Optical Fiber Communications

The growing maturity of nanofabrication has ushered massive sophisticated optical structures available on a photonic chip. The integration of subwavelength-structured metasurfaces and metamaterials on the canonical building block of optical waveguides is gradually reshaping the landscape of photonic integrated circuits, giving rise to numerous metawaveguides with unprecedented strength in controlling guided electromagnetic waves. Here, we review recent advances in meta-structured waveguides that synergize various functional subwavelength photonic architectures with diverse waveguide platforms, such as dielectric or plasmonic waveguides and optical fibers. Foundational results and representative applications are comprehensively summarized. Brief physical models with explicit design tutorials, either physical intuition-based design methods or computer algorithms-based inverse designs, are cataloged as well. We highlight how meta-optics can infuse new degrees of freedom to waveguide-based devices and systems, by enhancing light-matter interaction strength to drastically boost device performance, or offering a versatile designer media for manipulating light in nanoscale to enable novel functionalities. We further discuss current challenges and outline emerging opportunities of this vibrant field for various applications in photonic integrated circuits, biomedical sensing, artificial intelligence and beyond.

Lightwave communications is a necessity for the information age. Optical links provide enormous bandwidth, and the optical fiber is the only medium that can meet the modern society's needs for transporting massive amounts of data over long distances. Applications range from global high-capacity networks, which constitute the backbone of the internet, to the massively parallel interconnects that provide data connectivity inside datacenters and supercomputers. Optical communications is a diverse and rapidly changing field, where experts in photonics, communications, electronics, and signal processing work side by side to meet the ever-increasing demands for higher capacity, lower cost, and lower energy consumption, while adapting the system design to novel services and technologies. Due to the interdisciplinary nature of this rich research field, Journal of Optics has invited 16 researchers, each a world-leading expert in their respective subfields, to contribute a section to this invited review article, summarizing their views on state-of-the-art and future developments in optical communications.

We propose a surface plasmon resonance (SPR) sensor based on photonic crystal fiber (PCF) with selectively filled analyte channels. Silver is used as the plasmonic material to accurately detect the analytes and is coated with a thin graphene layer to prevent oxidation. The liquid-filled cores are placed near to the metallic channel for easy excitation of free electrons to produce surface plasmon waves (SPWs). Surface plasmons along the metal surface are excited with a leaky Gaussian-like core guided mode. Numerical investigations of the fiber's properties and sensing performance are performed using the finite element method (FEM). The proposed sensor shows maximum amplitude sensitivity of 418 Refractive Index Units (RIU-1) with resolution as high as 2.4 x 10(-5) RIU. Using the wavelength interrogation method, a maximum refractive index (RI) sensitivity of 3000 nm/RIU in the sensing range of 1.46-1.49 is achieved. The proposed sensor is suitable for detecting various high RI chemicals, biochemical and organic chemical analytes. Additionally, the effects of fiber structural parameters on the properties of plasmonic excitation are investigated and optimized for sensing performance as well as reducing the sensor's footprint.

Link to Full-Text Articles :
http://www.ncbi.nlm.nih.gov/pubmed/25996510
http://umexpert.um.edu.my/file/publication/00012149_120843.pdf
http://europepmc.org/abstract/med/25996510 
http://www.mdpi.com/1424-8220/15/5/11499/pdf

For the first time, we report femtosecond pulses from a passive single-section InAs/InP quantum-dot (QD) mode-locked laser (MLL) with the active length of 456 µm and ridge width of 2.5 µm at the C-band wavelength range. Without any external pulse compression, the transformlimited Gaussian-pulses are generated at the 92 GHz repetition rate with the 312 fs pulse duration, which is the shortest pulse from any directly electricpumping semiconductor MLLs to our best knowledge. The lasing threshold injection current and external differential quantum efficiency are 17.2 mA and 38%, respectively. We have also investigated the working principles of the proposed QD MLLs.

This paper theoretically and experimentally investigate the spectrum attenuation of free space optical (FSO) communication systems operating at visible and near infrared (NIR) wavelengths $(0.6 mu{rm m}<lambda<1.6 mu{rm m})$ under fog and smoke in a controlled laboratory condition. Fog and smoke are generated and controlled homogeneously along a dedicated atmospheric chamber of length 5.5 m. A new wavelength dependent empirical model is proposed to predict the fog and smoke attenuation operating at visible and NIR wavelengths. Comparison of the new proposed model with the measured continuous attenuation spectrum from visible—NIR in the fog and smoke channels shows a close relationship than the semi-empirical Kim and Kruse fog models. The experimental results also show the selection for the possible appropriate wavelengths from visible—NIR for FSO links to achieve the maximum link span in dense fog conditions.

