Slow Light Effect Research Articles

Dynamically tunable optical properties in graphene-based plasmon-induced transparency metamaterials**Project supported by the Key Science and Technology Research Project of Henan Province, China (Grant Nos. 162102210164 and 1721023100107) and the Natural Science Foundation of Henan Educational Committee, China (Grant No. 17A140002).

A graphene-based metamaterial for THz plasmon induced transparency (PIT) is presented and numerically studied in this paper, which consists of two horizontal graphene strips attached to a continuous vertical wire separately. The calculated surface current distributions demonstrate that the distinct PIT window results from the near-field coupling of two bright modes. To explore the physical mechanism of PIT effect, we employ the coupled Lorentz oscillator model. The transmission spectra obtained with this model fits well with the simulation results. The performance of the PIT system can be controlled through the geometry parameters of graphene strips. Moreover, the transparency window can be dynamically tuned by varying the Fermi energy and the carrier mobility of the graphene strips. The slow light effect is also explored in our proposed structure and it can achieve 1.25 ps when Fermi energy is 1.3 eV. Finally, the position of the transmission window with the variation of the nearby medium refractive index is examined. Such a proposed graphene-based PIT system may have great potential applications in photonic devices.

Ultrabroadband Near-perfect Anisotropic Metamaterial Absorber Based on a Curved Periodic W/TPX Stack

ABSTRACTA one-dimensional periodic microstructure was presented for an ultrabroadband near-perfect absorber for thermal radiation. The microstructure comprised a curved periodic stack of tungsten (15 nm) and polymethylpentene (TPX) (35 nm) with 20 layers deposited on a half-cylindrical cavity fabricated on a tungsten substrate. Visible to midinfrared regions (200 nm to 10.9 μm) allow an average measured light absorptivity of approximately 90% for transverse magnetic polarized waves at normal incidence; this property is insensitive to polar angle even when the incident angle is 80°. These superior performances were primarily attributed to intrinsic bandgap absorption in tungsten, excitation of SPPs at the air/W interface, and the resonance of the slow-light effect and its higher-order modes. Furthermore, the spectrum range of near-perfect absorption could be tuned by adjusting the center half-cylindrical shell radius, total pair number and dielectric permittivity. Moreover, the imperfection tolerance of the proposed system was studied by varying the filling ratio of metal in a periodic shell. This work may provide new guidelines for designing metamaterials absorbers that can obtain highly enhanced absorption over an ultrabroadband and in a wide range of angle of incidence.

Quantum control of fast/slow light in atom-assisted optomechanical cavity

In recent years, due to the rapid development of nano science and advanced semiconductor technology, one is able to observe more significant quantum optomechanical effects as optomechanical system turns smaller in size. Optomechanically induced transparency, fast and slow light, optical storage as well as other quantum optical and nonlinear optical effects have become the focus of research. On the other hand, the optomechanical systems coupled to other small subsystems (such as atoms, quantum dots, single electron transistors, etc.) also attract great attention in research. This is because the coupling system has not only provided more degrees of freedom for quantum manipulation, but also opened up more channels for classical and quantum information transfer. In this paper we study the optomechanically induced transparency and fast/slow light phase control in atom-assisted optomechanical cavity. Unlike the traditional systems, in this model the mechanical resonator is directly driven by a weak auxiliary driving field. We therefore find that with the change of amplitude ratio and phase difference between the auxiliary driving field and the probe field, the absorption and dispersion properties of the whole system and the group delay time vary accordingly. In the absence of auxiliary field, we observe the spectral features of the hybrid electromagnetically induced transparency and optomechanically induced transparency (OMIT) in an atom-cavity-oscillator tripartite optomechanical system. When there exists no phase difference between the auxiliary field and the probe field, we find that the membrane resonance absorption is enhanced with the increase of auxiliary field strength at resonance, causing the the optomechanically induced transparency to be suppressed, and therefore we can modify the amplitude of auxiliary field to control the depth of the OMIT window. When keeping amplitude ratio between the auxiliary field and the probe field unchanged, the modification of the phase difference between the auxiliary field and the probe field directly affects the we can not only realize the manipulation of OMIT window depth, but also control the transformation of tunable optical switch among "absorption", "transparent" and "gain" of the system. Therefore, through changing the phase of auxiliary field and probe field, we can not only realize the manipulation of OMIT window depth, but also control the transformation of tunable optical switch among "absorption" , "transparent" and "gain". In the meantime, we find that the system’s group delay time varies periodically with the change of phase difference. It is worth noting that by adjusting the phase difference and the atomic number, we can not only change the magnitude of the group delay, but also realize the conversion between slow light and fast light effect.

