Wavelength Division Multiplexing Research Articles

Design of terahertz plasmonic wavelength division multiplexer assisted by whispering gallery mode resonators

Design of terahertz plasmonic wavelength division multiplexer assisted by whispering gallery mode resonators

Analysis of atmospheric attenuation of a FSO–WDM system for long-range communication

Abstract An FSO system can provide a solution to the problem of last-mile connectivity while also offering a high degree of security and a large capacity for high-speed information transmission, making it a versatile and powerful option for data communication. Despite the above-mentioned advantages, some factors have to be considered when establishing long-range communication, one such factor is atmospheric turbulence (haze, light fog, moderate fog) which degrades the ideal characteristics of the FSO channel and causes a loss in the signal’s power. This loss of power during transmission can be improved by using suitable amplifiers (hybrid optical amplifier, semiconductor optical amplifier) to provide better performance. The next-generation networks must be capable of supporting a significant amount of backhaul data traffic, accommodating a larger number of users, and increasing channel capacity to meet the demands of modern data communication. By implementing wavelength division multiplexing (WDM) and free space optical (FSO) communication techniques, the capacity of the channel can be increased, and more users can be accommodated. The maximum link length offered by the FSO–WDM system has been investigated with hybrid optical amplifier considering the minimum bit error rate, which can provide reliable and long-distance communication.

Trench-assisted multi-ring-core fiber for orbital angular momentum modes

Orbital angular momentum (OAM) multiplexing technology has attracted significant interest due to its ability to increase the data transmission capacity in optical communications. By combining OAM-based mode division multiplexing (MDM) and wavelength division multiplexing (WDM) techniques in multi-core fiber (MCF), the transmission rate and spectral efficiency of the optical communication systems can be greatly enhanced. In this paper, we present a design of a multi-ring air-core trench-assisted fiber that supports transmission over the entire C + L (1530–1625 nm) band with low inter-ring crosstalk. The high-contrast ring and trench design can effectively suppress the inter-modal crosstalk. The effects of the ring spacing, wavelength range and doping concentration on the crosstalk suppression are also systematically investigated. Furthermore, the complexity of the MIMO processing system is greatly reduced with a fewer-optical-core structure while keeping low inter-ring crosstalk. The results demonstrate that our designed fiber can support 140 OAM modes at 1550 nm with < −79.4 dB inter-ring crosstalk at low Ge-doped concentration (12.5 mol%), and it can keep the inter-ring crosstalk below −66.56 dB across the C + L band, which features lower inter-ring crosstalk than the other reports while supporting more OAM modes. Furthermore, to support more OAM modes with lower inter-ring crosstalk and intra-modal crosstalk, we further provide a second low-doping-concentration (12.5 mol%) fiber design, which can support 196 OAM modes with < −35.74 dB inter-ring crosstalk and Δneff > 5.39 × 10−4. Additionally, our designed fiber can support 224 OAM modes (37.5 mol% Ge-doped) and < −63 dB inter-ring crosstalk with low intra-modal crosstalk (Δneff > 5.45 × 10−4) and flat dispersion distribution (chromatic dispersion slope lower than 0.171 ps/nm2/km) across the C + L band.

Effect of Gain Saturation on Wideband WDM Signal in PPLN-Based Optical Parametric Amplifier

The periodically poled LiNbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (PPLN) based optical parametric amplifier (OPA) is a technology that contributes to the construction of multi-band wavelength-division multiplexing (WDM) optical networks thanks to its wide amplification bandwidth and wavelength conversion function. In addition, the fast response of the OPA means it is unaffected by sudden changes of wavelength channels due to dynamic channel add-drop. However, such fast response leads to nonlinear signal distortion when operating in the gain saturation region. This paper experimentally investigates the conversion of gain saturation into the nonlinear amplitude distortion in a 64-Gbaud 64QAM WDM signal. We characterized the input power tolerance of a PPLN-based OPA in wideband WDM applications and found that the nonlinear amplitude distortion can be suppressed by increasing the number of WDM channels. For a 75-GHz-spacing 64-channel WDM configuration, the total input power tolerance was improved by ∼10 dB compared to a single-channel case. We also confirmed that there is almost no wavelength dependence of the effect of gain saturation on the signal distortion. These results show that PPLN-based OPAs have a wide total input power range for amplifying wideband WDM signals in terms of the nonlinear distortion.