This paper presents a review of the numerical methods for the analysis of the homogeneous and inhomogeneous, isotropic and anisotropic, microwave and optical dielectric waveguides with arbitrarily-shaped cross sections. The characteristics of various methods are compared, and a set of qualitative criteria to guide the selection of an appropriate method for a given problem is proposed. The main approaches discussed are those of point matching, integral equations, finite difference, and finite element.

Current Gigabit-class passive optical networks
(PONs) evolve into next-generation PONs, whereby high-speed
10+ Gb/s time division multiplexing (TDM) and long-reach
wavelength-broadcasting/routing wavelength division multiplexing
(WDM) PONs are promising near-term candidates. On
the other hand, next-generation wireless local area networks
(WLANs) based on frame aggregation techniques will leverage
physical layer enhancements, giving rise to Gigabit-class very
high throughput (VHT) WLANs. In this paper, we develop
an analytical framework for evaluating the capacity and delay
performance of a wide range of routing algorithms in converged
fiber-wireless (FiWi) broadband access networks based
on different next-generation PONs and a Gigabit-class multiradio
multi-channel WLAN-mesh front-end. Our framework is
very flexible and incorporates arbitrary frame size distributions,
traffic matrices, optical/wireless propagation delays, data rates,
and fiber faults. We verify the accuracy of our probabilistic
analysis by means of simulation for the wireless and wirelessoptical-
wireless operation modes of various FiWi network architectures
under peer-to-peer, upstream, uniform, and nonuniform
traffic scenarios. The results indicate that our proposed optimized
FiWi routing algorithm (OFRA) outperforms minimum (wireless)
hop and delay routing in terms of throughput for balanced and
unbalanced traffic loads, at the expense of a slightly increased
mean delay at small to medium traffic loads.

The exact contribution of this paper is a review of existing state-of-the-art routing strategies for optical
burst switched networks developed by researchers to deal with burst contention before it happens. Routing
schemes are implemented in space domain, which make them simple and cost effective. Additionally, the
paper points out the importance of routing as an effective way to deal with burst contention compared to other
solutions. It also underlines the main differences between contention avoidance schemes and contention resolution
techniques for optical burst switched networks.We believe that this review will help different optical
burst switched researchers involved in the development of route optimization algorithms to control burst
contention.

We assess the influence of the degree of quantum confinement on the carrier recovery times in semiconductor optical amplifiers (SOAs) through an experimental comparative study of three amplifiers, one InAs-InGaAsP-InP quantum dot (0-D), one InAs-InAlGaAs-InP quantum dash (1-D), and one InGaAsP-In-GaAsP-InP quantum well (2-D), all of which operate near 1.55-m wavelengths. The short-lived (around 1 ps) and long-lived (up to 2 ns) amplitude and phase dynamics of the three devices are characterized via heterodyne pump-probe measurements. The quantum-dot device is found to have the shortest long-lived gain recovery ( 80 ps) as well as gain and phase changes indicative of a smaller linewidth enhancement factor, making it the most promising for high-bit-rate applications. The quantum-dot amplifier is also found to have reduced ultrafast transients, due to a lower carrier density in the dots. The quantum-dot gain saturation characteristics and temporal dynamics also provide insight into the nature of the dot energy-level occupancy and the interactions of the dot states with the wetting layer.

Two fundamental laser physics phenomena -dissipative soliton and polarisation of light are recently merged to the concept of vector dissipative soliton (VDS), viz. train of short pulses with specific state of polarisation (SOP) and shape defined by an interplay between anisotropy, gain/loss, dispersion, and nonlinearity. Emergence of VDSs is both of the fundamental scientific interest and is also a promising technique for control of dynamic SOPs important for numerous applications from nano-optics to high capacity fibre optic communications. Using specially designed and developed fast polarimeter, we present here the first experimental results on SOP evolution of vector soliton molecules with periodic polarisation switching between two and three SOPs and superposition of polarisation switching with SOP precessing. The underlying physics presents an interplay between linear and circular birefringence of a laser cavity along with light induced anisotropy caused by polarisation hole burning.

