Long-haul Communication Research Articles

5G NR sub-THz fiber-wireless integrated systems using polarization multiplexing-multiband technique and self-polarization diversity scheme

Fifth generation (5G) new radio (NR) fiber-wireless integrated systems using polarization multiplexing-multiband technique and self-polarization diversity scheme are successfully implemented. Polarization multiplexing-multiband technique is an effectual method to enhance the transmission capacity and spectral efficiency of systems. Self-polarization diversity scheme is an efficient scheme for polarization demultiplexing, in which an x-polarized (y-polarized) optical carrier with multiple x-polarized (y-polarized) optical signals can be detected using single-ended photodiodes. The transmission of 5G NR sub-terahertz (THz) signals through fiber-wireless integrated systems holds promise to afford high-speed and long-haul wired-wireless communications. It shows the robustness to achieve high aggregate data rates and lays the foundation to meet the evolving demands of future communication systems. Through an integrated medium of 20 km single-mode fiber, 1.6 km optical wireless, and 4/8/12 m 5G NR wireless, four 5G sub-THz 32-quadrature amplitude modulation-orthogonal frequency-division multiplexing signals at x- and y-polarizations are transmitted with good transmission performance in terms of low bit error rates and error vector magnitudes. The successful transmission of sub-THz signals at different carrier frequencies and polarizations over fiber-wireless integrated systems proves system’s ability to support cutting-edge 5G NR fiber-wireless integrated systems.

A Numerical Assessment of the Effect of Concatenating Arbitrary Uncoupled Multicore Fiber Segments on Intercore Crosstalk in Long-Haul Communication Links

Random core dependent loss (CDL) has been shown to increase the direct average intercore crosstalk (ICXT) power in long-haul uncoupled multicore fiber (MCF) links. Longer links are composed of multiple MCF segments, and random CDL may arise on these links from manufacturing imperfections. During link implementation, other random effects may arise and enhance the ICXT power. In this work, the effect of concatenating MCF segments with random characteristics on the direct average ICXT power in long-haul links is assessed numerically by studying the influence of the randomness of segment length, coupling coefficient, and random CDL on the mean, standard deviation, relative spread, and excess kurtosis of the ICXT power. The numerical results show that the segment length randomness marginally affects the ICXT power. For 2000 km long links and a 6 dB maximum random variation of the coupling coefficients, the mean almost doubles and the standard deviation almost triples, relative to considering only random CDL. However, the effect of the coupling coefficients randomness on the relative spread and excess kurtosis is reduced, not affecting significantly the nearly Gaussian distribution of the direct average ICXT power and the excess of direct average ICXT power (less than a 0.26 dB increase relative to considering only random CDL).

Design and performance of WDM system for high-speed optical communication on different modulation formats

Abstract In this paper, the performance analysis of the WDM (wavelength division multiplexing) system on the optical fiber transmission link is proposed. High data transmission is possible by implementing a WDM optical communication system using different modulation formats. Firstly, the WDM optical communication system is designed on an Optiwave simulation tool and distortion in the optical fiber by “eye pattern analysis” is analyzed. Secondly, the optical SNR of the proposed WDM optical communication system is studied. Further, the bit-error rate (BER) plot is studied and optimization techniques are applied to enhance the proposed system for long-haul communication. Furthermore, the BER plots are analyzed by varying the length of the fiber and applying different coding techniques like NRZ (non-return zero), RZ (return to zero), QAM (quadrature amplitude modulation) etc. using the Optiwave simulation tool. The results obtained in the Optiwave simulation tool are validated by theoretical implementation in the MATLAB tool.

Partial coherence enhances parallelized photonic computing

Advancements in optical coherence control1–5 have unlocked many cutting-edge applications, including long-haul communication, light detection and ranging (LiDAR) and optical coherence tomography6–8. Prevailing wisdom suggests that using more coherent light sources leads to enhanced system performance and device functionalities9–11. Our study introduces a photonic convolutional processing system that takes advantage of partially coherent light to boost computing parallelism without substantially sacrificing accuracy, potentially enabling larger-size photonic tensor cores. The reduction of the degree of coherence optimizes bandwidth use in the photonic convolutional processing system. This breakthrough challenges the traditional belief that coherence is essential or even advantageous in integrated photonic accelerators, thereby enabling the use of light sources with less rigorous feedback control and thermal-management requirements for high-throughput photonic computing. Here we demonstrate such a system in two photonic platforms for computing applications: a photonic tensor core using phase-change-material photonic memories that delivers parallel convolution operations to classify the gaits of ten patients with Parkinson’s disease with 92.2% accuracy (92.7% theoretically) and a silicon photonic tensor core with embedded electro-absorption modulators (EAMs) to facilitate 0.108 tera operations per second (TOPS) convolutional processing for classifying the Modified National Institute of Standards and Technology (MNIST) handwritten digits dataset with 92.4% accuracy (95.0% theoretically).

