Fiber Channel Research Articles

Chirped Gaussian pulse propagation with various data rates transmission in the presence of group velocity dispersion (GVD)

Abstract Linear/Measured chirped Gaussian pulse propagation is simulated at various data rates transmission in the presence of group velocity dispersion without amplification unit. The power variations (PVs) vs. frequency, time period are also clarified after 250 km fiber channel length and 10 Gb/s bit rate (BR) of for Gaussian pulse generators with linear chirp factor of 2 rad/s, measured chirp factor (alpha parameter of 2 rad/W, Adiabatic chirp of 10 s−1). Moreover the overall total light power after fiber, the overall total electrical power after APD receiver are studied and clarified for Gaussian pulse generators with linear chirp, measured chirp factor. PVs vs. frequency, time period are simulated after APD receiver for Gaussian pulse generators with linear chirp, measured chirp factor. Maximum signal amplitude variations vs. time after APD receiver for Gaussian pulse generators with linear chirp, measured chirp factor are also clarified with the numerical simulation results.

A novel framework for content connectivity through optical data centers

Abstract Nowadays, the data centers have become a significant physical infrastructure for the purpose of supporting various Internet applications like cloud services, entertainment, web search and social networking. The traffic among the data centers is growing rapidly accompanied by the services that are obtained. The data centers are connected via fiber channels to support long-haul networks and high data rate transmissions by utilizing various modulation techniques. However, it has some drawbacks such as increased delay, computational complexities, high wavelength consumption, link failures, etc. Recently, researchers are focusing on improving the survivability and wavelength usage efficiency in optical data center networks. In this work, a novel framework depending on the concept of content connectivity is proposed for optical data center networks. Here, a mixed integer linear programming (MILP) is utilized for transmitting the data through optical data centers. The main intention of this research is to improve the performance and wavelength efficiency in optical data center networks. The performance of the MILP approach is evaluated and compared with the existing integer linear programming (ILP) technique and found that this new approach provides better performance with higher wavelength efficiency and reduced wavelength consumption.

Simultaneous Decoherence and Mode Filtering in Quantum Channels: Theory and Experiment

Quantum networks require robust quantum channels for fast and reliable entanglement distribution over long distances. As quantum communication technology matures, it moves towards utilizing actual fibers and free-space optical channels; hence, there is a growing need for physical models describing decoherence. The primary challenge is to concisely account for numerous elements distributed along a lengthy optical path. We approach this by starting with an analytical model of a channel with just two lumped elements, one representing decoherence and the other representing mode filtering. Interestingly, we find that, while the order and relative orientation of the two elements produce a wealth of different biphoton states, the amount of entanglement in all those states is exactly the same. Then, we conduct experiments that implement this channel and verify our analytical findings. Finally, we expand our analysis to the most general fiber polarization channel, comprising a statistically significant number of arbitrarily oriented elements. We show that, over an ample range of parameters, our two-element analytical model is quite accurate in describing the fiber channel, which makes it an effective tool for gaining insights into channel decoherence.

Interference at the single-photon level based on silica photonics robust against channel disturbance

Quantum key distribution (QKD) provides a solution for communication of unconditional security. However, the quantum channel disturbance in the field severely increases the quantum bit-error rate, degrading the performance of a QKD system. Here we present a setup comprising silica planar light wave circuits (PLCs), which is robust against the channel polarization disturbance. Our PLCs are based on the asymmetric Mach–Zehnder interferometer (AMZI), integrated with a tunable power splitter and thermo-optic phase modulators. The polarization characteristics of the AMZI PLC are investigated by a novel pulse self-interfering method to determine the operation temperature of implementing polarization insensitivity. Over a 20 km fiber channel with 30 Hz polarization scrambling, our time-bin phase-encoding QKD setup is characterized with an interference fringe visibility of 98.72%. The extinction ratio for the phase states is kept between 18 and 21 dB for 6 h without active phase correction.