The optical wireless communication systems are rapidly gaining popularity as effective means of transferring data at high rates over short distances. These systems facilitate rapidly deployable, lightweight, high-capacity communication without licensing fees and tariffs. On the other hand, the performance of this new technology depends strongly on the atmospheric conditions and the parameters of the link such as the length and the operation wavelength. In this work, we extract closed form mathematical expression for the evaluation of the average (ergodic) capacity of such a system, using the log-normal and gamma-gamma distribution, in order to model the atmospheric turbulence conditions and we study the influence of the above parameters on it.

We report on the generation of dual-wavelength self-mode-locking pulses from an InP-based quantum dot laser. The demonstrated device operates simultaneously at both 1543.7 and 1571.7 nm and has a repetition rate of 92.5 GHz. The pulse width is below 960 fs, and the average power coupled to a cleaved single-mode fiber is nearly 9 mW at a current bias of 60 mA.

Assessing the average energy intensity of Internet transmissions is a complex task that has been a controversial subject of discussion. Estimates published over the last decade diverge by up to four orders of magnitude — from 0.0064 kilowatt-hours per gigabyte (kWh/GB) to 136 kWh/GB. This article presents a review of the methodological approaches used so far in such assessments: i) top–down analyses based on estimates of the overall Internet energy consumption and the overall Internet traffic, whereby average energy intensity is calculated by dividing energy by traffic for a given period of time, ii) model-based approaches that model all components needed to sustain an amount of Internet traffic, and iii) bottom–up approaches based on case studies and generalization of the results. Our analysis of the existing studies shows that the large spread of results is mainly caused by two factors: a) the year of reference of the analysis, which has significant influence due to efficiency gains in electronic equipment, and b) whether end devices such as personal computers or servers are included within the system boundary or not. For an overall assessment of the energy needed to perform a specific task involving the Internet, it is necessary to account for the types of end devices needed for the task, while the energy needed for data transmission can be added based on a generic estimate of Internet energy intensity for a given year. Separating the Internet as a data transmission system from the end devices leads to more accurate models and to results that are more informative for decision makers, because end devices and the networking equipment of the Internet usually belong to different spheres of control.

We present an experimental study and analysis of a travelling wave series push-pull silicon photonic multi-electrode Mach-Zehnder modulator (ME-MZM) and compare its performance with a single-electrode travelling wave Mach-Zehnder modulator (TWMZM). Utilizing the functionality of the ME-MZM structure plus digital-signal-processing, we report: 1) the C-band transmission of 84 Gb/s OOK modulated data below the KP4 forward error correction threshold with 2 Vpp drive voltage over a distance of 2 km; 2) the transmission of a 128 Gb/s optical 4-level pulse amplitude modulated signal over 1 km of fiber; and 3) the generation of a 168 Gb/s PAM-4 signal using two electrical OOK signals. By comparing the transmission system performance measurements for the ME-MZM with measurements performed using a similar series push-pull TWMZM, we show that the ME-MZM provides a clear advantage in achieving higher baud PAM-4 generation and transmission compared to a TWMZM.

Optical fibers composed of highly birefringent material are studied. One of the two fundamental modes can be made leaky when the birefringence is sufficiently large. This suggests a novel single-mode, single-polarization fiber design that can be realized by stress-induced birefringence. The leakage rate is calculated by a perturbation method, which accounts for degeneracy between a bound mode and a packet of radiation modes.

Harmonically mode-locked Er-f iber soliton lasers have become a reliable source of high-repetition-rate picosecond pulses in high-speed communications and photonic analog-to-digital conversion systems because of their low-noise, dropout-free operation. We have fabricated such a laser with a strongly dispersion-managed cavity and modeled its operation, and we have found that dispersion management signif icantly extends the power range over which uninterrupted single-pulse production is attained and dramatically decreases the effects of amplif ied spontaneous emission on the phase noise of the laser.

Background: Up to 10% of epidurals fail due to incorrect catheter placement. We describe a novel optical method to assist epidural catheter insertion in a porcine model. Methods: Optical emissions were tested on ex vivo tissues from porcine paravertebral tissues to identify optical reflective spectra. The wavelengths of 650 and 532 nm differentiated epidural space from the ligamentum flavum. We then used a hollow stylet that contained optical fibers to place epidural needles in anesthetized pigs. Real-time data were displayed on an oscilloscope and stored for analysis. A total of 50 punctures were done in four laboratory pigs. Data were expressed as mean Ϯ SD.

