Showing papers on "Coupled mode theory published in 2018"
TL;DR: A bulk Dirac semimetals based tunable narrowband absorber at terahertz frequencies is proposed and it has the attractive property of being polarization-independent at normal incidence because of its 90° rotational symmetry.
Abstract: In this paper, a bulk Dirac semimetals (BDSs) based tunable narrowband absorber at terahertz frequencies is proposed and it has the attractive property of being polarization-independent at normal incidence because of its 90° rotational symmetry. Numerical results show that the absorption bandwidth is about 1.469e-2 THz and the total quality factor Q, defined as Q = f0/Δf, reaches about 94.6, which can be attributed to the low power loss of the guided mode resonance in the dielectric layer. The simulation results are analyzed with coupled mode theory. Interestingly, on the premise of maintaining the absorbance at a level greater than 0.95, the absorption frequency can be tuned from 1.381 to 1.395 THz by varying the Fermi energy of BDSs from 50 to 80 meV. Our results may also provide potential applications in optical filter and bio-chemical sensing.
98 citations
20 Oct 2018
TL;DR: In this paper, the role of mesoscopic fluctuations and noise on the spectral and temporal properties of PT-symmetric-coupled gain-loss resonators operating near the exceptional point was explored.
Abstract: Exceptional points of parity-time (PT) symmetric systems hold an intriguing potential for highly sensitive sensors. Here, we theoretically explore the role of mesoscopic fluctuations and noise on the spectral and temporal properties of systems of PT-symmetric-coupled gain–loss resonators operating near the exceptional point, where eigenvalues and eigenvectors coalesce. We show that experimentally inevitable detuning in the frequencies of the uncoupled resonators leads to an unavoidable modification of the conditions for reaching the exceptional point, while, as this point is approached in ensembles of resonator pairs, statistical averaging significantly smears the spectral features. We discuss how these fluctuations affect the sensitivity of sensors based on coupled PT-symmetric resonators. Finally, we show that temporal fluctuations in the detuning and gain of these sensors lead to at least a quadratic growth of the optical power in time, implying that maintaining operation at the exceptional point over a long period can be rather challenging. Our theoretical analysis clarifies issues central to the realization of PT-symmetric devices, and should facilitate future experimental work in the field.
89 citations
TL;DR: A metamaterial perfect absorber composed of a black phosphorus monolayer, a photonic crystal, and a metallic mirror is designed and investigated to enhance light absorption at terahertz frequencies, and this easy-to-fabricate structure will provide potential applications in BP-based devices.
Abstract: A metamaterial perfect absorber composed of a black phosphorus (BP) monolayer, a photonic crystal, and a metallic mirror is designed and investigated to enhance light absorption at terahertz frequencies. Numerical results reveal that the absorption is enhanced greatly with narrow spectra due to critical coupling, which is enabled by guided resonances. Intriguingly, the structure manifests the unusual polarization-dependent feature attributable to the anisotropy of black phosphorus. The quality factor of the absorber can be as high as 95.1 for one polarization while 63.5 for another polarization, which is consistent with the coupled wave theory. The absorption is tunable by varying key parameters, such as period, radius, slab thickness, incident angle, and polarization angle. Furthermore, the state of the system (i.e., critical coupling, over coupling, and under coupling) can be tuned by changing the electron doping of BP, thus achieving various applications. This work offers a paradigm to enhance the light-matter interaction in monolayer BP without plasmonic response, and this easy-to-fabricate structure will provide potential applications in BP-based devices.
84 citations
TL;DR: In this paper, a refractive index sensor based on Fano resonances in metal-insulator-metal (MIM) waveguides coupled with rectangular and dual side rings resonators is proposed.