Dispersion characteristics of nonreciprocal gyroelectric silicon-on-insulator rectangular waveguide

A C-band rectangular waveguide with gyroelectric semiconductor is designed to study the non-reciprocal propagation characteristics of surface magnetoplasmons (SMPs), which are generated by an external magnetic field. The effective refractive index method is used to obtain the effective refractive index and transverse electric field distribution of the waveguide, and a two-dimensional rectangular waveguide is approximately regarded as a combination of two one-dimensional planar waveguides. The dispersion equation of planar waveguide with <inline-formula><tex-math id="M2">\begin{document}$ {\rm{E}}_{mn}^x$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="15-20190109_M2.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="15-20190109_M2.png"/></alternatives></inline-formula> mode in rectangular waveguide is derived. The influences of the structural parameters of rectangular waveguide and the refractive index of material on the non-reciprocal dispersion relation and time-delay characteristics are analyzed by numerical method. Due to the effect of external magnetic field, the off-diagonal elements of dielectric tensor in magnetic photonic crystal are changed. The generation of electrical anisotropy leads the time reversal symmetry to be broken. As a result, the dispersion curves of the rectangular waveguide are asymmetric with respect to propagation constant, and the complete one-way transmission of SMPs can be realized in the asymmetric frequency region. The dispersion curve tends to be a dispersion curve of planar waveguide as the width of rectangular waveguide increases, but the non-reciprocal frequency range is approximately unchanged. The width of the core region and the refractive index of the side material have a significant influence on the non-reciprocal dispersion characteristics: the group velocity of SMPs decreases with <i>ω</i> and propagation constant decreasing. The group velocity is related to the waveguide width, propagation constant and the operating wavelength. The relationship between the normalized group velocity and the width of the waveguide separately operating at 1530, 1550 and 1565 nm are studied. The group velocity is relatively slow when the width of waveguide’s core region is between 140 nm and 233.5 nm, and the minimum group velocity reaches 5.43 × 10<sup>－2</sup><i>c</i>. As for the slow light effect, the rectangular waveguide is better than planar waveguide. The rectangular waveguide has a large engineering tolerance in the width of core region, which is 93.5 nm. In addition, the dispersion curves of the rectangular waveguide with SiO<sub>2</sub>, Air, Au and Ag as the left and right cladding layers are calculated. As a result, the group velocity is proportional to the refractive index of the side material in the <i>y</i> direction of the rectangular waveguide. The slow light effect is the most obvious when the material is silver, and the minimum transmission speed can reach 2.8 × 10<sup>－3</sup><i>c</i>.

砷化镓六边形散射元构建的光子晶体慢光效应分析

砷化镓六边形散射元构建的光子晶体慢光效应分析

Photonic crystal enhanced laser desorption and ionization substrate for detection of stress biomarkers under atmospheric pressure.

Enhanced efficiency for generating molecular ions is essential for high-throughput and sensitive detection using mass spectrometry in clinical diagnostics and biomarker discovery. In this study, we developed a novel strategy to promote laser desorption and ionization by using photonic crystals as substrates. The WO3-TiO2 inverse opal photonic crystal, with a coupling stop band and laser wavelength, significantly enhanced the efficiency of laser desorption and ionization owing to the slow light effect and the porous structure of the inverse opal, which increased the interaction between the laser and WO3-TiO2. Furthermore, stress biomarkers were conveniently measured under atmospheric pressure by using WO3-TiO2 inverse opal as an enhanced substrate to evaluate the impact of chronic unpredictable mild stress. The universal and highly sensitive substrate has promised for application in the highly sensitive detection and quantification of biomarkers.

Force-dependent induced transparency in an atom-assisted optomechanical system

We theoretically investigate force-dependent induced transparency effect of an output field in an atom-assisted optomechanical system where a mechanical resonator is driven by a time-dependent force. It is shown that there exists an additional transparency window besides a standard optomechanical induced transparency window due to the Jaynes–Cummings coupling between a two-level atom and cavity. We find that the transmission amplitude of optomechanical induced transparency effect is largely suppressed or enhanced by adjusting the amplitude and phase of the external force. Benefiting from the atom and the external force, the effect of tunable fast and slow light can be realizable, which may be helpful for quantum information storage processing.

