Slow Light Phenomenon Research Articles

Localized slow light phenomenon in symmetry broken terahertz metamolecule made of conductively coupled dark resonators

We demonstrate a localized slow light phenomenon in a symmetry broken metamolecule (MM) of conductively coupled dark resonators at a terahertz band. Under a dark-mode excitation condition, the single mode resonance becomes dual modes by breaking the uniaxial symmetry of MM. Thus, a transparency window exists in between dual modes. An interaction of V-shaped plasmonic antenna-type (VA) resonances results in a plasmon-induced transparency (PIT) when the asymmetric deviation is below 13 μm. A maximum 25.9 ps group-delay of incident THz pulse is observed at the transparency window. When the asymmetric deviation is beyond 13 μm, one excitation pathway switches from VA resonance to the inductor-capacitor (LC) resonance, which dominates the high-frequency side-mode. Then, the PIT effect transfers to the PIT-like behavior and the slow light phenomenon vanishes. The aforementioned discovery allows for a speed modulation of slow light via symmetry breaking in MM.

Fast and slow light enhancement using cascaded microring resonators with the Sagnac reflector

A cascaded microring resonator based on silicon waveguides with an MMI (Multimode Interference) based Sagnac reflector is proposed in this study. By controlling the coupling coefficients with the used of the MMI based Sagnac reflector, the double of both pulse delay and advancement for the slow and fast light can be achieved. The new structure can produce the fast and slow light phenomenon on one chip with a double of the time delay and pulse advancement. By using the Sagnac reflector, the device is very compact. Transfer matrix method and FDTD (Finite Difference Time Domain) simulation are used to obtain the characteristics of the device. The transmission, phase, group delay and pulse propagation are analyzed in detail. Our FDTD simulations show a good agreement with the analytical theory.

Simulation of an all-optical photonic crystal switch using nonlinear optics and slow light for hetero structures y-junctions

In this paper we shows a photonic crystal mach-zender interferometer (MZI) based on new structure by coupled-cavity waveguide using slow light to shorten the length of waveguide arms and nonlinear properties of GaAs for design of an all optical switch. So we comparison with optical switches at arm’s length that approximately is 10m. The design of y-juntion is performed using finite-difference time-domain method. finally the physical principals behind the phenomenon of slow light in photonic crystal waveguide is discussed.

Unfolding the band structure of non-crystalline photonic band gap materials.

Non-crystalline photonic band gap (PBG) materials have received increasing attention, and sizeable PBGs have been reported in quasi-crystalline structures and, more recently, in disordered structures. Band structure calculations for periodic structures produce accurate dispersion relations, which determine group velocities, dispersion, density of states and iso-frequency surfaces, and are used to predict a wide-range of optical phenomena including light propagation, excited-state decay rates, temporal broadening or compression of ultrashort pulses and complex refraction phenomena. However, band calculations for non-periodic structures employ large super-cells of hundreds to thousands building blocks, and provide little useful information other than the PBG central frequency and width. Using stereolithography, we construct cm-scale disordered PBG materials and perform microwave transmission measurements, as well as finite-difference time-domain (FDTD) simulations. The photonic dispersion relations are reconstructed from the measured and simulated phase data. Our results demonstrate the existence of sizeable PBGs in these disordered structures and provide detailed information of the effective band diagrams, dispersion relation, iso-frequency contours, and their angular dependence. Slow light phenomena are also observed in these structures near gap frequencies. This study introduces a powerful tool to investigate photonic properties of non-crystalline structures and provides important effective dispersion information, otherwise difficult to obtain.

Vacuum induced transparency and slow light phenomena in a two-level atomic ensemble controlled by a cavity**Project supported by the National Natural Science Foundation of China (Grant No. 11304010).

We study the optical properties of a two-level atomic ensemble controlled by a high-finesse cavity. Even though the cavity is initially in the vacuum state in the absence of external driving, the probe response of the atomic ensemble can be dramatically modified. When the collectively enhanced atom–cavity coupling is strong enough and the cavity decay rate is much smaller than the atomic damping rate, an electromagnetically induced transparency-like coherent phenomenon emerges with a dip absorption for the response of the two-level atoms in the cavity without driving, and thus is called vacuum induced transparency. We also show the slow light with very low group velocity in such an atomic ensemble.

Investigation of uniaxial anisotropic chiral metamaterial waveguide with perfect electromagnetic conductor loading

The paper presents investigations of the electromagnetic characteristics of circular waveguides made of uniaxial anisotropic chiral medium; the outer surface of the guide being coated with a PEMC (perfect electromagnetic conductor) medium. The emphasis is given on the energy flux density patterns of such guides with varieties of anisotropic chiral materials. Dispersion relation of the guide is developed, and followed by the evaluation of sustained modes, which determine the energy flux density patterns corresponding to different low-order hybrid modes. The flux density characteristics provide the evidence of existing backward waves in uniaxial anisotropic mediums, contributing more to the phenomenon of slow light in chiral metamaterials.

