Fast Optical Switching Research Articles

Spectrally Selective Smart Window with High Near-Infrared Light Shielding and Controllable Visible Light Transmittance.

Smart windows with high near-infrared (NIR) light shielding and controllable visible light transmittance are highly sought after for cooling energy saving in buildings. Herein, we present a rationally designed spectrally selective smart window which is capable of shielding 96.2% of the NIR irradiation from 800 to 2500 nm and at the same time permitting acceptable visible light (78.2% before and 45.3% after its optical switching) for indoor daylighting. The smart window synergistically integrates the highly selective and effective NIR absorption based photothermal conversion of cesium tungsten bronze (Cs xWO3) with the transparent thermoresponsive poly( N-isopropyl acrylamide) (PNIPAM) microgel-polyacrylamide (PAM) hydrogel. Optical switching of the smart window is a direct result of the phase transition of PAM-PNIPAM hydrogel, which in turn is induced by the photothermal effect of Cs xWO3 under sunlight irradiation. The smart window exhibits fast optical switching, shows long-term operational stability, and can be made highly flexible. Under the experimental conditions in this work, the indoor temperature with the smart window is ∼21 °C lower than that with a regular single-layered glass window under one sun irradiation. The smart window design in this work is meaningful for further development of effective smart windows for energy saving in the build environment.

Flexible, Low-Voltage, and n-Type Infrared Organic Phototransistors with Enhanced Photosensitivity via Interface Trapping Effect

Flexible and low-voltage near-infrared organic phototransistors (NIR OPTs) were prepared with a low-band gap donor-acceptor conjugated polymer as the semiconductor layer and n-octadecyl phosphonic acid modified anodic alumina (AlO x/ODPA) as the insulating layer. The phototransistors exhibit the typical n-type transistor characteristics at a voltage below 5 V. The photosensitivity of phototransistors can be enhanced by regulating the packing densities of the ODPA self-assembled monolayers and forming different trap states. The enhanced OPTs exhibit good photosensitivity to 808-980 nm NIR with the photocurrent/dark current ratio and photoresponsivity as high as 5 × 103 and 20 mA W-1, respectively, benefiting from the charge-trapping effect at the AlO x/ODPA interface. The OPTs also present a fast optical switching speed of 20/30 ms and an excellent mechanical flexibility. The outstanding performance of the NIR OPTs indicates that the development of wearable electronics is, indeed, possible.

Transition from saturable absorption to reverse saturable absorption in MoTe2 nano-films with thickness and pump intensity

Nonlinear optical effect such as saturable absorption (SA) and reverse saturable absorption (RSA) play a key role for all-optical logic gates, in which transition between them is a challenging issue for the optoelectronic applications. Herein, we find MoTe2 nano-films fabricated with liquid-phase exfoliation and a vacuum filtration method which demonstrate both SA and RSA with different thicknesses and pump intensity. The SA nonlinear optical susceptibility for thick film (100 nm) is Imχ(3) ∼ 10−11 esu. However, the thin film (30 nm) exhibited RSA with the Imχ(3) as high as ∼9.96 × 10−11 esu. The different nonlinear optical response with the thickness is due to the interlayer coupling effect. Under high pump intensity, the thick MoTe2 film also demonstrates transition from SA to RSA. The four energy-level model is employed to analyze the competition between the ground-state and excited-state absorption. We found that the conversion of SA to RSA depends not only on pump intensity but also on the absorption cross-section and transition probability between energy level. The transition properties of SA and RSA for MoTe2 films can be used in all-optical logic gates, fast optical switch, optical limiter, mode storage and so on.