Abstract: A refractive index sensor based on Fano resonances in metal-insulator-metal (MIM) waveguides coupled with rectangular and dual side rings resonators is proposed The sensing properties are numerically simulated by the finite element method (FEM) For the interaction of the narrow-band spectral response and the broadband spectral response caused by the side-coupled resonators and the rectangular resonator, respectively, the transmission spectra exhibit a sharp and asymmetric profile Results are analyzed using the coupled-mode theory based on the transmission line theory The coupled mode theory is employed to explain the Fano resonance effect The results show that with an increase in the refractive index of the fill dielectric material in the slot of the system, the Fano resonance peak exhibits a remarkable red shift Through the optimization of structural parameters, we achieve a theoretical value of the refractive index sensitivity (S) as high as 1160 nm/RIU, and the corresponding sensing resolution is 862 × 10–5 RIU In addition, the coupled MIM waveguide structure can be easily extended to other similar compact structures to realize the sensing task and integrated with other photonic devices at the chip scale This work paves the way toward the sensitive nanometer scale refractive index sensor for design and application
82 citations
TL;DR: By combining different techniques, including judiciously positioning silicon loading segments within the evanescent field of the SWG waveguide and making use of its dispersion properties, it is possible to attain sub-nanometer spectral bandwidths for both reflection and transmission filters in the wavelength range of 1550 nm while keeping minimum structural features of the filters as large as 100 nm.
Abstract: Properties of reflection and transmission spectral filters based on Bragg gratings in subwavelength grating (SWG) metamaterial waveguides on silicon-on-insulator platform have been analyzed using proprietary 2D and 3D simulation tools based on Fourier modal method and the coupled-mode theory. We also demonstrate that the coupled Bloch mode theory can be advantageously applied to design of Bragg gratings in SWG waveguides. By combining different techniques, including judiciously positioning silicon loading segments within the evanescent field of the SWG waveguide and making use of its dispersion properties, it is possible to attain sub-nanometer spectral bandwidths for both reflection and transmission filters in the wavelength range of 1550 nm while keeping minimum structural features of the filters as large as 100 nm. Numerical simulations have also shown that a few nanometer jitter in the size and position of Si segments is well tolerated in our filter designs.
78 citations
TL;DR: Control of the resonant eigenmodes supported by Huygens' metasurface (HMS) absorbers through optical excitation is proposed and demonstrated and demonstrates wide tunability and versatility, not limited to the spectral range demonstrated.
Abstract: Conventional dielectric metasurfaces achieve their properties through geometrical tuning and consequently are static. Although some unique properties are demonstrated, the usefulness for realistic applications is thus inherently limited. Here, control of the resonant eigenmodes supported by Huygens' metasurface (HMS) absorbers through optical excitation is proposed and demonstrated. An intensity transmission modulation depth of 99.93% is demonstrated at 1.03 THz, with an associated phase change of greater than π/2 rad. Coupled mode theory and S-parameter simulations are used to elucidate the mechanism underlying the dynamics of the metasurface and it is found that the tuning is primarily governed by modification of the magnetic dipole-like odd eigenmode, which both lifts the degeneracy, and eliminates critical coupling. The dynamic HMS demonstrates wide tunability and versatility which is not limited to the spectral range demonstrated, offering a new path for reconfigurable metasurface applications.
77 citations
TL;DR: In this paper, the authors proposed a framework for the realization of non-reciprocal photonic devices based on time-modulated graphene capacitors coupled to photonic waveguides, without relying on magneto-optic effects.
Abstract: We propose a paradigm for the realization of nonreciprocal photonic devices based on time-modulated graphene capacitors coupled to photonic waveguides, without relying on magneto-optic effects. The resulting hybrid graphene-dielectric platform is low loss, silicon compatible, robust against graphene imperfections, scalable from terahertz to near-infrared frequencies, and it exhibits large nonreciprocal responses using realistic biasing schemes. We introduce an analytical framework based on solving the eigenstates of the modulated structure and on spatial coupled mode theory, unveiling the physical mechanisms that enable nonreciprocity and enabling a quick analysis and design of optimal isolator geometries based on synthetic linear and angular momentum bias. Our results, validated through harmonic-balance full-wave simulations, confirm the feasibility of the introduced low-loss ($l3$ dB) platform to realize large photonic isolation through various mechanisms, such as narrow-band asymmetric band gaps and interband photonic transitions that allow multiple isolation frequencies and large bandwidths. We envision that this technology may pave the wave to magnetic-free, fully integrated, and CMOS--compatible nonreciprocal components with wide applications in photonic networks and thermal management.
