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This paper proposes an efficient optical fiber communication scheme for an optical metro access network (OMAN) based on an optical multicarrier (OMC) generator. The central office (CO)'s foundation is a novel, cost‐effective OMC‐generating technique. The OMC is designed from a pulsed laser source and three cascaded electro‐optic modulators (EOMs) driven by an amplified RF source of 20 GHz signal that has generated more than 60 frequencies with excellent tone‐to‐noise ratio (TNR) ~ 40 dB and amplitude excursions from zero to 3 dB. The conventional CO is replaced with a cost‐effective OMC‐based source with an effective switching mechanism, which is necessary and equally important to be handled reliably. The downstream data of 20 Gbps per carrier is transmitted using a duo‐binary coding scheme. Six remote nodes (RNs) supported by the suggested OMC source, at each RN 10 optical network units (ONUs), can be deployed having distance laps of 5 km between the RNs, the distance between the RNs and the ONUs is kept at 2 km, the ONUs were tested w.r.t the bit error rate (BER) and the power penalties for the proposed transmissions. The BER for different fiber lengths from 5 to 25 km at various RNs and ONUs ranges were calculated and demonstrated from 1e−3 to 1e−13, showing the feasibility of the proposed OMAN. [ABSTRACT FROM AUTHOR]

This paper introduces a new bidirectional integration approach that combines fiber sensor/free space optics (FSO) communication using an intensity and wavelength division multiplexer (IWDM) techniques-based long-distance fiber Bragg grating (FBG) sensor strain-sensing system. By implementing coarse wavelength division multiplexing (CWDM), the system achieves the simultaneous transmission of optical communication and fiber optical sensor (FOS) sensing signals, resulting in a highly capable, flexible, and cost-effective solution. The proposed FSO transmission technique addresses complex fiber cable installation concerns with topographical limitations. This bidirectional structure ensures the reliability and stability of the long-distance FBG sensor system, supported by extensive research and experimentation. A hybrid stacked gated recurrent units and long short-term memory (SGRU-LSTM) model is proposed to enhance strain measurement accuracy by predicting and measuring the central wavelength of overlapped strain-sensing FBG sensor signals. The results demonstrate the superiority of the proposed model in peak wavelength detection accuracy. The primary benefit of integrating communication and sensing is the significant reduction in construction costs by eliminating the requirement for two individual fiber optic systems, as the integration allows for a single system to fulfill both functions, resulting in more efficient and cost-effective implementation. Overall, this paper contributes to advancing long-distance FBG sensor systems by integrating fiber sensor/FSO communication and deep learning techniques, improving transmission distance, multiplexing capacity, measurement accuracy, system survivability, and cost-effectiveness. [ABSTRACT FROM AUTHOR]

Optical signal processing (OSP) technology is a crucial part of the optical switching node in the modern optical-fiber communication system, especially when advanced modulation formats, e.g., quadrature amplitude modulation (QAM), are applied. However, the conventional on–off keying (OOK) signal is still widely used in access or metro transmission systems, which leads to the compatibility requirement of OSP for incoherent and coherent signals. In this paper, we propose a reservoir computing (RC)-OSP scheme based on nonlinear mapping behavior through a semiconductor optical amplifier (SOA) to deal with the non-return-to-zero (NRZ) signals and the differential quadrature phase-shift keying (DQPSK) signals in the nonlinear dense wavelength-division multiplexing (DWDM) channel. We optimized the key parameters of SOA-based RC to improve compensation performance. Based on the simulation investigation, we observed a significant improvement in signal quality over 10 dB compared to the distorted signals on each DWDM channel for both the NRZ and DQPSK transmission cases. The compatible OSP achieved by the proposed SOA-based RC could be a potential application of the optical switching node in the complex optical fiber communication system, where incoherent and coherent signals meet. [ABSTRACT FROM AUTHOR]

In this paper, we investigate various designs of distributed Raman amplifier (DRA) to extend amplification bandwidth in mid-link optical phase conjugation (OPC) systems and compare bands 191–197 THz and 192–198 THz giving a total bandwidth of 6 THz using a single wavelength pump. We demonstrate the use of highly reflective fiber Bragg grating (FBG) to minimize gain variation across a WDM grid by optimizing forward and backward pump powers as well as the wavelength of FBGs for original and conjugated channels. Finally, we also simulate OSNR and Kerr nonlinear reduction as a product of signals asymmetry and nonlinear phase shift (NPS) for all channels. [ABSTRACT FROM AUTHOR]

The aim of this study is to present a proposed chromatic dispersion compensation model for single mode optical fiber. The proposed model consists of 4-stages of cascaded identical linear chirped fiber Bragg grating (CFBG) in post-compensation connection scheme. It is based on differential phase shift keying modulation format. To evaluate the performance of the proposed model, a comparative study is conducted using offset quadrature phase shift keying modulation technique. This comparative study includes four cases with and without using CFBG. For system performance evaluation, a 10 Gbps wavelength division multiplexing link is simulated at a distance of 70 km under conventional operating parameters. Optisystem 7.0 has been used for simulation and evaluation process. Quality factor (Q-factor) and bit error rate (BER) are used as evaluation metrics. The proposed model shows the best performance in case of using CFBG compared to the other cases. A maximum Q-factor of 7.22, and a corresponding minimum BER of 2.59 × 10−13are obtained. The proposed system performance is enhanced by at least 53% as compared to related work. [ABSTRACT FROM AUTHOR]

Over last decades, the free space optics (FSO) emerged as most prominent way of communication over radio frequency communication and microwave communication. The FSO works in the same way optical fiber cable (OFC) network works with the only difference that the optical beams were transmitted through the free space and not by using the OFC core i.e. the glass fiber. The presence of mist, fog, rain and clouds in the atmosphere directly affects the performance of FSO and the power of propagating signal is degraded significantly. Since the wavelength of propagating beam is comparable to size of fog particles, they mainly lead to atmospheric attenuation. To mitigate the impact of atmospheric attenuation on signals, the present study develops a spectrum slicing (SS)-wavelength division multiplexing (WDM) system with Pre and Post Amplification. The performance of the proposed SS-WDM-Pre and SS-WDM-Post scheme is analyzed and then compared with the traditional SS-WDM model in the Opti-system in terms of Q-factor and BER values. The analysis of the proposed and traditional scheme is done under varying attenuation and power signals during summer, winter, autumn and spring season.The comparative analysis proved that the performance of the proposed SS-WDM-Post and SS-WDM-Pre-model is more effective and efficient when compared with the traditional SS-WDM model in terms of Q-Factor and BER during all 4 seasons. [ABSTRACT FROM AUTHOR]