Cascaded stages of parametric optical fiber amplifiers with Raman fiber amplifiers for upgrading of telecommunication networks through optical wireless communication channel

Abstract This paper contains a main model which concludes a two optical fiber cable along 70 km and with Parametric/Raman amplifiers with a result of total power 0.781 dBm that computed by the optical power meter which is located before the receiver part and the second optical fiber channel, a total power −44.186 dBm at the end of model which is computed by the electrical power meter visualizer, and a max. Q factor 2.548 computed by the BER analyzer. The suggested model has outlined some updates on the previous model to improve the results so that the results are increased at the same length as the following: total power of optical signal becomes 10.039 dBm, total power of electrical signal becomes 0.624 dBm, and the max. Q factor becomes 9.60787.

Wavelength attack on atmospheric continuous-variable quantum key distribution

Recently, several practical wavelength attacks on continuous-variable quantum key distribution (CVQKD) were proposed based on the wavelength-dependent property of a beam splitter in Bob's station. These attack schemes are limited to the fiber channel systems with a relatively stable transmittance. However, unlike the fiber channel, the transmittance of the atmospheric channel is complex and fluctuates dramatically in time, which may invalidate the attack equations that must be satisfied in the optical fiber channel. In this paper, we propose two wavelength attack schemes against complex atmospheric CVQKD systems and formulize the two schemes based on the parameter estimation method. To verify the feasibility and availability of this attack, we deduce the success criteria for the two attack schemes. By numerical analysis, our attack schemes are proved to be feasible in the permitted parameter regimes. The secret key rate and propagation distance of CVQKD can be further overestimated by selecting the condition parameters effectively. Moreover, we discuss the possible prevention countermeasures to resist these attack schemes. The proposed method will fill the gap of wavelength attack for the implementation of practical atmospheric CVQKD.

Performance analysis of grating-assisted passive mode-division multiplexing device using silicon photonics for high-speed RoF/RoFSO communication

The performance of a bidirectional silicon mode-division (de)multiplexer has been analyzed in the radio over fiber passive optical network system. The device uses two grating-assisted contra-directional coupler sections to demultiplex the transmitted fundamental, first-order, and second-order quasi-transverse electric (TE) modes. A bandwidth of 791 GHz and acceptable crosstalks of −25.73 dB (TE0m), −10.30 dB (TE1m), and −11.84 dB (TE2m) have been achieved from the 2.5D finite-difference time-domain method at a wavelength of 1550 nm. The system uses parabolic index multimode fiber (MMF) and free-space optics channels alternatively. A 120-Gbps data rate has been obtained using differential quadrature phase-shift keying scheme and hybrid mode-division multiplexing techniques. The system maintains an acceptable bit error rate (≤10 − 12) over transmission distances of ≤5.3 km MMF and ≤1.9 km for free-space optics link with receiver sensitivities of ≥ − 26.2 and ≥ − 24.8 dBm, respectively.

Low-Complexity Geometric Shaping

Approaching Shannon's capacity via geometric shaping has usually been regarded as challenging due to modulation and demodulation complexity, requiring look-up tables to store the constellation points and constellation bit labeling. To overcome these challenges, in this paper, we study lattice-based geometrically shaped modulation formats in multidimensional Euclidean space. We describe and evaluate fast and low complexity modulation and demodulation algorithms that make these modulation formats practical, even with extremely high constellation sizes with more than $10^{28}$ points. The uncoded bit error rate performance of these constellations is compared with the conventional QAM formats in the additive white Gaussian noise and nonlinear fiber channels. At a spectral efficiency of 2 bits/sym/polarization, compared with 4-QAM format, transmission reach improvement of more than 38% is shown at the hard-decision forward error correction threshold of $2.26\times 10^{-4}$.