55 citations
TL;DR: Based on the traditional directional coupler, a scheme to design on-chip polarization beam splitters using an inverse design method was proposed in this article, where the coupling area of the designed devices are only 0.48 μm×6.4
Abstract: Based on the traditional directional coupler, we proposed a scheme to design on-chip polarization beam splitters using an inverse design method. In our scheme, the coupling area of the designed devices are only 0.48 μm×6.4 μm. By manipulating the refractive index of the coupling region, the devices can work in C-band, L-band, O-band, or any other communication band. Different from conventional design methods, which need to adjust the design parameters artificially, if the initial conditions are determined, the proposed scheme can automatically adjust the design parameters of devices according to specific requirements. The simulation results show that the insertion losses of the designed polarization beam splitters can be less than 0.4 dB (0.35 dB) for TE (TM) mode at the wavelengths of 1310, 1550, and 1600 nm, and the extinction ratios are larger than 19.9 dB for the TE and TM modes at all three wavelengths. Besides, the extinction ratios of both polarization states are more than 14.5 dB within the wavelength range of 1286–1364 nm, 1497–1568 nm, and 1553–1634 nm. At the same time, the insertion losses are smaller than 0.46 dB.
54 citations
TL;DR: A unidirectional single-moded parity-time symmetric laser is shown by incorporating active S-bend structures with opposite chirality in the respective ring resonators by Measure the extinction ratio between the CW and CCW modes in a single ring resonator in the presence of an S- bend waveguide and experimentally investigate the uniddirectional emission in PT-symmetric systems below and above the exceptional point.
Abstract: The synergetic use of gain and loss in parity-time symmetric coupled resonators has been shown to lead to single-mode lasing operation. However, at the corresponding resonance frequency, an ideal ring resonator tends to support two degenerate eigenmodes, traveling along the cavity in opposite directions. Here, we show a unidirectional single-moded parity-time symmetric laser by incorporating active S-bend structures with opposite chirality in the respective ring resonators. Such chiral elements break the rotation symmetry of the ring cavities by providing an asymmetric coupling between the clockwise (CW) and the counterclockwise (CCW) traveling modes, hence creating a new type of exceptional point. This property, consequently, leads to the suppression of one of the counter-propagating modes. In this paper, we first measure the extinction ratio between the CW and CCW modes in a single ring resonator in the presence of an S-bend waveguide. We then experimentally investigate the unidirectional emission in PT-symmetric systems below and above the exceptional point. Finally, unidirectional emission will be shown in systems of two S-bend ring resonators coupled through a link structure.
46 citations
20 Oct 2018
TL;DR: In this article, a series of experimental, analytical, and numerical studies demonstrating strong circular dichroism for the HE11-like core mode in helically twisted hollow-core single-ring photonic crystal fiber (SR-PCF), formed by spinning the preform during fiber drawing.
Abstract: We report a series of experimental, analytical, and numerical studies demonstrating strong circular dichroism for the HE11-like core mode in helically twisted hollow-core single-ring photonic crystal fiber (SR-PCF), formed by spinning the preform during fiber drawing. In the SR-PCFs studied, the hollow core is surrounded by a single ring of nontouching capillaries. Coupling between these capillaries results in the formation of helical Bloch modes carrying orbital angular momentum. When twisted, strong circular birefringence appears in the ring, so that coupling to the core mode is possible for only one circular polarization state. The result is a SR-PCF that acts as a circular polarizer, offering 1.4 dB/m for the low-loss polarization state and 9.7 dB/m for the high-loss state over a 25 nm band centered at 1593 nm wavelength. In addition, we report for the first time that the vector fields of the helical Bloch modes are perfectly periodic when evaluated in cylindrical coordinates. Such fibers have many potential applications, such as generating circularly polarized light in gas-filled SR-PCF and realizing polarizing elements in the deep and vacuum ultraviolet.