Performance improvements of a VLC system, in a V2X context, using a different multiplexing technique

This paper scrutinizes visible light communication (VLC) employing hybrid optical time division multiplexing (OTDM) wavelength division multiplexing (WDM). It also demonstrates the simulation of VLC using the direct sequence optical code division multiple access (DS-OCDMA) system developed by OptiSystem-Matlab Co-simulation. The profits of WDM and OTDM capacities have been combined using two levels of freedom to build up of the system. The performances are demonstrated in the simulated findings of the bit error rate (BER) in relationship with the data rate and the number of users. First, the simulated results display the usefulness of the system. Then, the number of users has been significantly enhanced. Besides, the OCDMA functions by appointing a specific code to each user and could provide asynchronous and simultaneous access to numerous users. One drawback is multiple access interference (MAI). The use of very long code sequences is crucial in order to lessen this effect. Hence, very large bandwidths are essential. This study aims at demonstrating, through system simulation, the practicability of an all-optical conventional correlation receiver dedicated to a DS-OCDMA access network link. Again, OptiSystem has been used to realize our blocks.

3.61 Pbit/s S, C, and L-Band Transmission With 19-Core Single-Mode Fiber

We experimentally demonstrate a 3.61 Pbit/s generalized mutual information (GMI) estimated throughput by space division multiplexing (SDM) and wavelength division multiplexing (WDM) combined transmission over 19-core single-mode fiber. Covering 17 THz bandwidth with a 25-GHz grid in S, C, and L band, 680 wavelength channels are used to deliver 24.5 GBaud probabilistically constellation-shaped (PCS) 256 quadrature amplitude modulation (QAM) and PCS-64QAM signals. The measured data rate shows a great potential for S/C/L-band transmission to dramatically enhance the achievable data rate in multi-core fibers.

Investigation of Doppler Frequency Shift Effect on the Performance of Four-Channel Space Chaotic Laser Communication

In this article, the wavelength division multiplexing (WDM) technology is applied to the space chaotic laser communication system. We deduce the bit error rate (BER) model of multi-channel space chaotic laser communication with Doppler frequency shift. Based on the BER model, the effect of Doppler frequency shift on the performance of four-channel space chaotic laser communication systems on the synchronous orbit(GEO)-low earth orbit(LEO) and GEO-mid earth orbit(MEO) has been discussed in detail. The numerical simulation results indicate that the effect of Doppler frequency shift on GEO-LEO system is much less than GEO-MEO system. Therefore, the Doppler frequency shift effect of GEO-LEO system can be overcome by redundant design, and the Doppler frequency shift effect of GEO-MEO system must be paid more attention to the optimum design. Besides, the relationship between the performance of communication system and frequency shift under different channels are similar. The result has an important implication for reducing the complexity of the system design. These results of the article are significant for the design of the four-channel space chaotic laser communication system.

On chip optical neural networks based on MMI microring resonators for image classification

We propose a new on-chip optical neural network (OONN) based on multimode interference-microring resonators (MMI-RRs). The suggested structure eliminates the need for wavelength division multiplexers (WDM) to create an optical neuron on a single chip. New microring resonator structure based on 4×4 MMI coupler with a size of 24µm × 2900 µm is used for the basic elements of the computation matrix, as a result a higher bandwidth and free spectral range (FSR) can be achieved. The Si3N4 platform along with the graphene sheet is designed to modulate the signals and weights of the neural networks at a very high speed. The Si3N4 can provide wide range of operating wavelengths and can work directly with the wavelengths of color images. The structure's benefits include rapid computing speed, little loss, and the ability to handle both positive and negative values. The OONN has been applied to the MNIST dataset with a speed faster than 2.8 to 14x times compared with the conventional GPU methods.