We have developed an InAs/InP quantum dot (QD) gain material using a double cap growth procedure and GaP sublayer to tune QDs into the L-band. By using it, a passive L-band mode-locked laser with pulse duration of 445 fs at the repetition rate of 46 GHz was demonstrated. The 3-dB linewidth of the RF spectrum is less than 100 KHz. The lasing threshold injection current is 24 mA with an external differential quantum efficiency of 22% and an average output power of 27 mW. The relationship between pulse duration and 3-dB spectral bandwidth as a function of injection current was investigated.

A complementary-metal-oxide semiconductor (CMOS) compatible all-silicon TM-pass polarizer using plasmonic bends is proposed. To simplify the fabrication and be compatible with the CMOS process, we employ only two materials: silicon and silicon dioxide. Highly doped silicon is used to support the plasmons. We obtain an extinction ratio and an insertion loss of 45.4 and 1.7 dB, respectively, at 1550 nm and a maximum extinction ratio of 58 dB. This is the highest reported extinction ratio for a TM-pass polarizer to the best of our knowledge. Furthermore, we achieved >20 dB of extinction ratio and <2 dB of insertion loss over 72 nm bandwidth for a device footprint <8.8 × 5.4 μm 2. To achieve this, we exploit the properties of tight bends in plasmonic waveguides. Another advantage of the device is that it is robust against fabrication variations.

In this paper, we present the design and analysis of a novel hybrid porous core octagonal lattice photonic crystal fiber for terahertz (THz) wave guidance. The numerical analysis is performed using a full-vector finite element method (FEM) that shows that 80% of bulk absorption material loss of cyclic olefin copolymer (COC), commercially known as TOPAS can be reduced at a core diameter of 350 μm. The obtained effective material loss (EML) is as low as 0.04 cm −1 at an operating frequency of 1 THz with a core porosity of 81%. Moreover, the proposed photonic crystal fiber also exhibits comparatively higher core power fraction, lower confinement loss, higher effective mode area, and an ultra-flattened dispersion profile with single mode propagation. This fiber can be readily fabricated using capillary stacking and sol-gel techniques, and it can be used for broadband terahertz applications.

With rapidly growing bandwidth demands in Local Area Networks, it is imperative to support next generation speeds beyond 40Gbit/s. Various holographic optimization techniques using spatial light modulators have recently been explored for adaptive channel impulse response improvement of MMF links. Most of these experiments are algorithmic-oriented. In this paper, a set of lenses and a spatial light modulator, acting as a binary amplitude filter, played the pivotal role in generating the input modal electric field into a graded-index MMF, rather than algorithms. By using a priori theoretical information to generate the incident modal electric field at the MMF, the bandwidth was increased by up to 3.4 times.

Note: This paper was published in Optics Express and is made available as an electronic reprint with the permission of OSA. The paper can be found at the link to the OSA website provided below. Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under law.

Optical interconnects have attracted considerable attention for use in short-reach communication links within high-performance electronic systems, such as data centers, supercomputers, and data storage systems. Multimode polymer waveguides, in particular, constitute an attractive technology for use in board-level interconnects as they can be cost-effectively integrated onto standard PCBs and allow system assembly with relaxed alignment tolerances. However, their highly multimoded nature raises important concerns about their bandwidth limitations and their potential to support very high on-board data rates. In this paper, we report record error-free (BER < 10 −12) 40 Gb/s data transmission over a 1-m-long multimode polymer spiral waveguide and present thorough studies on the waveguide bandwidth performance. The frequency response of the waveguide is investigated under a wide range of launch conditions and in the presence of input spatial offsets, which are expected to be highly-likely in real-world systems. A robust bandwidth performance is observed with a bandwidth-length product of at least 35 GHz×m for all launch conditions studied. The reported results clearly demonstrate the potential of this technology for use in board-level interconnects, and indicate that data rates of at least 40 Gb/s are feasible over waveguide lengths of 1 m.

