significantly improved with the shielding TSVs. Moreover, the de-embedding results based on the measurements show good agreements with those of the simulation ones.

This paper presents a series of scalable equivalent circuits using an analytical method describing the electromagnetic coupling in the lightly doped CMOS substrate and the isolation structures such as the implanted guard ring. Implemented in Grace Semiconductor Manufacturing Corporation (GSMC) generic 0.13μm RF CMOS technology, the measurement and full-wave simulation are carried out to verify the proposed models in a broad frequency band ranging from 100 MHz to 40 GHz. By analyzing these layout-dependant models in detail, some layout and substrate characteristics impacting on guard ring performance are concluded and the design flow with guidelines for the guard ring structures implementation in engineering practice for RF signal isolation are presented.

A low-profile broadband bandpass frequency selective surface (FSS) with two rapid band edges is proposed in this paper for 5G near-field applications. The overall structure consists of three metallic layers, separated by two thin substrates with a thickness of 0.07λ. In addition, some centro-symmetric miniaturized slots are introduced in the middle metallic layer to further improve its stability and reduce its physical dimensions. A corresponding equivalent circuit model (ECM) is also proposed to better analyze the principles of the proposed FSS. Finally, an FSS prototype working at the center frequency of 27.5 GHz with a relative -3 dB bandwidth of 20.5% is fabricated and measured. More than 25 dB shielding effectiveness can be obtained out of the passband for a bandwidth of 1.46 GHz in this experiment. Both 3-D full-wave simulations and ECM results are in good agreement with the experimental results, having a maximum deviation of only 2.257% in the transmission zeros and poles. These results demonstrate that the proposed FSS is a good candidate for 5G near-field EMI shielding.

Being invisible at will has been a long-standing dream for centuries, epitomized by numerous legends; humans have never stopped their exploration steps to realize this dream. Recent years have witnessed a breakthrough in this search due to the advent of transformation optics, metamaterials, and metasurfaces. However, the previous metasurface cloaks typically work in a reflection manner that relies on a high-reflection background, thus limiting the applications. Here, we propose an easy yet viable approach to realize the transmitted metasurface cloak, just composed of two planar metasurfaces to hide an object inside, such as a cat. To tackle the hard-to-converge issue caused by the nonuniqueness phenomenon, we deploy a tandem neural network (T-NN) to efficiently streamline the inverse design. Once pretrained, the T-NN can work for a customer-desired electromagnetic response in one single forward computation, saving a great amount of time. Our work opens a new avenue to realize a transparent invisibility cloak, and the tandem-NN can also inspire the inverse design of other metamaterials and photonics.

An all-fiber structured electro-absorption (EA) modulator based on graphene is proposed. The graphene is directly attached to the core of the fiber to ensure the coupling efficiency. Mode analysis is used to reveal the light modulation mechanism under the anisotropic graphene modeling, which is merely conducted in previous studies. Compared with conventional semiconductor EA modulators, it exhibits an excellent performance with the advantages such as small footprint (50.2 μm), small voltage swing (0.2 V), and broad operation bandwidth. In addition, the proposed modulator features simple structure, low optical propagation and coupling loss, and good integrated compatibility as the fiber modulator. All these edges prospect the great potentiality in future high-speed optic fiber communications, optical signal processing, and all-fiber systems.

This publisher’s note contains corrections to Opt. Lett. 44, 2586 (2019)OPLEDP0146-959210.1364/OL.44.002586.

This letter presents a novel graphene-embedded optical ring modulator that significantly enhances the modulation efficiency and tunability. Due to the enhanced light-matter interaction of graphene-embedded design, the shift rate of the resonance peak has been improved to 1.08 nm per applied voltage, which is two orders of the magnitude higher than previous ring modulators. The narrow bandwidth of the resonant modulator has been ameliorated to 149 GHz. In addition, our proposed modulator exhibits the advantages of high extinction ratio (22.13 dB) and smaller power consumption. Furthermore, a good tolerance of temperature drift (27 K) has been demonstrated in the proposed modulator.

The power distribution network (PDN) impedance of 3-D-through silicon vias (TSVs) interposer layer is modeled by considering the metal-oxide-semiconductor (MOS) structure effects. The Lambert W function is proposed to simulate the change of depletion width with the bias voltage in the static field, and the high-frequency MOS capacitance is obtained while considering the charges at the semiconductor-insulator interface. Furthermore, based on the depletion width and the insulating dielectric layer assumption, the electrical model of power-ground TSVs pair is presented by combining the MOS capacitance with TSVs parasitic RLGC (resistance-inductance-capacitance-conductance). Finally, the PDN impedance characteristics of the 3-D-IC integrated system with multiple TSVs are performed by using the proposed multitransmission line and model reduction methods, and the importance of the capacitance is presented.