Ultra-Broadband Integrated Optical Filters Based on Adiabatic Optimization of Coupled Waveguides

Broadband spectral filters are highly sought-after in many integrated photonics applications such as ultra-broadband wavelength division multiplexing, multi-band spectroscopy, and broadband sensing. In this study, we present the design, simulation, and experimental demonstration of compact and ultra-broadband silicon photonic filters with adiabatic waveguides. We first develop an optimization algorithm for coupled adiabatic waveguide structures, and use it to design individual, single-cutoff spectral filters. These single-cutoff filters are 1×2 port devices that optimally separate a broadband signal into short-pass and long-pass outputs, within a specified device length. We control the power roll-off and extinction ratio in these filters using the adiabaticity parameter. Both outputs of the filters operate in transmission, making it possible to cascade multiple filters in different configurations. Taking advantage of this flexibility, we cascade two filters with different cutoff wavelengths on-chip, and experimentally demonstrate band-pass operation. The independent and flexible design of these band edges enables filters with bandwidths well over 100 nm. Experimentally, we demonstrate band-pass filters with passbands ranging from 6.4 nm up to 96.6 nm. Our devices achieve flat-band transmission in all three of the short-pass, band-pass, and long-pass outputs with less than 1.5 dB insertion loss and extinction ratios of over 15 dB. These ultra-broadband filters can enable new capabilities for multi-band integrated photonics in communications, spectroscopy, and sensing applications.

Robust traffic grooming and infrastructure placement in OTN-over-DWDM networks

The advent of next-generation networks has revolutionized modern networking practices through its improved service capability as well as its numerous emerging use cases. Coupled with the increasing number of connected devices, 5G and beyond (5G+) network traffic is expected to be increasingly diverse and high in volume. To address the large amount of data exchanged between the 5G+ core and external data networks, optical transport networks (OTNs) with dense wavelength-division multiplexing (DWDM) will be leveraged. In order to prepare for this increase in traffic, network operators (NOs) must develop and expand their existing backbone networks, requiring significant levels of capital expenditures. To this end, the traffic grooming and infrastructure placement problem is critical to supporting NO decisions. The work presented in this paper considers the traffic grooming and infrastructure placement problem for OTN-over-DWDM networks. The dynamicity and diversity of 5G+ network traffic are addressed through the use of robust optimization, allowing for increasing levels of solution conservativeness to protect against various levels of demand uncertainty. Furthermore, a robust traffic grooming and infrastructure placement heuristic (RGIP-H) solution capable of addressing the scalability concerns of the optimization problem formulation is presented. The results presented in this work demonstrate how the tuning of the robust parameters affects the cost of the objective function. Additionally, the ability of the robust solution to protect the solution under demand uncertainty is highlighted when the robust and deterministic solutions are compared during parameter deviation trials. Finally, the performance of the RGIP-H is compared to the optimization models when applied to larger network sizes.

Simulation of Coherent Electromagnetic Waves in Wavelength Division Multiplexing (WDM) Transmission

This study analyzes the application of Wavelength Division Multiplexing (WDM) in fiber optic networks which aims to find the wavelength, WDM optical spectrum and modes, as well as the CPR estimated phase and modes. In this study WDM allows the simultaneous transmission of different data streams through a single optical fiber, using different wavelengths. This research was conducted using the python OptiCommPy module. This module is used to perform modeling of complex optical fiber transmission systems by considering the various parameters and disturbances involved in optical transmission. The results obtained from this study are that WDM networks can use full or limited wavelength conversion, depending on the wavelength conversion capability of each network node. Whereas multifiber networks use fiber pools between network nodes, and multifiber WDM networks can be implemented without or with full wavelength conversion. This research can be a guide for designing coherent electromagnetic waves in WDM transmissions using the OptiCommPy python module.

