Showing papers on "Coupled mode theory published in 2020"
TL;DR: In this paper, a biorthogonal approach for modeling the response of localized electromagnetic resonators using quasinormal modes is presented, which represent the natural, dissipative eigenmodes of the system with complex frequencies.
Abstract: We present a biorthogonal approach for modeling the response of localized electromagnetic resonators using quasinormal modes, which represent the natural, dissipative eigenmodes of the system with complex frequencies. For many problems of interest in optics and nanophotonics, the quasinormal modes constitute a powerful modeling tool, and the biorthogonal approach provides a coherent, precise, and accessible derivation of the associated theory, enabling an illustrative connection between different modeling approaches that exist in the literature.
90 citations
TL;DR: In this paper, an analytical model analysis of reflection/transmission characteristics of long-period fiber Bragg grating (LPFBG) by using coupled mode theory is presented.
Abstract:
This study presents an analytical model analysis of reflection/transmission characteristics of long-period fiber Bragg grating (LPFBG) by using coupled mode theory. Reflected signal power is deeply studied against grating length at the optimum operating signal wavelength of 1550 nm for the proposed and previous models. Reflectivity and transmission coefficient are also clarified versus operating wavelength for the previous model and proposed a model with a central wavelength of 1550 nm, Δn = 0.003 and optimum grating length of 30 mm. In the same way, the reflectivity and transmission coefficient are outlined against relative refractive grating difference step at the optimum wavelength of 1550 nm and optimum grating length of 30 mm. The optimum LPFBG can be achieved with the optimum grating length of 30 mm, operating wavelength of 1550 nm and relative refractive grating difference step of 0.3 %.
85 citations
20 Nov 2020
TL;DR: In this article, an analytical model based on temporal coupled mode theory is proposed to realize an "accidental" (i.e., parameter-tuned) Friedrich-Wintgen BIC.
Abstract: The concept of “bound states in the continuum” (BIC) describes an idealized physical system exhibiting zero radiative loss composed, for example, of an infinitely extended array of resonators. In principle, vanishing of radiative losses enables an infinitely high-quality factor and corresponding infinite lifetime of the resonance. As such, BIC inspired metasurfaces and photonic designs aim to achieve superior performance in various applications including sensing and lasing. We describe an analytical model based on temporal coupled mode theory to realize an “accidental” (i.e., parameter-tuned) Friedrich–Wintgen BIC. Further, we experimentally verify this model with measurements of quasi-BICs in a metallic terahertz metasurface (MS) and the corresponding complementary metasurface (CMS) using terahertz time domain spectroscopy. For the MS and CMS structures, quality factors of ∼20 are achieved, limited by non-radiative intrinsic loss in the materials. Our results reveal that Babinet’s principle qualitatively holds for the MS and CMS quasi-BIC structures. In addition, ultra-high electric and magnetic field enhancement MS and CMS structures, respectively, are presented.
85 citations
TL;DR: The results show that the quality factor and dephasing time for the Fano resonance can be effectively tuned by the thickness of Au and TiO2 structures, the length of each unit in x and y directions, as well as the structural defect, and multiple Fano resonances can be tuning by the size and position of the stub-shaped defect.
Abstract: We investigate Fano resonances and sensing enhancements in a simple Au/TiO2 hybrid metasurface through the finite-different time-domain (FDTD) simulation and coupled mode theory (CMT) analysis. The results show that the Fano resonance in the proposed simple metasurface is caused by the destructive interaction between the surface plasmon polaritons (SPPs) and the local surface plasmon resonances (LSPRs), the quality factor and dephasing time for the Fano resonance can be effectively tuned by the thickness of Au and TiO2 structures, the length of each unit in x and y directions, as well as the structural defect. In particular, single Fano resonance splits into multiple Fano resonances caused by a stub-shaped defect, and multiple Fano resonances can be tuned by the size and position of the stub-shaped defect. Moreover, we also find that the sensitivity in the Au/TiO2 hybrid metasurface with the stub-shaped defect can reach up to 330 nm/RIU and 535 nm/RIU at the Fano resonance 1 and Fano resonance 2, which is more than three times as sensitive in the Au/TiO2 hybrid metasurface without the stub-shaped defect, and also higher than that in the TiO2 metasurface reported before. These results may provide further understanding of Fano resonances and guidance for designing ultra-high sensitive refractive index sensors.