In this paper, we propose a novel double-shielded interposer design with two metal layers directly contacting to the silicon substrate surfaces for high-speed signal propagating along through silicon vias (TSVs). To enhance the shielding effects, shallow highly doped silicon is made on both sides of the silicon interposer forming ohmic contact between the metallization layer and silicon. The metallization layer is etched into meshed pattern to prevent delamination. Based on the imaging method, we derive the equivalent circuit model of the proposed double-shielded interposer, and the accuracy and efficiency of the equivalent circuit model is verified by full-wave method. The proposed design can concentrate the electromagnetic field around TSVs, so that it has a lower insertion loss than the conventional ground-signal (GS) structure without shielding. This is especially useful when the low-resistivity silicon is used for the interposer. Finally, some applied guidelines are proposed to strengthen the performance and simplify the silicon fabrication processes.

We propose a graphene-based modulator integrated into currently used communication fibers. The graphene is directly built into the core of the fiber to ensure the coupling efficiency. The fiber is deliberately side-polished to enhance the light-graphene interaction. The two-dimensional model analysis method and three-dimensional finite difference time domain method are used to rigorously disclose the light modulation mechanism under the anisotropic graphene modeling, which is merely conducted in previous studies. Based on such a structure, a phase modulator with an arm length of 127 μm is numerically demonstrated with enhanced modulation efficiency. A quasi-linear relation between the phase change and chemical potential of graphene is found theoretically for the first time, providing a large linear dynamic range to control the phase of optical modulation.

The investigation of few-layer graphene embedded in silicon waveguide (GESW) exhibits it has a superior performance than monolayer GESW where the effective mode index variation ( Δ n e f f ) at the given chemical potential change and the number of graphene layers N (N Δ n e f f of quadri-layer GESW can be as large as 0.047, based on which a Mach–Zehnder modulator has been proposed with the advantages of only 16.5 μm arm length, low energy consumption (8 fJ/bit), high extinction ration (31.8 dB) and small applied voltage (

In this Letter, we report a graphene-based hybrid plasmonic modulator (GHPM) realized by employing the electro-absorption effect of graphene. The simulation results show that the modulation efficiency of GHPM, i.e., extinction ratio per length, can be as large as 0.417 dB/μm, which is more than twice as much as that of recently presented graphene-on-silicon modulator. It was found that the improvement in modulation efficiency is mainly due to the enhancement of the overlap between graphene and the mode field in GHPM. A prototype of GHPM was fabricated. The measurement results showed that the GHPM can work in a broadband from 1530 to 1570 nm and an improved modulation efficiency of 1.08 dB (at 30 μm). Finally, we have discussed the factors that influence the modulation efficiency. Our proof-of-concept design may promote the development of on-chip graphene-based plasmonic devices.

We analyze and optimize the performance of unconventional negative permeability (μ) metamaterial and demonstrate its ability to focus and restore the decaying Fourier harmonics (FH) in microwave regime operating frequencies. We show that multiple real μr' and imaginary μr'' values of μr at same or multiple operating frequencies for a resonant type of -μ metamaterial could not exhibit finest resolution at the region of interest (ROI), unless and until the distance of the source plane with respect to metamaterial and ROI could be re-optimized in accordance with μr' and μr'' of μr. Using the variable parameters to enhance the resolution limit of -μ metamaterial, we optimize the metamaterial's configuration for maximum propagation field absorption and regeneration of decaying FH at ROI. The optimization of the test bed that contains the source plane, -μ metamaterial, and ROI followed by the regeneration of the decaying FH from the source plane at the surface of the material, yielded a high image resolution at ROI.

Slow light, a technology to control the optical signal by reducing the group velocity, has been widely studied to obtain enhanced nonlinearities and increased phase shifts owing to its promoting of the light–matter interaction ability. In this work, a wideband slow light is achieved in a simple one-dimensional fishbone grating waveguide. A flat band indicating slow light with a group index of 13 and bandwidth over 10 nm is obtained by the plane wave expansion calculation, and the corresponding experimental results agree well with the theoretical prediction. A step taper is designed to compensate the coupling loss. The proposed fishbone grating waveguide is a good candidate for wideband slow light devices in light communication.