The performance of moment generating function approaches, specifically Chernoff bound (CB) and modified Chernoff bound (MCB), is examined and improved in this study. We evaluates and enhances the performance of a wavelength division multiplexing (WDM) technique for free-space optical (FSO) fibre communications based on passive optical network (PON) using the M-ary digital pulse-position modulation (M-ary DPPM) schemes under amplified spontaneous emission (ASE) noise effects, interchannel crosstalk (ICC), and atmospheric turbulence (AT). We use a data rate of 2.5 Gbps for eight channels over a PON/DWDM-FSO optical fibre system in the C-band with 100 GHz channel spacing start from 1550 nm. The results achieve 20 Gbit/s transmissions (2.5 Gbps × 8 channels). This is a technology that can have extended leverage, higher data rates, power-efficient, and is considered an ideal option for the provision of bandwidth for potential access networks. When compared to the CB at a low gain (G = 8), the MCB outperforms the Gaussian approximation at high gain (G = 30). Because of its superior performance at a high gain (G = 30), the MCB offers the tightest limit on the bit error rate (BER). In comparison to an equivalent on–off keying (OOK) non-return-to-zero (NRZ), the M-ary DPPM scheme with a coding level (M) of 2 improves average power about by 2.9 dB at a data rate of 2.5 Gbps on the 1550 nm wavelength and BER of 10 - 9 . The sensitivity of the M-ary DPPM modulation scheme remains improved over OOK in the presence of ICC. The lower power penalty is predicted to be approximately 0.2–3.0 dB in the DWDM-FSO systems for low coding level M = 2. We achieve a lower power penalty at 0.2–3.0 dB for the hybrid fiber DWDM/PON-FSO optical communication system at a BER of 10 - 9 . At a target BER of 10 - 12 , the hybrid OOK-NRZ/M-ary DPPM offers about 4–8 dB of optical signal-to-noise-ratio improvements over the M-DPPM of the WDM-PON/FSO link for strong turbulence. The results demonstrated that the M-ary DPPM and the optical relaying amplification technique are powerful treatments for mitigating the impacts of ASE noise, AT, and ICC. [ABSTRACT FROM AUTHOR]

In this paper, we present a novel erbium–ytterbium doped fiber amplifier (EYDFA) + Raman + EYDFA hybrid optical amplifier (HOA) for a super-dense wavelength division multiplexing (SD-WDM) system application. The performance of the 100-channel system has been investigated for an overall data rate and channel spacing of 100 Gb/s and 0.4 nm, respectively, over a wavelength span of 1550–1589.9 nm. HOA has been optimized for Raman length, EYDFA lengths, pump powers and Er + concentrations to achieve high average gain and low gain variation ratio of 40.41 dB and 0.40 respectively. The optimized configuration of the proposed HOA has been compared with EYDFA + Raman and Raman + EYDFA HOA configurations. The achieved high and flat gain with an acceptable output optical signal to noise ratio (OSNR) in case of EYDFA + Raman + EYDFA HOA; makes it an optimum choice for SD-WDM systems. [ABSTRACT FROM AUTHOR]

A method of engineering spectrum of mode converter based on cascaded Bragg gratings is investigated in detail. Due to the cascaded structures, the proposed mode converter owns higher design degrees of freedom comparing with mode converter based on traditional Bragg grating. Meanwhile, thanks to various light responses of gratings, conversion spectrum can be easily tailored by designing grating structures. As examples, mode converters with specific conversion spectra such as single-band pass, double-band pass, multi-band pass, narrow-band backward spectra have been designed. Besides, the same triangle-shaped band pass spectrum is obtained by two converters based on different grating structures with the aid of distribute-layer-peeling algorithm, which further shows the high design flexibility of the proposed method. We think the proposed method gives a new way for advanced mode converter with required conversion spectrum. [ABSTRACT FROM AUTHOR]

In this study, an ultra-broadband orbital angular momentum (OAM) mode generator based on a phase-modulated helical long period fiber grating (HLPG) working at highradial order cladding mode is firstly proposed and numerically demonstrated. The proposed phase-only modulation method can considerably facilitate the HLPG’s fabrication by eliminating the grating’s apodization, which is extremely difficult to realize in the screw-type grating. Meanwhile, the proposed method provides more flexibilities in the design of HLPGs. As a typical example, a first-order OAM (OAM −1) mode generator with a bandwidth of ~63 nm, a conversion efficiency of ~100%, and purity of ~ 91% has been numerically demonstrated. Moreover, an OAM −1 mode generator with a bandwidth of ~469 nm, a conversion efficiency of ~100%, and purity of ~ 91% has been successfully obtained, covering all bands of fiber communication, i.e., o riginal- (O-), extended- (E-), short- (S-), conventional- (C-), long- (L-), and ultralong- (U-) wavelength bands, which, based on our knowledge, are the best results reported to date among those of the HLPG-based OAM mode generators. The proposed component may find potential applications in the OAM mode division multiplexing (MDM) system combined with the wavelength division multiplexing technique. [ABSTRACT FROM AUTHOR]

This study presents modulated-wavelength division radio signals over fiber with mixed modulation techniques in the transmitter stage. Hybrid optical sources are used to achieve optimal performance and enhancement for an optical fiber communication network. The proposed modulation techniques work at a frequency of 250 GHz. Optical quadrature phase shift keying (OQPSK) and phase modulation (PM) techniques were merged to create OQPSKPM. This was in addition to the minimum shift keying (MSK) modulation scheme that was applied in the proposed model. The modulated wavelength division multiplexing design to four subscribers was examined with a single mode optical fiber at a 1550 nm wavelength. The proposed and previous simulation models were executed, investigated and measured on important operating parameter quantities that expressed the behavior of the optical fiber network in detail, like maximum quality factor, minimum bit error rate, and output power. The obtained simulation results demonstrated the priority of the proposed simulation model. [ABSTRACT FROM AUTHOR]

