Optical Buffer Research Articles

Zero-GVD slow light of coupled topological edge states in a sandwiched photonic crystal waveguide

We propose a new scheme to realize topological photonic states with low group velocity (vg) and zero group velocity dispersion (zero-GVD) based on a sandwiched photonic crystal (PC) waveguide, which are composed of finite sized PCs with different topological phases. In our proposed sandwiched heterostructure, two coupled topological edge states (CTESs) can be found, one of which can be applied to slow light by modifying the radii of the dielectric rods. The slow light characteristics of CTES, including zero-GVD, large average group index and normalized delay-bandwidth product, are discussed in detail based on finite element method (FEM) simulation. Besides, the robustness of CTES with slow light is verified, when introducing random disorders. Time-domain simulation results demonstrate the dispersionless transport of CETS in zero-GVD region. Our findings pave a way of topological slow light, enrich the topological PC research, and have new application in optical buffers and optical delay lines.

Topological Slow Light Rainbow Trapping and Releasing Based on Gradient Valley Photonic Crystal

Slow light topological photonic crystal waveguide offers an attractive platform for enhancing light-matter interaction. We design a slow light rainbow trapping based on translational valley photonic crystal waveguides constructed by a gradient interface width. Through theoretical analysis and numerical calculation, the resulting structure supports topologically protected edge states at different frequencies. The edge state can be slowed down to zero group velocity and trapped at different positions. Moreover, the switch between slow light trapped states and transport states can be easily realized by tuning the structural parameter. Our work can help open up a new avenue to control the flow of light and find great potential for applications such as optical buffers and wavelength-division multiplexing.

Theoretical and Simulation Investigation for Create Optical Buffer in Semiconductor Optical Ring Resonators

Theoretical and Simulation Investigation for Create Optical Buffer in Semiconductor Optical Ring Resonators

Realization of tunable index-near-zero modes in nonreciprocal magneto-optical heterostructures.

Epsilon-near-zero (ENZ) metamaterial with the relative permittivity approaching zero has been a hot research topic for decades. The wave in the ENZ region has infinite phase velocity (v=1/ε μ), but it cannot efficiently travel into the other devices or air due to the impedance mismatch or near-zero group velocity. In this paper, we demonstrate that the tunable index-near-zero (INZ) modes with vanishing wavenumbers (k = 0) and nonzero group velocities (vg ≠ ~0) can be achieved in nonreciprocal magneto-optical systems. The INZ modes have been experimentally demonstrated in the photonic crystals at Dirac point frequencies, and that impedance-matching effect has been observed as well [Nat. Commun.8, 14871 (2017)10.1038/ncomms14871]. Our theoretical analysis reveals that the INZ modes exhibit tunability when changing the parameters of the one-way (nonreciprocal) waveguides. Moreover, owing to the zero-phase-shift characteristic and decreasing vg of the INZ modes, several perfect optical buffers are proposed in the microwave and terahertz regimes. The theoretical results are further verified by the numerical simulations using the finite element method. Our findings may open new avenues for research in the areas of ultra-strong or -fast nonlinearity, perfect cloaking, high-resolution holographic imaging, and wireless communications.

Valley-Dependent Topological Photonic Crystals With Heterogeneous Bearded Interfaces for SOI-Based Integrated Optical Devices

Topologically protected photonic edge states allow backscattering-free and disorder-immune light propagations, offering a new scheme for the development of on-chip information systems. Valley degree of freedom is one of the most reliable way to achieve topologically non-trivial states. Here, we take advantage of heterogeneous topological interfaces to construct integrated optical devices in the valley-dependent photonic crystals. Localized Berry curvature around the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K</i> / <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K′</i> point guarantees the existence of valley kink states at telecom wavelengths below the light cone, ensuring both optical robustness and light confinement. We harness the combination of two kinds of bearded interfaces to realize wavelength-selective topological routing of light in the micro-ring resonators. The proposed bearded interfaces can support edge modes with large group indices up to 90, showing a great potential to obtain remarkable slow light effects. This work paves the way to implement optical buffers and reconfigurable photonic devices with the adoption of photonic valley pseudospin.

Controllable fast light in quantum dot molecules assisted hybrid optomechanical system

AbstractWe investigate the superluminal effect of transmitted probe field in three‐level quantum dot molecules (QDMs) assisted optomechanical system which consist of mechanical resonator. We show that the superluminal behavior of transmitted probe field can be controlled by changing the tunneling strength and number of QDMs inside the cavity. Furthermore, it is shown that in the absence of tunneling strength, the transmitted probe field shows the fast light effect and by increasing the number of QDMs, the enhancement in superluminal behavior is decreased and converts into slow light. While, in the presence of the tunneling strength, with the increase of the number of QDMs the superluminal behavior of transmitted field is obtained at smaller detuning frequency. The influence of tunneling strength and number of QDMs on superluminal part of the transmitted probe field is quite useful in optical memory, optical buffers, and quantum information processing.