We propose a single negative metamaterial (MTM)-based hollow-core fiber
with multilayer cladding employing zero-effective-phase bandgap for optical confinement
in this paper. The cladding is formed from a ternary 1-D photonic crystal (T-1DPC) unit
cell, which is basically a Mu-negative material sandwiched by different Mu-negative and
Epsilon-negative materials. We demonstrate its capability for broadband transmission by
numerically simulating and analyzing the photonic bandgap (PBG) and the modal loss
characteristics. The results show that the T-1DPC-based cladding can effectively
broaden the PBG. Compared with that for the binary 1-D photonic crystal unit cell-based
fiber, the radiation loss for the T-1DPC-based fiber can be reduced by three orders of
magnitude over most of the PBG range for equal number of unit cells. This MTM fiber,
depending on the operating wavelength, shows surface plasmon guidance or classical
wave guidance or both simultaneously. We also investigate the effect of variations in the
design parameters and material absorption on the wave guidance of this fiber.

Although research has an important place in language teaching, and language teachers are encouraged to conduct research for professional development, not much has been published about teachers' aspirations and beliefs about research, and their actual experience with it. Even less is known about what teachers working in developing countries such as Vietnam believe about research, how they are rewarded and challenged in the process of conducting research and disseminating results. This paper investigates the research culture of English language professionals at the university level in Vietnam. Data gathered from official documents and interviews show that Vietnamese English language educators espouse the need to conduct research. However, multiple factors, such as researchers' dissatisfaction with current evaluation regulations, as well as conventions and formats in reporting research results, lack of time, lack of materials and opportunities to disseminate results, and contextually inappropriate training tend to discourage teachers' aspirations to do research. Suggestions are then offered with a view to promoting the research culture in Vietnam as well as in similar contexts.

This article presents a three-layer index guided lead silicate (SF57) photonic crystal fiber which simultaneously promises to
yield large effective optical nonlinear coefficient and low anomalous dispersion that makes it suitable for supercontinuum
(SC) generation. At an operating wavelength 1550 nm, the typical optimized value of anomalous dispersion and effective
nonlinear coefficient turns out to be ~4 ps/km/nm and ~1078 W−1km−1, respectively. Through numerical simulation, it is
realized that the designed fiber promises to exhibit three octave spanning SC from 900 to 7200 nm using 50 fs ‘sech’
optical pulses of 5 kW peak power. Due to the cross-phase modulation and four-wave mixing processes, a long range of
red-shifted dispersive wave generated, which assists to achieve such large broadening. In addition, we have investigated
the compatibility of SC generation with input pulse peak power increment and briefly discussed the impact of nonlinear
processes on SC generation.

The ant colony optimization for continuous domains (ACOR) approach is deployed in order to solve two resource allocation (RA) optimization problems associated to the signal-to- noise plus interference ratio (SNIR) metric with quality-of-service (QoS) constraints in the context of hybrid wavelength division multiplexing/optical code division multiplexing (WDM/OCDM) networks. The ACOR-based RA optimization strategy allows regulate optimally the transmitted optical powers, as well as to maximize the overall energy efficiency (sum EE) of the optical network. In this context, a suitable model for heuris- tic optimization approach is developed, with emphasis on the network performance under optimized ACOR input parameters. Extensive simulation results for both power allocation and EE optimization problems are discussed taking into account realistic networks operation scenarios. Computational complexity analysis is performed in order to obtain a suitable, yet sturdy algorithm regarding the robustness versus complexity trade-off. The per- formance and complexity of the proposed heuristic approach are compared with a disciplined convex optimization approach based on CvX tools.

We report on the characterization of the ultrafast gain and refractive index dynamics of an InAs/InGaAsP self-assembled quantum dot semiconductor optical amplifier (SOA) operating at 1.55 μ m through heterodyne pump-probe measurements with 150 fs resolution. The measurements show a 15 ps gain recovery time at a wavelength of 1560 nm, promising for ultrafast switching at >40 GHz in the important telecommunications wavelength bands. Ultrafast dynamics with 0.2-1.5 ps lifetimes were also found consistent with carrier heating and spectral hole burning. Comparing with previous reports on quantum dot SOAs at 1.1-1.3 μ m wavelengths, we conclude that the carrier heating is caused by a combination of free-carrier absorption and stimulated transition processes.

In this letter, we propose a new pulse position modulation (PPM) scheme, called expurgated PPM (EPPM), for application in peak power limited communication systems, such as impulse radio (IR) ultra wide band (UWB) systems and free space optical (FSO) communications. Using the proposed scheme, the constellation size and the bit-rate can be increased significantly in these systems. The symbols are obtained using symmetric balanced incomplete block designs (BIBD), forming a set of pair-wise equidistant symbols. The performance of Q-ary EPPM is better than any Q-ary pulse position-based modulation scheme with the same symbol length. Since the code is cyclic, the receiver for EPPM is simpler compared to multipulse PPM (MPPM).