• Novel bidirectional full-duplex transmitting WDM-PON over single SSMF is proposed. • SRS + FWM impact on the proposed system performance is evaluated. • SXR-input power, SXR-channel spacing, SXR-channel length variations are simulated. • Results show a reliable communication with the system under SRS + FWM impact. • Proposed system and analyses are important for 5G and beyond fronthaul networks. Wavelength division multiplexing (WDM) is an important method in modern optical communication systems for both long-haul and access networks. Particularly, after being standardized by Telecommunication Standardization Sector of International Telecommunication Union (ITU-T), WDM passive optical network (WDM-PON) becomes a considerable choice for fronthaul implementations of 5G networks. Stimulated Raman scattering (SRS) and four-wave mixing (FWM) are crucial nonlinear impacts that significantly limit the performance of WDM-based optical fiber communication systems. In this paper, an ultra-dense/dense WDM-PON (UDWDM/DWDM-PON) architecture has been proposed and combined dual impact of SRS and FWM on performances of upstream channels (USCs) and downstream channels (DSCs) of the proposed UDWDM/DWDM-PON has been numerically analyzed. USCs have been assumed to operate in 1310 nm region while operating wavelength region of DSCs has been taken as 1550 nm. Simulations have been performed on both UDWDM-PON architectures with 3.125 GHz and 6.25 GHz channel spacings and DWDM-PON architectures with channel spacings between 12.5 GHz and 100 GHz. 2x15-channel and 2x63-channel system structures have been considered in simulations. Signal-to-crosstalk ratio (SXR) has been chosen as performance parameter and its variation with channel input powers, channel spacings and channel lengths have been simulated for both USCs and DSCs of 2x15- and 2x63-channel UDWDM/DWDM-PONs. Results show that the proposed UDWDM/DWDM-PONs using single G.652 fiber can exhibit a reliable communication with minimum 23 dB SXR performance under combined dual impact of SRS and FWM unless some highlights about input powers and channel lengths mentioned in the paper are neglected. [ABSTRACT FROM AUTHOR]

At present days, metropolitan and access communication networks are markedly developing utilizing a variety of technologies. Their bearer communication infrastructures will be mostly exploiting the optical transmission medium where wavelength division multiplexing techniques will play a key role. Wavelength-Division Multiplexed Passive Optical Networks (WDM-PON) attract considerable attention for the next generation optical metropolitan and access networked systems. Simultaneously, the utilization of common optical network resources in wavelength domains will be more important. The main purpose of this paper is presented by the evaluation of resource efficiencies for the non-symmetric dynamic wavelength allocation method applied in the WDM-PON network design with a conventional topology. This contribution introduces a novel non-symmetric Dynamic Wavelength Allocation (DWA) method for a selected network design with the utilization only passive optical splitters in remote nodes. This novel wavelength allocation method is oriented on minimizing a number of working wavelengths that will be used for compliance of customers' requests for data transmitting in the common point-to-multipoint WDM–PON network design. For evaluation of wavelength scheduling, a simulation model related to the conventional WDM-PON network design is realized in the MATLAB programming environment is presented with results. Finally, different traffic loading scenarios are determined and, subsequently, resource efficiencies of the presented non-symmetric DWA method are evaluated from a viewpoint of application in future WDM-PON network designs. [ABSTRACT FROM AUTHOR]

In this paper, an ultra-long distance transmission fiber link based on bidirectional Raman amplifier is studied by theoretical simulation and experimental verification. The power evolution of pump and WDM signals in optical fiber in 355 km transmission link is simulated theoretically. The performance of the ultra-long distance system based on co-pump/counter-pump/bidirectional-pump Raman amplifier (CORA/CTRA/BiRA) are simulated. And the power budget is also predicted by simulation. The performance of 10*100 Gb/s signal transmission in 355 km fiber link based on bidirectional Raman amplifier are tested experimentally. The theoretical and experimental results are in good agreement. [ABSTRACT FROM AUTHOR]

We investigated the X-ray [40 keV, 700 Gy(SiO2), ~80 mGy/s] radiation effects on the performances (gain) of Er-doped fiber preamplifier (EDFA) and Er/Yb codoped fiber boost amplifier (EYDFA). Various EDFA and EYDFA architectures have been designed to operate either in wavelength division multiplexing (WDM) or dense WDM (DWDM) schemes. We compare the performances of amplifiers based on conventional or radiation-hardened (RH) versions of the active Er-doped or Er/Yb-codoped fibers. Our results show that for all amplifier architectures, the various channels undergo similar gain degradation levels and kinetics, as expected from the measured spectral dependence of the radiation-induced attenuation of the phosphosilicate (ErYb-doped) and aluminosilicate (Er-doped) glass matrixes of these fibers. This degradation remains very limited for the amplifiers based on RH fibers, with a gain decrease of less than 0.3 mdB.Gy−1 for the EDFA (~30 dB initial gain) and less than 0.8 mdB.Gy−1 for the EYDFA (~18 dB initial gain) in the DWDM architecture. [ABSTRACT FROM AUTHOR]

• Based on EFPI sensor, PB-AOF and wavelength division multiplexing technology, the system realizes one-way four-channel passive audio parallel transmission. • Achieve 20 km long distance optical fiber audio communication. • No difference between the EFPI sensors used by each channel. • Be used in scenarios with special requirements, such as security monitoring and mines. To meet sound transmission requirements in complex work environments, this paper constructs a passive audio pickup sensor based on an extrinsic Fabry-Perot interferometer (EFPI) and develops a one-way four-channel passive audio parallel transmission system based on a passive bidirectional audio over fiber(PB-AOF) transmission system and wavelength division multiplexing technology. The system realizes optical fiber audio transmission over a distance of 20 km. The experimental results show that the signal-to-noise ratio (SNR) is greater than 64 dB, and the highest sensitivity of the four channels in the proposed system is 1.06 V/Pa. Thus, the proposed long-distance terminal passive audio communication network is ideally suited for applications in certain fields. [ABSTRACT FROM AUTHOR]

An efficient procedure is presented for evaluating the effects of modulation format on the accumulation of nonlinear interference noise (NLIN) in probabilistically shaped 28 Gbaud 64-quadrature amplitude modulation (QAM) wavelength division multiplexed (WDM) systems. The shaped symbol sequences are generated by the rate adaptive scheme concatenating a constant composition distribution matcher and a systematic forward error correction encoder. A shaping distribution based on the Maxwell-Boltzmann and the uniform distribution with the same net bit rate is considered. The NLIN variance is emulated using the accurate enhanced modulation-dependent Gaussian noise model. Accounting for the impact of higher-order standardized moments of the modulation, the dependence of NLIN variance on probabilistic shaping is determined using the proposed procedure. In addition, an increase in NLIN variance for shaping over uniform input is demonstrated. For a dual polarization (DP) fully loaded C-band WDM optical fiber system with a channel spacing of 37.5 GHz, probabilistic shaping leads to a reduction of 0.036 in the ratio of intrachannel and interchannel contributions to nonlinear noise over uniform 64-QAM for a 1500-km distance. Finally, for nine channels with DP probabilistically shaped 64-QAM input over 1500-km transmission, distributed amplification enables a reduction of 2.54 dB in the accumulation of normalized NLIN power compared to lumped amplification. [ABSTRACT FROM AUTHOR]