HiFOST: A Scalable and Low-Latency Hybrid Data Center Network Architecture Based on Flow-Controlled Fast Optical Switches

To solve the bandwidth and latency issues in current hierarchical data center network (DCN) architectures based on electrical switches, we propose a novel hybrid DCN architecture based on distributed flow-controlled fast optical switches (FOS) and modified top-of-the-rack (TOR) switches (HiFOST). The intra-cluster interconnection of HiFOST is built by FOS with wavelength switching in nanoseconds’ time for an efficient statistical multiplexing operation, while the inter-cluster interconnection is connected by the TOR interfaces directly. Due to the lack of practical optical buffers, optical flow control is implemented to retransmit packets in case of contention. We investigate the performance of HiFOST DCN with different TOR buffer sizes, optical link capacities, elastic allocation of transceivers, and network scales under realistic data center (DC) traffic. The results show an average server-to-server latency of less than 2.8 μs, a packet loss <5.6×10−6 at load of 0.5 for a DC size of 94,080 servers with limited 50 KB TOR buffer. In addition, for scaling out the servers’ number and scaling up the data rate of connected servers, the cost and power consumption of the HiFOST DCN have been investigated and compared with the electrical Fat-Tree and Leaf-Spine DCN architectures, as well as with the optical H-LION and OPSquare DCN architectures. Results indicate that, for 94,080 servers operating at 10 Gb/s, HiFOST has a 48.2% and 34.1% savings of the cost and 46.3% and 32.5% savings of the power consumption with respect to the Fat-Tree and Leaf-Spine, respectively. For a HiFOST DCN supporting a 10880 server, scaling up the operating data rate of the server to 100 Gb/s, the HiFOST solution has a cost savings of 35.6% and 34.1% and power consumption of 56.5% and 59.2% as compared to the Fat-Tree and Leaf-Spine, respectively.

All-Optical Switching and Two-States Light-Controlled Coherent-Incoherent Random Lasing in a Thiophene-Based Donor-Acceptor System.

We describe herein the synthesis and characterization of a thiophene-based donor-acceptor system, namely (E)-2-(4-nitrostyryl)-5-phenylthiophene (Th-pNO2 ), which was prepared under Horner-Wadsworth-Emmons conditions. The UV/Vis absorption bands, including the intramolecular charge transfer (ICT) band, were fully assigned using DFT and TD-DFT computations. The results of both efficient third-order nonlinear optical properties and light-amplification phenomena are presented. Investigations of photoinduced birefringence (PIB) in optical Kerr effect (OKE) experiments showed a great potential for this particular compound as an efficient, fully reversible, and fast optical switch. Time constants for the observed trans-cis-trans molecular transitions are in the range of microseconds and give a competitive experimental result for the well-known and exploited azobenzene derivatives. Random lasing (RL) investigations confirmed that this organic system is potentially useful to achieve strong light enhancement, observed as a multimode lasing action. Both RL and OKE measurements indicate that this material is a representative of thiophene derivatives, which can be utilized to fabricate fast all-optical switches or random lasers (light amplifiers).

Influence of fluoropolymer surface wettability on electrowetting display performance

Amorphous fluoropolymer (FP), as a material for both insulating and hydrophobic coating, plays an essential role in electrowetting displays (EWD). In this work, three FPs based on Teflon AF1600, Hyflon AD60 and Cytop 809A were studied according to their influence on the EWD performance. Both water/air and oil/water contact angles were utilized to compare the surface wettability of these three FPs. Reversible and fast optical switch could be achieved in the EWD devices fabricated using all three FPs; however, the less hydrophobicity of the Cytop 809A surface would lead to a slower Off-switching speed or even incomplete close of the micro-pixels. The “reflow” temperature for restoring the hydrophobicity of fluoropolymer surface should be high enough to achieve a sufficient surface recovery, and at the same time avoid inducing failures like film dislocation and breakdown. The optimal “reflow” temperature has been investigated and evaluated based on the EWD performance. This work would help us deeply understand the surface wettability effect on fluidic behavior in micro-pixels driven by electrowetting, and related optical phenomena in EWDs as well.

Realization and Application of Large-Scale Fast Optical Circuit Switch for Data Center Networking

Applying optical switching to data center networks can greatly expand network bandwidth and reduce electrical power consumption, both of which are needed to meet the explosive traffic increase. The optical switch offers large bandwidth switching capability, and so eliminates the multistage switch network architecture needed with electrical switching. Furthermore, the single stage architecture of the optical switch greatly simplifies operating costs, which include cabling, while substantially reducing the number of transponders needed. Data center networks place very different demands on optical systems than communication networks. Grasping the right direction to proceed is of paramount importance. To realize the full potential of optical switches, such as scalability and cost effectiveness, we analyze the role of large-scale optical circuit switches and discuss the realization technologies that combine the two dimensions of space and wavelength. Our recent advances in large port-count optical switches are presented.