Tunable and polarization insensitive electromagnetically induced transparency using planar metamaterial

Abstract We demonstrate a classical analogue of electromagnetically induced transparency (EIT) metamaterial that consisting of anomalous split resonance ring and cross-shaped wire with simulations and experiments. The transmission spectrum is tunable with the incident angles varies from 0° to 60° in different modes. Under normal incident wave, the metamaterial leads to polarization insensitive EIT-like effect. The distributions of surface current at peaks and dips of transmission have been analyzed. Furthermore, the group index presents maximum at the transparency peak, which verifies the slow light effect. The proposed metamaterial could provide an avenue for various applications, such as refractive index sensor and microwave switch.

Broadband LWIR and MWIR absorber by trapezoid multilayered grating and SiO2 hybrid structures

A broadband metamaterial absorber with high absorption simultaneously in mid-wave infrared (MWIR) and long-wave infrared (LWIR) was proposed. In the MWIR, the absorption higher than 0.8 is from 4 to 6.3 µm, while the absorption in the LWIR is from 8.7 and 9.6 µm. The absorber is insensitive to the incident angle. The broadband absorption in the MWIR is due to the slow-light effect of the trapezoid multilayered grating structure. And the broadband absorption in the LWIR is due to the phonon polariton resonant of trapezoid SiO2 layer. In the broadband high absorption region, the atmosphere is transparent, which may greatly promote the practical application of the absorber in double-color IR imaging, detecting, infrared stealth and thermal emitting.

Dispersion engineering and thermo-optic tuning in mid-infrared photonic crystal slow light waveguides on silicon-on-insulator.

In this Letter, the design, fabrication, and characterization of slow light devices using photonic crystal waveguides (PhCWs) in the mid-infrared wavelength range of 3.9-3.98μm are demonstrated. The PhCWs are built on the silicon-on-insulator platform without undercut to leverage its well-developed fabrication process and strong mechanical robustness. Lattice shifting and thermo-optic tuning methods are utilized to manipulate the slow light region for potential spectroscopy sensing applications. Up to 20nm wavelength shift of the slow light band edge is demonstrated. Normalized delay-bandwidth products of 0.084-0.112 are obtained as a result of dispersion engineering. From the thermo-optic characterization results, the slow light enhancement effect of thermo-optic tuning efficiency is verified by the proportional relationship between the phase shift and the group index. This work serves as a proof of concept that the slow light effect can strengthen light-matter interaction and thereby improve device performance in sensing and nonlinearity applications.

Dual plasmon-induced transparency and slow light effect in monolayer graphene structure with rectangular defects

A novel monolayer graphene structure whose unit cell possesses two rectangular defects is proposed. A very obvious dual plasmon-induced transparency (PIT) effect can be successfully achieved by the destructive interference in the terahertz region. The dual PIT effect can be easily tuned by changing the Fermi energy of the monolayer graphene. Since the graphene of our structure exists in a continuous form, we can simply apply a bias voltage to achieve the tuning performance compared to those structures with discontinuous graphene patterns. We have deduced the expression of the theoretical transmittance and the numerical simulation results are very consistent with the theoretical data. Moreover, we find that this structure has a good slow light property and its group refractive index is as high as 545. Thus, the proposed structure and findings may provide a good guidance for the highly tunable optoelectronic devices and excellent slow light device.

Tunable slow and fast light in parity-time-symmetric optomechanical systems with phonon pump.

We study the response of parity-time (PT)-symmetric optomechanical systems with tunable gain and loss to the weak probe field in the presence of a strong control field and a coherent phonon pump. We show that the probe transmission can exceed unity at low control power due to the optical gain of the cavity and it can be further enhanced or suppressed by tuning the amplitude and phase of the phonon pump. Furthermore, the phase dispersion of the transmitted probe field is modified by controlling the applied fields, which allows one to tune the group delay of the probe field. Based on this optomechianical system, we can realize a tunable switch between slow and fast light effect by adjusting the gain-to-loss ratio, power of the control field as well as the amplitude and phase of the phonon pump. Our work provides a platform to control the light propagation in a more flexible way.

Manipulation of fast and slow light propagation by photonic-molecule optomechanics

We demonstrate theoretically coherent optical propagation in a composite photonic-molecule-cavity optomechanical system consisting of two whispering-gallery microcavities in which one of the optical cavities is optomechanical with high cavity dissipation and the other is an auxiliary with a high quality factor. Optomechanically induced transparency and its related propagation properties such as fast and slow light effects are investigated based on the hybrid system for suitable parametric regimes. By controlling the coupling strength J between the two cavities, which is determined by their distance and the decay rate ratio δ of the two cavities, tunable and controllable fast-to-slow light propagation (or vice versa) can be achieved. Our study may provide a further insight of the composite photonic-molecule optomechanical systems and may open up promising on-chip applications in quantum information processing.