73 citations
TL;DR: This research provides a significant design guide for developing tunable multi-resonant THz devices based on all-dielectric configuration and physical mechanism is deeply revealed with magnetic and electric field distributions, which demonstrate a totally different principle with traditional plasmonic absorber.
Abstract: In this paper, we theoretically design a dual-band graphene-based terahertz (THz) absorber combining the magnetic resonance with a THz cold mirror without any metallic loss. The absorption spectrum of the all-dielectric THz absorber can be actively manipulated after fabrication due to the tunable conductivity of graphene. After delicate optimization, two ultra-narrow absorption peaks are achieved with respective full width at half maximum (FWHM) of 0.0272 THz and 0.0424 THz. Also, we investigate the effect of geometric parameters on the absorption performance. Coupled mode theory (CMT) is conducted on the dual-band spectrum as an analytic method to confirm the validity of numerical results. Furthermore, physical mechanism is deeply revealed with magnetic and electric field distributions, which demonstrate a totally different principle with traditional plasmonic absorber. Our research provides a significant design guide for developing tunable multi-resonant THz devices based on all-dielectric configuration.
55 citations
TL;DR: The cross-circle resonance structure provides novel potential for the design of a dual-band unpatterned graphene perfect absorber in the near-infrared band, and possesses practical application significance in photoelectric detectors, modulators, optical switching, and numerous other photoelectric devices.
Abstract: The combination of critical coupling and coupled mode theory in this study elevated the absorption performance of a graphene-based absorber in the near-infrared band, achieving perfect absorption in the double bands (98.96% and 98.22%), owing to the guided mode resonance (the coupling of the leak mode and guided mode under the condition of phase matching, which revealed 100% transmission or reflection efficiency in the wavelet band), and a third high-efficiency absorption (91.34%) emerged. During the evaluation of the single-structure, cross-circle-shaped absorber via simulation and theoretical analysis, the cross-circle shaped absorber assumed a conspicuous preponderance through exploring the correlation between absorption and tunable parameters (period, geometric measure, and incident angle of the cross-circle absorber), and by briefly analyzing the quality factors and universal applicability. Hence, the cross-circle resonance structure provides novel potential for the design of a dual-band unpatterned graphene perfect absorber in the near-infrared band, and possesses practical application significance in photoelectric detectors, modulators, optical switching, and numerous other photoelectric devices.
48 citations
TL;DR: The insights gained into the synchronous or asynchronous switching and the polarization sensitivity of triple-PIT provide a valuable platform and ideas to inspire the design of novel optoelectronic devices.
Abstract: A monolayer graphene metamaterial comprising four graphene strips and four graphene blocks is proposed to produce triple plasmon-induced transparency (PIT) by the interaction of three bright modes and one dark mode. The response of the proposed structure is analyzed by using couple mode theory and finite-difference time-domain simulations, with the results of each method showing close agreement. A quadruple-mode on-to-off modulation based on synchronous or asynchronous switching is realized by tuning the Fermi levels in the graphene, its modulation degrees of amplitude are 77.7%, 58.9%, 75.4%, and 77.6% corresponding to 2.059 THz, 2.865 THz, 3.381 THz, and 3.878 THz, respectively. Moreover, the influence of the polarized light angle on triple-PIT is investigated in detail, demonstrating that the polarization angle affects PIT significantly. As a result, a multi-frequency polarizer is realized, its polarization extinction ratios are 4.2 dB, 7.8 dB, and 12.5 dB. Combined, the insights gained into the synchronous or asynchronous switching and the polarization sensitivity of triple-PIT provide a valuable platform and ideas to inspire the design of novel optoelectronic devices.
