Optical Buffer Research Articles

Phase change foam with temperature-adaptive radiative cooling feature for all-day building energy saving

Radiation cooling is an emerging energy-saving technology that requires a minimal energy input to achieve passive cooling. To date, the majority of research has focused on maximizing the cooling power. However, a powerful cooling performance may lead to overcooling at night or during cold seasons. In this study, we developed a phase change radiation cooling material (PCRCM) with temperature-adaptive cooling features to meet dynamic cooling requirements. Polydimethylsiloxane was selected as the flexible thermal emission substrate, while boron nitride nanosheets were chosen as the optical fillers. Consequently, radiation cooling materials exhibiting 97.5% reflectance and 94% emissivity were achieved. The phase change material (PCM) was then loaded onto the foam as an optical and thermal buffering medium. The obtained PCRCM exhibited 96% reflectance in hot atmosphere and 82.6% reflectance in cold atmosphere, passively cooling through thermal emission and PCM endotherms during the daytime, and actively heating through PCM exotherms at nighttime. Simulation and outdoor tests demonstrated that the PCRCM shows an excellent building energy-saving potential in different seasons.

Pseudospin-polarized slow light waveguides with large delay-bandwidth product

Delay-bandwidth product (DBP) is a key metric in slow light waveguides, requiring a balance between a large group index and broad bandwidth—two parameters that often involve a trade-off. Here, we propose and demonstrate a slow light waveguide with large DBP using a pseudospin-polarized transverse electromagnetic mode. This waveguide features a folded edge configuration that supports a 200% relative bandwidth from quasistatic limit (zero frequency) and an arbitrarily large group index. Owing to the pseudospin-polarized design, the dense folding would not introduce backscattering and the associated group velocity dispersion (GVD). The resulting gapless linear dispersion and pulse transmission behavior in folded edge waveguide are observed in microwave experiments. Our scheme provides a way to overcome the trade-off between group index and working bandwidth in slow light waveguide, which has potential applications in broadband optical buffering, light-matter interaction enhancement, terahertz radiation source and time domain processing.

Exceptional points in the microcavity with phonon pump enhance the transparency and slow light.

We theoretically investigated optomechanically induced transparency (OMIT) and slow light in a microcavity optomechanical system containing three nanoparticles, where the pump-probe field drives the cavity and a weak phonon pump drives the mechanical resonator. When the phonon pump frequency matches the pump-probe field frequency difference, adjusting the phonon pump's amplitude and phase can result in the transparency window exceeding unity. Tuning the relative positions of nanoparticles can periodically steer the system to exceptional points (EPs), further enhancing and modulating the transparency window. Furthermore, the phonon pump causes the phase dispersion at the transparency window to become highly steep, resulting in a large value and tunable group delay. Notably, when the system is at EPs, the slow light can be enhanced by approximately two times compared to when the system is not at EPs. Our research demonstrates a way to control optical transmission with potential applications in quantum communications and optical buffers.

Topological slow light and rainbow trapping of surface wave in valley photonic crystal bounded by air

Abstract Topological slow light and rainbow trapping tend to rely on large-scale interface structure in previous research work, which have restricted further miniaturization. In this work, we propose a method to realize slow light and rainbow trapping at the zigzag edge of a single valley photonic crystals (VPCs) bounded by air, which is very different from previous studies where rainbow trapping is supported at the interface separating two VPCs with inversion symmetry. By constructing the VPC–air boundaries and VPC–VPC interfaces experimentally, we have observed the topologically protected rainbow trapping simultaneously at the external and internal boundary. This work provides a feasible platform for the miniaturized optical communication devices such as optical buffers, optical storage and optical routing.

Optically Delaying a Radio Frequency–Linear Frequency-Modulated (RF-LFM) Pulse Using Kerr Comb Carriers and Off-the-Shelf Concatenation of a Linearly Chirped Fiber Bragg Grating and a Chirped-and-Sampled Fiber Bragg Grating

We demonstrate a low latency delay of a radio frequency (RF)–linear frequency-modulated (LFM) pulse by modulating it onto optical carriers from a Kerr comb and sending the signal through a concatenation of off-the-shelf linearly chirped fiber Bragg gratings (LC-FBGs) and chirped-and-sampled FBG (CS-FBG). We characterize the frequency response and latency of the LC-FBG and CS-FBG. Then, experimentally, the LFM pulse performance is characterized by measuring the peak sidelobe level (PSL) at the output of the tunable delay system. The experiment, performed with an LFM pulse of 1 GHz bandwidth at a 10 GHz center frequency, shows a PSL better than 34.4 dB, attesting to the high quality of the buffer RF transfer function. Thus, the proposed optical memory buffer architecture, utilizing compact devices based on a Kerr comb and FBGs, offers several benefits for delaying LFM pulses, including (i) a larger tunable delay range, (ii) low latency, (iii) wide bandwidth, and (iv) high PSL.