Transmission of 10 Gbps C-band-signal-based Radio Over Fiber for Next Generation Communication Systems

Rapid development of 5G networks encourages researchers to improve the radio-over-fiber (RoF) technique in order to reach 10 Gbps data transmission rates, to increase bandwidth and range, while reducing latency and implementation cost. This paper evaluates an analog radio-over-fiber (ARoF) technique that is compatible with long-distance communication systems. We demonstrate a long distance transmission of a 28 GHz 64 QAM signal via a single mode fiber (SMF) after modulating it with the use of two parallel Mach-Zehnder modulators, without any optical amplifiers. The results show that our prototype solution is capable of transferring data over distances of up to 140 km, via SMF, with a 10 Gbps data rate. The error vector magnitude (EVM) was found to be 7.709%. The proposed system offers exceptional capabilities in terms of supporting high bitrates, while ensuring that EVM remains within the 3GPP limits. Compared to other works, the proposed solution proves to be superior in terms of performance, making it an ideal choice for next generation long-haul communication systems.

Enhancing network performance in a long-haul communication system a wavelength division multiplexing and coherent optical orthogonal frequency division multiplexing approach

Enhancing network performance in a long-haul communication system a wavelength division multiplexing and coherent optical orthogonal frequency division multiplexing approach

An Efficient Distributed Reinforcement Learning Architecture for Long-Haul Communication Between Actors and Learner

An Efficient Distributed Reinforcement Learning Architecture for Long-Haul Communication Between Actors and Learner

On the exploration of structured light transmission through a multimode fiber in a reference-less system

Recent advancements in optical wavefront shaping have brought multimode fibers (MMFs) into the spotlight as potential contenders for long-haul communication, positioning them as promising substitutes to single-mode fibers. MMFs offer greater data rates, countering the impending congestion of fiber-based networks. Additionally, their suitability for single fiber endoscope procedures presents them as compelling alternatives for minimally invasive endoscopy, providing information comparable to, if not surpassing, current cutting-edge technology. However, the complex modal behavior of light in MMFs hinders the implementation of these promising applications. Hence, precise modal excitation and control are crucial for improving the transmission of structured light in MMFs. This study introduces a groundbreaking approach that achieves the retrieval of the transmission matrix in a single step, thereby facilitating coherent light propagation through highly dispersive MMFs. By combining iterative phase retrieval algorithms with the measurement of phase shifts between experimentally established focal points, potential arbitrary interference control is enabled, leading to effective phase correction. The efficacy of our method is validated through the successful transmission of diverse structured light beams, including Laguerre–Gauss and Hermite–Gaussian types, as well as handwritten characters via MMF. The examination of structured light is simplified using an off-axis holographic technique that accurately captures both intensity and phase information. These results hold significant potential, paving the way for major advancements in long-distance communication and minimally invasive medical procedures, thereby transforming the telecommunications and healthcare sectors.

Qualitative analysis of PMD-induced long-haul optical fiber link

Abstract This paper studies the detrimental effect of polarization mode dispersion on long-haul optical fiber communication in terms of the quality factor and bit error rate. The dispersion value is varied for different fiber lengths, specifically for long-haul communication, and the results obtained are analyzed in terms of the quality factor. The polarization mode dispersion causes pulse broadening, leading to interchannel interference. There is a need to check the occurrence and the associated effects of this dispersion. The communication range for conducting the analysis varies from 150 km to 350 km. The analysis is first conducted on varied communication fiber link length for different dispersion values, and it is observed that a fiber length of 200 km gives comparatively favorable results, as seen from the BER analysis.