43 citations
TL;DR: The work provides a new method for designing terahertz multi-function switches and optical storages that can generate a significant triple plasmon-induced transparency (triple-PIT) and an excellent optical storage.
Abstract: A terahertz metasurface consisting of a graphene ribbon and three graphene strips, which can generate a significant triple plasmon-induced transparency (triple-PIT), is proposed to realize a multifunction switch and optical storage. Numerical simulation triple-PIT which is the result of destructive interference between three bright modes and a dark mode can be fitted by coupled mode theory (CMT). The penta-frequency asynchronous and quatary-frequency synchronous switches can be achieved by modulating the graphene Fermi levels. And the switch performance including modulation depth (83.5% < MD < 93.5%) and insertion loss (0.10 dB < IL < 0.26 dB) is great excellent. In addition, the group index of the triple-PIT can be as high as 935, meaning an excellent optical storage is achieved. Thus, the work provides a new method for designing terahertz multi-function switches and optical storages.
40 citations
TL;DR: The intersection of high quality-factor resonances, active materials, and ultrafast transient spectroscopy leads to the demonstration of metasurfaces operating in a time-variant regime that enables enhanced control over light-matter interaction.
Abstract: The color of light is a fundamental property of electromagnetic radiation; as such, control of the frequency is a cornerstone of modern optics. Nonlinear materials are typically used to generate new frequencies, however the use of time-variant systems provides an alternative approach. Utilizing a metasurface that supports a high-quality factor resonance, we demonstrate that a rapidly shifting refractive index will induce frequency conversion of light that is confined in the nanoresonator meta-atoms. We experimentally observe this frequency conversion and develop a time-dependent coupled mode theory model that well describes the system. The intersection of high quality-factor resonances, active materials, and ultrafast transient spectroscopy leads to the demonstration of metasurfaces operating in a time-variant regime that enables enhanced control over light-matter interaction.
37 citations
TL;DR: In this paper, the authors proposed a multipolar model to capture the physics behind linear and nonlinear response driven by high-quality supercavity modes in subwavelength particles.
Abstract: We put forward the multipolar model which captures the physics behind linear and nonlinear response driven by high-quality (high-Q) supercavity modes in subwavelength particles. We show that the formation of such trapped states associated with bound states in the continuum (quasi-BIC) can be understood through multipolar transformations of coupled leaky modes. The quasi-BIC state appears with increasing the order of the dominating multipole, where dipolar losses are completely suppressed. The efficient optical coupling to this state in the AlGaAs nanodisk is implemented via azimuthally polarized beam illumination matching its multipolar origin. We establish a one-to-one correspondence between the standard phenomenological non-Hermitian coupled-mode theory and multipolar models. The derived multipolar composition of the generated second-harmonic radiation from the AlGaAs nanodisk is then validated with full-wave numerical simulations. Back-action of the second-harmonic radiation onto the fundamental frequency is taken into account in the coupled nonlinear model with pump depletion. A hybrid metal-dielectric nanoantenna is proposed to augment the conversion efficiency up to tens of per cent due to increasing quality factors of the involved resonant states. Our findings delineate novel promising strategies in the design of functional elements for nonlinear nanophotonics applications.
36 citations
TL;DR: A basic plasmonic system, consisting of a stub metal-insulator-metal (MIM) waveguide coupled with a ring resonator, is presented to realize Fano resonance and electromagnetically induced transparency-like (EIT-like) effect, which are numerically calculated by the finite element method.