Routing, Core and Wavelength Allocation in Multi-Core-Fiber-Based Quantum-Key-Distribution-Enabled Optical Networks

Quantum-key-distribution (QKD) enabled optical networks can provide secure keys for different kinds of applications to ensure the high security of communication processes. As the number of wavelength channels in a single-core fiber is limited, space division multiplexing (SDM) has been considered to be a valuable technique to provide more wavelength resources, which solves the problem of insufficient channel capacity. Due to the rapid expansion of data volume, the SDM-based QKD network has been regarded as an important paradigm. At the same time, resource allocation in multi-core optical networks is a problem worthy of studying. In this work, four routing, core, and wavelength allocation (RCWA) algorithms are proposed in the multi-core optical network for quantum service requests and classical service requests, which are referred to as RCWA without perception (RCWA-WP), RCWA with crosstalk perception (RCWA-XTP), RCWA with spectrum perception (RCWA-SP), and RCWA with core perception (RCWA-CP). Simulations are carried out to evaluate the network performance in terms of blocking probability, key utilization, and average crosstalk intensity. The comparative results indicate that the RCWA-SP algorithm can improve network performance and reduce the blocking probability, while the RCWA-XTP algorithm can reduce inter-core crosstalk during transmission.

Channel Estimation Based on Interference Cancellation Method for FBMC-PON

Based on the traditional orthogonal frequency division multiplexing passive optical network (OFDM-PON) system, filter bank multi-carrier passive optical network (FBMC-PON) eliminates the CP by introducing a prototype filter, dramatically improving spectral efficiency. Meanwhile, thanks to its excellent bit error rate (BER) performance, FBMC-PON becomes one of the significant alternatives to OFDM-PON. In previous practical cases, the interference approximation method (IAM) based channel estimation algorithm, which mainly enhances the power of train sequence, plays superior in FBMC-PON. However, the interference cancellation method (ICM) channel estimation method is a better choice due to the self-cancellation of imaginary interference, especially for short-distance optical fiber access channels. We analyze the different train sequences and consider that in the short fiber channel of PON, it is more vital to suppress the imaginary interference rather than improve the train sequence’s power. The simulation results show that the performance of FBMC-PON based on ICM is one order of magnitude higher than that of OFDM-PON and half an order of magnitude higher than that of IAM in the case of 20km fiber. Our proposed channel estimation algorithm only changes the structure of the train sequence and does not increase any additional computational complexity.

Modal-Chromatic Dispersion Interaction Effects for 850 nm VCSEL Channels at 100 Gb/s per Wavelength

We present a theoretical model and experiments to estimate and measure the magnitude of modal and chromatic dispersion interaction (MCDI) over multimode optical channels using vertical-cavity surface-emitting laser (VCSEL) based transceivers. The effects of MCDI and bit error rate performance are also evaluated for PAM-4 signals at data rates from 100 Gbps to 112 Gbps. A section of the article is dedicated to the characterization of the spectral coupling between VCSEL and fiber, including a multimode and a VCSEL with a dominant fundamental mode that has shown the potential to increase the reach of MMF channels. For the experiments, several types of OM4 and OM3 fibers, with accurate bandwidth characterization over a broad range of wavelengths were utilized. The reported analysis applies to future Ethernet and Fibre Channel applications requiring ≥100 Gb/s per wavelength over multimode fibers.

The Influence of Signal Polarization on Quantum Bit Error Rate for Subcarrier Wave Quantum Key Distribution Protocol.

In this paper, we consider the influence of a divergence of polarization of a quantum signal transmitted through an optical fiber channel on the quantum bit error rate of the subcarrier wave quantum key distribution protocol. Firstly, we investigate the dependence of the optical power of the signal on the modulation indices’ difference after the second phase modulation of the signal. Then we consider the Liouville equation with regard to relaxation in order to develop expressions of the dynamics of the Stokes parameters. As a result, we propose a model that describes quantum bit error rate for the subcarrier wave quantum key distribution depending on the characteristics of the optical fiber. Finally, we propose several methods for minimizing quantum bit error rate.

284.8-Mb/s Physical-Layer Cryptographic Key Generation and Distribution in Fiber Networks

Key distribution is a major challenge of secure communication. Computational approaches to key distribution are breached by quantum algorithms, while quantum key distribution (QKD) is an expensive, slow, and sophisticated solution. Secure key generation and distribution from unpredictable and inherent physical-layer properties of optical fiber channel is a classical, simple and cost-effective solution. However, the quasi-static nature of fiber channels dramatically limits the available key generation rate (KGR) to the order of ~kbit/s. Here we effectively accelerate the KGR by six orders of magnitude using a developed high-speed chaotic polarization scrambler (CPS) driven by digital chaos in fiber channels. An error-free KGR of 284.8 Mbit/s is experimentally demonstrated over a 24 km standard single-mode fiber (SSMF), where the generated key passes the random test suite. Moreover, we fully analyze the security mechanism and find that a strong asymmetry exists between legal and illegal users, ensuring a high-level of security against potential fiber-tapping attacks. This scheme provides a major step towards the practical implementation of the “one-time-pad” in secure data transmission over fiber networks.

