On-chip Communication Research Articles

Dark-exciton giant Rabi oscillations with no external magnetic field

Multi-phonon physics is an emerging field that serves as a test bed for fundamental quantum physics and several applications in metrology, on-chip communication, among others. Quantum acoustic cavities or resonators are devices that are being used to study multi-phonon phenomena both theoretically and experimentally. In particular, we study a system consisting of a semiconductor quantum dot pumped by a driving laser, and coupled to an acoustic cavity. This kind of systems has proven to yield interesting multi-phonon phenomena, but the description of the quantum dot has been limited to a two-level system. This limitation restrains the complexity that a true semiconductor quantum dot can offer. Instead, in this work we consider a model where the quantum dot can have both bright and dark excitons, the latter being particularly useful due to their lower decoherence rates, because they do not present spontaneous photon emission. In this setup, we demonstrate that by fine-tuning the driving laser frequency, one is able to realise giant Rabi oscillations between the vacuum state and a dark exciton state with $N$-phonon bundles. From this, we highlight two outstanding features: first, we are able to create dark states excitations in the quantum dot without the usual external magnetic field needed to do so; and second, in a dissipative scenario where the acoustic cavity and the quantum dot suffer from losses, the system acts as a phonon gun able to emit $N$-phonon bundles.

Generation and Detection of Strain-Localized Excitons in WS2 Monolayer by Plasmonic Metal Nanocrystals.

Excitons in a transition-metal dichalcogenide (TMDC) monolayer can be modulated through strain with spatial and spectral control, which offers opportunities for constructing quantum emitters for applications in on-chip quantum communication and information processing. Strain-localized excitons in TMDC monolayers have so far mainly been observed under cryogenic conditions because of their subwavelength emission area, low quantum yield, and thermal-fluctuation-induced delocalization. Herein, we demonstrate both generation and detection of strain-localized excitons in WS2 monolayer through a simple plasmonic structure design, where WS2 monolayer covers individual Au nanodisks or nanorods. Enhanced emission from the strain-localized excitons of the deformed WS2 monolayer near the plasmonic hotspots is observed at room temperature with a photoluminescence energy redshift up to 200 meV. The emission intensity and peak energy of the strain-localized excitons can be adjusted by the nanodisk size. Furthermore, the excitation and emission polarization of the strain-localized excitons are modulated by anisotropic Au nanorods. Our results provide a promising strategy for constructing nonclassical integrated light sources, high-sensitivity strain sensors, or tunable nanolasers for future dense nanophotonic integrated circuits.

Design of a 32-Bit, Dual Pipeline Superscalar RISC-V Processor on FPGA: A Review

Abstract: A 40 MHz with 32-bit and 5-stage dual-pipeline superscalar processor based on RISC-V Instruction Set Architecture is presented. It supports integer, multiply-divide and atomic read-modify-write operations. The proposed system implements inorder issuing of instructions. The design includes a dynamic branch prediction unit, memory subsystem with virtual memory, separate instruction cache and data cache, integer and floating-point execution units, interrupt controller, error control module, and a UART peripheral. Individual interrupts can have up to four levels of primary priority set in the interrupt controller. For the main memory, the error control module provides single error correction and double error detection. For on-chip communication, the Wishbone B.3 bus standard is used. On a Virtex-7 XC7VX485T FFG 1761-2 FPGA-based board, the processor is implemented. The architecture has CoreMark and Dhrystone benchmark ratings of 3.84/MHz and 1.0603 DMIPS/MHz, respectively

A Review on Design Implementation and Verification of AMBA AXI- 4 lite Protocol for SoC Integration

Abstract: The present modern bus protocols used for communication between different functional blocks on a System-on-Chip (Soc) designs face many different challenges among which complexity and communication management are the most important factors. These on-chip communications directly impact performance and functionality, hence depending on the application where the bus protocol is to be used, a perfect communication protocol is chosen. AMBA (Advanced Microcontroller Bus Architecture) provides various types of protocols to be used as IP, of which AXI4 (Advance Extensible Interface), is one of the widely used protocols for SoC designs. Out of its three different interconnect protocols: lite, stream and burst, AXI4-lite has the simplest architecture design that best suits to be used in applications where power, area and performance play a vital role. This paper briefs about using AMBA AXI4-lite bus protocol with more bus efficiency and performance in an SoC design for proper communication between various functional blocks present. The RTL is verified using UVM (Universal Verification Methodology) and various designing process is carried out using cadence tools.