43 citations
TL;DR: A directional curvature sensor based on tilted few-mode fiber Bragg gratings inscribed by a UV laser demonstrates the potential to simultaneous directional curvatures and temperature measurement with the resolutions of 9.15×10-4 m-1 and 0.952°C, respectively.
Abstract: We demonstrate a directional curvature sensor based on tilted few-mode fiber Bragg gratings (FM-FBGs) inscribed by a UV laser. The eigenmodes of LP01 and LP11 mode groups are simulated along with the fiber bending. The directional curvature sensor is based on the LP11 mode resonance in the tilted FM-FBG. For curvature from 4.883 to 7.625 m−1, the curvature sensitivities at direction of 0° and 90° are measured to be −2.67 and 0.128 dB/m−1, respectively. The temperature variation barely affects the resonance depth of LP11 mode. The proposed curvature sensor clearly demonstrates the potential to simultaneous directional curvature and temperature measurement with the resolutions of 9.15×10−4 m−1 and 0.952°C, respectively.
TL;DR: In this article, a metallic double-baffle contained metal-dielectric-metal (MDM) waveguide coupled ring resonator is proposed to achieve the Fano resonance.
Abstract: Based on the transmission property and the photon localization characteristic of the surface plasmonic sub-wavelength structure, a metallic double-baffle contained metal-dielectric-metal (MDM) waveguide coupled ring resonator is proposed. Like the electromagnetically induced transparency (EIT), the Fano resonance can be achieved by the interference between the metallic double-baffle resonator and the ring resonator. Based on the coupled mode theory, the transmission property is analyzed. Through the numerical simulation by the finite element method (FEM), the quantitative analysis on the influences of the radius R of the ring and the coupling distance g between the metallic double-baffle resonator and the ring resonator for the figure of merit (FOM) is performed. And after the structure parameter optimization, the sensing performance of the waveguide structure is discussed. The simulation results show that the FOM value of the optimized structure can attain to 5.74 × 10 4 and the sensitivity of resonance wavelength with refractive index drift is about 825 nm/RIU. The range of the detected refractive index is suitable for all gases. The waveguide structure can provide effective theoretical references for the design of integrated plasmonic devices.
TL;DR: In this paper, a novel directional coupler based on surface plasmon-polaritons (SPPs) evolution in three layers of graphene sheets in some curved configuration is proposed, which can transfer SPPs efficiently from the input graphene sheet to the output graphene sheet, and the coupling is also robust that it is not sensitive to the length of the device configuration's parameters.
20 Oct 2018
TL;DR: In this article, a nonlinear parametric upconversion of millimeter-wave radiation to the optical domain inside high-quality (Q) lithium niobate whispering-gallery mode (WGM) resonators is proposed for ultra-low noise detection.
Abstract: Conventional ultra-high sensitivity detectors in the millimeter-wave range are usually cooled as their own thermal noise at room temperature would mask the weak received radiation. The need for cryogenic systems increases the cost and complexity of the instruments, hindering the development of, among others, airborne and space applications. In this work, the nonlinear parametric upconversion of millimeter-wave radiation to the optical domain inside high-quality (Q) lithium niobate whispering-gallery mode (WGM) resonators is proposed for ultra-low noise detection. We experimentally demonstrate coherent upconversion of millimeter-wave signals to a 1550 nm telecom carrier, with a photon conversion efficiency surpassing the state-of-the-art by 2 orders of magnitude. Moreover, a theoretical model shows that the thermal equilibrium of counterpropagating WGMs is broken by overcoupling the millimeter-wave WGM, effectively cooling the upconverted mode and allowing ultra-low noise detection. By theoretically estimating the sensitivity of a correlation radiometer based on the presented scheme, it is found that room-temperature radiometers with better sensitivity than state-of-the-art high-electron-mobility transistor (HEMT)-based radiometers can be designed. This detection paradigm can be used to develop room-temperature instrumentation for radio astronomy, earth observation, planetary missions, and imaging systems.
TL;DR: A silicon integrated OAM (de)multiplexer with a very simple structure is demonstrated using a pair of silicon devices, which shows low-level mode crosstalk and favorable link performance.