Abstract: A basic plasmonic system, consisting of a stub metal-insulator-metal (MIM) waveguide coupled with a ring resonator, is presented to realize Fano resonance and electromagnetically induced transparency-like (EIT-like) effect, which are numerically calculated by the finite element method (FEM). Meanwhile, the formation mechanism of Fano resonance is analyzed according to numerical simulations. Besides, the coupled mode theory (CMT) and the standing wave theory are used for explaining the Fano and EIT-like resonances phenomenon. Based on this system, an inner ring cavity is connected to the ring resonator by a slot and another ring cavity is later introduced under the stub resonator in order to constitute a new coupled plasmonic resonator system, providing quadruple Fano resonances and double EIT-like responses finally. In addition, the Fano and EIT-like resonances can be independently tuned by adjusting the structural parameters, which makes the design of highly integrated photonic circuits more flexible. The main contribution of this paper is that the proposed structure has a relatively good sensitivity of 1600 nm/RIU and an ultra-high FOM value of $1.2\times 10^{6}$ as a refractive index nanosensor. Moreover, it can serve as an all-optical switch with a high on/off extinction ratio of about 43 dB. Additionally, its maximum group delay time and group index are about 1.49 ps and 221, indicating that the proposed system has a pretty good slow light effect. Therefore, the proposed structures are believed to have significant applications in high-performance nanosensors, switches, slow light devices and nonlinear areas in highly integrated plasmonic devices.
TL;DR: The experiments demonstrate that one fabricated AS-LPFG can convert the LP01 mode to the third-azimuthal-order (3AO, LP31 or OAM±3) guided mode with efficiency of ∼99.8%.
Abstract: The third-order orbital angular momentum (OAM±3) guided mode generation is demonstrated for the first time, to the best of our knowledge, by employing an asymmetric long-period fiber grating (AS-LPFG). The proposed AS-LPFG is modeled by coupled local-mode theory, which is extended to the coupling of core modes and is fabricated by multicycle scanning ablation with increasing power in a six-mode fiber. The experiments demonstrate that one fabricated AS-LPFG can convert the LP01 mode to the third-azimuthal-order (3AO, LP31 or OAM±3) guided mode with efficiency of ∼99.8%. The model and the method presented, in principle, can be used to generate any other high-order modes.
TL;DR: A multilayer patterned graphene metamaterial composed of rectangular graphene, square graphene, and X-shaped graphene is proposed to achieve dual plasmon-induced transparency (PIT) at terahertz frequency and it is reasonable to believe that a multifunctional device can be realized by the proposed structure.
Abstract: A multilayer patterned graphene metamaterial composed of rectangular graphene, square graphene, and X-shaped graphene is proposed to achieve dual plasmon-induced transparency (PIT) at terahertz frequency. The coupled mode theory calculations are highly consistent with the finite-difference time-domain numerical results. Interestingly, a photoelectric switch has been realized, whose extinction ratio and modulation degree of amplitude can be 7.77 dB and 83.3% with the insertion loss of 7.2%. In addition, any dips can be modulated by tuning the Fermi levels of three graphene layers with minor or ignorable changes of the other two dips. The modulation degrees of frequency are 8.0%, 7.4% and 11.7%, respectively, which can be used to design a triple-mode frequency modulator. Moreover, the group index of the multilayer structure can be as high as 150. Therefore, it is reasonable to believe that a multifunctional device can be realized by the proposed structure.
TL;DR: In this article, a plasmonic structure made up of a metal baffle in the middle of the metal-insulator-metal (MIM) waveguide coupled with an isosceles triangular cavity is reported to achieve triple Fano resonances.
TL;DR: Ultra-compact mode-order converters with dielectric slots are demonstrated on a silicon-on-insulator platform and two mode converters that convert the TE0 mode into the TE1 mode and the TE2 mode with footprints of 0.8×1.2µm2 are proposed.