Experiment demonstration of high speed 1.3 µm grating assisted surface-emitting DFB lasers.

Surface emitting lasers are attractive light sources for silicon integrated photonic circuits. High speed direct operation is of great importance for these lasers in high capacity and low cost on-chip communication system. Here, we demonstrate a 1.3 µm surface emitting ridge-waveguide distributed feedback (DFB) laser with second order grating and λ/4 phase shift grating, which can achieve a 24 Gb/s operation over a wide temperature. The fabricated lasers can achieve low threshold current as 6.8 mA, and 12.5 mA at 20, and 70°C, respectively. Stable single mode operation has been observed with high side mode suppression ratio (SMSR) > 40 dB at all temperatures (20-70 °C). Meanwhile, the surface emitting optical power can reach 1.7 mW at high temperature as 70 °C. 3 dB bandwidth of small signal response is 21 GHz and 12 GHz at 20 °C and 70 °C respectively. The far-field divergence angle of surface emitting beam is 13.4°×20.2° of 10 µm length second order grating coupler. The proposed laser may have great advantages of single mode, high speed modulation and good temperature tolerance. In addition, compared with conventional DFB lasers, the surface emitting DFB laser has no additional manufacturing process, which is simple to fabricate and easy to integrate with silicon platform.

Nonscattering Photodetection in the Propagation of Unidirectional Surface Plasmon Polaritons Embedded with Graphene.

Recently, nanoscale light manipulation using surface plasmon polaritons (SPPs) has received considerable research attention. The conventional method of detecting SPPs is through light scattering or using bulky Si or Ge photodetectors. However, these bulky systems limit the application of nanophotonic circuits. In this study, the light-matter interaction between graphene and SPP was investigated. For realizing an improved integration in nanocircuits, single-layer graphene was added to asymmetric SPP nanoantenna arrays for nonscattering detection in the near field. The developed device is capable of detecting the controlled propagation of SPPs with a photoresponsivity of 15 mA/W, which paves the way for the new-generation on-chip optical communication.

Ultrafast dynamic switching of optical response based on nonlinear hyperbolic metamaterial platform

The pursuit of high-speed and on-chip optical communication systems has promoted extensive exploration of all-optical control of light-matter interactions via nonlinear optical processes. Here, we have numerically investigated the ultrafast dynamic switching of optical response using tunable hyperbolic metamaterial (HMM) which consists of five pairs of alternating layers of indium tin oxide (ITO) and SiO2. The nonlinearity of the HMM is analyzed by the ultrafast dynamics of the hot electrons in the epsilon-near-zero (ENZ) ITO. Our approach allows large and broad all-optical modulation of the effective permittivity and topology of the HMM on the femtosecond time-scale. Based on the proposed HMM platform, we have shown considerable tunability in the extinction ratio and Purcell enhancement under various pump fluence. In addition, we have achieved all-optical control of the coupling strength through depositing plasmonic resonators on the HMM platform. A significant tuning of the coupled resonance is observed by changing pump fluence, which leads to a switching time within 213 fs at a specific wavelength with a relative modulation depth more than 15 dB.

Monolithic In2Se3–In2O3 heterojunction for multibit non-volatile memory and logic operations using optoelectronic inputs

Stable ferroelectricity at room-temperature down to the monolayer limit, harnessed with strong sensitivity towards visible-to-near-infrared illumination in α-In2Se3, facilitates its potential as versatile building block for developing ultrathin multifunctional photonic integrated networks. Herein, we demonstrated a planar ferroelectric-semiconductor heterojunction (FeS-HJ) field-effect transistor (FET) fabricated out of α-In2Se3 and In2O3, where the ferroelectric-polarization state in α-In2Se3 is utilized to control the device characteristics. The robust in-plane (IP) polarization flipping triggered by out-of-plane (OOP) electrostatic field along with clear anticlockwise hysteresis loop were readily revealed by scanning Kelvin-probe force microscopy (KPFM) and electrical probing. The orthogonally tangled ferroelectric switching was used to manipulate the HJ channel conductance and thereby to realize non-volatile memory (NVM) states. Moreover, gate-tuneable diode-like characteristics and superior photoresponse in HJ compared to its individual constitutes were observed. Utilizing the concurrent ferro-photonic coupling, high bandwidth optical inputs further tailored the outputs into four distinguished current states induced by different polarization directions. Our results pave the way for developing advanced (opto) electronic devices with diverse signal modulation capability to realize next generation low-power neurocomputing, brain-inspired visionary systems, and on-chip optical communications.

