High-Speed Optical Devices for Data Center Networks

Optical fiber communication has become the mainstream transmission medium for access networks due to its large capacity and low loss. With the development of 5G, the rise of various social and live broadcast platforms, and the emergence of cloud computing and other applications, users' demands for bandwidth and speed have grown rapidly. Therefore, the future optical access network will develop towards large capacity, high speed, and low cost. The characteristics of optical fiber such as dispersion and non-linear effects will decrease system performance. In order to improve system performance, it is necessary to adopt high-order modulation and digital signal processing technology. In this paper, the modulation formats for large-capacity optical access are investigated, including pulse amplitude modulation (PAM), carrier-less amplitude and phase modulation(CAP), direct detection orthogonal frequency division multiplexing (DD-OFDM). The principles and research progress of the three modulation formats are discussed. At the same time, in order to further increase the system capacity and the number of users supported, large-capacity optical access technology based on space division multiplexing (SDM) are also be introduced, including multi-core fiber based PON and OAMbased PON architecture.

Our focus here is on data communications within IT equipment and in IT data centers. Optical communications is not new. Thus the obvious question is likely; why a paper entitled, “Why optical data communications and why now?”. The reasons are twofold. First, optical data communications is more necessary now than it has ever been in the past. It is not excessive to even consider that it will be required in the not too distant future. Second, the advances in the broad field of photonics and optics have brought optical communications nearly to the point that it can finally cross over the threshold to be less expensive than electronic signaling. In this paper we make the case why we must aggressively pursue optics for data communications at all length scales within the data center. The summarization of this paper is that optical communications is inevitable, and we offer reasons why we believe this is true.

The paper presents the design of all-optical OR gate based on the 2-D photonic crystal. The proposed structure consists of Si rod placed in the air of having the size 15μm×18μm with point and line defects. The Finite difference time domain (FDTD) and plane wave expansion (PWE) methods are used for simulating the structure at 1550 nm wavelength. The forbidden gap of 0.0425 in the range of 0.316417 ≤ (1/λ) ≤ 0.358938 has been obtained for Transverse Magnetic (TM) mode. The obtained contrast ratio is 10dB for this design which makes it advantageous as a basic component for the design of high-speed optical communication devices.

Recent developments in optical communications have led to the creation of large scale optical networks allowing its users to run distributed applications with high QoS requirements. In this context, this paper focuses on a strategy of reservation of temporal virtualized resources in an high bandwidth optical network for service composition. In this strategy, the service composition requirements are modeled by a specific workflow graph with constraints. To satisfy such demands, the workflow graph is embedded in a graph modeling the network in which the availability of resources is scheduled in consecutive equal time periods. We first present the models of workflow and network graphs we use and the theoretical problems we focus on. Then, we describe an online embedding algorithm and we evaluate its performances on various demand scenarii.

In the recent past, there has been an explosive growth in data traffic within data center systems. This rapid increase in data volume has put significant constraints on the speed of current data communication networks, which are predominantly based on electronic controllers and memory. The speed limitations of electronic devices hinder their ability to process data at higher rates efficiently. To address this issue and enable faster data processing, the use of optical communication emerges as the most promising solution. Optical communication leverages the capabilities of light signals and optical components, which can handle data at much higher rates compared to their electronic counterparts. One key element in optical communication systems is the utilization of fiber delay lines (FDLs) as optical storage for packets. FDLs offer the ability to temporarily store and delay optical signals, providing buffering capabilities within optical networks. These FDLs can be configured in various setups, including feed forward, feed backward, and recirculating configurations, each with its own set of advantages and disadvantages. In this context, this article explores several state-of-the-art arrayed waveguide grating (AWG)-based optical packet switch (OPSW) architectures. These switches are designed to efficiently route and manage optical packets within data center networks. Each architecture is summarized, highlighting its unique features and capabilities. To compare the different AWG-based OPSW architectures, various key parameters are considered, such as the cost, physical losses, bit error rate (BER), and the number of tunable components required. These parameters are critical in determining the performance, efficiency, and cost-effectiveness of the switches.

Guest Editorial

Position-sensitive devices (PSDs) in which the junction capacitance is reduced by using a mesh-type resistive layer with 125- mu m pitch and 30- mu m stripwidth are discussed. The temporal responses to pulsed excitation illuminated at the center are characterized by a rise time of less than 550 ns, which is shorter than that of the conventional type. The 14-mm*14-mm PSD has a junction capacitance of less than 180 pF, which is estimated to be lower than that of a conventional-type PSD by a factor of 2.4. By suitably selecting the mesh pitch and width, it is possible to reduce the temporal response by one or two orders of magnitude.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Multi-structural optical devices modeling using graphene tri-layer sheets