Abstract: Orbital angular momentum (OAM) multiplexing has emerged as an important method to increase the communication capacities in future optical information technologies. In this work, we demonstrate a silicon integrated OAM (de)multiplexer with a very simple structure. By simply tapping the evanescent wave of two different whispering gallery modes rotating inside a multimodal micro-ring resonator, four in-plane waveguide modes are converted to four free-space vector OAM beams with high mode purity. We further demonstrate chip-to-chip OAM multiplexing transmission using a pair of silicon devices, which shows low-level mode crosstalk and favorable link performance.
TL;DR: This work demonstrates asymmetric contradirectional couplers (contra-DCs) using sidewall-corrugated subwavelength grating (SWG) waveguides for broadband add-drop Bragg filters and shows that a SWG can effectively increase the overlap of coupled modes and thus the photonic band gap.
Abstract: Manipulating the coupling coefficient at subwavelength scales provides an additional degree of freedom in designing integrated Bragg gratings. We demonstrate asymmetric contradirectional couplers (contra-DCs) using sidewall-corrugated subwavelength grating (SWG) waveguides for broadband add-drop Bragg filters. We show that a SWG can effectively increase the overlap of coupled modes and thus the photonic band gap. The measured spectra show good agreement with the prediction of photonic band structure simulations. A record bandwidth of 4.07 THz (33.4 nm) has been achieved experimentally. A four-port Bragg resonating filter made of a phase-shifted Bragg grating SWG contra-DC is also demonstrated for narrow-band (near 100 GHz) filtering. All these devices are achieved on the 220-nm silicon-on-insulator platform with a compact length of less than 150 μm. These large stopband filters may find important applications such as band splitting, reconfigurable channel band switching, bandwidth-tunable filtering, and dispersion engineering.
TL;DR: In this paper, a theory of the optical response induced by bound states in the continuum (BICs) in arrays of dielectric spheres was proposed. And the results obtained are verified in comparison against exact numerical solutions to demonstrate that the CMT approximation is capable of reproducing Fano features in the spectral vicinity of the BIC.
Abstract: We consider an optical response induced by bound states in the continuum (BICs) in arrays of dielectric spheres. By combining the quasi-mode expansion technique with coupled mode theory (CMT), we put forward a theory of the optical response by high-Q resonance surrounding BICs in momentum space. The central results are analytical expressions for the CMT parameters, which can be easily calculated from the eigenfrequencies and eigenvectors of the interaction matrix of the scattering systems. The results obtained are verified in comparison against exact numerical solutions to demonstrate that the CMT approximation is capable of reproducing Fano features in the spectral vicinity of the BIC. Based on the quasi-mode expansion technique, we derived the asymptotic scaling law for the CMT parameters in the vicinity of the Γ-point. It is rigorously demonstrated that the linewidth in the CMT approximation exhibits different asymptotic behavior depending on the symmetry of the BIC.
TL;DR: The results show that the proposed sensor can achieve better performance than that of the sensors based on silver nano-continuous grating and plane silver film structures and can have promising applications in medical and environmental monitoring and biochemical detection.
Abstract: Two kinds of photonic crystal fiber (PCF) sensors based on surface plasmon resonance (SPR) with silver nano-continuous gratings (i) and (ii) are designed. The coupling characteristics and sensing properties are analyzed numerically by the finite element method (FEM). The results show that the proposed sensor based on silver nano-continuous grating (i) can achieve better performance than that of the sensors based on silver nano-continuous grating (ii) and plane silver film structures. When the segmented number is 50 and segmented angle is 0.5°, a wavelength sensitivity of the proposed sensor with silver nano-continuous grating (i) is obtained as high as 13,600 nm/RIU in the refractive index (RI) range from 1.330 to 1.365, corresponding to a maximum RI resolution of 7.35×10−6 RIU, which can have promising applications in medical and environmental monitoring and biochemical detection.
TL;DR: In this article, the dispersion and coupling characteristics of terahertz surface plasmons polaritons (SPPs) in bulk Dirac semimetals (BDS) sheets were theoretically investigated.