Traditional wired data center networks (DCNs) suffer from cabling complexity, lack flexibility, and are limited by the speed of digital switches. In this paper, we alternatively develop a top-down traffic grooming (TG) approach to the design and provisioning of mission-critical optical wireless DCNs. While switches are modeled as hybrid optoelectronic cross-connects, links are modeled as wavelength division multiplexing capable free-space optic channels. Using the standard TG terminology, we formulate the optimal mixed-integer TG problem considering the virtual topology, flow conversation, connection topology, non-bifurcation, and capacity constraints. Thereafter, we develop a fast yet efficient sub-optimal solution, which grooms mice flows (MFs), mission-critical flows (CFs), and forward on predetermined rack-to-rack (R2R) lightpaths. On the other hand, elephant flows (EFs) are forwarded over dedicated server-to-server express lightpaths whose routes and capacity are dynamically determined based on the availability of wavelength and capacity. To prioritize the CFs, we consider low and high-priority queues and analyze the delay characteristics such as waiting times, maximum hop counts, and blocking probability. As a result of grooming, the sub-wavelength traffic and adjusting the wavelength capacities, numerical results show that the proposed solutions can achieve significant performance enhancement by utilizing the bandwidth more efficiently, completing the flows faster than delay sensitivity requirements, and avoiding the traffic congestion by treating EFs and MFs separately. [ABSTRACT FROM AUTHOR]

Multiple transition levels covering S and near-C bands (1460 to 1565 nm) of thulium-doped fiber amplifiers (TDFAs) allows them as potential alternative to erbium-doped fiber amplifiers (EDFAs) hence getting employed in dense wavelength division multiplexing (DWDM) in optical fiber communication. We present overmodulation gain dynamics (OGD) on TDFAs using the EDFA's Bononi and Rusch (1998) model. The paper portrays overmodulation of digital optical communication signal, of which amplitude was modulated by low-frequency (~100 kHz), for line-surveillance and management control of optical information in DWDM TDFA systems. Signal-to-signal and signal-to-amplified spontaneous emission (ASE) transfer functions were derived to predict the system's performance under high input signal power conditions and its variation on input modulation indices. Difference of -10.3 dB (0.093 W) in output signal gain was observed at 1490 nm signal wavelength with ASE. Output modulation index of 15% having high pass signal characteristics as of a lead compensator was observed with the applied signal frequency sweep. Overmodulation sensitivity for various levels of input signal power demonstrates undesirable 30% increment in the output modulation index at 8 dBm and 1490 nm signal wavelength, respectively, at corner frequency. [ABSTRACT FROM AUTHOR]

This work experimentally shows a transmission path based on standard single‐mode optical fiber and perfluorinated graded‐index plastic optical fiber with the connections between distinct optical fibers being made by fiber collimators using free‐space optical transmission. The data stream consists of a bidirectional 400 Gbps optical transmission using four wavelength channels with quadrature phase‐shift keying modulation format, combined with dual‐polarization and Nyquist pulse‐shaped. The results obtained seeks to study the use of short‐distance cables in plastic optical fiber as a flexible means of interconnection, when inserted between single‐mode optical fibers or as a coupling medium between devices with single‐mode optical inputs/outputs located in data centers/video headends. [ABSTRACT FROM AUTHOR]

In this paper, we propose and experimentally demonstrate an OFDM/OQAM based WDM fiber visible laser light communication (VLLC) system employing improved channel estimation method. The improved channel estimation method is based on conventional interference approximation method (IAM) combined with the discrete Fourier transform (DFT) based channel estimation (IADF-CE). It is used to mitigate the intrinsic imaginary interference (IMI) and noise from the estimated channel response for OFDM/OQAM signal. Enabled by IADF-CE scheme, 1 dB and 1.2 dB power penalty improvement can be achieved in comparison with conventional IAM after transmission over 50 km standard single mode fiber (SSMF) and 4.5 m free space link for 16 OQAM and 4 OQAM modulations, respectively. Furthermore, each user can achieve a maximum aggregate data rate of 3.2 Gbps under the bit error rate (BER) of 2 . 7 × 1 0 − 2 in the system. [ABSTRACT FROM AUTHOR]

Highlights • Wavelength reuse based bidirectional coherent OFDMA access network. • Enhancement of spectral efficiency by using the proposed reflective coherent PON. • Verification of the proposed technique in future WDM-PON. Abstract This paper demonstrates wavelength reused bidirectional transmission for a reflective coherent passive optical network (R-Co-PON). By reusing the downstream optical signal as the upstream optical carrier, the proposed R-Co-PON enhances the optical spectral efficiency. In an experimental demonstration, the proposed R-Co-PON achieved a symmetrical bidirectional transmission rate of 12 Gb/s using a 73-km-long fiber loopback architecture. The experiments confirmed the potential applicability of the proposed system in future optical access networks, particularly those using wavelength-division multiplexing. [ABSTRACT FROM AUTHOR]

The passive optical network (PON) has recently emerged as the most widely deployed and successful optical access solution. Data rate demands, driven by the growing use of broadband services, are expected to increase continuously over the next few decades. TWDM PONs and WDM PONs show the most promise for emerging broadband services involving various applications. In both TWDM and WDM PONs, a colorless light source or tunable transmitter is used on the ONU side and is indispensable for low-cost and plug-and-play ONUs. This article describes the principles of different colorless- light-source schemes and the architectures of the corresponding TWDM and WDM PON systems. Also, their transmission performances are analyzed and compared. Further, four types of wavelength control methods for light sources based on tunable laser diodes are described and analyzed. The features, characteristics, and applicability of the various colorless-light and tunablelight- source schemes are analyzed and compared. [ABSTRACT FROM AUTHOR]

We numerically and experimentally compared the BER performance of 128-level set-partitioning quadrature amplitude modulation (128-SP-QAM) and polarization multiplexed 16-ary quadrature amplitude modulation (PM-16QAM). From our experimental results and numerical simulation, it can be concluded that 128-SP-QAM has significant BER improvement compared to PM-16QAM when optical signal to noise ratio (OSNR) is high. However, when it comes to low OSNR scenario such as transmission over a very long distance, 128-SP-QAM and PM-16QAM have similar performance. [ABSTRACT FROM AUTHOR]