HIGH DATA RATE WDM SYSTEMS-BASED GRAPHENE CARRIERS

In this paper, carrier’s generation-based graphene with applicability for wavelength division multiplexing (WDM) systems have been produced via an illumination of graphene by 980 nm. This technique allowed for servicing of a greater number of channels in a WDM system, and the carriers were able to travel in an optical channel with high data rate. Eight carriers, having a frequency spacing (FS) of 25 GHz and full-width at half-maximum (FWHM) of 500 MHz, were created. These generated carriers were separately modulated with eight optical quadrature phase shift keying (QPSK) signals and subsequently optically multiplexed and transmitted to an optical fiber channel. At the receiver side, the received signal was demultiplexed, and the performance of the system was analyzed via calculating the error vector magnitude and constellation diagram of the entire system. Opti System version 17.1 and Matlab software are used for demonstration of WDM system and carrier generation.

Fast and Accurate Optical Fiber Channel Modeling Using Generative Adversarial Network

In this work, a new data-driven fiber channel modeling method, generative adversarial network (GAN) is investigated to learn the distribution of fiber channel transfer function. Our investigation focuses on joint channel effects of attenuation, chromic dispersion, self-phase modulation (SPM), and amplified spontaneous emission (ASE) noise. To achieve the success of GAN for channel modeling, we modify the loss function, design the condition vector of input and address the mode collapse for the long-haul transmission. The effective architecture, parameters, and training skills of GAN are also displayed in the paper. The results show that the proposed method can learn the accurate transfer function of the fiber channel. The transmission distance of modeling can be up to 1000 km and can be extended to arbitrary distance theoretically. Moreover, GAN shows robust generalization abilities under different optical launch powers, modulation formats, and input signal distributions. Comparing the complexity of GAN with the split-step Fourier method (SSFM), the total multiplication number is only 2% of SSFM and the running time is less than 0.1 seconds for 1000-km transmission, versus 400 seconds using the SSFM under the same hardware and software conditions, which highlights the remarkable reduction in complexity of the fiber channel modeling.

Polarization Division Multiplexing-Based Hybrid Microwave Photonic Links for Simultaneous mmW and Sub-6 GHz Wireless Transmissions

A new hybrid microwave photonic link based on a polarization division multiplexing Mach-Zehnder modulator (PDM-MZM) is proposed. The link enables co-transmission of millimeter-wave (mmW) and sub-6 GHz wireless signals over a seamless single-mode fiber (SMF) and free-space optics (FSO) channels. Optimization of the chromatic dispersion (CD)-induced power fading regardless of the power fading due to the non-deterministic atmospheric turbulence (AT) is simultaneously demonstrated. Extensive simulation analysis is first presented to examine (i) the impact of CD on mmW (25 GHz) and sub-6 GHz (2.6 GHz) signals, envisioned for the 5th generation networks, and (ii) optimization of CD-induced power fading by changing the phase relations between the optical carrier and optical sidebands in each polarization channel using single tunable polarization controller. A proof-of-concept experiment is finally performed to simultaneously deliver 25 GHz and 2.6 GHz signals with 4/16/64-quadrature amplitude modulation over (i) 20 km SMF and 2 m radio wireless link and (ii) 20 km SMF, 4.2 m FSO (with AT) and 2 m radio wireless links. The optimization of the CD-induced power fading is experimentally verified and link performance shows high tolerance to CD with no power penalties and the measured error vector magnitudes well below the required limits. The predicted bit error rates are also below the forward error correction threshold of $2 \times {10^{ - 4}}$.