Abstract: We theoretically investigate the dispersion and coupling characteristics of terahertz surface plasmons polaritons (SPPs) in bulk Dirac semimetals (BDS) sheets, which indicate that symmetric and anti-symmetric modes are attributed to the odd and even superpositions of the anti-symmetric eigenmode supported by the single-layer BDS sheet. Interestingly, the symmetric mode has better confinement than the eigenmode and anti-symmetric mode. By introducing two silicon bars, the highly-confined symmetric mode is modulated in resonance frequency and transmission intensity by the designed novel band-pass filter. Numerical results show good agreement with the theoretical analysis based on the coupled mode theory and the Fabry-Perot resonance theory. The developed Dirac semimetal plasmonic structures pave the way to the development of novel THz active devices for light modulation platform.
TL;DR: In this paper, a high-order sapphire fiber Bragg grating (HO-SFBG) written with a femtosecond (fs) laser in a large-diameter SA-plastic fiber is demonstrated.
Abstract: Aiming for structural health monitoring applications in harsh environments, a high-order sapphire fiber Bragg grating (HO-SFBG) written with a femtosecond (fs) laser in a large-diameter sapphire fiber is demonstrated. The radial refractive index modulation area induced by scanning exposure is greater than 60% of the fiber cross-section area. The large mode overlapping area leads to a transmission resonance strength of approximately 3.0 dB. As demonstrated by numerical simulations of mode excitation and multimode resonance, each mode resonance is significantly superposed when the coupling coefficient is above 0.0005. A study of the high-temperature and strain sensing characteristics of the HO-SFBG shows that each high-order resonance has different response characteristics. This type of large-diameter SFBG has important application potential for high-temperature smart materials with embedded fiber sensors.
TL;DR: In this paper, the authors investigated the energy transfer of surface plasmon polaritons (SPPs) based on adiabatic passage in a non-Hermitian waveguide composed of three coupled graphene sheets.
Abstract: We investigate the energy transfer of surface plasmon polaritons (SPPs) based on adiabatic passage in a non-Hermitian waveguide composed of three coupled graphene sheets. The SPPs can completely transfer between two outer waveguides via the adiabatic dark mode as the waveguides are lossless and the coupling length is long enough. However, the loss of graphene can lead to breakdown of adiabatic transfer schemes. By utilizing the coupled mode theory, we propose three approaches to cancel the nonadiabatic coupling by adding certain gain or loss in respect waveguides. Moreover, the coupling length of waveguide is remarkably decreased. The study may find interesting application in optical switches on a deep-subwavelength scale.
TL;DR: In this article, a metal-dielectric-metal waveguide system consisting of a stub coupled with a U-cavity is proposed to produce sharp and asymmetric Fano resonance.
Abstract: A new compact metal-dielectric-metal waveguide system consisting of a stub coupled with a U-cavity is proposed to produce sharp and asymmetric Fano resonance. The transmission properties of the proposed structure are numerically studied by the finite element method and verified by the coupled mode theory. Simulation results reveal that the spectral profile can be easily tuned by adjusting the geometric parameters of the structure. One of the potential application of the proposed structure as a highly efficient plasmonic refractive index nanosensor was investigated with its sensitivity of more than 1000 nm/RIU and a figure of merit of up to 5500. Another application is integrated slow-light device whose group index can be greater than 6. In addition, multiple Fano resonances will occur in the broadband transmission spectrum by adding another U-cavity or (and) stub. The characteristics of the proposed structure are very promising for the highly performance filters, on-chip nanosensors, and slow-light devices.
TL;DR: In this article, the authors developed a rigorous mathematical framework based on perturbation theory and temporal coupled-mode theory capable of analyzing third-order nonlinear processes in resonant systems comprising 2D materials.