Slow light in topological coupled-corner-state waveguide

We theoretically propose a uide (CCSW), which is composed of a zigzag edge-like structure based on C-4 symmetrical lattice. CCSW mode is achieved by weak coupling between a sequence of higher order topological corner state (TCS). Based on the tight-binding approximation, the flat dispersion relation of CCSW mode is obtained, and suitable for slowing down light. The characteristics of slow light, including the group index, group velocity dispersion, normalized bandwidth and normalized delay-bandwidth product, are discussed in detail. At the Eigen frequency of individual TCS, the group velocity dispersion of CCSW mode is zero. Importantly, the CCSW mode shows strong robustness when introducing disorders, compared with the conventional Coupled-Resonator-Optical Waveguide based on photonic crystal defect cavities. Our findings may find topological slow light applications such as optical buffers, the processing of optical signals, optical delay lines and so on.

Silicon-on-Insulator Optical Buffer Based on Magneto-Optical 1 × 3 Micro-Rings Array Coupled Sagnac Ring

Optical buffer is a key technology to control optical routing and solve channel competition, which directly determines the performance of information processing and storage. In this study, a switchable optical buffer using the nonreciprocal silicon-on-insulator (SOI) magneto-optical micro-ring (MOMR) array coupled with Sagnac ring was introduced, which can exceed the time-bandwidth limitation. The transmission equations and propagation characteristics of optical signal in 1 × 3 micro-rings and Sagnac ring coupled 1 × 3 micro-rings based on two kinds of phase-change materials were studied. The group time delay, effective buffer time and readout operation in the buffer were also investigated.

Time advancement and distortionless of optical pulses via stimulated Brillouin scattering by broadband pump in optical fibers

The broadening Brillouin absorption spectrum of stimulated Brillouin scattering (SBS) in optical fibers by multiple monochromatic pumps is investigated. The results show that the bottom of the effective absorption spectrum becomes flatter with increasing the number of spectrum lines, and the spectral bandwidth is effectively expanded by multiple monochromatic pumps. but the spectral spacing should be tailored reasonably to ensure a broad linear range of the refractive index to reduce the pulse distortion. The time advancement and the pulse distortion induced by SBS pumped by broadband Gaussian and rectangular spectra are demonstrated respectively. The simulation results indicate that the pulse distortion induced by broadband rectangular spectral pump is smaller than that of broadband Gaussian spectral pump, and the time advancement can be improved effectively by increasing signal light power. We believe that these results are very promising for designing optical buffering or sensing components based on SBS fast light.

Flow-Controlled and Clock-Distributed Optical Switch and Control System

Switching the traffic in the optical domain has been considerably investigated as a future-proof solution to overcome the intrinsic bandwidth bottleneck of electrical switches in data center networks (DCNs). However, due to the lack of fast and scalable optical switch control mechanism, the lack of optical buffers for contention resolution, and the complicated implementation of fast clock and data recovery (CDR), the practical deployment of fast optical switches in data centers (DCs) remains a big challenge. In this work, we develop and experimentally demonstrate for the first time a flow-controlled and clock-distributed optical switch and control system, implementing 43.4 ns optical switch configuration time, less than 3.0E-10 packet loss rate resulting from the packet contention, and 3.1 ns fast CDR time. Experimental results confirm that zero buffer overflow caused packet loss and lower than <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3~ \boldsymbol {\mu }\text{s}$ </tex-math></inline-formula> server-to-server latency are achieved for network deploying a smaller electrical buffer of 8192 bytes at a traffic load of 0.5. Real servers running the Transmission Control Protocol (TCP) traffic generating and monitoring tools are exploited in this switch and control system as well, validating its capability of running practical DCNs services and applications with full TCP bandwidth.

Nanosecond optical switching and control system for data center networks

Electrical switching based data center networks have an intrinsic bandwidth bottleneck and, require inefficient and power-consuming multi-tier switching layers to cope with the rapid growing traffic in data centers. With the benefits of ultra-large bandwidth, high-efficient cost and power consumption, switching traffic in the optical domain has been investigated to replace the electrical switches inside data center networks. However, the deployment of nanosecond optical switches remains a challenge due to the lack of corresponding nanosecond switch control, the lack of optical buffers for packet contention, and the requirement of nanosecond clock and data recovery. In this work, a nanosecond optical switching and control system has been experimentally demonstrated to enable an optically switched data center network with 43.4 nanosecond switching and control capability and with packet contention resolution as well as 3.1 nanosecond clock and data recovery.