Graphene metamaterials-based plasmon-induced terahertz modulator for high-performance multiband filtering and slow light applications.

We proposed multilayered graphene (Gr)-based surface plasmon resonance-induced high-performance terahertz (THz) modulators with tunable resonance frequencies. Previously reported Gr metamaterials-based THz plasmonic modulators had small group delay, low extinction ratio (ER), and difficult-to-tune resonant frequency without changing structural parameters in the THz range. A comprehensive investigation employing the finite-difference time-domain (FDTD) simulation technique revealed high group delay, broad tunability independent of structural parameters, and large ER for our proposed quadband and pentaband plasmonic modulators. We obtained tunable group delays with a maximum of 1.02 ps and 1.41 ps for our proposed quadband and pentaband plasmonic modulators, respectively, which are substantially greater compared to previously reported Gr-based metamaterial structures. The maximum ER of 22.3 dB was obtained, which was substantially high compared to previous reports. Our proposed modulators were sensitive to the polarization angle of incident light; therefore, the transmittance at resonant frequencies was increased while the polarization angle varied from 0° to 180°. These high-performance plasmonic modulators have emerging potential for the design of optical buffers, slow light devices, multistop band filters, integrated photonic circuits, and various optoelectronic systems.

Photothermally and optomechanically induced transparency in a hybrid optomechanical system

AbstractWe theoretically investigated the photothermally and optomechanically induced transparency (PTIT and OMIT) in an optomechanical system filled with quantum dots (QDs). In our proposed system, the right mechanical resonator couples with the optical cavity via radiation pressure, and the left mechanical resonator couples with the optical cavity through the photothermal effects. The system is driven by a strong pump field and a weak probe field. It is shown that double transparency windows can be observed due to PTIT and OMIT. When considering the Jaynes‐Cummings coupling between the QDs and the optical cavity, three transparency windows are observed. We also show that the PTIT can be adjusted by the OMIT and the QDs in the optical cavity. What is more, the coupling strength and the frequency detuning can be used effectively to change the system absorption and dispersion in the PITT transparency window. This indicates that the group delay of the probe light can also be manipulated by the system parameters. The obtained results may be applied in the optical communication such as optical buffer, and so forth.

Tunable optical buffer based on VO2/Si hybrid waveguide by optically induced phase transition

Tunable optical buffer based on VO2/Si hybrid waveguide by optically induced phase transition

Architecture of Optical Fiber Loop for Efficient Optical Buffer and an Ultra-Fast Optical Switching Service

Architecture of Optical Fiber Loop for Efficient Optical Buffer and an Ultra-Fast Optical Switching Service

Topological edge state assisted dynamically tunable microwave propagations in photonic crystals

Topological photonics has emerged as a cutting-edge and intriguing field that permits electromagnetic waves to transmit with minimal losses even when they come in contact with sharp turns or imperfections or defects. In this study, we validate a strategy to realize dynamically amplitude tunable light propagation in a topological waveguide based on a three-dimensional printed valley Hall photonic crystal structure operating in the microwave frequency region. Here, tunable light propagation is facilitated by inserting an active defect in the form of a semiconductor (silicon) material slab across the domain boundary of the topological waveguide. In this configuration, dynamic variation of transmission amplitude is realized via photoexcitation of the semiconductor defect using an external laser of wavelength, nm. This results in active amplitude tunability of dB in topological wave propagation under a photoexcitation of 100 mW. Our demonstrated route can lead to the design of dynamically controlled topological photonic devices such as optical modulators, switches, optical buffers, etc which are important for the development of 6G communication systems.

Polarization-isolated stretched-pulse mode-locked swept laser for 10.3-MHz A-line rate optical coherence tomography.

Stretched-pulse mode-locked (SPML) lasing based on a chirped fiber Bragg grating (CFBG) has proven to be a powerful method to generate wavelength-swept lasers at speeds of tens of megahertz. However, light transmitted through the CFBG may lead to undesirable laser oscillation that disrupts the mechanism of the laser active mode locking in the theta ring cavity. In this Letter, we demonstrate a simple and low-cost approach to suppress the transmitted light and achieve an effective duty cycle of ∼100% with only one CFBG and no need for intra-cavity semiconductor optical amplifier (SOA) modulation, extra-cavity optical buffering, and post amplification. By utilizing polarization isolation of the bi-directional CFBG, a swept laser centered at 1305 nm, with repetition rate of 10.3 MHz, optical power of 84 mW, and 3 dB bandwidth of 109 nm, is demonstrated. Ultrahigh speed 3D optical coherence tomography (OCT) structural imaging of a human palm in vivo using this swept laser is also demonstrated. We believe that this ultrahigh speed swept laser will greatly promote the OCT technique for industrial and biomedical applications.

