Emerging short-reach data center interconnect (typically in the range of tens of km) is a scenario wherein the capacity has to be maximized over point-to-point optical links without intermediate optical amplification, i.e. unrepeated links. For this application, cost and compactness of the optical transceiver form factor to fit the faceplate density requirement are essential to keep up with the bandwidth demand inside hyper-scale data centers. For the optical module to fit in the current dimensions of client routers without compromising the performance, both the electronics and the optics have to be efficiently designed. As far as the opto-electronic is concerned, photonic integrated circuits (PIC) have been discussed in the community so that all the photonic functionalities are performed accordingly with the physical dimensions, power budget and performance specifications. This paper addresses the basic building blocks of silicon photonics coherent optical transceivers, from the design to experimental validation. In addition to the silicon optical modulator, basic components such as polarization splitter-rotators (PSRs) and optical filters will be addressed.
KEYWORDS: Data centers, Receivers, Optoelectronics, Transceivers, Coherent optics, Modulation, Transmittance, Singular optics, Terahertz radiation, Modulators, Photodetectors, Analog electronics, Quantization, Signal to noise ratio
Emerging short-reach data center interconnect is a scenario wherein the capacity has to be maximized over point- to-point optical links without intermediate optical amplification. Most of the transceiver solutions are based on 100G modules with direct detection modulation. Although these legacy solutions are cost-efficient in a short- term, they are not scalable in a long-term, when the capacity x distance product will become more and more stringent. This paper addresses coherent optical solutions for emerging data center interconnect, with optical transmission reach being limited to around unrepeated 100 km. The main advantage of coherent solutions, when compared to legacy direct detection technologies, is the inherently improved spectral efficiency (e.g. 400 Gb/s channels in a 50 GHz grid) and receiver sensitivity provided with high baudrate (>40 GBd) transceiver modules. In this paper, two technological options for single-carrier optical 400 Gb/s modules are exploited for high capacity links over short reach scenarios: 43 GBd polarization-division-multiplexed (PDM)-64QAM,
suitable for a 50-GHz grid; and 64 GBd PDM-16QAM, suitable for a 75-GHz grid. These two solutions are compared in terms of capacity allocated in C band (∼4 THz bandwidth), when considering 50 GHz (80 channels
at 400G, 32 Tb/s) and 75 GHz (53 channels with 21.2 Tb/s) grids and back-to-back requirements in terms of optoelectronics (digital-to-analog and analog-to-digital converters, modulators, receivers etc.).
Optical propagation modeling is being pushed to the limits as the usage of optical fiber bandwidth is taken to the limits. Also, the widespread deployment of Passive Optical Networks (PON) requires extra power budgets, which are normally achieved by increased laser optical power or amplification. In these conditions the nonlinear effects become an extra impairment factor, which has to be brought to attention. Furthermore, while compensating their impacts into propagation by means of back-propagation the precise definition of their impact and magnitude is required. In this work we will observe the potential and validity of the Volterra series when applied to both high powers, high channel densities and back-propagation conditions.
In spite of the significant increase of the use of Wireless Local Area Network (WLAN) experienced in the last years, design aspects and capacity planning of the network are still systematically neglected during the network implementation. For instance, to determine the location of the access point (AP), important factors of the environment are not considered in the project. These factors become more important when several APs are installed, sometimes without a frequency planning, to cover a unique building. Faults such as these can cause interference among the cells generated by each AP.
Therefore, the network will not obtain the QoS patterns required for each service. This paper proposes a strategy to determine how much a given network can affect the QoS parameters of another network, by interference. In order to achieve this, a measurement campaign was carried out in two stages: firstly with a single AP and later with two APs using the same channel. A VoIP application was used in the experiment and a protocol analyzer collected the QoS metrics. In each stage 46 points were measured , that are insufficient for statistically characterize the environment. For expanding this data, an Artificial Neural Network (ANN) was used. After the measurement, an analysis of the results and a set of inferences were made by using Bayesian Networks, whose inputs were the experimental data, i.e., QoS metrics like throughput, delay, jitter, packet loss, PMOS and physical metrics like power and distance.
This paper describes Sequence Time Domain Reflectometry (STDR) and Spread Spectrum Time Domain Reflectometry (SSTDR), which utilizes concepts from direct sequence spread spectrum communications, as a technique
for detecting impedance mismatches in telephone lines (twisted pair). The aim of this paper is to present methodologies for characterizing a subscriber loop, which is used for Digital Subscriber Line (DSL) technology, based
on STDR and SSTDR tests. Those tests enable the TDR functionality to be incorporated into a DSL transceiver integrated circuit eliminating the need for costly test equipment. In addition to the cost savings, the
characteristics of the STDR and SSTDR offer improved spectral compatibility, interference immunity and fault
resolvability.
This paper presents methodologies that could be used for characterizing subscriber telephone loops that carry DSL services (ADSL and ADSL2+), by determination and analysis of frequency response, time domain reflectometry, and impulse response of the line. From this analysis, the subscriber loop length, identification and location of impairments such as bridged taps, gauge changes, and open ended termination across the line are carried out. To verify the methodologies presented, results obtained from measurements are drawn and compared to results obtained from computational simulations.
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