In this paper, two lower and upper bounds for the bit error rate of codes with fixed cross correlation in spectral-amplitude-coding optical code-division multiple access systems are offered. In this study, we consider only the phase-induced intensity noise and neglect other noises such as shot and thermal noises, in the performance analysis. Also, it is assumed that users are synchronous. This bound is obtained using combinatorics approach and utilizing simple inequalities. In numerical results, the comparison between the upper bound, lower bound, and simulation results for MQC, MFH, BIBD, and Hadamard codes is presented, and the tightness of the bounds is evaluated.

A triangular lattice dispersion compensating photonic crystal fiber is presented in this paper. The fiber produces high birefringence and operates at fundamental mode only. The full vector finite element method with a perfectly matched absorbing layer boundary condition is applied to investigate the guiding properties of the proposed fiber. The designed fiber demonstrates that it is possible to obtain a very large negative dispersion of −9486.1 ps∕ nm · km† at 1550 nm wavelength with a negative dispersion more than −7000 ps∕nm · km† over the entire C-band (1530-1565 nm), which is suitable for broadband dispersion compensation. The birefringence is about 4.13 × 10 −2 at 1550 nm wavelength, which is also very high. All these properties make this fiber very suitable in the area of broadband dispersion compensation and polarization-maintaining applications.

A recursive perturbation theory to model the fiber-optic system is developed. Using this perturbation theory, a multi-stage compensation technique to mitigate the intra-channel nonlinear impairments is investigated. The technique is validated by numerical simulations of a single-polarization single-channel fiber-optic system operating at 28 Gbaud, 32-quadrature amplitude modulation (32-QAM), and 40 × 80 km transmission distance. It is found that, with 2 samples per symbol, the multistage scheme with eight compensation stages increases the Q-factor as compared with linear compensation by 4.5 dB; as compared with singlestage compensation, the computational complexity is reduced by a factor of 1.3 and the required memory for storing perturbation coefficients is decreased by a factor of 13.

We calculate the pulse compression in a tapered microstructure optical fiber with four layers of holes. We show that the primary limitation on pulse compression is the loss due to mode leakage. As a fiber’s diameter decreases due to the tapering, so does the air-hole diameter, and at a sufficiently small diameter the guided mode loss becomes unacceptably high. For the four-layer geometry we considered, a compression factor of 10 can be achieved by a pulse with an initial FWHM duration of 3 ps in a tapered fiber that is 28 m long. We find that there is little difference in the pulse compression between a linear taper profile and a Gaussian taper profile. More layers of air-holes allows the pitch to decrease considerably before losses become unacceptable, but only a moderate increase in the degree of pulse compression is obtained.

According to the Organisation for Economic Co-operation and Development (OECD), broadband access networks
enable the emergence of new business models, processes, inventions, as well as improved goods and
services. In fact, broadband access is viewed as a so-called general purpose technology (GPT) that has the
potential to fundamentally change how and where economic activity is organized. In this paper, we focus on
the implications of the emerging Third Industrial Revolution (TIR) economy, which goes well beyond current
austerity measures, and has recently been officially endorsed by the European Commission as the economic growth
roadmap toward a competitive low carbon society by 2050. This roadmap has been receiving an increasing amount
of attention by other key players, e.g., the Government of China most recently. More specifically, we describe
a variety of advanced techniques to render converged bimodal fiber-wireless (FiWi) broadband access networks
dependable, including optical coding based fiber fault monitoring techniques, localized optical redundancy strategies,
wireless extensions, and availability-aware routing algorithms, to improve their reliability, availability, survivability,
security, and safety. Next, we elaborate on how the resultant dependent FiWi access networks can be exploited to enhance the dependability of other critical infrastructures of our society, most notably the future smart power
grid and its envisioned electric transportation, by means of probabilistic analysis, co-simulation, and experimental
demonstration.

Four wave mixing (FWM) induced power penalty is investigated theoretically for asymmetrical dispersion-managed fibers in wavelength division multiplexing (WDM) systems. The power penalty in these fibers is analyzed for various values of channel spacing, maximum dispersion and number of sections in different channels. Using numerical simulations, it is illustrated that the FWM induced power penalty is minimized for the case of two fiber sections with unequally special lengths and symmetrical dispersion values.