Tunable plasmonically induced transparency with giant group delay in gain-assisted graphene metamaterials.

We propose a graphene metamaterial consisting of several layers of longitudinally separated graphene nanoribbon array embedded into gain-assisted medium, demonstrating electromagnetically induced transparency-like spectra. Combined with finite-difference time-domain simulations, the transfer matrix method and temporal coupled-mode theory are adopted to quantitatively describe its transmission characteristics. These transmission characteristics can be tuned by altering the gain level in medium layer and the Fermi energy level in graphene. Additionally, it is the incorporation between gain medium and graphene nanoribbons with optimized geometrical parameters and Fermi energy level that the destructive interference between high order graphene plasmonic modes can be obtained, suggesting drastic phase transition with giant group delay and ultra-high group index up to 180 ps and 104, respectively. Our results can achieve efficient slow light effects for better optical buffers and other nonlinear applications.

Effect of Mg Doping on the Physical Properties of Fe2O3 Thin Films for Photocatalytic Devices.

Undoped and Mg-doped (y = [Mg2+]/[Fe3+] = 1, 2, 3, and 4 at.%) Fe2O3 thin films were synthesized by a simple spray pyrolysis technique. The thin films were extensively characterized. X-ray diffraction (XRD) and energy-dispersive spectroscopy (EDS) analysis confirmed the successful insertion of Mg in the rhombohedral structure of Fe2O3. In addition, scanning electronic microscope (SEM) and confocal microscope (CM) images showed a homogenous texture of the film, which was free of defects. The rough surface of the film obtained by spray pyrolysis is an important feature for photocatalysis and gas sensor applications. The direct band gap of the doped Fe2O3 films obtained for [Mg2+]/[Fe3+] = 3 at.% was Edir = 2.20 eV, which recommends the Mg-doped iron oxide as an optical window or buffer layer in solar cell devices. The photodegradation performance of Mg-doped Fe2O3 was assessed by studying the removal of methylene blue (MB) under sunlight irradiation, with an effective removal efficiency of 90% within 180 min. The excellent photodegradation activity was attributed to the strong absorption of Mg-doped Fe2O3 in the UV and most of the visible light, and to the effective separation of photogenerated charge carriers.

Engineering rainbow trapping and releasing in valley photonic crystal with electro-optical material

Topological photonic insulators provide a robust platform for controlling the flow of light. Here, we propose a method to realize slow light rainbow trapping and releasing based on valley photonic crystals, which is created by gradually increasing the structure parameter. The edge waves of different frequencies are spatially separated and trapped at different positions to form topological rainbow trapping. Furthermore, the system is constructed by electric-optical material whose refractive index is tuned by applied voltages. Therefore, the switchable between slow light trapping states and releasing states can be realized by tuning the external voltage. The position where the wave stops propagating is given by theoretical analysis and numerical simulation. These results offer a novel, to the best of our knowledge, scheme for realizing multi-frequency routing. Such a structure could find application prospects in optical buffers, optical storage, and other optical communication devices.

Slow-light dispersion of a cavity polariton in an organic crystal microcavity

Herein, we have measured the phase dispersion of a cavity polariton in a single-crystalline anthracene microcavity via interference spectroscopy. Results show slow-light dispersion at the cavity polariton's lower polariton resonance, which agrees well with the transfer matrix method calculation results. According to the theoretical calculations, the slow-light dispersion's group refractive index is 24. We found that the structural dispersion due to a phenomenological photon cavity and material dispersion caused by the exciton contributed to the large group refractive index. These efforts will aid in realizing optical buffer memories for organic microcavities.

Performance analysis comparison of optical burst switching networks' contention resolution techniques

&lt;p&gt;&lt;span&gt;Optical burst switching (OBS) is a transporting network for the optical internet in the years ahead vision. As OBS depends on statistical multiplexing, the effect of contention resolution is the main issue to achieve a low probability losing of burst. Basically, there are different ways to resolve contentions in the OBS networks like wavelength conversion, deflection routing, burst segmentation and optical buffering using fiber delay lines. Burst segmentation and deflection routing as well as fiber delay lines technologies, are discussed among the various accessible conflict resolution techniques in this study. However, the main aim of this study is to demonstrate that, the performance of fiber delay line (FDL) is better than other techniques to resolve contention by comparing the performance of these different schemes based on burst losing probabilities and the data handling capability. To evaluate the performance, appropriate mathematical formulae were used. Under the MATLAB environment, the performance was measured based on the probability of burst loss versus incoming traffic (load). The outcomes suggest that deflection routing outperforms fiber delay lines and burst segmentation in the OBS network in terms of resolve the contention. &lt;/span&gt;&lt;/p&gt;