Recurrent Neural Networks and Recurrent Optical Spectrum Slicers as Equalizers in High Symbol Rate Optical Transmission Systems

The transition to the edge-cloud era makes ultra-high data rate signals indispensable for covering the immense and increasing traffic demands created. This ecosystem also seeks for power efficient optical modules that will deliver this enormous data load. Optical communication systems and their continuous evolution have responded to the upward trend of capacity needs in all different network ecosystems, scaling from short-reach links serving data center, fiber-to-the-home and 5G/B5G services to metro and long-haul transoceanic cables. Kerr induced non-linearities at long haul and dispersion induced power fading at short reach remain intractable problems that vastly affect high symbol rate systems. So, they must be addressed in a power efficient way in order to cope with the ever-increasing traffic requirements. <p xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">In this paper, we review our recent work in machine learning and neuromorphic processing in the optical domain for the mitigation of transmission impairments at very high symbol rates. Post-detection techniques based on bidirectional recurrent neural networks for non-linearity compensation and neuromorphic recurrent optical spectrum slicers for power fading mitigation and self-coherent detection emerge as promising solutions for mid-term deployment in long-haul and short-reach communication systems respectively. The current work provides new results in both fields focusing on multi-channel detection in the coherent long-haul domain and on a cost/consumption/performance assessment of neuromorphic photonic processing based on recurrent spectrum slicing in comparison to the state-of-the-art. A thorough analysis of other state-of-the-art techniques in both domains is also provided revealing the merits and shortcomings of recurrent neural networks and neuromorphic photonic processing in high-speed optical communication systems.

Modeling and computational analysis of the combined impact of optical Kerr nonlinearities on the performance of DWDM long-haul communication systems

Modeling and computational analysis of the combined impact of optical Kerr nonlinearities on the performance of DWDM long-haul communication systems

High Spectral Efficiency Photonics-Based Polarization Multiplexing OFDM Signal Delivery at W-Band

We have implemented a large-capacity, long-haul, and high spectral efficiency photonics-based polarization multiplexing communication system at W-band. The signal delivery up to 119.1 Gb/s with spectral efficiency of 9.9 bit/s/Hz is achieved over a 10 km optic-fiber link and 4600 m wireless link. In our study, we utilize an orthogonal frequency division multiplexing (OFDM) scheme to compensate for the signal impairments caused by the dispersion effect and the wireless multipath effect. Based on a pair of antennas, the antenna polarization multiplexing technique is used to realize the polarization-multiplexed mm-wave signal delivery. Also, only one communication link is required, instead of the complex 2×2 line-of-sight multiple-input multiple-output (MIMO) link. Instead of Cassegrain antennas, the combination of plano-convex lens and horn antenna greatly extends the wireless distance. For increasing the spectral efficiency and throughput of the communication system, we employ higher-order modulation formats, probabilistic shaping (PS) techniques, and a series of equalization algorithms. Based on photonics technology, we have created a record-setting distance-rate product of 547.9 Gb/s•km (119.1 Gb/s × 4.6 km) for an independent channel at W-band.

5G Mobile Wireless Access and Digital Channeling with RF Over Fiber for Long-Haul 64-QAM Communication

This paper presents the experimental results of a novel radio-over-fiber (RFoF) architecture that is capable of transmitting data at 20 Gb/s over a 600 km fiber. Such high bit rates required by 5G systems for long-haul communication. This is accomplished by overcoming the limitation of single mode fibers (SMF) of power attenuation and chromatic dispersion. This is achieved by interspersing sections of the SMF with a dispersion compensating filter (DCF) and embedding midway of the fiber length with chirped fiber Bragg grating (CFBG). Moreover, the proposed approach is shown to enhance the total bandwidth over a long-haul gigabit passive optical network (GPON) using integrated channel coarse wavelength division multiplexing (CWDM). In the experiment, a 64-quadrature amplitude modulation (64-QAM) signal was modulated onto CWDM signal. With the proposed RFoF architecture the signal power received over a 600 km fiber is greater than a conventional optical architecture by 19 dB for identical applied input optical power of 20 dBm. This translates to significant power savings that can be achieved with the proposed architecture over existing architectures that should reduce the carbon footprint of long-haul optical communications systems. The optical receiver is shown to have a sensitivity of −28.3 dBm for a bit-error rate (BER) of 10−9. These results demonstrate the viability of the proposed RFoF architecture in providing significant improvement in the bit rate over a transmission distance.