In this paper, unique design of an optimal broadband optical dispersion flattened fiber (DFF) is proposed, which is capable of supporting the data rate of the order of Tb/s. The analysis of the single mode fiber for the design of the proposed DFF has been carried out by employing the quadratic Finite Element Method (FEM) with generalized refractive index (R. I.) profile. The minimization of the dispersion with respect to various profile parameters within the specified wavelength band is the essential optimization criteria. Computations show that a DFF can be designed where the overall dispersion can be restricted within ± 1 ps/km-nm over the entire spectral span ranging from 1290 to 1540 nm (250 nm) exhibiting a very small maximum value of dispersion slope ( ± 0.02  ps / ( nm 2 -km ) ) in particular. The detailed performance analysis of the proposed DFF with different modulation techniques has been carried out in order to critically evaluate the performance of the DFF with respect to various significant parameters. The results suggest an excellent design of broadband optical waveguide capable of supporting high-speed data rate (40 Tb/s) through the single DFF, ideally suitable for the long haul dense wavelength division multiplexing (DWDM) optical transmission systems. [ABSTRACT FROM AUTHOR]

Next-generation Passive Optical Networks (PONs), which are considered one of the most encouraging optical access networks, has remarkably developed in the past few years and intended to greatly go forward in the nigh future. By this development the power requirements of NGPON will growth and make it no longer coveted. This paper presents Hybrid (WDM/ TDM) XGPON architecture, where in this optical fiber communication system a bidirectional optical fiber has been applied with downstream and upstream NRZ and RZ (0.6 and 0.8 duty cycle)Data Format transmission. Distributed Raman amplification is employed for upstream signal for improving the loss budget of XGPON system. Fiber attenuation, splice losses, and back-reflections as in realistic fiber plant have been considered for this XGPON system. These impairments effects on 1270 nm upstream Raman amplified signal XGPON system have been investigated numerically. [ABSTRACT FROM AUTHOR]

A new materials group to implement dense wavelength division multiplexing (DWDM) in Si photonics is proposed. A large thermo-optic (TO) coefficient of Si malfunctions multiplexer/demultiplexer (MUX/DEMUX) on a chip under thermal fluctuation, and thus DWDM implementation, has been one of the most challenging targets in Si photonics. The present study specifies an optical materials group for DWDM by a systematic survey of their TO coefficients and refractive indices. The group is classified as mid-index contrast optics (MiDex) materials, and non-stoichiometric silicon nitride (SiNx) is chosen to demonstrate its significant thermal stability. The TO coefficient of non-stoichiometric SiNx is precisely measured in the temperature range 24-76 °C using the SiNx rings prepared by two methods: chemical vapor deposition (CVD) and physical vapor deposition (PVD). The CVD-SiNx ring reveals nearly the same TO coefficient reported for stoichiometric CVD-Si3N4, while the value for the PVD-SiNx ring is slightly higher. Both SiNx rings lock their resonance frequencies within 100 GHz in this temperature range. Since CVD-SiNx needs a high temperature annealing to reduce N-H bond absorption, it is concluded that PVD-SiNx is suited as a MiDex material introduced in the CMOS back-end-of-line. Further stabilization is required, considering the crosstalk between two channels; a 'silicone' polymer is employed to compensate for the temperature fluctuation using its negative TO coefficient, called athermalization. This demonstrates that the resonance of these SiNx rings is locked within 50 GHz at the same temperature range in the wavelength range 1460-1620 nm (the so-called S, C, and L bands in optical fiber communication networks). A further survey on the MiDex materials strongly suggests that Al2O3, Ga2O3 Ta2O5, HfO2 and their alloys should provide even more stable platforms for DWDM implementation in MiDex photonics. It is discussed that the MiDex photonics will find various applications such as medical and environmental sensing and in-vehicle data-communication. [ABSTRACT FROM AUTHOR]

We experimentally demonstrate a novel method based on electrical spectral interferometry with optical frequency comb for characterizing the modal dispersion between the higher-order modes and fundamental mode in a 1- km four-mode few-mode fiber (FMF). In this method, an optical frequency comb (OFC) is used to generate many subwavelengths with the same frequency interval to improve the measurement accuracy and speed. Based on the electrical spectral interferometry, the differential mode group delay (DMGD) and modal dispersion of the tested FMF are obtained by applying the simple FFT processing. The measured DMGD and modal dispersion within the whole C-band are about (3.2032–3.3033) ps/m , (2.5573–4.2085) ps/nm.km and (5.5055–5.7057) ps/m , (−11.2112–−4.1486) ps/nm.km and (11.1111–11.3113) ps/m , (−10.2454–−14.1332) ps/nm.km for LP11, LP21 and LP02 modes respectively. Meanwhile, we achieved a precision of ±0.002 ps/m for DMGD measurement. Compared with previous methods, our method has the advantage of high measurement accuracy, simple configuration and fast speed. The experimental results show that the demonstrated method could be a good solution to the characterization of a long FMF used in large capacity mode-division-multiplexing transmission systems. [ABSTRACT FROM AUTHOR]

Two discrete-time interference channel models are developed for information transmission over a single span of optical fiber using wavelength-division multiplexing (WDM) and lumped amplification. The models are derived from the nonlinear Schrödinger equation by including the nonlinear phenomena of self-phase modulation (SPM) and cross-phase modulation (XPM), but ignoring four-wave mixing, polarization effects and group velocity dispersion (GVD) within WDM bands. The first model also ignores GVD across WDM bands, referred to as group velocity mismatch (GVM). For the case of two users, a new technique called interference focusing is proposed where each carrier achieves the capacity pre-log 1, thereby doubling the pre-log of 1/2 achieved by using conventional methods. For three users, interference focusing is also useful under certain conditions. The second model captures GVM and the effect of filtering at the receivers in addition to SPM and XPM. In a 3-user system, it is shown that all users can achieve the maximum pre-log factor 1 simultaneously by using interference focusing, a time-limited pulse and a bank of filters at the receivers. [ABSTRACT FROM PUBLISHER]

This article describes the performance and capabilities of an all-optical network featuring low latency, high speed file transfer between serially connected optical nodes. A basic component of the network is a network interface card (NIC) implemented through a unique planar lightwave circuit (PLC) that performs add/drop data and optical signal amplification. The network uses a linear bus topology with nodes in a “T” configuration, as described in the text. The signal is sent optically (hence, no latency) to all nodes via wavelength division multiplexing (WDM), with each node receiver tuned to wavelength of choice via an optical de-multiplexer. Each “T” node routes a portion of the signal to/from the bus through optical couplers, embedded in the network interface card (NIC), to each of the 1 through n computers. [ABSTRACT FROM PUBLISHER]