Abstract: Ultra-compact mode-order converters with dielectric slots are demonstrated on a silicon-on-insulator platform. We propose a mode converter that converts the TE0 mode into the TE1 mode with an ultra-small footprint of only 0.8×1.2µm2. The measured insertion loss is less than 1.2 dB from 1520 nm to 1570 nm. To reduce the insertion loss, we further optimize the structure and design two mode converters that convert the TE0 mode into the TE1 mode and the TE2 mode with footprints of 0.88×2.3µm2 and 1.4×2.4µm2, respectively. Their measured insertion losses are both less than 0.5 dB. Additionally, the proposed devices are cascadable and scalable for high-order mode conversion.
TL;DR: This work investigates the coupling mechanism between a plasmonic resonator array and a waveguide using temporal coupled-mode theory and numerical simulation and concludes that the waveguide transmission extinction ratio reaches maxima when the resonator-waveguide coupling rate is maximal.
Abstract: Advances in mid-IR lasers, detectors, and nanofabrication technology have enabled new device architectures to implement on-chip sensing applications. In particular, direct integration of plasmonic resonators with a dielectric waveguide can generate an ultra-compact device architecture for biochemical sensing via surface-enhanced infrared absorption (SEIRA) spectroscopy. A theoretical investigation of such a hybrid architecture is imperative for its optimization. In this work, we investigate the coupling mechanism between a plasmonic resonator array and a waveguide using temporal coupled-mode theory and numerical simulation. The results conclude that the waveguide transmission extinction ratio reaches maxima when the resonator-waveguide coupling rate is maximal. Moreover, after introducing a model analyte in the form of an oscillator coupled with the plasmonics-waveguide system, the transmission curve with analyte absorption can be fitted successfully. We conclude that the extracted sensing signal can be maximized when analyte absorption frequency is the same as the transmission minima, which is different from the plasmonic resonance frequency. This conclusion is in contrast to the dielectric resonator scenario and provides an important guideline for design optimization and sensitivity improvement of future devices.
TL;DR: A universal overview of the rapidly developing photonic molecules quantum optics field, including fundamental mechanisms, realization frameworks, novel quantum optical phenomena, and applications in newly developed photonic devices while also giving a general summary of the remaining challenges as discussed by the authors.
Abstract: Photonic molecules (PMs) are artificial nanoscale photonic structures that play important roles in the fundamental optics field. PM quantum optics has recently become a promising research field, because it provides novel quantum optical phenomena including Rabi oscillation, the Stark effect, the Purcell effect, the photon blockade effect, bound states in the continuum, electromagnetically induced transparency, and Autler–Townes splitting. With the constant improvements in theoretical PM quantum optics research, many newly integrated photonic devices have been proposed and experimentally demonstrated, showing major potential for fabrication of next-generation, high-performance integrated photonic chips. This review provides a universal overview of the rapidly developing PM quantum optics field, including fundamental mechanisms, realization frameworks, novel quantum optical phenomena, and applications in newly developed photonic devices while also giving a general summary of the remaining challenges and proposing possible development directions for PM quantum optics.
TL;DR: In this paper, a photonic super-honeycomb lattice (sHCL) was established experimentally using a cw-laser writing technique, and two distinct flatband line states that manifest as noncontractible-loop-states in an infinite flatband lattice.
Abstract: We establish experimentally a photonic super-honeycomb lattice (sHCL) by use of a cw-laser writing technique, and thereby demonstrate two distinct flatband line states that manifest as noncontractible-loop-states in an infinite flatband lattice. These localized states (straight and zigzag lines) observed in the sHCL with tailored boundaries cannot be obtained by superposition of conventional compact localized states because they represent a new topological entity in flatband systems. In fact, the zigzag-line states, unique to the sHCL, are in contradistinction with those previously observed in the Kagome and Lieb lattices. Their momentum-space spectrum emerges in the high-order Brillouin zone where the flat band touches the dispersive bands, revealing the characteristic of topologically protected bandcrossing. Our experimental results are corroborated by numerical simulations based on the coupled mode theory. This work may provide insight to Dirac like 2D materials beyond graphene.