Realization of Multicore Fiber Reconfigurable Optical Add–Drop Multiplexer

Space-division multiplexing (SDM) is a calling for devices that fully replace their single-mode fiber counterparts. Fast optical switches represent one such type of key devices. In this letter, we present a free-space optical add-drop multiplexer for multicore fiber (MCF) optical communications. Microelectromechanical mirrors were used as the optical switching element. We first detail the implementation steps leading to the proposed device and then characterize its performance in terms of crosstalk and insertion loss. Overall average crosstalk is around -38 dB, while insertion losses remain large. The device investigated here is another step towards the practical adoption of SDM for optical networks based on MCFs.

High stiffness polymer composite with tunable transparency

Abstract Biological materials are multifunctional performing more than one function in a perfect synergy. These materials are built from fairly simple and limited components at ambient conditions. Such judicious designs have proven elusive for synthetic materials. Here, we demonstrate a multifunctional phase change (pc) composite from simple building blocks, which exhibits high stiffness and optical transmittance control. We show an increase of more than one order of magnitude in stiffness when we embed paraffin wax spheres into an elastomer matrix, polydimethylsiloxane (PDMS) in a dynamic compression test. High stiffness is mainly influenced by presence of microcrystals within the wax. We further show fast temperature-controlled optical switching of the composite for an unlimited number of cycles without any noticeable mechanical degradation. Through experimental and finite element method, we show high energy absorption capability of pc-composite. Based on these properties, the pc-composite could be used as an effective coating on glasses for cars and windows. This simple approach to multi-functionality is exciting and could pave way for designs of other multifunctional materials at the macro-scale.

Performance evaluation of TCP over software-defined optical burst-switched data centre network

In this paper, we consider the performance of TCP when used in data centre networks (DCNs) featuring optical burst switching (OBS) using two-way reservation. The two-way reservation is not suitable in wide-area OBS networks due to high bandwidth-delay product (BDP). The burst loss using traditional methods of one-way reservation can be mistakenly interpreted by the TCP layer as congestion instead of contention in OBS network, leading to serious degradation of the TCP performance. The reduced BDP in DCNs allows the use of two-way reservation that results in zero burst loss. The modelled architecture features fast optical switches in a single hop topology. We apply different workloads with various burst assembly parameters to evaluate the performance of TCP. Our results show significant improvement in TCP performance as compared to traditional methods of OBS as well as to a conventional electronic packet switching DCN.

Fast photoresponse and high detectivity in copper indium selenide (CuIn7Se11) phototransistors

The fast and sensitive detection of light can lead to a variety of optoelectronics and/or photonic-based applications in fields ranging from fast optical switching devices to health and environmental monitoring systems. Although several systems based on organic and inorganic materials show high sensitivity to visible light, in general they suffer from slow response times. Here we show that phototransistors fabricated using multilayers of CuIn7Se11 exhibit response times of ~ tens of µs with responsivity (R) values > 10 AW−1 and with external quantum efficiencies reaching beyond 103 % when excited with a 658 nm wavelength laser. These devices also show high specific detectivity (D*) values of ~1012 Jones. The responsivity and detectivity exhibited by these phototransistors are at least an order of magnitude better than commercially available conventional Si-based photodetectors, coupled with response times that are orders of magnitude better than several other families of layered materials investigated so far. The properties of the CuIn7Se11 phototransistor can be further tuned and enhanced by applying a back-gate voltage. Our investigations indicate that such layered ternary compounds can potentially be used as components in opto-electronics-related applications.