Metal–insulator–metal waveguide‐coupled asymmetric resonators for sensing and slow light applications

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.

Flat-top optical resonance in a single-ring resonator based on manipulation of fast- and slow-light effects.

Optical single-ring resonance inherently generates Lorentzian-shape magnitude and group-delay responses, leading to critical performance limitation in photonics, cavity quantum electrodynamics, cavity optomechanics, and atomic and optical physics. Here, we propose a new type of microresonator that stimulates flat-top resonance in a single-ring cavity. By manipulating the fast and slow light effects in the microresonator, the flat-top group delay can be tuned with an ignorable magnitude variation. In addition, the bandpass response can be switched to a notch, which can enable function-reconfigurable photonic integrated circuits (PICs) without a physical change in the architecture. Our demonstration provides the possibility of developing microresonator-based PICs with unprecedented high flexibility and capacity.

Chirality-dependent electromagnetically induced transparency based on a double semi-periodic helix metastructure.

A chiral metastructure composed of spatially separated double semi-periodic helices is proposed and investigated theoretically and experimentally in this Letter. Chirality-dependent electromagnetically induced transparency (EIT) and a slow light effect in the microwave region are observed from a numerical parameter study, while experimental results from the 3D printing sample yield good agreement with the theoretical findings. The studied EIT phenomenon arises as a result of destructive interference by coupled resonances, and the proposed chiral metastructure can be applied in areas such as polarization communication, pump-probe characterization, and quantum computing areas.

Dynamically tunable electromagnetically induced transparency in a terahertz hybrid metamaterial

A novel mechanism to realize dynamically tunable metamaterial analogue of electromagnetically induced transparency (EIT) in the terahertz (THz) regime is proposed. By putting a monolayer graphene under the dark resonator, the amplitude of the EIT resonance in the metal-based metamaterial can be substantially modulated via altering the Fermi level of graphene. The amplitude modulation can be attributed to the change in the damping rate of the dark mode caused by the recombination effect of the conductive graphene. This work provides an alternative way to achieve tunable slow light effect and has potential applications in THz wireless communications.

Investigation of tunable plasmon-induced transparency and slow-light effect based on graphene bands

We have constructed a graphene-based planar metamaterial structure. This structure can achieve a clear plasmon-induced transparency phenomenon via destructive interference. We further find that this structure has an excellent tuning function. The tuning function can be realized only by adjusting the Fermi level of graphene, and the structure is a simple and continuous design. In addition, we find that the structure has excellent slow-light properties through an analysis of the dispersion relation, and the slow-light coefficient can approach 439. This lays a solid theoretical foundation for the construction and design of tunable devices and slow-light devices.

Investigation of A Slow-Light Enhanced Near-Infrared Absorption Spectroscopic Gas Sensor, Based on Hollow-Core Photonic Band-Gap Fiber.

Generic modeling and analysis of a slow-light enhanced absorption spectroscopic gas sensor was proposed, using a mode-tuned, hollow-core, photonic band-gap fiber (HC-PBF) as an absorption gas cell. Mode characteristics of the un-infiltrated and infiltrated HC-PBF and gas absorption enhancement of the infiltrated HC-PBF were analyzed. A general rule of microfluidic parameters for targeting different gas species in the near-infrared was obtained. Ammonia (NH3) was used as an example to explore the effects of slow light on gas detection. The second harmonic (2f) signal and Allan deviation were theoretically investigated based on the derived formulations.

Efficient Thermal Tuning Employing Metallic Microheater With Slow-Light Effect

Thermal tuning acts as one of the most fundamental roles in integrated silicon photonics since it can provide flexibility and reconfigurability. Low tuning power and fast tuning speed are long-term pursuing goals in terms of the performance of the thermal tuning. Here, we propose and experimentally demonstrate an efficient thermal tuning scheme employing the metallic metal heater. The slow-light effect in the photonic crystal waveguide is employed to enhance the performance of the metal microheater. Meanwhile, the metal microheater is integrated on the side of the waveguide rather than on the top. Thanks to both the slow-light effect and the side-integrated microheater, the tuning efficiency is significantly enhanced, and the response time as fast as 2 $\mu \text{s}$ is obtained. Since the thermal tuning with metal heater has been widely applied in silicon photonics, the proposed scheme may provide a valuable solution towards the performance enhancement of the thermal tuning in silicon photonics.