A Fully Symmetrical Quantum Key Distribution System Capable of Preparing and Measuring Quantum States* *Supported by the Fundamental Research Funds for the Central Universities (Grant No. 2019XD-A02), and the State Key Laboratory of Information Photonics and Optical Communications, Beijing University of Posts and Telecommunications (Grant No. IPO2019ZT06).

We propose a fully symmetrical QKD system that enables quantum states to be prepared and measured simultaneously without compromising system performance. Over a 25.6 km fiber channel, we demonstrate point-to-point QKD operations with asymmetric Mach–Zehnder interferometer modules. Two interference visibilities of above 99% indicate that the proposed system has excellent stability. Consequently, the scheme not only improves the feasibility of distributing secret keys, but also enables QKD closer to more practical applications.

Extending Quantum Links: Modules for Fiber‐ and Memory‐Based Quantum Repeaters

AbstractElementary building blocks for quantum repeaters based on fiber channels and memory stations are analyzed. Implementations are considered for three different physical platforms, for which suitable components are available: quantum dots, trapped atoms and ions, and color centers in diamond. The performances of basic quantum repeater links for these platforms are evaluated and compared, both for present‐day, state‐of‐the‐art experimental parameters as well as for parameters that can in principle be reached in the future. The ultimate goal is to experimentally explore regimes at intermediate distances—up to a few 100 km—in which the repeater‐assisted secret key transmission rates exceed the maximal rate achievable via direct transmission. Two different protocols are considered, one of which is better adapted to the higher source clock rate and lower memory coherence time of the quantum dot platform, while the other circumvents the need of writing photonic quantum states into the memories in a heralded, nondestructive fashion. The elementary building blocks and protocols can be connected in a modular form to construct a quantum repeater system that is potentially scalable to large distances.

High-speed Gaussian-modulated continuous-variable quantum key distribution with a local local oscillator based on pilot-tone-assisted phase compensation.

A high-speed Gaussian-modulated continuous-variable quantum key distribution (CVQKD) with a local local oscillator (LLO) is experimentally demonstrated based on pilot-tone-assisted phase compensation. In the proposed scheme, the frequency-multiplexing and polarization-multiplexing techniques are used for the separate transmission and heterodyne detection between quantum signal and pilot tone, guaranteeing no crosstalk from strong pilot tone to weak quantum signal and different detection requirements of low-noise for quantum signal and high-saturation limitation for pilot tone. Moreover, compared with the conventional CVQKD based on homodyne detection, the proposed LLO-CVQKD scheme can measure X and P quadrature simultaneously using heterodyne detection without need of extra random basis selection. Besides, the phase noise, which contains the fast-drift phase noise due to the relative phase of two independent lasers and the slow-drift phase noise introduced by quantum channel disturbance, has been compensated experimentally in real time, so that a low level of excess noise with a 25 km optical fiber channel (with 5 dB loss) is obtained for the achievable secure key rate of 7.04 Mbps in the asymptotic regime and 1.85 Mbps under the finite-size block of 107.

Geometric Shaping of 2-D Constellations in the Presence of Laser Phase Noise

In this article, we propose a geometric shaping (GS) strategy to design 8, 16, 32, and 64-ary modulation formats for the optical fibre channel impaired by both additive white Gaussian (AWGN) and phase noise. The constellations were optimised to maximise generalised mutual information (GMI) using a mismatched channel model. The presented formats demonstrate an enhanced signal-to-noise ratio (SNR) tolerance in high phase noise regimes when compared with their quadrature amplitude modulation (QAM) or AWGN-optimised counterparts. By putting the optimisation results in the context of the 400ZR implementation agreement, we show that GS alone can either relax the laser linewidth (LW) or carrier phase estimation (CPE) requirements of 400 Gbit/s transmission links and beyond. Following the GMI validation, the performance of the presented formats was examined in terms of post forward error correction (FEC) bit-error-rate (BER) for a soft decision (SD) extended Hamming code (128, 120), implemented as per the 400ZR implementation agreement. We demonstrate gains of up to 1.2 dB when compared to the 64-ary AWGN shaped formats.