Performance Analysis of the WDM Schemes for RoF System with Various Bit Rate

Communication that combines the methodologies of the two communications can be considered as communication fiber optic communication and can be used in communication systems and wireless. The integration of optical and wireless networks can function to increase mobility and capacity as well as reduce costs in access networks. Radio over fiber (RoF) can be a solution for many problems because it can control many base stations (BS) connected to a central station (CS) with an optical fiber. The high bit error rate (BER) and low Q factor value are caused by the Rof signal head received in low quality, so the receiver may not operate on high data speed networks. The solution to different signal problems and can be done with single mode fiber is the Wavelength Division Multiplexing (WDM) network. BER must be reduced to a guaranteed value, and the Q factor must be increased. WDM-RoF probes with different fiber lengths at various channel distances will be: simulated using Optisystem software, and the performance of the RoF receiver is measured and analyzed depending on the obtained BER, Q-factor value, and eye aperture height. The effects of degradation factors such as attenuation and dispersion are very limited with the addition of EDFA amplifier to Single Mode Fiber (SMF). The higher the bit rate of a communication system, the lower the performance of the system. In this study, analysis of the WDM-Rof system with bit rate variations was carried out to determine the bit rate value that still met the standard. From the simulation results, the Q-Factor and BER values at a bit rate of 11 Gbps do not meet the standards, i.e 4.50508 and 2.5390e-006.

High-accuracy wide-range refractive index demodulation based on under-sampled fiber F-P cavity length spectrum.

A scheme of fiber Fabry-Perot (F-P) cavity refractive index (RI) demodulation named under-sampled length spectrum retrieval (ULSR) is proposed. Unlike the wavelength spectrum method, ULSR can be used for physical quantity detection with just a monochromatic laser and photodetectors, avoiding the need for wideband lasers or expensive infrared spectrometers. Eight F-P cavities of different lengths were fabricated to sample the cavity length spectrum, and then the obtained under-sampled length spectrum was used to demodulate the RI of F-P cavity fillings. It was demonstrated that the ULSR system can achieve an index measurement accuracy of 1 × 10-4 in the glucose solution index range of 1.3294-1.3746 at wavelength λ = 1.55 µm. An index demodulation with higher accuracy and wider range is expected when more than 8 F-P cavities are used. The proposed scheme, with advantages of low system complexity, low cost, high reliability, high detecting accuracy, and wide detecting range, holds great promise for facilitating the wide application of F-P cavity sensors. Additionally, ULSR liberates wavelength freedom, making it a strong candidate for multiplexed sensing based on wavelength division multiplexing.

Intelligent and adaptive intra-channel and inter-channel fiber nonlinearity compensation in coherent optical transmission systems.

Fiber nonlinearity mitigation is a crucial technology for extending transmission reach and increasing channel capacity in high-baud rate wavelength division multiplexing (WDM) systems. In this work, we propose a novel, to the best of our knowledge, architecture that combines learned modified digital back-propagation (L-MDBP) to compensate for intra-channel nonlinearity and a two-stage decision-directed least mean square (DDLMS) adaptive equalizer to mitigate inter-channel nonlinearity. By leveraging globally optimized model parameters and adaptive channel estimation, the proposed scheme achieves superior performance and lower computation complexity compared with conventional DBP. Specifically, in an 8 × 64 Gbaud 16-ary quadrature amplitude modulation (16QAM) experimental system over 1600 km of standard single-mode fiber (SSMF), our approach shows a 0.30-dB Q2-factor improvement and a complexity reduction of 82.3% compared with DBP with 8 steps per span (SPS). Furthermore, we enhance the adaptability of the architecture by introducing an online transfer learning (TL) technique, which requires only 2% of initial training epochs.