We present a method for measuring quantum states encoded in temporal modes of photons. The basis for the multilevel quantum states is defined based on modes propagating in a dispersive medium, which is a fiber in this case. The propagation and time-resolved single photon detection allows us to define a positive-operator valued measurement (POVM). The POVM depends on the amount of dispersion and the characteristics of a detector. This framework is numerically tested by performing quantum state tomography on a large number of states for a set of realistic experimental settings. Finally, the average fidelity between the expected and reconstructed states for qubits and qutrits is computed.

Optical interconnects have attracted significant research interest for use in short-reach board-level optical communication links in supercomputers and data centers. Multimode polymer waveguides in particular constitute an attractive technology for on-board optical interconnects, as they provide high bandwidth, offer relaxed alignment tolerances, and can be cost-effectively integrated onto standard printed circuit boards (PCBs). However, the continuing improvements in bandwidth performance of optical sources make it important to investigate approaches to develop high-bandwidth polymer waveguides. In this paper, we present dispersion studies on a graded-index (GI) waveguide in siloxane materials designed to deliver high bandwidth over a range of launch conditions. Bandwidth-length products of >70 and ∼65 GHz×m are observed using a 50/125 μm multimode fibre (MMF) launch for input offsets of ±10 μm without and with the use of a mode mixer (MM), respectively; and enhanced values of >100 GHz×m are found under a 10× microscope objective launch for input offsets of ∼18 × 20 μm 2. The large range of offsets is within the –1 dB alignment tolerances. A theoretical model is developed using the measured refractive index profile of the waveguide, and general agreement is found with experimental bandwidth measurements. The reported results clearly demonstrate the potential of this technology for use in high-speed board-level optical links, and indicate that data transmission of 100 Gb/s over a multimode polymer waveguide is feasible with appropriate refractive index engineering.

This paper presents an overview of future research activities in the field of optical telecommunications. The year 2020 is considered a milestone, when the capacity of optical communication links via a single optical fiber will reach the physical limitation called the "fiber wall". It is expected that advances in systems with a standard, single-mode, optical fiber, which enables increasingly higher transmission capacities due to accelerated scientific research, will reach the point where the capacity of the optical link via a single optical fiber will no longer grow. Due to this collision with the "fiber wall", research efforts to develop future solutions are all the more necessary. This article provides an overview of the fields in which the future development of optical communications will give the most focus. In the field of optical devices and components, the development goes in the direction of integrated optics and new optical fibers. In order to achieve the objectives, the new communication techniques comprise coherent communications, multidimensional modulation formats and multiplexing techniques, as well as the use of digital signal processing. Modern optical networks extend from the high-performance fiber optic connections in the backbone to broadband access in user's home, in the future their architecture will enable an adaptability to wavelength, bandwidth and modulation format. The main aim of the development towards 2020 and beyond is to build optical communication systems that will enable the transfer of large amounts of data with the minimum power consumption using the simplest and cheapest equipment.

We have designed, grown and fabricated InAs/InP quantum dot (QD) waveguides as the gain materials of mode-locked lasers (MLLs). Passive InAs/InP QD MLLs based on single-section Fabry–Perot (F–P) cavities with repetition rates from 10 GHz to 100 GHz have been demonstrated in the C- and L-band. Femtosecond (fs) pulses with pulse duration of 295 fs have been achieved. The average output power is up to 50 mW at the room temperature of 18 °C. By using the external fiber mixed cavities fs pulse train with a repetition rate of 437 GHz has been generated. We have also discussed the working principles of the developed QD MLLs.► Developed InAs/InP quantum dot (QD) gain materials for mode-locked lasers (MLLs). ► Demonstrated InAs/InP QD MLLs with repetition rate from 10 GHz to 100 GHz. ► Achieved fs pulses with pulse duration of 295 fs and output power of up to 50 mW. ► Generated 437-GHz pulse trains by using the external fiber mixed cavities.

This paper presents a qualitative, real-time backlighting positioning sensor for the alignment of an optical beam to a minutely deviated diffraction order axis to increase the power coupling efficiency into a multimode fiber in selective launches. Results show that the technique facilitates the alignment of the lenses to the first diffraction order axis and improves the power coupling efficiency into a multimode fiber.