Abstract: Two-dimensional (2D) or sheet materials have been recently recognized as fascinating materials for nonlinear photonics. Here, we develop a rigorous mathematical framework based on perturbation theory and temporal coupled-mode theory capable of analyzing third-order, ${\ensuremath{\chi}}^{(3)}$, multichannel nonlinear processes in resonant systems comprising 2D materials. The framework is applied to model degenerate four-wave mixing in a guided-wave graphene plasmon-polariton resonant structure, consisting of a standing-wave resonator directly coupled to access waveguides. The results obtained with the proposed framework are compared with full-wave finite-element simulations revealing excellent agreement. Aside from being accurate and efficient, our framework allows for selectively incorporating different nonlinear phenomena, identifying their unique impact on the nonlinear response and providing valuable physical insight. We are, thus, able to specify the optimal operating point leading to maximum conversion efficiency for the generated wave in a multiparameter space. In addition, we identify unstable operating regimes exhibiting optical bistability or limit cycles, thoroughly characterizing the component performance. Our framework enables the study of diverse multichannel phenomena (frequency generation, frequency mixing, and parametric amplification) in the thriving field of 2D material photonics, thus allowing for assessing the potential of these exciting materials for practical nonlinear applications.
TL;DR: A plasmonic structure based on the metal-insulator-metal waveguide with the side-coupled isosceles trapezoid cavities was proposed in this article.
Abstract: We propose a plasmonic structure based on the metal-insulator-metal waveguide with the side-coupled isosceles trapezoid cavities. Both of the structures based on the side-coupled trapezoid cavities separated or connected with waveguides can realize the plasmon-induced transparency (PIT). By adjusting the structure parameters, the off-to-on PIT response can be tunably achieved. The coupled mode theory (CMT) method is used to study the PIT phenomenon and explain the transmission characteristics. This work may provide a potential way for designing highly integrated photonic devices.
TL;DR: It is shown that the combination of an asymmetric Fano resonance and carrier-induced nonlinear effects in a nanocavity can be used to realize a nonlinear power transfer function, which is a key functionality for optical signal regeneration, particularly for suppression of amplitude fluctuations of data signals.
Abstract: We experimentally demonstrate the use of photonic crystal Fano resonances for reshaping optical data signals. We show that the combination of an asymmetric Fano resonance and carrier-induced nonlinear effects in a nanocavity can be used to realize a nonlinear power transfer function, which is a key functionality for optical signal regeneration, particularly for suppression of amplitude fluctuations of data signals. The experimental results are explained using simulations based on coupled-mode theory and also compared to the case of using conventional Lorentzian-shaped resonances. Using indium phosphide photonic crystal membrane structures, we demonstrate reshaping of 2 Gbit/s and 10 Gbit/s return-to-zero on-off keying (RZ-OOK) data signals at telecom wavelengths around 1550 nm. Eye diagrams of the reshaped signals show that amplitude noise fluctuations can be significantly suppressed. The reshaped signals are quantitatively analyzed using bit-error ratio (BER) measurements, which show up to 2 dB receiver sensitivity improvement at a BER of 10−9 compared to a degraded input noisy signal. Due to efficient light-matter interaction in the high-quality factor and small mode-volume photonic crystal nanocavity, low energy consumption, down to 104 fJ/bit and 41 fJ/bit for 2 Gbit/s and 10 Gbit/s, respectively, has been achieved. Device perspectives and limitations are discussed.
TL;DR: The present work varies material loss to explore the rich electromagnetic response of this class of metasurface to find perfect absorption to be analogous to the driven damped harmonic oscillator, with critical damping occurring at resonance.
Abstract: Arrays of dielectric cylinders support two fundamental dipole active eigenmodes, which can be manipulated to elicit a variety of electromagnetic responses in all-dielectric metamaterials. Dissipation is a critical parameter in determining functionality; the present work varies material loss to explore the rich electromagnetic response of this class of metasurface. Four experimental cases are investigated which span electromagnetic response ranging from Huygens surfaces with transmissivity T = 94%, and phase ϕS21 = 235°, to metasurfaces which absorb 99.96% of incident energy. We find perfect absorption to be analogous to the driven damped harmonic oscillator, with critical damping occurring at resonance. With high phase contrast, transmission, and absorption all accessible from a single system, we present a uniquely diverse all-dielectric system.