Room temperature excitonic nonlinear absorption in multiple quantum wells (MQW) has great potential for making low-power high-speed optical switching devices. The required ultrathin multilayers have been grown by both molecular beam epitaxy (MBE) and metalorganic chemical vapor deposition (MOCVD). Efficient, narrow-linewidth luminescence and low-threshold laser operation have been achieved in MQW’s with both techniques. However, virtually all of the reported work to date dealing with nonlinear optical properties has employed MBE-grown materials CHEMLA /1/, CHEMLA /2/, MILLER /3/. The implementation of arrays of photonic switches in optical computing and processing systems will require large area devices with uniformity that exceeds the capability of current technology. The potential advantages of MOCVD for large area, multiple wafer growth of these complex structures provides motivation to explore this technique for their fabrication. In this paper, the growth by MOCVD of GaAs/AlGaAs MQW structures that exhibit narrow-line, room temperature excitonic absorption are reported. We further describe the linear and nonlinear optical properties of these structures and discuss the implications of this work for the construction of large area arrays of switches.

Strong interaction of graphene with light accounts for one of its most remarkable properties: the ability to absorb 2.3% of the incident light's energy within a single atomic layer. Free carrier injection via field-effect gating can dramatically vary the optical properties of graphene, thereby enabling fast graphene-based modulators of the light intensity. However, the very thinness of graphene makes it difficult to modulate the other fundamental property of the light wave: its optical phase. Here we demonstrate that considerable phase control can be achieved by integrating a single-layer graphene (SLG) with a resonant plasmonic metasurface that contains nanoscale gaps. By concentrating the light intensity inside of the nanogaps, the metasurface dramatically increases the coupling of light to the SLG and enables control of the phase of the reflected mid-infrared light by as much as 55° via field-effect gating. We experimentally demonstrate graphene-based phase modulators that maintain the amplitude of the reflected light essentially constant over most of the phase tuning range. Rapid nonmechanical phase modulation enables a new experimental technique, graphene-based laser interferometry, which we use to demonstrate motion detection with nanoscale precision. We also demonstrate that by the judicious choice of a strongly anisotropic metasurface the graphene-controlled phase shift of light can be rendered polarization-dependent. Using the experimentally measured phases for the two orthogonal polarizations, we demonstrate that the polarization state of the reflected light can be by modulated by carrier injection into the SLG. These results pave the way for novel high-speed graphene-based optical devices and sensors such as polarimeters, ellipsometers, and frequency modulators.

Recent challenges facing research and development on high-speed optical and electrical devices, and their integration for 100GbE are explained. The prospects regarding low-power-consumption technology and optical and electrical integration technology are verified.

Optical Set-Reset Flip-Flop based on Dielectric-Loaded Graphene-Plasmonic waveguides

Photoelectric film is an important information functional material transforming optical signals into electric signals. Composite dielectric photoelectric films formed by burying metal nanoparticles in semiconductors are different from traditional photoelectric films and semiconductor films, which will show special performance and may be applied in high-speed optical and optoelectronic devices. time response of photoelectrons to emission increases with the increase in the energy of incident photons; when the surface barrier decreases, response time increases; The smaller the film thickness is, the faster the time response of photoelectrons will be.

Traditionally, wireless and optical fiber networks have been designed separately from each other. Wireless networks aimed at meeting specific service requirements while coping with particular transmission impairments and optimizing the utilization of the system resources to ensure cost-effectiveness and satisfaction for the end user. In optical networks, on the other hand, research efforts rather focused on cost reduction, simplicity, and future-proofness against legacy and emerging services and applications by means of optical transparency. With the ultimate goal of providing access to information when needed, wherever needed, and in whatever format it is needed, the vision of technological convergence of wireless and optical networks is not only becoming a necessity but also plays a key role in future communications networks. Towards the technical evolution of wireless-optical access networks and the seamless coexistence of both technologies, this paper provides a review of state-of-the-art developments and advances in wireless and optical communications, presents key technical challenges for providing seamless communications in fiber-wireless (FiWi) access networks, and highlights important research issues for providing intelligence, transport, access, and convergence of these future networks.

To achieve continuous size, weight and cost reductions, wireless handset manufacturers and their semiconductor suppliers have been developing new semiconductor devices and packaging technologies that enable high levels of functional integration at the smallest most cost effective level, which is through silicon (Si) integration. The high levels of Si integration for baseband functions have come the quickest due the system level integration nature of ASICs (Application Specific IC) and the common CMOS processing for baseband functions. The memory and RF functional integration for cellphones is currently being accomplished through application specific packaging advancements or System-in-a-Package (SiP) technologies. This is due to the complications of integrating different IC technologies or densities in a single chip or System-on-a-Chip (SoC) solution. This paper will look at advancements in Stacked CSP (S-CSP) technology that allow further system integration of diverse device technologies including: Flash, SRAM and DRAM memory as well as baseband, mixed signal and logic functions. Stacked chip package integration, will be critical to allow the torrid pace of handset size, weight and cost reductions to continue.