The energy-momentum dispersion relation is a fundamental property of plasmonic systems. In this paper, we show that the method of dispersion engineering can be used for the design of ultra-compact graphene-based superscatterers. Based on the Bohr model, the dispersion relation of the equivalent planar waveguide is engineered to enhance the scattering cross section of a dielectric cylinder. Bohr conditions with different orders are fulfilled in multiple dispersion curves at the same resonant frequency. Thus the resonance peaks from the first and second order scattering terms are overlapped in the deepsubwavelength scale by delicately tuning the gap thickness between two graphene layers. Using this ultra-compact graphene-based superscatterer, the scattering cross section of the dielectric cylinder can be enhanced by five orders of magnitude., This paper has been accepted by IEEE Journal of Selected topics in Quantum Electronics

The effects of process-induced disorder location on planar photonic crystal waveguide properties are numerically investigated using three-dimensional finite difference time domain simulation by introducing random fluctuations of the hole radius, size, position, and shape of air-holes of two-dimensional planar photonic crystal slab. Results reveal that bandgap properties are extremely robust with respect to disorder. It is shown that the very first rows of holes play a major role in the amount of disorder-induced optical loss, and that keeping the first two rows of holes unchanged leads to a blue-shift of slow light waveguide properties.

An ultra-compact and low-loss transverse-electric (TE)-pass polarizer is proposed by utilizing a hybrid plasmonic ridge waveguide structure on a silicon-on-insulator platform. Since the transmission of a plasmonic polarizer is greatly influenced by the interaction between the metal and the optical field, there is a large insertion loss (IL) in the polarizer based on a hybrid plasmonic waveguide. Here, the electric field distribution and the periodic coupling between the fundamental transverse magnetic mode and plasmonic mode are taken into consideration to decrease the IL and shorten the length of the device. For a 4.2 μm-long polarizer, numerical simulations with the finite-differential-time-domain method show that it has a large extinction ratio (ER) of ∼29.5 dB with a low IL of 0.18 dB at the central wavelength 1550 nm. In addition, a more than 23 dB ER is achieved across a wide bandwidth of 100 nm.

This letter proposes a novel demodulation method for fiber-optic interferometer sensors. A fast square wave is added to the reference arm of the interferometer sensor in the form of phase modulation. Starting from this, we successfully developed a simple demodulation method that can greatly improve the conversion efficiency and overcome the unbalanced influences. Our experiment results show that a very small phase shift of about 6.3 × 10-5 rad can be detected, which proves high signal-to-noise ratio demodulated signal and low distortion in our demodulation method. The linearity between demodulated signal and test signal is shown to be over 99%.

Metasurfaces, the phase-engineered quasi-2D interfaces, have attracted intensive interest due to their great capabilities in manipulating the reflection, refraction and transmission of electromagnetic waves. Here, we demonstrate the design and realization of a gradient chiral metamirror tailored for spin-selective anomalous reflection based on the theory of Pancharatnam-Berry phase. Asymmetric split ring resonators are employed as the basic meta-atoms for strong circular dichroism. Dispersionless phase discontinuities are achieved by adjusting the orientation of the meta-atoms, and spin-dependent absorption is realized by introducing a chiral resonance. Theoretical results predict both broadband beam deflection and spin-selective absorption for circularly polarized waves in a designer metamirror. Experimental verification of this bifunctional performance is implemented at microwave frequencies and the measured results agree well with the simulation ones. Such chiral metamirrors could pave an avenue towards spin-selective modulation of the wavefront and might find promising applications in planar electromagnetic devices.

We propose a highly efficient graphene-on-gap modulator (GOGM) by employing the hybrid plasmonic effect, whose modulation efficiency (up to 1.23 dB/μm after optimization) is ∼12-fold larger than that of the present graphene-on-silicon modulator (∼0.1 dB/μm). The proposed modulator has the advantage of a short modulation length of ∼3.6 μm, a relatively low insertion loss of ∼0.32 dB, and a larger modulation bandwidth of ∼0.48 THz. The physical insight is investigated, showing that both the slow light effect and the overlap between graphene and the mode field contribute. Moreover, an efficient taper coupler has been designed to convert the quasi-transverse electric mode of conventional silicon waveguide to the hybrid plasmonic mode of GOGM, with a high coupling efficiency of 91%. This Letter may promote the design of high-performance on-chip electro-optical modulators.

Enlarged group index has been reported previously when surface plasmons propagate through the graphene sheet, yet a clear slow wave performance in graphene has not been explored. We proposed and numerically analyzed here for the first time to the best of our knowledge an extremely wideband slow surface wave in a graphene-based grating waveguide. The strongly delayed wave (120n(g)167) with extremely large bandwidth (2.7 THzΔf0.7 THz) can be dynamically controlled via the gate-voltage dependent optical properties of graphene. Our results suggest that graphene may be a very promising slow light medium, promoting future slow light devices based on graphene.

Wideband slow light away from band edge in one-dimensional (1-D) structure is proposed and theoretically investigated for the first time. With carefully chosen structure parameters of the 1-D holey grating waveguide, an ideal chair shape band with unique inflection points of high group index beyond 1000 can be obtained. By chirping the structure according to the scaling law, wideband up to 31-nm slow light pulse propagation with a moderate group index of 14.6 is demonstrated by finite-difference time-domain simulation, and the relative pulse shape expansion is only 2.34%.