TL;DR: In this article, a theoretical study on the design of long period fiber grating (LPFG) sensor where its add-layer sensitivity is enhanced is presented, where two different methodologies: dual overlay layer and tailoring of the intermodal separation between two cladding modes have been used to enhance the add layer sensisstivity.
Abstract: We present our theoretical study on the design of long period fiber grating (LPFG) sensor where its add-layer sensitivity is enhanced. Add-layer sensitivity quantifies the sensitivity of the sensor to the changes taking place within few tens of nanometers around the receptor molecules. Two different methodologies: the use of dual overlay layer and tailoring of the intermodal separation between two cladding modes have been used to enhance the add-layer sensisstivity. Using coupled mode analysis, we compute several examples to carry out a detailed comparative analysis between the results obtained, focusing on the cladding mode near mode transition.
TL;DR: In this article, a self-coupled optical waveguide (SCOW) with four coupling points is investigated and an implicit standing-wave resonance mode is formed inside the SCOW structure.
Abstract: We investigate the resonance property of a self-coupled optical waveguide (SCOW) with four coupling points. Under a special condition that the two outer couplers are in weak coupling and the two inner couplers are in strong coupling, an implicit standing-wave resonance mode is formed inside the SCOW structure. As the resonance is feedback coupled via an S-shape bus waveguide, electromagnetically induced transparency (EIT)-like resonance features are observed in the output transmission spectrum. The SCOW resonator is analyzed using the coupled mode theory and finite-difference time-domain simulation. The device is experimentally demonstrated on the silicon-on-insulator platform. The measurement results overall agree well with the theoretical calculation. The EIT-like peak can be tuned by a thermo-optic phase shifter made of a NIN-type silicon resistor integrated in the feedback waveguide. The results point to new ways of creating on-chip optical analog of the EIT phenomenon that can be utilized for various optical signal processing applications.
TL;DR: In this article, a double side-coupled square ring resonators based on a metal-insulator-metal platform is proposed for realising plasmon-induced transparency.
Abstract: In this study, a compact plasmonic structure for realising plasmon-induced transparency is proposed and numerically investigated by using the finite-difference time-domain method. The suggested device consists of double side-coupled square ring resonators based on a metal–insulator–metal platform. The coupled mode theory is introduced to describe the spectral response of the proposed structure, which is verified by numerical simulations. By changing the geometrical and material parameters such as outer side length and width of square ring resonators and metal collision frequency, the transmission characteristics can be easily tuned. The simulation results show that the proposed plasmonic system is used as a sensor by filling the insulator region with different refractive index. The sensitivity and figure of merit of this sensor are calculated, 806 nm/RIU and 66 RIU
–1
, respectively. It is found that the slow light effect can appear in the proposed structure. By design optimisation, the maximum value of the group index is achieved close to 65. Meanwhile, the group index profile is obtained for different values of geometrical parameters like coupling aperture widths. The proposed structure provides a new way to utilise in nanosensor devices and slow light systems.
TL;DR: This work proposes a flexibly designed photonic system based on ultrathin corrugated metallic "H-bar" waveguide that supports spoof surface plasmon polariton (SPP) at microwave frequencies and constructs a coupled waveguide array that followed the Su-Schrieffer-Heeger (SSH) model.
Abstract: We propose a flexibly designed photonic system based on ultrathin corrugated metallic “H-bar” waveguide that supports spoof surface plasmon polariton (SPP) at microwave frequencies. Five designs were presented, in order to demonstrate flexibility according to varying height, period, core width, rotation, and shifting on the “H-bar” unit of the waveguide. The propagation constant between two hybrid designs of period and height structure was then shown in order to study the coupling effect. Next, we constructed a coupled waveguide array that followed the Su-Schrieffer-Heeger (SSH) model. This model was constructed by a hybrid design with the identical propagation constant of each waveguide, except it had dimerized spacing. The propagation feature of topological zero mode was then observed as theoretically expected in the dimerized array. Our proposed spoof SPP waveguide array has great flexibility to be used as a powerful experiment platform, particularly in photonic simulation of the quantum or topological phenomena described by Schrodinger equation in condensed matters.