Synergistic Switch Control Enabled Optical Data Center Networks

Optical switching, which benefits from high bandwidth and low latency, promises to revolutionize data center networks that suffer from a bandwidth bottleneck and hierarchical structure. However, the lack of adaptable and fast optical switch control schemes, the lack of optical buffers for contention resolution, and the high cost of clock and data recovery (CDR) impede the practical deployment of optical switches in data centers. Networking communities have tried to address these challenges from different perspectives. However, the proposed solutions may be interdependent and thus introduce unexpected issues. In this article, a synergistic optical switch control mechanism is proposed to simultaneously solve the aforementioned challenges. The developed label control technique allows for controlling and configuring packet switching within 43.4 ns. The implementation of clock distribution achieves a fast CDR of 3.1 ns at low cost, and the design of an optical flow control protocol prevents packet loss caused by packet contention.

Slow Light Effect and Tunable Channel in Graphene Grating Plasmonic Waveguide

A graphene plasmon waveguide composed of silicon grating substrate and a silica separator is proposed to generate the slow-light effect. A bias voltage is applied to tune the optical conductivity of graphene. The tunability of the slow-light working channel can be achieved due to the adjustable bias voltage. With an increase in the bias voltage, the working channel exhibited obvious linear blue-shift. The linear correlation coefficient between the working channel and the bias voltage was up to 0.9974. The average value of the normalized delay bandwidth product (NDBP) with different bias voltages was 3.61. In addition, we also studied the tunable group velocity at a specific working channel. Due to the tunability of this miniaturized waveguide structure, it can be used in a variety of applications including optical storage devices, optical buffers and optical switches.

Electrically controlled on-demand photon transfer between high-Q photonic crystal nanocavities on a silicon chip

Optical buffer memories, which do not rely on an intermediate conversion between optical and electrical signals, can be used to realize optical networks with low latency and low energy consumption. Photonic-crystal nanocavities can confine photons in a very small region for a long time, and thus may be used as core components of such optical buffer memories. However, a scalable method for on-demand photon transfer between nanocavities is required. Here we demonstrate a photonics–electronics integration solution that realizes electrical control of a coupled ultrahigh-quality-factor nanocavity system on a silicon chip. In this system, the photons confined in one of the two storage nanocavities can be transferred to the other storage nanocavity by applying a voltage pulse to the control cavity. A transfer efficiency of 76% and a cavity photon lifetime of 1.3 ns after the transfer are achieved. Researchers demonstrate the transfer of photons from one storage nanocavity into another by applying a voltage pulse. A transfer efficiency of 76% is achieved.

Synthesis and Characterization of MgO Thin Films Obtained by Spray Technique for Optoelectronic Applications

Magnesium oxide (MgO) thin films with different magnesium concentrations ([Mg2+] = 0.05, 0.1, 0.15 and 0.2 mol·L−1) in a spray solution have been successfully grown using a spray pyrolysis technique. X-ray diffraction (XRD), Maud software, FTIR spectroscopy, a confocal microscope, Wien2k software, spectrophotometry and a Photoluminescence spectrometer were used to investigate the structural, morphological and optical properties. XRD analysis revealed a better crystalline quality of the MgO thin layer synthesized with [Mg2+] = 0.15 mol·L−1, which crystallized into a face-centered cubic structure along the preferred orientation (200) lattice plan. The enhancement of the crystalline quality for the MgO thin film ([Mg2+] = 0.15 mol·L−1) was obtained, which was accompanied by an increment of 94.3 nm of the crystallite size. No secondary phase was detected and the purity phase of the MgO thin film was confirmed using Maud software. From the transmission spectra results, high transparent and antireflective properties of the MgO thin film were observed, with an average transmission value of about 91.48% in the visible range, which can be used as an optical window or buffer layer in solar cell applications. The films also have a high reflectance value in the IR range, which indicates that the highly reflective surface will prevent an increase in surface temperature under solar irradiation, which could be beneficial in solar cell applications. A direct band gap type was estimated using the Tauc relation which is close to the experimental value of 4.0 eV for optimal growth. The MgO material was tested for the degradation of methylene blue (MB), which reached a high photodegradation rate of about 83% after 180 min under sunlight illumination. These experimental trends open a new door for promising the removal of water contaminants for photocatalysis application.