Telecom C-band photon emission from (In,Ga)As quantum dots generated by filling nanoholes in In0.52Al0.48As layers

We present the fabrication of strain-free quantum dots in the In0.53Ga0.47As/In0.52Al0.48As-system lattice matched to InP, as future sources for single and entangled photons for long-haul fiber-based quantum communication in the optical C-band. We achieved these quantum dots by local droplet etching via InAl droplets in an In0.52Al0.48As layer and subsequent filling of the holes with In0.53Ga0.47As. Here, we present detailed investigations of the hole morphologies measured by atomic force microscopy. Statistical analysis of a set of nanoholes reveals a high degree of symmetry for nearly half of them when etched at optimized temperatures. Overgrowth with 50–150 nm In0.52Al0.48As increases their diameter and elongates the holes along the [01̄1]-direction. By systematically scanning the parameter space, we were able to fill the holes with In0.53Ga0.47As, and by capping the filled holes and performing photoluminescence measurements, we observe photoluminescence emission in the O-band up into the C-band depending on the filling height of the nanoholes.

Mitigation of nonlinearities in long-haul DWDM soliton-based communication system

Abstract The ongoing challenge of research and development is focusing on increasing the overall capacity of the transmission medium, achieving a high bit rate, and designing long-haul optical communication systems. The main requirement of the transmission system in supporting high bit rates in optical communication systems is their tolerance to nonlinear fiber impairments. Optical soliton pulses that preserve their shape over long distances are the straightforward solution to this problem. In this paper, DWDM soliton-based optical communication system is designed to mitigate the nonlinear effects at a data rate of 10 Gbps with channel spacing of 100 GHZ by using a microring resonator (MRR) device which acts as an add/drop filter that generates a filter narrowband wavelength from a wider optical spectrum. The transmission link of the optical fiber has a total length of 180 km and MRR is inserted at the end of the loop which provides the required bandwidth. The high bit rate signals can be transmitted through this MRR system to get the filtered signal which is less affected by the nonlinearities. This filtered signal is observed at a total transmission distance of 54,000 km. Also, by using dispersion compensation techniques, the impact of four-wave mixing (FWM) is mitigated. The performance of the designed system is evaluated based on the quality factor (Q-factor) along with the bit error rate (BER) obtained.

OAM-SDM Solution Toward a Submarine Cable

Determining how to add more signal channels without enlarging the cable volume is continually an issue in managing submarine cables. To improve the cost per bit and the power efficiency, space division multiplexing (SDM) is regarded as a promising solution that could be used to address optical density and cable capacity challenges regarding submarine cables. In this study, we focus on angular momentum (OAM) modes supporting few-mode ring-core fiber (RCF) solutions for submarine cables. Considering the inhibition of the hydrogen loss for the submarine cable, we propose a center-region-lifted 3-OAM-mode-group supporting RCF (abbreviated to 3-OAM-MG RCF) with a core-cladding index contrast of 0.6 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${\%}$</tex-math></inline-formula> , and meanwhile we also design and fabricate a matched 3-OAM-MG erbium-doped fiber (EDF). To confirm the short-haul transmission ability, we conduct a wavelength/mode/polarization division multiplexing (WDM-MDM-PDM) transmission test through a 25.3-km 3-OAM-MG RCF, where the coupled modes inside MG are demultiplexed by using 2 × 2 multiple-input multiple-out (MIMO) equalization. The transmission capacity is approximately 35 Tbit/s and the bit error rates (BERs) of all the channels are less than 2.4 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\times 10^{-2}$</tex-math></inline-formula> . For the application scenario of long-haul submarine communication, a cascade WDM-MDM transmission system consisting of 3-OAM-MG RCF and 3-OAM-MG EDF is set up, which makes the BERs of all the mode and wavelength channels below the 20 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${\%}$</tex-math></inline-formula> soft-decision forward error correction (SD-FEC) threshold. It indicates that data-carrying OAM mode multiplexing transmission has potential application in a long-haul submarine cable system.