The importance of single-span systems is emphasized by the fact that they currently constitute the fastest growing section of the fiber communication markets. In such systems, the correlation time of the nonlinear phase noise is too short to allow the nonlinear phase-noise mitigation such as adaptive phase-recovery or equalization, while it is sufficient for the shaping approaches. The multi-dimensional (MD) coded-modulation based standard shell mapping (SM) algorithm can realize signal shaping and mitigate the nonlinear phase noise in single-span optical fiber transmissions. However, the standard SM algorithm has poor performance resulted from the decoding penalty in two-dimensional (2D) decoding with a low signal-to-noise (SNR) ratio. In this paper, we propose a phase rearrangement shell mapping (PRSM) algorithm to improve the 2D decoding performance by rearranging the constellation sequence in order of signal phase for each shell. This proposed technique is verified through the simulation of a 5 × 70-GBaud 4D/8D modulated signal in a 5-channel wavelength division multiplexing (WDM) system after a single span transmission of 100-km standard single mode fiber (SSMF). We also conduct an experiment to verify the performance of 3 × 45-GBaud 4D/8D-16QAM with PRSM algorithm after unrepeated transmission of 100-km SSMF. The simulation and experimental results show that the Q 2 factor gain of PRSM-4D/8D-16QAM is about 0.2 ∼ 0.3 dB compared with standard SM-4D/8D-16QAM using 2D decoding. There is about 1.6-dB or 1.8-dB launch optical power (LOP) dynamic range improvement by PRSM compared with standard SM for 4D/8D-16QAM, respectively. • Phase rearrangement shell mapping to guarantee both the Hamming distance and Euclidean distance to be smaller. • This algorithm can reduce the intra-shell and alleviate the inter-shell errors. • The algorithm will not change the shaping gain of MD signals. • The algorithm can improve the decoding performance of MD signals. [ABSTRACT FROM AUTHOR]

The wavelength division multiplexing (WDM) method for near infrared (NIR) optical fiber (1530-1565 nm) is the system that is wildly used for intercontinental communication. WDM achieves high-speed and large-capacity communication, but costs a lot because the high-resolution (~10 pm) wavelength locker for wavelength stabilization only corresponds to a single wavelength. In this report, we propose a highly sensitive sub-picometer multi-wavelength detector that substitutes a typical single-wavelength detector for WDM. Our wavelength detector consists of a narrow band (FWHM<10 nm) photonic absorber with an aligned gold nano-fin array on a high-Q (Q-factor>20 000) nanomechanical resonator. The photonic absorber confines and transforms the illuminated NIR light wave into thermal stress, and then, the thermal stress in the nanomechanical resonator will appear as the eigenfrequency shift of the nanomechanical resonator. Through experimental works with an NIR laser and optical Doppler vibration meter, the sensitivity of our wavelength detector was determined to be 0.196 pm in the 10-nm-range of the NIR region. Our sub-picometer multi-wavelength detector will achieve a fast, wide-band, and cost-effective optical communication system. [ABSTRACT FROM AUTHOR]

We propose a promising fiber nonlinearity-tolerant optical signal-to-noise ratio (OSNR) monitoring technique for high speed long haul polarization multiplexed-quadrature phase shift keying (PM-QPSK) Nyquist wavelength division multiplexing (WDM) coherent optical fiber transmission system, in which the correlation function between the symbols in all states of polarization as well as neighboring channels are exploited instead of the traditional GN model, thus it does not need the prior knowledge of the fiber transmission link nor the complicated integrals. The method is demonstrated to have the OSNR measurement error below 1.28 dB over a wide OSNR range from 10 dB to 28 dB in 100 Gb/s per channel PM-QPSK-Nyquist-WDM system when the launch power is up to 4 dBm and transmission distance is as long as 1600 km. [ABSTRACT FROM AUTHOR]

This paper investigates the dynamic behavior of a thulium doped fiber amplifier (TDFA) operating in the 2 µm region for reconfigurable wavelength division multiplexing (WDM) systems. We show deleterious channel power fluctuations may be generated by input power variation at the amplifier and we propose the use of an optical gain-clamping technique. The investigated system consists of 20 channels with −4 dBm total input power. Our findings revealed that the effects of power transients due to channel reconfigurations are significantly reduced by a lasing feedback signal. Simulation results show that a power excursion of 4.3 dB is produced after dropping 19 channels when the amplifier gain is unclamped and only 0.0062 dB when the amplifier gain is clamped. The dynamics of GC-TDFA are mainly influenced by the value of the pump power factor and thus the laser signal achieves a stronger stabilization condition with increasing pump power factor. Hence, optical gain clamping is a simple and robust technique to control the power transient in the thulium-doped fiber amplifier of WDM systems at 2 µm. [ABSTRACT FROM AUTHOR]

A mathematical framework is presented to study the evolution of multi-point cumulants in nonlinear dispersive partial differential equations with random input data, based on the theory of weak wave turbulence (WWT). This framework is used to explain how energy is distributed among Fourier modes in the nonlinear Schrödinger equation. This is achieved by considering interactions among four Fourier modes and studying the role of the resonant, non-resonant, and trivial quartets in the dynamics. As an application, a power spectral density is suggested for calculating the interference power in dense wavelength-division multiplexed optical systems, based on the kinetic equation of the WWT. This power spectrum, termed the Kolmogorov-Zakharov (KZ) model, results in a better estimate of the signal spectrum in optical fiber, compared with the so-called Gaussian noise model. The KZ model is generalized to non-stationary inputs and multi-span optical systems. [ABSTRACT FROM PUBLISHER]

• Triple impact of SRS, FWM and ASE noise on UDWDM/DWDM systems with EDFAs is analyzed. • OSNR variations with input powers, channel lengths, channel spacing values are simulated. • OSNR values obtained from UDWDM/DWDM systems with 1, 2, 4, 5 EDFAs are compared. • Results show complexity of SRS, FWM and ASE noise triple impact on multi-span UDWDM/DWDM systems. • Paper give hints for reliable multi-span system design providing minimum 23 dB OSNR. In this paper, the combined impact of SRS, FWM and ASE noise in center channels of 7-, 15-, 31- and 63-channel UDWDM/DWDM long-haul multi-span optical fiber communication systems using different numbers of EDFAs has been analyzed with simulations. UDWDM/DWDM systems with varying system parameters, i.e. channel input powers, channel spacing values, multi-span fiber lengths and numbers of EDFAs, have been taken into account in simulations. Comparative OSNR simulation results satisfying a minimum 23 dB OSNR criterion under the combined impact of SRS, FWM and ASE noise have been presented and evaluated. OSNR vs channel input power simulation results show that FWM becomes the most dominant effect with respect to SRS and ASE noise in UDWDM systems. Therefore, OSNR values decrease as channel input powers increase in multi-span UDWDM systems having 3.125 GHz and 6.25 GHz channel spacing values. However, both ASE noise and SRS become more dominant with respect to FWM in DWDM systems with 100 GHz channel spacing values. OSNR values increase as the channel input powers increase in those multi-span DWDM systems. Simulation results for OSNR vs channel spacing values show that OSNR values obtained in multi-span UDWDM systems increase as channel spacing values increase in the 3.125 GHz–6.25 GHz range. This is due to the decrease in FWM crosstalk, which has a dominant effect in UDWDM systems, with increasing channel spacing values in those UDWDM systems. However, OSNR values obtained in multi-span DWDM systems decrease as channel spacing values increase in the 12.5 GHz–100 GHz range. This is due to the increase in ASE noise, which has a dominant effect in DWDM systems, with increasing optical filter bandwidths of those DWDM systems. OSNR vs channel length simulation results show that OSNR values generally decrease with increasing total fiber lengths and inter-amplifier fiber lengths in both UDWDM and DWDM multi-span systems. This is due to the FWM crosstalk and the ASE noise, which become more dominant with respect to the SRS as the total fiber length and inter-amplifier fiber lengths increase. Simulation results for OSNR vs number of EDFAs show that OSNR values obtained in multi-span UDWDM systems having 3.125 GHz channel spacing values decrease with increasing numbers of EDFAs. However, OSNR values in multi-span UDWDM/DWDM systems having 6.25 GHz-100 GHz channel spacing range increase with increasing numbers of EDFAs. Simulation results provide important clues for the design and implementation of reliable long-haul UDWDM/DWDM systems. [ABSTRACT FROM AUTHOR]