A novel type of semislow light photonic crystal waveguide obtained by shifting the boundaries of a W1 waveguide in the direction of light propagation is presented. The structure produces unusual "U-type" group index -frequency curves, which results in a nearly constant group index ng over large bandwidth. A versatile control of ng (11

Flat band slow light in symmetric line defect photonic crystal waveguides formed by adding dielectric pillars in the air holes nearest to the waveguide core is investigated. By adjusting the radii of the new dielectric pillars, a linear band in the photonic band structure appears which denotes low group velocity dispersion. High average group index of 74.4 with 2.3-nm bandwidth is demonstrated in an optimized waveguide by finite-difference time-domain simulation.

We present the design of realistic annular photonic-crystal (APC) structures of finite thickness aiming to obtain a complete photonic bandgap (PBG). The APC is composed of dielectric rods and circular air holes in a triangular lattice such that each rod is centered within each hole. The optical and geometrical values of the structure are studied, and the interplay between various design parameters is highlighted. The coupled role of the inner-dielectric-rod radius, material types, and slab thickness is investigated. It is shown that the slab thickness is vital to obtain a complete photonic bandgap below the light line, and the specific value of the inner-dielectric-rod radius to sustain the maximum PBG if the hole radius is fixed at proper value is found.

We present a hybrid graphene–silicon waveguide, which consists of a lateral slot waveguide with three layers of graphene flakes inside. Through a theoretical analysis, an effective index variation for about 0.05 is found in the waveguide by applying a voltage on the graphene. We designed a Mach–Zehnder modulator based on this waveguide and demonstrated it can process signals nearly chirp-free. The calculation shows that the driving voltage is only 1 V even if the length of the arm is shortened to be 43.54 μm. An extinction up to 34.7 dB and a minimum chirp parameter of −0.006 are obtained. Its insertion loss is roughly −1.37 dB. This modulator consumes low power and has a small footprint. It can potentially be ultrafast as well as CMOS compatible.

A hybrid plasmonic parallel transmission line scheme constructed by a spatial single mode with time-domain multiline waveguide is presented in this paper. The proposed configuration enables a nanometer light localization while retaining a long propagation distance (~74 μm) at optical communication wavelengths with no crosstalk between data channels. High extinction ratio between the nanoribs peak energies (~20 dB) has been achieved after optimization. Furthermore, the proposed optical parallel transmission line scheme shows the advantages of enabling an optical device with a large number of parallel transmission channels, as well as a good robustness with respect to the fabrication tolerances.

We report a numerical study of plasmonic waveguides that localize light in two dimensions at a cross section of 4.2 nm × 2.1 nm with the propagation length of 38 μm. By varying the geometrical parameters, strong mode confinements (range from λ(2)/3352 to λ(2)/2557525) are achieved with controllable propagation distance (44.68-40.988 μm), and mode size below 1 nm(2) has been demonstrated for the first time. Furthermore, a cross-index-modulation mechanism is proposed to explain the strong field localization behavior, providing guidelines for future waveguide designs.

This paper is devoted to the study of a polarization independent reflector made with a multilayered configuration grating structure with a multi-subpart profile. Rigorous coupled-wave analysis for multilayered grating structures is adopted to investigate the properties of the reflector. It is shown that over a broadband spectrum of 1.57–1.8 µm, the reflector demonstrates high reflectivity (R > 99%) and a wide angular bandwidth (about 21.2°) for both transverse electric (TE) and transverse magnetic (TM) polarized waves. Effects of deviation from the design parameters on the performance of the reflector are also presented, and a reasonable tolerance of fabrication error is exhibited in the proposed device.

In this paper, we propose a broadband compact polarizing beam splitter (PBS) constructed by only a single layer subwavelength asymmetric profile grating. The properties of the grating PBS are investigated by rigorous coupled-wave analysis. It is shown that, over a broadband spectrum of 1.53–1.62 µm, the grating PBS demonstrates high diffraction efficiencies (>97%) with extinction ratio (ER) greater than 16 dB and a comparatively wide angular bandwidth (about 8 ◦ ). Effects of deviation from the design parameters on the performance of the grating PBS are

We demonstrate a novel type of slow light photonic crystal waveguide which can produce unusual "U" type group index - frequency curves with constant group index n(g) over large bandwidth. By shifting the boundaries of this waveguide, flexible control of n(g) (10n(g)210) with large bandwidth (1nmDeltalambda43nm centered at 1550nm) and normalized Delay-Bandwidth Product (0.1363DBP0.3143) are achieved. Additionally, depending on the chosen waveguide geometry, extremely low group velocity dispersion (GVD0.5 ps x nm(-1) x mm(-1)), with controllable group velocity dispersion of both signs is obtained.