Stability of Optically Injected Two‐State Quantum‐Dot Lasers

AbstractSimultaneous two‐state lasing is a unique property of semiconductor quantum‐dot (QD) lasers. This not only changes steady‐state characteristics of the laser device but also its dynamic response to perturbations. In this paper we investigate the dynamic stability of QD lasers in an external optical injection setup. Compared to conventional single‐state laser devices, we find a strong suppression of dynamical instabilities in two‐state lasers. Furthermore, depending on the frequency and intensity of the injected light, pronounced areas of bistability between both lasing frequencies appear, which can be employed for fast optical switching in all‐optical photonic computing applications. These results emphasize the suitability of QD semiconductor lasers in future integrated optoelectronic systems where a high level of stability is required.

Beat Noise Reduction by Fast Optical Switching in Brillouin Grating-Based FMCW Reflectometry

We demonstrated an optical switching method for deriving a Brillouin reflectogram from a 1-m-long optical fiber without the use of a polarization diversity technique or a least-squares procedure in coherent frequency-modulated continuous wave reflectometry. We reduced the intrinsic beat noise by blocking one pump light from entering the balanced mixer for $120~\mu \text{s}$ with an acousto-optic modulator while sweeping the laser wavelength at a rate of 0.5 nm/s. The variations in the derived reflectograms at the center of the Brillouin spectrum were within ±14 %, and these were governed mainly by the multiplicative noise.

Photoluminescence Segmentation within Individual Hexagonal Monolayer Tungsten Disulfide Domains Grown by Chemical Vapor Deposition.

We show that hexagonal domains of monolayer tungsten disulfide (WS2) grown by chemical vapor deposition (CVD) with powder precursors can have discrete segmentation in their photoluminescence (PL) emission intensity, forming symmetric patterns with alternating bright and dark regions. Two-dimensional maps of the PL reveal significant reduction within the segments associated with the longest sides of the hexagonal domains. Analysis of the PL spectra shows differences in the exciton to trion ratio, indicating variations in the exciton recombination dynamics. Monolayers of WS2 hexagonal islands transferred to new substrates still exhibit this PL segmentation, ruling out local strain in the regions as the dominant cause. High-power laser irradiation causes preferential degradation of the bright segments by sulfur removal, indicating the presence of a more defective region that is higher in oxidative reactivity. Atomic force microscopy (AFM) images of topography and amplitude modes show uniform thickness of the WS2 domains and no signs of segmentation. However, AFM phase maps do show the same segmentation of the domain as the PL maps and indicate that it is caused by some kind of structural difference that we could not clearly identify. These results provide important insights into the spatially varying properties of these CVD-grown transition metal dichalcogenide materials, which may be important for their effective implementation in fast photo sensors and optical switches.

High-Capacity Angularly Multiplexed Holographic Memory Operating at the Single-Photon Level.

We experimentally demonstrate an angularly multiplexed holographic memory capable of intrinsic generation, storage, and retrieval of multiple photons, based on an off-resonant Raman interaction in warm rubidium-87 vapors. The memory capacity of up to 60 independent atomic spin-wave modes is evidenced by analyzing angular distributions of coincidences between Stokes and time-delayed anti-Stokes light, observed down to the level of single spin-wave excitation during the several-microsecond memory lifetime. We also propose how to practically enhance rates of single- and multiple-photon generation by combining our multimode emissive memory with existing fast optical switches.

Electrical Thermo-Optic Tuning of Whispering Gallery Mode Microtube Resonator

We demonstrate a very simple electrically assisted technique for broad-range tuning of whispering gallery modes in microtube resonator, which is fabricated by embedding a FeCrAl heating wire with small resistance into a tapered silica microtube. The huge Joule heat generated by the heating wire can be effectively and thermally conducted to the microtube and consequently changes the path of the optical whispering gallery modes due to the thermo-optic effect. Experimental results show that such a device has a tuning range of 0.57 nm with excellent stability under the applied current of 200 mA, fast response (<100 ms), and low power consumption (~0.1 mW). This makes it to have potentials in tunable filters or fast optical switches.