An optical network has a major role to play in modern computer networks. The optical network is providing a platform for transmission of huge amount of data at very high speed. These networks may fail due to various reasons. These failures may result in significant loss of revenue and time. Since this loss has a considerable effect on user and service provider, so the survivability of these optical networks has become very important issue to address. The survivability of a network is the capability of network to provide continuous services. The link failure is one of the very common failures in optical networks. A failed link is required to restore accurately and quickly so that failure impact can be minimized. In this paper, we have proposed a method to address survivability in all optical networks in case of single link failure. This method minimizes the recovery time for single link failure. Ant Colony Optimization (ACO) technique along with adjacent shortest cycle is used to calculate alternative path for retransmission of data. [ABSTRACT FROM AUTHOR]

A compact and portable microresonator-based optical frequency comb generation system was developed to provide an array of multiwavelength laser sources for dense wavelength division multiplexing (DWDM) fiber optic communication. The reported comb generation system was capable of producing comb lines after 7 km of travel without environmental control, indicating the effectiveness of the packaging. The comb spacing is about 98.3 GHz (i.e., ~0.79 nm around 1553 nm), thus the comb line frequencies coincide nicely with 100-GHz DWDM channel frequencies, assuming the suggested channel bandwidth is 0.3 nm. The quality of selected comb lines was evaluated individually based on error vector magnitude (EVM) measurements along with RF spectrum measurements. An average EVM value observed is as low as 3.8%, close to typical EVM values of less than 3% used for fiber optic communication. [ABSTRACT FROM AUTHOR]

CWDM networks have proven to be a promising first-step metro and access network architecture, offering a significant cost advantage over DWDM due to the lower cost of lasers and the filters used in CWDM modules. If demand grows beyond the capacity covered by CWDM channels, DWDM network elements can be introduced to merge CWDM and DWDM traffic at the optical layer. This ensures two advantages: reduced initial investment and scalability for deploying DWDM channels in the future. This article presents various ROADM architectures, and explores the novel optical node architecture of hybrid C/DWDM networks, consisting of CWDM, hybrid C/DWDM, and junction nodes connecting two rings. Evaluation has shown that the hybrid ROADM architecture is superior to other conventional ROADM architectures in terms of scalability and the initial cost of optical nodes and networks. [ABSTRACT FROM AUTHOR]

The technical feasibility (pre-FEC BER<3.8×10 −5 ) of an unamplified 4×100 Gb/s wavelength division multiplexed direct-detection optical orthogonal frequency division multiplexing (OFDM) system that uses electro-absorption modulators is numerically demonstrated for 2 and 10-km reach of single-mode fiber in C-band. Based on the use of specifications of currently available (realistic) components, error-free operation is achieved by finding optimum values for bias voltage and electrical gain in the modulator, and by employing a simple, yet powerful, peak-to-average power ratio (PAPR)-reduction technique. A performance comparison with a Mach-Zehnder driven system is presented too. The architecture here put forward can be used to define next-generation 400 Gb/s Ethernet standard. [ABSTRACT FROM AUTHOR]

In this paper, the filtering properties of photonic crystals (PCs) to perform narrow-channel transmission-type filters in second and third optical fiber telecommunication windows have been studied. Filtration of these zero dispersion and low-loss windows have simultaneously been established by utilizing of a triple-cavity transmission-type one-dimensional PC that provides perfect transmittances and narrow-channels at corresponding wavelengths. Such PC-based optical filter can be used in wavelength division multiplexing (WDM) optical communications systems. [ABSTRACT FROM AUTHOR]

Growth in the use of devices with Internet access and migration of telecommunications to Internet Protocol (IP) technology has made the bandwidth demanded by users appear for the first time as a limited resource. Optical fiber is demonstrating to be the solution to this issue based on the capability to provide enough bandwidth to manage large volumes of data at high speed featuring low loss transmission. Passive Optical Networks (PON) are presented as an alternative with respect to conventional copper-based access networks due to the use of distribution passive elements, which have a lower maintenance cost as compared to the active counterpart. In addition, the optical fiber capacity provides a future-proof platform to support the forthcoming bandwidth requested in the access segment. This paper presents and demonstrates through practical and simulation data analysis a proposal for next generation PON based on Time Division Multiplexing (TDM) and Wavelength Division Multiplexing (WDM). Complying with a typical PON power budget, the architecture envisages dynamic wavelength allocation and converged transport of wired and wireless services on a unified optical platform architecture. [ABSTRACT FROM AUTHOR]

We propose a novel non-contact optical fiber displacement sensor. It uses a radio frequency (RF) interrogation technique which is based on bidirectional modulation of a Mach-Zehnder electro-optical modulator (MZ-EOM). The displacement is measured from the free spectral range (FSR) which is determined by the dip frequencies of the modulated MZ-EOM transfer function. In experiments, the proposed sensor showed a sensitivity of 456 kHz/mm or 1.043 kHz/V in a measurement range of 7 mm. The displacement resolution of the proposed sensor depends on the linewidth and the power of the optical source. Resolution better than 0.05 μm would be achieved if an optical source which has a linewidth narrower than 1.5 nm and a received power larger than -36 dBm is used. Also, the multiplexing characteristic of the proposed sensor was experimentally validated. [ABSTRACT FROM AUTHOR]