Investigating the cross core octagonal photonic crystal fiber with high birefringence: A design and analysis study

In optical communication systems, the quality of transmitted signals can be compromised by random birefringence, which is caused by irregularities in the core-cladding boundaries. To eliminate this problem, high birefringence can be introduced through an asymmetrical fiber structure. Photonic crystal fibers (PCFs) are an ideal solution due to their high intrinsic index contrast and design flexibility, which allows for high birefringence to be achieved. This paper introduces a new PCF design that takes advantage of these features to provide a higher modal birefringence compared to conventional fibers. The design is a cross-core octagonal-shaped fiber, and its performance is evaluated in terms of birefringence and beat length. The results indicate that the proposed fiber provides a birefringence range of 1.3E-3 to 1.6E-3 for a transmission wavelength range of 1.4 μm to 1.8 μm (S, C, and L Bands) and a minimum beat length range of 1.02 mm to 1.12 mm. This fiber design enables long-haul fiber communication without polarization mode dispersion, even under conditions of external perturbation.

Master–slave carrier phase recovery using optical phase conjugation for frequency comb-based long-haul coherent communication systems

Taking optical frequency combs as WDM laser sources for coherent optical communication systems has great potential in low-cost, low-complexity, and large-capacity communications. Master–slave carrier phase recovery (MS-CPR) utilizes the phase coherence of received signals to reduce the computational complexity (CC) in frequency comb-based communication systems. In long-haul systems, chromatic dispersion (CD) weakens the phase coherence and makes MS-CPR ineffective. Besides, nonlinear effects greatly degrade the quality of received signals. A master–slave carrier phase recovery method using optical phase conjugation (OPC) is proposed for frequency comb-based long-haul coherent optical communication systems. By placing the OPC module in the middle of the link, not only the weakening of phase coherence caused by CD is solved, but also nonlinear effects are mitigated. The simulation results show that the proposed method has better performance than conventional MS-CPR and independent carrier phase recovery (ICPR). In the 1000 km long system with 16 quadrature amplitude modulation (QAM) signals, the BER of proposed method is 9.3% of conventional MS-CPR and even 40% lower than ICPR, and the BER of all channels is below the threshold for 7% overhead hard-decision forward error correction (7% HD-FEC).

Study of Chromatic Dispersion in Single-Mode Optical Fiber

In the optical communication system, optical fibers are used to transmit information in a long-haul communication system at a very high speed. However, attenuation causes loss in signal transmission. Chromatic dispersion is an ultimate limiting factor for attenuation in high-speed long-distance communication. The chromatic dispersion causes a broadening of the incident pulse while traversing along the fiber length. This broadening reduces the information-carrying capacity of the transmitted signal. Chromatic dispersion is caused by material and waveguide dispersion. We used COMSOL Multiphysics to evaluate chromatic dispersion for the different refractive indexes of silica glass by varying wavelengths from 1300 (nm) to 1600 (nm). We have modelled a 2D optical fiber using the Electromagnetic Wave, Frequency Domain. The effective mode index was computed using Mode Analysis and total dispersion is calculated theoretically. The computed values of chromatic dispersion are within 7% of theoretical values.

Failure-oriented-accelerated-testing (FOAT) and its role in assuring electronics reliability: review

A highly focused and highly cost-effective failure-oriented-accelerated-testing (FOAT) suggested about a decade ago as an experimental basis of the novel probabilistic design for reliability (PDfR) concept is intended to be carried out at the design stage of a new electronic packaging technology and when high operational reliability (like the one required, e.g., for aerospace, military, or long-haul communication applications) is a must. On the other hand, burn-in-testing (BIT) that is routinely conducted at the manufacturing stage of almost every IC product is also of a FOAT type: it is aimed at eliminating the infant mortality portion (IMP) of the bathtub curve (BTC) by getting rid of the low reliability “freaks” prior to shipping the “healthy” products, i.e., those that survived BIT, to the customer(s). When FOAT is conducted, a physically meaningful constitutive equation, such as the multi-parametric Boltzmann-Arrhenius-Zhurkov (BAZ) model, should be employed to predict, from the FOAT data, the probability of failure and the corresponding useful lifetime of the product in the field, and, from the BIT data, as has been recently demonstrated, - the adequate level and duration of the applied stressors, as well as the (low, of course) activation energies of the “freaks”. Both types of FOAT are addressed in this review using analytical (“mathematical”) predictive modeling. The general concepts are illustrated by numerical examples. It is concluded that predictive modeling should always be conducted prior to and during the actual testing and that analytical modeling should always complement computer simulations. Future work should be focused on the experimental verification of the obtained findings and recommendations.