TL;DR: The proposed strong plasMon-exciton coupling can find utility in highly integrated plasmonic circuits for optical switching and is further revealed by the coupled oscillator model (COM).
Abstract: The room-temperature strong plasmon-exciton coupling is first investigated in a metal-insulator-metal (MIM) waveguide-resonator system with WS2 monolayer. Finite-difference time-domain (FDTD) simulated results exhibit that the Fabry-Perot (F-P) cavity is realized by the MIM plasmonic waveguide with two separated metal bars. When the F-P resonance is tuned to overlap with the A-exciton absorption peak of WS2 monolayer, the strong plasmon-exciton coupling is obtained at visible wavelengths. As a result, the spectral splitting response confirmed by the coupled-mode theory (CMT) appears in the transmission spectrum. Intriguingly, the switching response is handily witnessed by tuning the orientation of WS2 monolayer along the cavity, and the coupling strength is dynamically tuned by changing the position of the WS2 monolayer. Simultaneously, the anticrossing behavior with the Rabi splitting up to 109 meV is achieved by small changes in the length of the F-P cavity and the refractive index of dielectric in the cavity, respectively. The underlying physics is further revealed by the coupled oscillator model (COM). The proposed strong plasmon-exciton coupling can find utility in highly integrated plasmonic circuits for optical switching.
TL;DR: In this paper, a single baffle metal-insulator-metal (MIM) waveguide coupled with a semi-circular cavity and a cross-shaped cavity is proposed based on the multiple Fano resonance characteristics of surface plasmon polaritons (SPPs) subwavelength structure.
Abstract: A single baffle metal–insulator–metal (MIM) waveguide coupled with a semi-circular cavity and a cross-shaped cavity is proposed based on the multiple Fano resonance characteristics of surface plasmon polaritons (SPPs) subwavelength structure. The isolated state formed by two resonators interferes with the wider continuous state mode formed by the metal baffle, forming Fano resonance that can independently be tuned into five different modes. The formation mechanism of Fano resonance is analyzed based on the multimode interference coupled mode theory (MICMT). The finite element method (FEM) and MICMT are used to simulate the transmission spectra of this structure and analyze the influence of structural parameters on the refractive index sensing characteristics. And the transmission responses calculated by the FEM simulation are consistent with the MICMT theoretical results very well. The results show that the figure of merit (FOM) can reach 193 and the ultra-high sensitivity is 1600 nm/RIU after the structure parameters have been optimized, and can provide theoretical basis for designing the high sensitive refractive index sensors based on SPPs waveguide for high-density photonic integration with excellent performance in the near future.
TL;DR: A metal-graphene hybrid non-Hermitian metasurface is proposed in the terahertz regime, whose unit cell is composed of two orthogonally oriented split-ring resonators (SRRs) with identical dimensions but only one SRR containing a graphene patch at the gap.
Abstract: Observation of exceptional points (EPs) in non-Hermitian parity-time (PT) symmetric systems has led to various nontrivial physics and exotic phenomena. Here, a metal-graphene hybrid non-Hermitian metasurface is proposed in the terahertz regime, whose unit cell is composed of two orthogonally oriented split-ring resonators (SRRs) with identical dimensions but only one SRR containing a graphene patch at the gap. An EP in polarization space is theoretically observed at a certain Fermi level of the graphene patch, where the induced asymmetric loss and the coupling strength between the two SRRs match a certain relation predicted by a coupled mode theory. The numerical fittings using the coupled mode theory agree well with the simulations. Besides, an abrupt phase flip around the EP frequency is observed in the transmission in circular polarization basis, which can be very promising in ultra-sensitive sensing applications.
TL;DR: In this paper, the authors investigate the propagation of Gaussian beams through optical waveguide lattices characterized by correlated non-Hermitian disorder and demonstrate how the imaginary part of the refractive index needs to be adjusted to achieve perfect beam transmission, despite the presence of disorder.