Broadband optical Ta2O5 antennas for directional emission of light.

Highly directive antennas with the ability of shaping radiation patterns in desired directions are essential for efficient on-chip optical communication with reduced cross talk. In this paper, we design and optimize three distinct broadband traveling-wave tantalum pentoxide antennas exhibiting highly directional characteristics. Our antennas contain a director and reflector deposited on a glass substrate, which are excited by a dipole emitter placed in the feed gap between the two elements. Full-wave simulations in conjunction with global optimization provide structures with an enhanced linear directivity as high as 119 radiating in the substrate. The high directivity is a result of the interplay between two dominant TE modes and the leaky modes present in the antenna director. Furthermore, these low-loss dielectric antennas exhibit a near-unity radiation efficiency at the operational wavelength of 780 nm and maintain a broad bandwidth. Our numerical results are in good agreement with experimental measurements from the optimized antennas fabricated using a two-step electron-beam lithography, revealing the highly directive nature of our structures. We envision that our antenna designs can be conveniently adapted to other dielectric materials and prove instrumental for inter-chip optical communications and other on-chip applications.

PAAD (Partially adaptive and deterministic routing): A deadlock free congestion aware hybrid routing for 2D mesh network-on-chips.

Due to the increase in integrated circuit technology processing, there is intense flooding of transistors on Multi-processor System-on-chips, making communication a more complex and costly asset. To regulate communication in such a complex environment, Network-on-chip (NoC) came up as a versatile and inflating communication architecture for large SoCs. It tackled various on-chip communication problems and increased performance. It also provided a great power tradeoff for large-scale System-on-chips (SoCs). Routing plays a very vital role in NoCs performance. Routing should not cause any deadlocks in the network as it can degrade the performance. So deadlock-free routing has been and is instill a concern in NoCs. In this paper, we have introduced a novel deadlock-free congestion-aware routing namely PAAD (Partially adaptive and deterministic routing). It is a conjunction of partially adaptive and deterministic routing which switch with each other based on network congestion. Here we have divided a mesh into different diagonal zones and different algorithms are followed in each zone. When there is no congestion, deterministic routing is followed in each zone, and when there is congestion partially adaptive routing is followed. Hence it takes the advantage of both and enhances the overall efficiency. We have compared our model with different algorithms with regard to latency, throughput, and power performance factor for various traffic patterns. The results reveal that our algorithm performs best than the rest.

Analytical prediction for quasi-TE mode in silicon nanowire optical rectangular waveguide

Theoretical and numerical mode estimation performed on silicon nanowire optical rectangular waveguide (SNORW) is presented for on-chip communication in photonic integrated circuits. The propagation behavior of electric and magnetic field is investigated, where zeroth order mode is found dominating inside the nanoslot region of SNORW, for the circularly symmetric quasi-TE mode to propagate. This SNORW structure supports hybrid mode, which derives its behavioral root from the rectangular waveguide and functional root from the slot waveguide. In periodic silicon nanowire-based waveguide, it is found that the envelope of mode field intensity closely matches with rectangular waveguide, and the guiding properties closely match with slot waveguide. The type of mode is analyzed by full-vectorial finite element method (FEM) and the analytical expression is derived using effective index method. Analytical expressions are used to express Quasi-TE mode in terms of material profile and waveguide physical parameters. The results obtained for SNORW are in S, C and L wavelength bands and are compared with the earlier reported work on slot waveguide, and the field intensity obtained with the theoretical equations is also compared with that of FEM results.

Dynamical emission of phonon pairs in optomechanical systems

The multiphonon state plays an important role in quantum information processing and quantum metrology. Here we propose a scheme to realize dynamical emission of phonon pairs based on the technique of stimulated Raman adiabatic passage in a single-cavity optomechanical system, where the optical cavity is driven by two Gaussian pulse lasers. By exploring quantum trajectories of the state populations and the average phonon number, we find that the dynamical phonon-pair emission can be realized under the appropriate parameter conditions and is tunable by controlling the time interval between the consecutive pulses of pump lasers. In particular, the numerical results for the standard and generalized second-order correlation functions of the mechanical mode show that the system can behave as an antibunched phonon-pair emitter. Our proposal can be extended to achieve an antibunched $n$-phonon emitter, which has potential applications for on-chip quantum communication.