10.51-Tbit/s multi-channel IF-over-fiber transmission with SDM/WDM/SCM for beyond-5G mobile fronthaul accommodating ultra-high-density antennas

In beyond-5G and 6G mobile communication systems, it is expected that massive numbers of antennas are densely deployed to provide a stable and high-speed communication environment. To efficiently accommodate high-density antennas, high-capacity mobile fronthaul (MFH) is also required. Intermediate-frequency-over-fiber (IFoF) is considered as one of the attractive solutions for realizing high-capacity MFH due to its high spectral efficiency and multi-channel transmission capability. In this paper, we demonstrate the highest-capacity IFoF transmission with combinations of space division multiplexing, wavelength division multiplexing, and subcarrier multiplexing; 4608 channels of 64-quadrature amplitude modulation orthogonal frequency division multiplexing signals with a total net bit rate of 10.51 Tbit/s (4608×380.16MHz/ch×6bit/s/Hz) are successfully transmitted over a 10.1-km uncoupled 12-core multi-core fiber.

Ultrabroadband 2D‐Dispersive Wavelength Selective Switch with 1.57 GHz Hyperfine Spectral Resolution and &gt;1600 Channels

AbstractWavelength selective switches (WSSs) are key components in commercial reconfigurable optical add/drop multiplexer systems that are essential for future wavelength‐division multiplexing (WDM) networks. With rapidly increasing data transmission, there is a demand for high‐capacity WSSs. However, in a WSS, the number of channels, which is related to the ratio of its band coverage relative to spectral resolution, is limited within a certain range, since the 1D dispersion of the grating fails to utilize the 2D selectivity of the liquid crystal on silicon (LCoS) pixel array in the “disperse and select” architecture.. To surpass this limitation, here a virtually imaged phased array (VIPA) is employed into the WSS system to expand 1D‐dispersion into 2D space in order to fully utilize the 2D selectivity of LCoS. According to the experimental results, this VIPA‐grating‐based 2D WSS approach enables a spectral resolution that can be narrowed to 1.57 GHz (18 times improvement from 1D WSS, and massive (&gt;1600) WDM channels can be predicted) and ultrabroadband spectral coverage across the S‐, C‐, and L‐bands of 20 THz. The data communication performance of the 2D WSS is also tested.

Next generation PON architecture using PD-NOMA employing OAM and WDM multiplexing

In this paper, we propose and experimentally demonstrate the efficacy of a next-generation passive optical network (PON) architecture for free space optical link, which utilizes power domain (PD) non-orthogonal multiple access (NOMA) along with simultaneous orbital angular momentum (OAM) mode and wavelength-division multiplexing (WDM) techniques. In this proposed architecture, many optical network units (ONUs) are accommodated by clustering them based on their power budgets and their data streams are allocated with different powers accordingly. The clustered ONUs are served with multiple OAM modes over multiple wavelengths to maintain high capacity, low latency, and increased reliability. As a proof-of-principle experimental demonstration of the proposed architecture, we have experimentally emulated two ONU clusters having a power ratio of (near:far)−3.17dB for implementing the PD-NOMA system for downlink. Each ONU cluster uses three 50 GHz spaced WDM channels, where each WDM channel carries two multiplexed OAM modes having opposite topological charge (l=±1 and ±2) values. Each cluster’s six ONUs is delivered with a 10 Gbps On-Off Keying (OOK) signal. We have demonstrated that all users can achieve a pre-forward error correction (pre-FEC) bit error rate (BER) below the 7% overhead-FEC (OH-FEC) BER limit of 3.8×10−3. We have also measured the x-talk due to WDM and mode multiplexing, and it has been revealed that the main contribution to the power penalty (relative to the no cross-talk condition) comes from OAM mode cross-talk.