AON, one of the most deployed fiber access solutions in Europe, needs to be upgraded in order to satisfy the ever growing bandwidth demand driven by new applications and services. Meanwhile, network providers want to reduce both capital expenditures and operational expenditures to ensure that there is profit coming from their investments. This article proposes several migration strategies for AON from the data plane, topology, and control plane perspectives, and investigates their impact on the total cost of ownership [ABSTRACT FROM PUBLISHER]

Service providers spend billions upgrading their broadband access networks to the latest access standards. Fiber has become the technology of choice in the medium and long term, thanks to its speed, reach, and future-proofness. A differential advantage of fiber over other broadband access technologies is that it makes it possible for operators to deliver symmetric-rate services. Most of today?s commercial offers based on regular PON range from 10 to 100 Mb/s of committed information rate, and higher rates are advertised as peak rates with unspecified guarantees. In this article we focus on delivering symmetrical 1 Gb/s access to residential users with a target temporal guarantee at the least cost using next-generation PON technologies. We compare four NG-PON standard access technologies, GPON, XGPON, WDM-PON, and the emerging TWDM-PON, from technical and economic perspectives. The study shows that if a service provider wants to keep up with the growing user traffic pattern in the long run, only TWDM-PON can provide 1 Gb/s nearly guaranteed at a moderate cost with respect to the fully dedicated 1 Gb/s point-to-point connection available in WDM-PON technologies. [ABSTRACT FROM PUBLISHER]

A novel device for data interchange among space-division multiplexed cores inside MCF is demonstrated using numerical simulations. The device allows complete exchange of all WDM data channels between MCF cores in propagation direction whether the channels have the same or different sets of wavelengths. This is crucial in future MCF optical networks where in-fiber data interchange over space-division multiplexed cores can allow for a simple and fast data swapping among cores without a need for space-division demultiplexing to single-mode single-core fibers. The data core-interchange (DCI) device consists of a graded refractive-index rectangular waveguide enclosing the two interchanged cores in addition to the cladding region in between them. Both finite-difference-time-domain (FDTD) and eigenmode expansion (EME) simulations are performed to verify the device operation and characterize its performance. The simulations demonstrate that the DCI has a very short-length with polarization independent operation, and high performance over the broadband wavelength range S, C, L, and U bands. Moreover, the device shows a high coupling-factor of −0.13 dB with small cross-talk, back-reflection, and return-loss of −26.3, −46.1, and −48.8 dB, respectively. [ABSTRACT FROM AUTHOR]

In this paper, we report the result of a field trial of 56-Gbaud (224-Gbit/s) and 57.5-Gbaud (230-Gbit/s) dual-polarization quadrature phase shift keying (DP-QPSK) coherent optical transmission over 820 km installed standard single mode fiber (SSMF). Offline digital signal processing (DSP) was applied for signal recovery and bit-error-rate (BER) counting in our field trial experiments, and BER performance well below the 7% overhead hard-decision forward error correction (FEC) error-free threshold (4.5×10 −3 ) at 2 31 -1 pseudo random bit sequence (PRBS) pattern length has been achieved, with the best achievable BERs of 2×10 −4 (56-Gbaud) and 3×10 −4 (57.5-Gbaud), respectively. In parallel a 1.15-Tbit/s (5×230-Gbit/s) quasi-Nyquist spaced wavelength division multiplexing (WDM) superchannel transmission over the same 820 km optical field link (FL) was also investigated through numerical simulations based on the same 57.5-Gbaud DP-QPSK signal using 1% roll-off Nyquist pulse shaping with 60-GHz channel spacing, and the results indicate that the BER performance well below the 7% overhead hard-decision FEC error-free threshold (4.5×10 −3 ) for the 1.15-Tbit/s DP-QPSK superchannel transmission can be achieved. [ABSTRACT FROM AUTHOR]

Quantum key distribution (QKD) ensures information-theoretic security for the distribution of random bits between two remote parties. To extend QKD applications to fiber-to-the-home optical communications, such as gigabit-capable passive optical networks (GPONs), an effective method is the use of wavelength-division multiplexing. However, the Raman scattering noise from intensive classical traffic and the huge loss introduced by the beam splitter in a GPON severely limits the performance of QKD. Here, we demonstrate the integration of QKD and a commercial GPON system with fiber lengths up to 14 km, in which the maximum splitting ratio of the beam splitter reaches 1:64. By placing the QKD transmitter on the optical line terminal side, we reduce the Raman noise collected at the QKD receiver. Using a bypass structure, the loss of the beam splitter is circumvented effectively. Our results pave the way to extending the applications of QKD to last-mile communications. [ABSTRACT FROM AUTHOR]

We propose a broadband tunable negative dispersion photonic crystal fiber (BT-ND-PCF) for dispersion compensation over the S + C + L wavelength bands. BT-ND-PCF is a dual-core structure in which air holes are arranged with a hexagonal lattice and temperature-sensitive liquid is infiltrated into the air holes of the fourth layer. The performance of BT-ND-PCF is numerically analyzed by the finite element method with an anisotropic perfect matching layer. The results show that BT-ND-PCF has a broadband negative dispersion coefficient of −1533.2 to −2836.4 ps / km / nm over the S + C + L wavelength bands, a dispersion coefficient of −2268.9 ps / km / nm at 1550 nm, and a kappa value of 287.9 nm at 1550 nm, which matches with Corning single-mode fiber 28 (SMF). The residual dispersion (RD) after compensating for the dispersion of 1 km SMF is in the range of −0.22 to +0.16 ps / nm. In addition, the dispersion coefficient is changed by 0.679 ps/km/nm per 1°C by controlling the temperature, which is conducive to the accurate compensation of RD. Due to its unique optical properties, BT-ND-PCF can be used in broadband dispersion compensation for dense wavelength division multiplexing optical fiber communication systems. [ABSTRACT FROM AUTHOR]

Motivated by results in optical communications, where the performance can degrade dramatically if the transmit power is sufficiently increased, the channel capacity is characterized for various kinds of memoryless vector channels. It is proved that for all static point-to-point channels, the channel capacity under an equal-power constraint is a nondecreasing function of power. As a consequence, maximizing the mutual information over all input distributions with a certain power is for such channels equivalent to maximizing it over the larger set of input distributions with upperbounded power. The channel coding theorem is formally proved for an equal-power constraint. For interference channels such as optical wavelength-division multiplexing systems, the primary channel capacity is always nondecreasing with power if all interferers transmit with identical distributions as the primary user. Also, if all input distributions in an interference channel are optimized jointly, then the achievable sum-rate capacity is again nondecreasing. The results generalize to the channel capacity as a function of a wide class of costs, not only power. [ABSTRACT FROM PUBLISHER]