Multifrequency on-off modulation and slow light characterization of the patterned black phosphorus metamaterial based on dual plasmon-induced transparency.

We present a monolayer patterned black phosphorus (BP) metamaterial for generating a tunable dual plasmon-induced transparency (PIT). We have derived the expression for the theoretical transmittance by introducing the coupled mode theory (CMT), and the calculated results of the expression highly overlap with the simulation results. The quarterly frequency synchronous switch with two different operating bands is designed by the carrier density and scattering rate on the dual PIT modulation effect. Two parameters were selected as important markers to show the performance of the optical switch: the modulation depth (MD) and the insertion loss (IL). The theoretical analysis of this structure shows that the higher modulation depth (5.45d B<M D<12.06d B) and lower insertion loss (0.60d B<I L<0.22d B) of these switches are of good application. In addition, we found the slow light properties of the structure were excellent with a group index of up to 219. This work provides a theoretical basis to prepare multifrequency optical switch and optical buffer devices.

Manipulation of giant Kerr nonlinearity and Doppler broadening on graphene’s Landau level

We propose monolayer graphene system and analyze the effects of giant Kerr nonlinearity and Doppler broadening. The focus is to construct and design experimentally viable model by which we can enhance the group index of the medium so that we have slow group velocity. For obtaining the desired goal, we consider Landau level of graphene monolayer placed perpendicular to magnetic field M Tokman et al (2013, Phys. Rev. lett. 110, 077404). Giant Kerr nonlinearity and Doppler broadening enhance the medium group index greatly, resulting in a slow group velocity that has uses in storage devices, optical buffering, quantum memory, and data processing. We also investigate the behavior exhibited by the weak probe’s transmission spectrum, which can change when the terahertz signal frequency is turned on and off. Advantages of under consideration model are its a 2D material whereas other materials are semiconductor or gaseous state. Also, Landau level of graphene has domains tuneable in tera hertz and infra-red region while we cannot tune the semiconductor and atomic media once the transition is chosen. Therefore, the proposed magnetized graphene system offers a tremendous opportunity for incorporating quantum interference into the development of optical solid-state devices.

Design of an optical buffer by using 1d quaternary photonic crystal

Design of an optical buffer by using 1d quaternary photonic crystal

Topological rainbow trapping based on gradual valley photonic crystals

Valley photonic crystals (PCs) play a crucial role in controlling light flow and realizing robust nanophotonic devices. In this study, rotated gradient valley PCs are proposed to realize topological rainbow trapping. A topological rainbow is observed despite the presence of pillars of different shapes, which indicates the remarkable universality of the design. Then, the loss is introduced to explore the topological rainbow trapping of the non-Hermitian valley PC. For the step-angle structure, the same or different losses can be applied, which does not affect the formed topological rainbow trapping. For a single-angle structure, the applied progressive loss can also achieve rainbow trapping. The rainbow is robust and topologically protected in both Hermitian and non-Hermitian cases, which is confirmed by the introduction of perturbations and defects. The proposed method in the current study presents an intriguing step for light control and potential applications in optical buffering and frequency routing.

Switchable multifunctional terahertz metamaterial with slow-light and absorption functions based on phase change materials