Highly Efficient Multicast over Surface Wave in Hybrid Wireless-Optical On-Chip Networks for IoT HPC

As an ideal platform for Internet of Things (IoT) High Performance Computing (HPC), the Network-on-Chip (NoC) implements the parallelized task processing of Intellectual Property (IP) cores. However, the data interaction of IoT HPC has increased exponentially, resulting in highly consumed energy and bandwidth of the electrical NoC. This problem can be solved by the Optical NoC (ONoC), but the flexibility should be further improved for the multicast message transmission. We design a novel hybrid wireless-optical on-chip network with an effective routing mechanism for the message multicast transmission of IoT HPC. We utilize the wireless single-hop transmission to reduce on-chip communication distance and to forward multicast messages. For the high attenuation on-chip wireless signal, we design an on-chip surface waveguide structure for the surface wave as a more reliable wireless transmission medium. A flexible routing mechanism is also proposed to ensure efficient coordination between optical and wireless layers, thus relieving the pressure of the single-layer message transmission. The simulation results show that, compared with the traditional ONoC using mesh topology, our scheme performs better in terms of average delay, average energy consumption, and network throughput.

LBF-NoC: Learning-Based Framework to Predict Performance, Power and Area for Network-On-Chip Architectures

Extensive large-scale data and applications have increasing requests for high-performance computations which is fulfilled by Chip Multiprocessors (CMP) and System-on-Chips (SoCs). Network-on-Chips (NoCs) emerged as the reliable on-chip communication framework for CMPs and SoCs. NoC architectures are evaluated based on design parameters such as latency, area, and power. Cycle-accurate simulators are used to perform the design space exploration of NoC architectures. Cycle-accurate simulators become slow for interactive usage as the NoC topology size increases. To overcome these limitations, we employ a Machine Learning (ML) approach to predict the NoC simulation results within a short span of time. LBF-NoC: Learning-based framework is proposed to predict performance, power and area for Direct and Indirect NoC architectures. This provides chip designers with an efficient way to analyze various NoC features. LBF-NoC is modeled using distinct ML regression algorithms to predict overall performance of NoCs considering different synthetic traffic patterns. The performance metrics of five different (Mesh, Torus, Cmesh, Fat-Tree and Flattened Butterfly) NoC architectures can be analyzed using the proposed LBF-NoC framework. BookSim simulator is employed to validate the results. Various architecture sizes from [Formula: see text] to [Formula: see text] are used in the experiments considering various virtual channels, traffic patterns, and injection rates. The prediction error of LBF-NoC is 6% to 8%, and the overall speedup is [Formula: see text] to [Formula: see text] with respect to BookSim simulator.

Ge–Ge0.92Sn0.08 core–shell single nanowire infrared photodetector with superior characteristics for on-chip optical communication

Recent development on Ge1−xSnx nanowires with high Sn content, beyond its solid solubility limit, makes them attractive for all group-IV Si-integrated infrared photonics at the nanoscale. Herein, we report a chemical vapor deposition-grown high Sn-content Ge–Ge0.92Sn0.08 core–shell based single nanowire photodetector operating at the optical communication wavelength of 1.55 μm. The atomic concentration of Sn in nanowires has been studied using x-ray photoelectron and Raman spectroscopy data. A metal–semiconductor–metal based single nanowire photodetector, fabricated via an electron beam lithography process, exhibits significant room-temperature photoresponse even at zero bias. In addition to the high-crystalline quality and identical shell composition of the nanowire, the efficient collection of photogenerated carriers under an external electric field results in the superior responsivity and photoconductive gain as high as ∼70.8 A/W and ∼57, respectively, at an applied bias of −1.0 V. The extra-ordinary performance of the fabricated photodetector demonstrates the potential of GeSn nanowires for future Si CMOS compatible on-chip optical communication device applications.

Electrically Controlled Wavelength-Tunable Photoluminescence from van der Waals Heterostructures.