We experimentally and via simulations demonstrate ultracompact single-stage and cascaded optical add-drop multiplexers using misaligned sidewall Bragg grating in a Mach-Zehnder interferometer for the silicon-on-insulator platform. The single-stage configuration has a device footprint of 400 μm × 90 μm, and the cascaded configuration has a footprint of 400 μm × 125 μm. The proposed designs have 3-dB bandwidths of 6 nm and extinction ratios of 25 dB and 51 dB, respectively, and have been fabricated for the transverse electric mode. A minimum lithographic feature size of 80 nm is used in our design, which is within the limitation of 193 nm deep ultraviolet lithography.

S emiconductor lasers have the potential to meet demands for next generation high speed optical networks. Their low cost, wide tunability, low power consumption, and very good s pectral response make them ideal transmission sources. This paper presents a review of the current applications, commercial availability, and future directions of semiconductor lasers. Comparative analysis of these lasers identifies their deployment in different optical networks.

We present the design and experimental evaluation of an Optical Multicast System for Data Center Networks, a hardware-software system architecture that uniquely integrates passive optical splitters in a hybrid network architecture for faster and simpler delivery of multicast traffic flows. An application-driven control plane manages the integrated optical and electronic switched traffic routing in the data plane layer. The control plane includes a resource allocation algorithm to optimally assign optical splitters to the flows. The hardware architecture is built on a hybrid network with both Electronic Packet Switching (EPS) and Optical Circuit Switching (OCS) networks to aggregate Top-of-Rack switches. The OCS is also the connectivity substrate of splitters to the optical network. The optical multicast system implementation requires only commodity optical components. We built a prototype and developed a simulation environment to evaluate the performance of the system for bulk multicasting. Experimental and numerical results show simultaneous delivery of multicast flows to all receivers with steady throughput. Compared to IP multicast that is the electronic counterpart, optical multicast performs with less protocol complexity and reduced energy consumption. Compared to peer-to-peer multicast methods, it achieves at minimum an order of magnitude higher throughput for flows under 250 MB with significantly less connection overheads. Furthermore, for delivering 20 TB of data containing only 15% multicast flows, it reduces the total delivery energy consumption by 50% and improves latency by 55% compared to a data center with a sole non-blocking EPS network.

We propose and demonstrate two novel techniques for 10 Gb/s polarization-mode-dispersion (PMD) monitoring for NRZ signals that use a regenerated RF clock tone as a monitoring signal. Our techniques regenerate the RF clock tone that is usually absent after square-law detection in the electrical NRZ data spectrum (in the absence of dispersion). Our first technique uses a dispersive element in the monitoring tap-line to put the beat terms between the optical clock sidebands and the carrier in phase and thus regenerates the RF clock tone after detection. Our second technique involves the use of an optical filter that is centered at the bit rate frequency on either the upper or lower sideband of the optical spectrum, removing one of the sidebands and thus preventing the beating that normally cancels the RF clock tone. We show (theoretically, via simulation, and experimentally) the effect that PMD has on these regenerated RF clock tones. We also demonstrate PMD compensation at 10 Gb/s using these techniques for monitoring and show a 6-dB improvement in the 1% power penalty tail. Our techniques are simple, do not require modification at the transmitter, and can be applied to WDM systems via the use of a multichannel dispersive element or a tunable filter swept across all channels.

In this paper, the cross-section images, of two different types of polarization maintaining (PM) optical fibers, are
employed to estimate the optical phase variation due to transverse optical rays passing through these optical
fibers. An adaptive algorithm is proposed to recognize the different areas constituting the PM optical fibers crosssections. These areas are scanned by a transverse beam to calculate the optical paths for given values of refractive indices. Consequently, the optical phases across the PM optical fibers could be recovered. PM optical
fiber is immersed in a matching fluid and set in the object arm of Mach-Zehnder interferometer. The produced
interferograms are analyzed to extract the optical phases caused by the PM optical fibers. The estimated optical
phases could be optimized to be in good coincidence with experimentally extracted ones. This has been achieved
through changing of the PM optical fibers refractive indices to retrieve the correct values. The correct refractive
indices values are confirmed by getting the best fit between the estimated and the extracted optical phases. The
presented approach is a promising one because it provides a quite direct and accurate information about refractive index, birefringence and beat length of PM optical fibers comparing with different techniques handle the
same task.