Study on transmission of photonic crystal waveguide with slow light phenomena

In this paper, we propose the transmission properties of three two-dimensional photonic crystal waveguides (PCWs) obtained by shifting the shape of air holes localized at each side of the waveguide using the finite difference time domain (FDTD) method. One modifies the radius of air holes and the permittivity of dielectric rods which replace air holes. The other substitute air rings for air holes. The last one is combination of air rings and air holes or dielectric rods. We show that we can achieve unusual “Г-type” or “n-type” transmission spectrum depending on the different parameters such as thickness of air holes, inner radius of air rings and permittivity of square dielectric rod. The notable difference is presented to different structures. Furthermore, we show the slow light phenomena using a unique geometrical parameter. This work will be of significance in fabricating PC devices.

Highly directed emission from self-assembled quantum dots into guided modes in disordered photonic-crystal waveguides

We explore the dynamics and directionality of spontaneous emission from self-assembled In(Ga)As quantum dots into TE-polarised guided modes in GaAs two-dimensional photonic crystal waveguides. The local group velocity of the guided waveguide mode is probed, with values as low as $\sim 1.5\%\times c$ measured close to the slow-light band edge. By performing complementary continuous wave and time-resolved measurements with detection along, and perpendicular to the waveguide axis we probe the fraction of emission into the waveguide mode ($\beta$-factor). For dots randomly positioned within the unit cell of the photonic crystal waveguide our results show that the emission rate varies from $\geq 1.55$ $ns^{-1}$ close to the slow-light band edge to $\leq 0.25$ $ns^{-1}$ within the two-dimensional photonic bandgap. We measure an average Purcell-factor of $\sim 2\times$ for dots randomly distributed within the waveguide and maximum values of $\beta\sim 90 \%$ close to the slow light band edge. Spatially resolved measurements performed by exciting dots at a well controlled distance $0-45$ {\mu}m from the waveguide facet highlight the impact of disorder on the slow-light dispersion. Although disorder broadens the spectral width of the slow light region of the waveguide dispersion from $\delta E_{d}\leq 0.5$ meV to $>6$ meV, we find that emission is nevertheless primarily directed into propagating waveguide modes. The ability to control the rate and directionality of emission from isolated quantum emitters by placing them in a tailored photonic environment provides much promise for the use of slow-light phenomena to realise efficient single photon sources for quantum optics in a highly integrated setting.

34.1: Invited Paper: Slowing Light in Liquid Crystals

AbstractSteep dispersion is obtained by exploiting the large optically induced refractive index change in liquid crystal media. This effect is observed either in devices made by the association of liquid crystals with a photoconductive substrate or by employing the photo‐isomerization of azo‐dye molecules hosted in a chiral liquid crystal structure. When interacting in these media, a pulse of light that is relatively long becomes delayed, hence, slow light phenomena are obtained with steep dispersion, a feature that can be exploited for improving the performances of optical sensors.

Optimal electromagnetic energy transmission and real-time dissipation in extended media

Pulse reshaping effects that give rise to fast and slow light phenomena are inextricably linked to the dynamics of energy exchange between the pulse and the propagation medium. Energy that is dissipated from the pulse can no longer participate in this exchange process, but previous methods of calculating real-time dissipation are not valid for extended propagation media. We present a method for calculating real-time dissipation that is valid for electromagnetic pulse propagation in extended media. This method allows one to divide the energy stored in an extended medium into the portion that can be later transmitted out of the medium, and that portion which must be lost to either dissipation or reflection.

Optical self-phase modulation using a new photonic crystal coupled-cavity waveguide

In this paper, self-phase modulation of an optical pulse using a new photonic crystal coupled-cavity waveguide is simulated and analyzed. The structure of the new coupled-cavity waveguide is introduced and its advantage over the previous type of coupled-cavity waveguide is discussed. In order to obtain a high group index over a large bandwidth and benefit from the slow light phenomenon, the group index and group velocity dispersion parameter curves of the guided mode are calculated. Finally, the transient simulation of the structure is performed using a finite-difference time-domain method. The calculated required length of the coupled-cavity waveguide for a maximum phase shift of π is about 31 μm. Spectral broadening of the optical pulse as a result of self-phase modulation is also presented and discussed.

Slow-Light and Enhanced Sensitivity in a Displacement Sensor Using a Lossy Fiber-Based Ring Resonator

Along the last years, much debate has been done on the efficiency of slow-light phenomena in order to enhance light-matter interactions, especially for sensing purposes. This improvement could be key to develop more compact and sensitive devices. In this work we develop an all-fiber sub-micrometric displacement sensor using slow-light sensitivity enhancement in a lossy ring resonator. In the proposed structure the losses produced by the displacement of a mechanic transducer can be translated into strong variations of group index and therefore strong transmittance variations. We show that this effect is strictly related to slow light, and not related to confinement effects or any other.