Efficient Blue-Green Light Phased Array Based on High-Contrast Grating as a Demultiplexer

Wavelength division multiplexing (WDM) technology has been proven to effectively increase the capacity of optical communications in the infrared light band. However, to date, the WDM systems in the visible band only support limited quantity of wavelength channels, with coarse channel spacing of over 20 nm. This is because there are no available multi/demultiplexers (MUX/DeMUX) with fine wavelength spacing for visible light. In this work, we use a high-contrast grating (HCG) structure to effectively separate the blue-green wavelengths with fine spacing. An efficient blue-green light phased array based on HCG aperture is demonstrated to work as the DeMUX in a WDM system. The HCG aperture presents more efficient main-lobe radiation than typical one-dimensional waveguide surface grating arrays with fishbone antennas. The measured main-lobe loss of optical phased array (OPA) with HCG is over 15 dB lower than that of OPA with fishbone antennas, because HCG provides maximum scatterings for blue-green light. A wavelength spacing as small as 4 nm is validated in a blue-green WDM system, which is the finest channel spacing for WDM in visible band to the best of our knowledge.

A 51 Gb/s Reconfigurable mmWave Fiber-Wireless C-RAN Supporting 5G/6G MNO Network Sharing

The growing demand for ubiquitous broadband connectivity in 5G/6G Radio Access Networks (RANs) has turned Centralized RAN (C-RAN) and reconfigurable Point-to-MultiPoint (PtMP) network topologies into the mainstream approach for keeping pace with the vastly increasing traffic capacities and connection densities. Relying on an all-passive Arrayed Waveguide Grating Router (AWGR), we propose and demonstrate reconfigurable allocation of multiple parallel Fiber-Wireless (FiWi) millimeter wave (mmWave) analog (Intermediate Frequency over Fiber) IFoF interfaces. The proposed technology provides a framework for the implementation of reconfigurable multiple FiWi backhaul /midhaul/fronthaul (X-haul) connections. The use of AWGR enables wavelength slicing and the co-existence of multiple transport links over the same X-haul network infrastructure. The proposed concept is experimentally validated by two sets of experimental measurements. More specifically a 4λ- Wavelength-Division Multiplexed (WDM) signals modulated by IFoF signals are routed through the AWGR and wirelessly transmitted over the air across a 1m V-band distance by two different pairs of mmWave 60 GHz antennas. In the first experiment, a Phased Array Antenna (PAA) operating at 60 GHz is utilized achieving a 2.5 Gb/s data rate per wavelength and beam pair with an Error Vector Magnitude (EVM) of less than 12.5% and an aggregate 10 Gb/s traffic capacity. The achieved performance meets for the first time the respective 5G Key Performance Indicator (KPI) requirements for EVM quality and peak data traffic while supporting the link reconfiguration wavelength routing and mmWave beam direction. In the second experiment, the PAA is replaced by a point-to-point 60 GHz link utilizing a high-end mm-wave transmitter, thus achieving a data rate of 12.75 Gb/s per wavelength-beam with an EVM of less than 6.5% and an aggregate capacity of 51 Gb/s. To this end, the proposed solution is shown to form a promising roadmap toward flexible and reconfigurable 5G/6G mmWave C-RAN architectures where multiple Mobile Network Operators (MNOs) can share the same network infrastructure and dynamically allocate fiber, antenna beams and wavelengths.

Topology Optimization-Based Design of Topological Edge-State Wavelength Division Multiplexer

Previous research processes on topological insulators were mainly based on the manual adjustment of a large number of fine parameters to achieve the desired properties. Here, we propose to treat the design process of photonic crystals as an objective function through topological optimization theory, allowing the desired properties to arise spontaneously with the optimization. Through topology optimization, we have designed and implemented three topological photonic crystals with different topological characteristics and dual-band protection common bandgap. The results show that functional edge modes with desired propagation properties can be generated within these two bandgaps by constructing domain walls between photonic crystal structures with different topological phases. The unidirectional transmission characteristics of the wave can also be observed, which provides an easy way to implement a wavelength division multiplexer.