Terahertz (THz) wave usually refers to the electromagnetic wave with a frequency between 0.1—10.0 THz. It has potential applications in wireless communication, biomedical image processing, nondestructive testing, military radar, and other fields. However, owing to function limitation of the natural material, multifunctional terahertz devices are difficult to design and fabricate, which becomes a bottleneck for THz technology. The emergence of metamaterials fills the gap in the electromagnetic materials in the THz frequency band, and now they are widely used in THz functional devices, such as THz modulators, THz absorbers, THz filters, THz sensors, and THz slow-light devices. However, the above-mentioned THz devices all have a single function. For practical application, multifunction integrated THz devices have broader application prospects. As is well known, the Ge&lt;sub&gt;2&lt;/sub&gt;Sb&lt;sub&gt;2&lt;/sub&gt;Te&lt;sub&gt;5&lt;/sub&gt; (GST) is a typical phase transition material. Under excitation of light or electronic field, GST can realize a reversible phase transition between insulating state and metallic state. In order to achieve a switchable multifunctional THz device, in this work we design a THz metamaterial based on the phase transition material GST and realize a switchable function with slow-light and absorption functions. The THz metamaterial consists of a microstructure layer, which is composed of gold rings arranged periodically, and a GST thin film spaced by an SiO&lt;sub&gt;2&lt;/sub&gt; dielectric layer. When GST is in an insulating state, the two gold rings are coupled to each other under the excitation of the THz pulse. Then, we can observe the EIT-like effect. The THz pulses propagating in the metamaterial we proposed can be slowed down, and a maximum group delay of the THz pulse can reach 3.6 ps. However, when GST is in a metallic state, we can observe two absorption peaks in the spectrum of the proposed THz metamaterial, and the absorption rate is 97% at a frequency of 0.365 THz and 100% at a frequency of 0.609 THz. Furthermore, we also investigate the polarization properties of the proposed THz metamaterial, and find that it has polarization insensitive characteristic. When the polarization angle of the incident THz light pulse changes from 0° to 90°, the slow-light and absorption properties of the THz metamaterial are unaffected. The proposed THz metamaterial has potential applications in THz biomedical image processing, THz optical switching, and THz optical buffer.

Fano resonances and slow light in a nanocavity assisted by metallic nanoparticles‐quantum dot system

AbstractDouble Fano resonances in a nanocavity assisted by metallic nanoparticles (MNPs)‐quantum dot (QD) system are demonstrated theoretically. The nanocavity is assumed to couple with the QD and QD is assumed to locate in the plasmon field produced by two excited MNPs nearby. The nanocavity is driven by a control field and a probing field. Double Fano resonances can be manipulated by the system parameters such as frequency detuning and coupling strength among the nanocavity, the mechanical oscillator, MNPs and QD. Especially, we find the second Fano resonance appears due to the interaction between the nanocavity with the QD‐MNPs. We also discuss the transmission and group delay in the double Fano resonance transparency windows which show tunable fast and slow light for different probe frequency. Our results may provide possible applications in designing optical buffer, switching, and so forth.

Switchable dual-function metasurfaces with electromagnetic induction transparency-like and absorption

Two terahertz switchable metasurfaces with dual-function are proposed in this paper. Both metasurfaces contain a periodically arranged pattern layer made of silver, which is mounted on the stacking layer of polyimide and phase change material vanadium dioxide (VO2). The simulation results show that the designed metasurfaces can be converted from multi-band absorbers to electromagnetically induced transparency-like (EIT-like) analogs. When VO2 is in conductive state, the above metasurfaces work as dual-band absorber and tri-band absorber respectively, with absorptivities over 90 %; while VO2 is in insulating state, both structures are EIT-like. The physical mechanism of absorption and EIT-like effect is explained by the surface current distribution. In addition, by adjusting the structural parameters, the peak frequency of the absorbers and the window bandwidth of the EIT-like changes. Meanwhile, the dual-function of the metasurfaces can be maintained within a certain range of incidence and polarization angles. These results show that the switchable metasurfaces can achieve potential applications of modulators, optical buffers, and sensors at terahertz frequencies in the infrared light range.

Topological polarization selection concentrator.

Topological polarization selection devices, which can separate topological photonic states of different polarizations into different positions, play a key role in the field of integrated photonics. However, there has been no effective method to realize such devices to date. Here, we have realized a topological polarization selection concentrator based on synthetic dimensions. The topological edge states of double polarization modes are constructed by introducing lattice translation as a synthetic dimension in a completed photonic bandgap photonic crystal with both TE and TM modes. The proposed device can work on multiple frequencies and is robust against disorders. This work provides a new,to the best of our knowledge, scheme to realize topological polarization selection devices, and it will enable practical applications such as topological polarization routers, optical storage, and optical buffers.

Rainbow trapping and releasing based on the topological photonic crystals and a gradient 1D array

Topological photonic crystal provides a platform for robust energy transport in photonic systems. In this letter, we propose a method for realizing rainbow trapping and releasing based on the topologically protected defect modes in dielectric photonic crystals. The photonic states of different frequencies are separated and trapped at different positions to form the topological rainbow. The all-dielectric planar nanostructures consist of deformed honeycomb lattices and a gradient 1D array, which is distinct from previous platforms where edge states appear at the interface between trivial and nontrivial crystals. Due to the simplification of the configuration, we can selectively control the stop position of the wave by modifying the bottom row of dielectric rods so that light can switch between the trapping state and releasing state. The robustness of the slowing light system is also investigated. These results are beneficial to multiple frequency tuning. The simplified structure could offer a novel method for micro-miniaturizing and applying optical communication equipment, such as optical storage and optical buffer.