Assessment of Scalable and Fast 1310-nm Optical Switch for High-Capacity Data Center Networks

The development of high-capacity 1310-nm optical interconnects and the limitation of the electrical switches have necessitated the investigation of 1310-nm optical switches for flat data center networks. We have performed an experimental assessment of the scalable and fast 1310-nm optical switching system with three types of traffic, namely, the waveband $4\times 25$ Gb/s on–off keying (OOK), 28 Gb/s 4-level pulse-amplitude modulation (PAM4), and 40 Gb/s discrete multi-tone (DMT) by using the prototyped 1310-nm optical switch. 10-dB input power dynamic range has been achieved at 16 ports for waveband $4\times 25$ Gb/s, 28-Gb/s PAM4, and 40-Gb/s DMT with power penalty of 1, 3, and 3.3 dB, respectively. Waveband $4\times 25$ Gb/s OOK traffic shows the most promising results with port-count scaling up to 64 ports with limited penalty and allows for the potential scaling to larger port-count and more wavelength channels.

Optical Bistability and Switching in Oppositely Directed Coupler

We report the optical bistability in two core oppositely directed coupler with negative index material channel. Using Langrangian variational method and Jacobi elliptic functions, we construct the solutions of the coupled nonlinear Schrodinger equations. The bistability arises due to the effective feedback mechanism as a result of opposite directionality of the phase velocity and energy flow in the negative index material channel. We report the various ways to control and manipulate the bistability threshold and hysteresis loop, which could be useful in the design and development of fast and low-threshold optical switches.

Software-Defined Optical Burst Switching for HPC and Cloud Computing Data Centers

In this paper, we assess the performance of techniques for optical burst switching (OBS) designed for high performance computing (HPC) and cloud computing data center networks (DCNs) by using network-level simulation. We consider short-duration bursts using the faster switching technologies that are now available. The modeled switch architecture features fast optical switches in a single-hop topology with a centralized, software-defined optical control plane. Instead of using OBS with traditional methods (i.e., one-way reservation), we consider OBS with a two-way reservation protocol that results in zero burst loss. We model different workloads with various data rates by considering different edge-to-core network oversubscription ratios to investigate the performance of such designs across usage patterns. Our results reveal that the proposed technique shows considerable improvement in terms of throughput and packet loss ratio and comparable performance in terms of delay when compared to traditional methods of OBS.

Deep blue energy harvest photovoltaic switching by heptazole-based organic Schottky diode circuits

We report novel photovoltaic (PV) switching based on the low exciton-binding energy property of an organic heptazole (C26H16N2) thin film after fabrication of an heptazole-based Schottky diode. The Schottky diode cell displayed an instantaneous voltage of 0.3 V as an open circuit voltage (VOC) owing to the work function difference between the Schottky and ohmic electrode under deep blue illumination. Four tandem diode cells therefore produced ~1.2 V. As a PV diode circuit can be formed using an even number of diodes, a photo-excited charge accumulation takes place, generating VOC in the central electrode of the tandem diode array by illuminating one half of the array. An electron–hole recombination then also takes place in that electrode by illuminating the other half, making the VOC decrease to 0 V. Utilizing this charge accumulation and recombination under deep blue illumination, we successfully demonstrated quite fast PV optical switching, logic gating and, ultimately, the gate switching of an organic field-effect transistor. We therefore concluded that our self-powered PV-induced switching was novel and promising enough to open a new door for energy harvest-related device applications in organics. Photovoltaic switching in organic thin films has been realized by a team in Korea. The photovoltaic effect is virtually synonymous with light harvesting using solar-cell technology, but researchers have now demonstrated another application of it — self-powered switching. Seongil Im of Yonsei University in Seoul and co-workers made Schottky diode cells that exploit the low exciton-binding energy of thin films made from heptazole (C26H16N2). Under deep-blue illumination, the cells generated a voltage of 0.3 volts. Furthermore, they exhibited relatively fast photovoltaic switching, logic gating and gate switching of an organic field-effect transistor. The team anticipates that this self-powered switching could be used for detection of ultraviolet and visible light, wireless healthcare devices and powerless communication. It is especially suited for devices designed to protect the eyes from ultraviolet light. Photovoltaic switching in organic heptazole Schottky diode circuits is successfully implemented under dynamic illumination. Blue energetic photons generate electron–hole pairs, and instantaneous voltage of 0.3 V is produced that is multiplied by tandem diode structure. Using the photovoltaic effects, NOT, OR and AND logics are demonstrated without any electric power.