Achieving facile control of the wavelength of light emitters is of great significance for many key applications in optoelectronics and photonics, including on-chip interconnection, super-resolution imaging, and optical communication. The Joule heating effect caused by electric current is widely applied in modulating the refractive index of silicon-based waveguides for reconfigurable nanophotonic circuits. Here, by utilizing localized Joule heating in the biased graphene device, we demonstrate electrically controlled wavelength-tunable photoluminescence (PL) from vertical van der Waals heterostructures combined by graphene and two-dimensional transition metal dichalcogenides (2D-TMDCs). By applying a moderate electric field of 6.5 kV·cm-1 to the graphene substrate, the PL wavelength of 2D-TMDCs exhibits a continuous tuning from 662 to 690 nm, corresponding to a bandgap reduction of 76 meV. The electric control is highly reversible during sweeping the bias back and forth. The temperature dependence of Raman and PL spectroscopy reveals that the current-induced local Joule heating effect plays a leading role in reducing the optical direct bandgap of TMDCs. The bias-dependent optical reflectivity and time-resolved photoluminescence measurements show a consistent reduction of the optical band gap of 2D-TMDCs and increased PL lifetimes with the electric field over the heterostructures. Moreover, we demonstrate the consistent device operation from 2D materials grown by chemical vapor deposition, showing great advantages for the scalability.

Terahertz topological photonic waveguide switch for on-chip communication

Terahertz (THz) topological photonic structures are promising for last-centimeter communication in intra/interchip communication systems because they support bit-error-free THz signal transmission with topological robustness. Active and dynamically tunable THz topological photonic components have not yet been experimentally realized. Here, we experimentally demonstrate a THz topological switch (270–290 GHz) based on a valley Hall photonic crystal structured high-resistivity silicon substrate, in which the THz waves can be dynamically turned on/off by an external 447 nm continuous-wave laser. Our device exhibited an on/off ratio of 19 dB under a pumping light intensity of 240 mW / mm 2 . The 3 dB switching bandwidth was ∼ 60 kHz .

An Efficient Algorithm for Mapping Deep Learning Applications on the NoC Architecture

Network-on-chip (NoC) is replacing the existing on-chip communication mechanism in the latest, very-large-scale integration (VLSI) systems because of their fault tolerant design. However, in addition to the design challenges, NoC systems require a mechanism for proper application mapping in order to produce maximum benefits in terms of application-level latency, platform energy consumption, and system throughput. Similarly, the neural-network (NN)-based artificial intelligence (AI) techniques for deep learning are gaining particular interest. These applications can be executed on a cloud-based system, but some of these applications have to be executed on private cloud to integrate the data privacy. Furthermore, the public cloud systems can also be made from these NoC platforms to have better application performance. Therefore, there is a need to optimally map these applications on existing NoC-based architectures. If the application is not properly mapped, then it can create a performance hazard that may lead to delay in calculations, increase in energy consumption, and decrease in the platform lifetime. Hence, the real-time applications requiring AI services can implement these algorithms in NoC-based architectures with better real-time performance. In this article, we propose a multilevel mapping of deep learning AI applications on the NoC architectures and show its results for the energy consumption, task distribution profile, latency, and throughput. The simulation is conducted using the OCTAVE, and the simulation results show that the performance of the proposed mapping technique is better than the direct mapping techniques.

Active optomechanics

Cavity optomechanics explores the coupling between optical and mechanical modes mediated by the radiation pressure force. Unlike the passive scheme, the active optomechanics with optical gain directly imposes the mechanical motion upon the lasing dynamics, unveiling the intrinsic properties determined by the system itself. Here we numerically explore the general characteristics of the active optomechanics. The effects of the mechanical oscillation on the macroscopic laser include introducing multiple unstable regimes in the lasing phase, shifting the laser central frequency, broadening the laser spectrum, and degrading the laser frequency stability. Reducing the optical gain down to one active atom highlights the quantum nature of atom–cavity and photon–phonon interactions. The one-atom optomechanical microlaser does not only emit nonclassical photons but also generate nonclassical photon–phonon pairs. Our work extends the cavity optomechanics to the active fashion, paving the way towards optomechanical light sources for photonic integrated circuits, on-chip quantum communication, and biosensing.

Single Microwire Optical Autocorrelator at 2-μm Wavelength

In recent years, significant efforts have been made to develop ultrafast laser source around 2- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> wavelength. Meanwhile, the characterization of the ultrashort pulses within ultracompact footprints has been attracting growing interests. Here relying on the transverse second-harmonic generation in a single CdTe microwire, we successfully demonstrate an optical autocorrelator for femtosecond pulse characterization at 2- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> wavelength. With 220-fs laser pulses (38 pJ/pulse) as input light, the measured pulse width after calibration is 236 fs, showing a good accuracy of this microwire autocorrelator. Due to the low-loss transmission window and high nonlinearity of CdTe in the mid-infrared (MIR) region, the microwire-based autocorrelator shows great potential for MIR applications ranging from on-chip optical communication to ultracompact laser spectroscopy.