Broadband plasmon induced transparency in terahertz metamaterials

Plasmon induced transparency (PIT) could be realized in metamaterials via interference between different resonance modes. Within the sharp transparency window, the high dispersion of the medium may lead to remarkable slow light phenomena and an enhanced nonlinear effect. However, the transparency mode is normally localized in a narrow frequency band, which thus restricts many of its applications. Here we present the simulation, implementation, and measurement of a broadband PIT metamaterial functioning in the terahertz regime. By integrating four U-shape resonators around a central bar resonator, a broad transparency window across a frequency range greater than 0.40 THz is obtained, with a central resonance frequency located at 1.01 THz. Such PIT metamaterials are promising candidates for designing slow light devices, highly sensitive sensors, and nonlinear elements operating over a broad frequency range.

Group velocity of the electromagnetic wave packet in a relativistic dispersive medium

This paper presents the fully relativistic, general expression for the group velocity Vg of the electromagnetic wave packet in a relativistic dispersive medium. Motion of the medium is accounted for with the relativistic index of refraction. The general formula for Vg is specialized to a few particular situations that are briefly discussed. The explicit, exact, fully relativistic expression for Vg is relevant to all issues where the electromagnetic wave packet travels through a medium in motion, especially where the velocity of the medium is high or utmost accuracy is essential, e.g. it pertains to the slow light phenomenon, pulsar radiation, GPS, radar, and LIDAR technologies.

The numerical study on large bandwidth photonic crystal waveguide with slow light phenomena

In this paper, two novel types of semi-slow light photonic crystal waveguide with large transmission bandwidth obtained by shifting the boundaries of a W1 waveguide in the direction of light propagation are presented. One includes air rings localized at only one side of the line defect and the other replaces the holes at each side of the waveguide by the uniform air rings which are constructed by the homocentric square dielectric rod inserted into the air holes. The structure produces unusual “n-type” transmission spectrum depending on the different parameters such as inner radius of air ring, dielectric constant of square dielectric rod, etc. It is shown that the transmission spectra of the two structures are completely different from each other. A versatile control of light propagation with large normalized bandwidth and slow light phenomena can be obtained using a unique geometrical parameter. Numerical simulation by the finite-difference time-domain (FDTD) method demonstrates the propagation of the broadband pulse.

薄膜介质内慢光现象及其理论研究

薄膜介质内慢光现象及其理论研究

Tunable flat band slow light in reconfigurable photonic crystal waveguides based on magnetic fluids

A kind of two-dimensional photonic crystal line-defect waveguide with 45°-rotated square lattice is proposed to present slow light phenomena. Infiltrating the photonic crystal waveguide with appropriate magnetic fluids can generate very wide flat bands of guided modes, which give rise to the excellent slow light properties. The bandwidth centered at λ0=1550nm of the designed W1 waveguide is considerably large (around 54nm). The obtained group velocity dispersion β2 within the bandwidth is ultralow (varying from −2118a/2πc2 to 1845a/2πc2, where a and c are the period of the lattice and the light speed in vacuum, respectively). Simultaneously, the normalized delay-bandwidth product is relatively large compared with other works. Reconfiguring the photonic crystal waveguide with magnetic fluids of different concentrations can remarkably tune the slow light parameters and the trade-off between them, while the type of magnetic nanoparticles constituting the magnetic fluids negligibly affect the slow light properties. The explicit linear variation of the slow light parameters with the magnetic fluid concentration is convenient for the practical tuning.

Trapped rainbow techniques for spectroscopy on a chip and fluorescence enhancement

We report on the experimental demonstration of the broadband "trapped rainbow" in the visible range using arrays of adiabatically tapered optical nano waveguides. Being a distinct case of the slow light phenomenon, the trapped rainbow effect could be applied to optical signal processing, and sensing in such applications as spectroscopy on a chip, and to providing enhanced light-matter interactions. As an example of the latter applications, we have fabricated a large area array of tapered nano-waveguides, which exhibit broadband "trapped rainbow" effect. Considerable fluorescence enhancement due to slow light behavior in the array has been observed.

Fast-Light to Slow-Light Switching in a Laser Cavity

We report on experimental work investigating slow- and fast-light in a ring-laser cavity that utilizes a semiconductor optical amplifier (SOA) as its primary gain medium. By allowing a pulse to propagate around the loop multiple times, we are able to achieve a tunable delay-bandwidth product near 10 for a 10-ps pulse. Our results show a shift between fast-light, as expected in a typical SOA, to slow-light as the pulse propagates around the loop. This slow-light phenomenon in a gain medium is not expected from an SOA, but arises due to the interaction between the lasing mode and the signal mode.

Micro-Ring Chains With High-Order Resonances

We analyze micro-ring resonator chains that have a system response with N-th order poles and zeroes when the chain consists of N unit cells. These include the recently proposed zigzag micro-ring resonator chains exhibiting new fast- and slow- light properties and a dual ring chain for which the explicit expression of the system function is given. We discuss the realization of ultrahigh order structures with sharp peaks and large out-of-band rejection filters, ultra-sharp notch optical filters for optical carrier suppression and the general properties of slow and fast light phenomena in this type of systems. All the analyses are based on the pole-zero representation of the system function. A tuning mechanism for the modified dual-ring structures acting as notch filters is also proposed.