Abstract: We investigate the propagation of Gaussian beams through optical waveguide lattices characterized by correlated non-Hermitian disorder. In the framework of coupled mode theory, we demonstrate how the imaginary part of the refractive index needs to be adjusted to achieve perfect beam transmission, despite the presence of disorder. Remarkably, the effects of both diagonal and off-diagonal disorder in the waveguides and their couplings can be efficiently eliminated by our non-Hermitian design. Waveguide arrays thus provide an ideal platform for the experimental realization of non-Hermitian phenomena in the context of discrete photonics.
TL;DR: In this paper, a Si-DC-PCF polarization beam splitter (PBS) based on the surface plasmon resonance effect is proposed, which can find important applications in mid-infrared laser and sensing systems.
Abstract: In this paper, a novel silicon dual-core photonic crystal fiber (Si-DC-PCF) polarization beam splitter (PBS) based on the surface plasmon resonance effect is proposed The mode-coupling characteristics between the X- and Y-polarized even and odd modes and surface plasmon polariton mode are analyzed by using the finite-element method and coupled-mode theory The influences of the structure parameters of the Si-DC-PCF on the coupling length and coupling length ratio are investigated The normalized output power of the X- and Y-polarized modes in cores A and B and the corresponding extinction ratio are also discussed By optimizing the structure parameters of the Si-DC-PCF, the PBS length of 192 µm and bandwidth of 830 and 730 nm in cores A and B are achieved It is believed that the proposed Si-DC-PCF PBS can find important applications in mid-infrared laser and sensing systems
TL;DR: In this paper, a tunable graphene plasmonic filter and a two-channel demultiplexer are proposed, simulated, and analyzed in the mid-infrared (MIR) region.
Abstract: In this study, a tunable graphene plasmonic filter and a two-channel demultiplexer are proposed, simulated, and analyzed in the mid-infrared (MIR) region. We discuss the optical transmission spectra of the proposed cross-shaped resonator and the two-channel demultiplexer. The transmission spectra of the proposed MIR resonator are tunable by change of its dimensional parameters and the Fermi energy of the graphene. Our proposed structures have a single mode in the wavelength range of 5–12 µm. The minimum full width at half maximum (FWHM) and the maximum transmission ratio of the proposed resonator respectively reached 220 nm and 55%. Simulations are performed by use of three-dimensional finite-difference time-domain (3D-FDTD) method. Coupled mode theory (CMT) is used to investigate the structure theoretically. The numerical and the theoretical results are in good agreement. The performance of the proposed two-channel demultiplexer is investigated based on its crosstalk. The minimum value of crosstalk reaches −48.30 dB. Our proposed structures are capable of providing sub-wavelength confinement of light waves, useful in applications in MIR region.
TL;DR: This Letter demonstrates a compact broadband directional coupler, fully suspended in air and exhibiting efficient power coupling in the cross state, designed and built based on IMEC's iSiPP50G standard platform, and hydrofluoric (HF) vapor-etching-based post-processing allows to release the freestanding component.
Abstract: Directional couplers are extensively used in photonic integrated circuits as basic components for efficient on-chip photonic signal routing. Conventionally, directional couplers are fully encapsulated in the technology’s waveguide cladding material. In this Letter, we demonstrate a compact broadband directional coupler, fully suspended in air and exhibiting efficient power coupling in the cross state. The coupler is designed and built based on IMEC’s iSiPP50G standard platform, and hydrofluoric (HF) vapor-etching-based post-processing allows to release the freestanding component. A low insertion loss of 0.5 dB at λ=1560nm and a 1 dB bandwidth of 35 nm at λ=1550nm have been confirmed experimentally. With a small footprint of 20µm×30µm and high mechanical stability, this directional coupler can serve as a basic building block for large-scale silicon photonic microelectromechanical systems (MEMS) circuits.
TL;DR: The sensing capabilities of this novel filtering component with rigorous electromagnetic simulations are assessed, showing that the sensor achieves a sensitivity of 507 nm/RIU and a quality factor of 4.9 × 104, over a large dynamic range circumventing the free spectral range limit of conventional devices.
Abstract: Subwavelength grating (SWG) waveguides have been shown to provide enhanced light-matter interaction resulting in superior sensitivity in integrated photonics sensors. Narrowband integrated optical filters can be made by combining SWG waveguides with evanescently coupled Bragg gratings. In this paper, we assess the sensing capabilities of this novel filtering component with rigorous electromagnetic simulations. Our design is optimized for an operating wavelength of 1310 nm to benefit from lower water absorption and achieve narrower bandwidths than at the conventional wavelength of 1550 nm. Results show that the sensor achieves a sensitivity of 507 nm/RIU and a quality factor of 4.9 × 104, over a large dynamic range circumventing the free spectral range limit of conventional devices. Furthermore, the intrinsic limit of detection, 5.1 × 10−5 RIU constitutes a 10-fold enhancement compared to state-of-the-art resonant waveguide sensors.
TL;DR: It is demonstrated that an ultrathin sponge coating can achieve high-efficiency absorptions if backed by a metasurface with moderate surface impedance, providing a practical way in constructing broadband low-frequency sound absorber.
Abstract: Suppressing broadband low-frequency sound has great scientific and engineering significance. However, normal porous acoustic materials backed by a rigid wall cannot really play its deserved role on low-frequency sound absorption. Here, we demonstrate that an ultrathin sponge coating can achieve high-efficiency absorptions if backed by a metasurface with moderate surface impedance. Such a metasurface is constructed in a wide frequency range by integrating three types of coiled space resonators. By coupling an ultrathin sponge coating with the designed metasurface, a deep-subwavelength broadband absorber with high absorptivity (
$${>}80\%$$
) exceeding one octave from 185 Hz to 385 Hz (with wavelength
$$\lambda $$
from 17.7 to 8.5 times of thickness of the absorber) has been demonstrated theoretically and experimentally. The construction mechanism is analyzed via coupled mode theory. The study provides a practical way in constructing broadband low-frequency sound absorber.
TL;DR: In this article, the interaction of the multi-mode fundamental field and its second harmonic in a ring microresonator with quadratic nonlinearity and quasi-phase-matching was derived.
Abstract: We use Maxwell’s equations to derive several models describing the interaction of the multi-mode fundamental field and its second harmonic in a ring microresonator with quadratic nonlinearity and quasi-phase-matching We demonstrate how multi-mode three-wave mixing sums entering nonlinear polarization response can be calculated via Fourier transforms of products of the field envelopes Quasi-phase-matching gratings with arbitrary profiles are incorporated seamlessly into our models We also introduce several levels of approximations that allow us to account for dispersion of nonlinear coefficients and demonstrate how coupled-mode equations can be reduced to the envelope Lugiato–Lefever-like equations with self-steepening terms An estimate for the χ(2) induced cascaded Kerr nonlinearity, in the regime of imperfect phase-matching, puts it above the intrinsic Kerr effect by several orders of magnitude
TL;DR: This brief presents a fractional coupled model of fractional-order wireless power transfer (FOWPT) system based on the fractional calculus that is in good agreement with the circuit model and experiment, which proves the correctness of the generalized fractional coupling mode equations.
Abstract: This brief presents a fractional coupled model of fractional-order wireless power transfer (FOWPT) system based on the fractional calculus. By applying coupled-mode theory (CMT), dynamic characteristics of fractional systems can be described clearly while avoiding complex circuit models. The theoretical simulation results indicate that the FOWPT system has better characteristics and greater design freedom. Furthermore, the fractional coupled model is in good agreement with the circuit model and experiment, which proves the correctness of the generalized fractional coupled mode equations. Therefore, the fractional coupled model provides a valuable tool for the further analysis of FOWPT systems and may be used in other fractional-order resonant circuits.