Optical Wavelength Division Multiplexing Research Articles

Dynamically controllable two-color electromagnetically induced grating via spatially modulated inelastic two-wave mixing

A scheme for controlling two-color electromagnetically induced grating (TCEIG) in a coherently prepared cold atomic ensemble with a four-level inverted Y-type configuration is proposed via exploiting inelastic two-wave mixing process. By adding an intensity mask behind the auxiliary control field, the transmission functions of the incident probe field and the generated signal field are modulated periodically, thereby leading to the formation of TCEIG. Using experimentally achievable parameters, both the probe and signal fields with different frequencies can be simultaneously diffracted into high-order diffractions. It is found that the diffraction efficiencies of TCEIG, especially the first-order diffraction efficiency, can be significantly improved via adjusting the detunings of the probe and signal fields. Furthermore, it is also demonstrated that the diffraction of TCEIG can be manipulated via tuning the intensity and detuning of the control field. Finally, we investigate the influence the phase mismatch on the diffraction of TCEIG. It is shown that the diffraction pattern of the probe field is rather robust against the phase mismatch, while the diffraction intensities of the signal field are suppressed by the phase mismatch. Our scheme may provide a possibility for the all-optical control of optical switch and wavelength division multiplexing.

From Optical Fiber Communications to Bioimaging: Wavelength Division Multiplexing Technology for Simplified in vivo Large-depth NIR-IIb Fluorescence Confocal Microscopy.

Near-infrared II (NIR-II, 900-1880nm) fluorescence confocal microscopy offers high spatial resolution and extensive in vivo imaging capabilities. However, conventional confocal microscopy requires precise pinhole positioning, posing challenges due to the small size of the pinhole and invisible NIR-II fluorescence. To simplify this, a fiber optical wavelength division multiplexer (WDM) replaces dichroic mirrors and traditional pinholes for excitation and fluorescence beams, allowing NIR-IIb (1500-1700 nm) fluorescence and excitation light to be coupled into the same optical fiber. This streamlined system seamlessly integrates key components-excitation light, detector, and scanning microscopy-via optical fibers. Compared to traditional NIR-II confocal systems, the fiber optical WDM configuration offers simplicity and ease of adjustment. Notably, this simplified system successfully achieves optical sectioning imaging of mouse cerebral blood vessels up to 1000µm in depth. It can discern tiny blood vessels (diameter: 4.57µm) at 800µm depth with a signal-to-background ratio (SBR) of 5.34. Additionally, it clearly visualizes liver vessels, which are typically challenging to image, down to a depth of 300µm.

DSP-based inter-channel interference monitoring in flexible wavelength-routed networks

The efficiency of optical networks employing flexible wavelength division multiplexing (WDM) can be increased by maximizing the throughput of each individual channel, provided that the position of its neighboring channel is known with sufficient accuracy in order to avoid inter-channel interference. In this paper, we propose a digital signal processing (DSP) algorithm, leveraging the use of an artificial neural network (ANN), to estimate the neighboring channels’ distance by processing raw digital samples from a standard coherent receiver. We present an efficient dataset design approach, based on Latin hypercube sampling (LHS), in order to effectively optimize and validate the algorithm under different assumptions on the optical WDM channels. We investigate the accuracy of the ANN-based DSP scheme through simulation analysis, highlighting its potential in relation to the characteristics of the optical network. Finally, we validate our approach in an experimental setup using standard commercial coherent transceivers. The experimental results show that the distance from the neighboring WDM channels can be estimated with a root mean square error of less than 1.5 GHz for a channel under test with a symbol rate of 52 GBaud.

Wavelength division multiplexing of free space optical system under the effect of oil fire smoke

Abstract In this paper, two wavelength division multiplexing (WDM) based free space optical (FSO) systems (single, multiple) are proposed and their performance is compared on the basis of Q-factor, eye opening diagrams and the total power of the received signal for different link distances under effect of oil fire smoke. The obtained results illustrate that the values of WDM single FSO of (1 km) distance exhibit good performance based on (Q-factor ≥ 6), but it was out of line performance at (2 km) FSO distance. The values of (1 km) distance exhibit good performance. On the other hand, the results of the FSO distance (2 km) indicate poor performance without signal loss. The presented results show that the eye opening for all the power values of (1 km) distance for both systems. Moreover, the eye opened only at the highest power value of (2 km) distance for single FSO systems. The eye opened partially at the lowest power of (2 km) distance and became fully opened at the mid-point and highest power values for multiple FSO systems. Thus, the proposed MIMO-FSO systems with multiplexes multiple optical carriers WDM demonstrates better results than SISO-FSO systems with WDM and the well knowing systems under similar atmospheric conditions.

Design of multiparameter fiber Bragg grating in optical transmission systems wavelength division multiplexing

Design of multiparameter fiber Bragg grating in optical transmission systems wavelength division multiplexing

A Comprehensive Study on EDFA Gain Flattening for WDM Transmission using Cascaded Fiber Bragg Gratings

The gain flattening of optical amplifiers plays a crucial role in optical Wavelength Division Multiplexing (WDM) communication systems, ensuring uniform amplification across all channels. This study focuses on investigating the gain flattening characteristics of Erbium-Doped Fiber Amplifiers (EDFAs) using cascaded Fiber Bragg Gratings (FBGs) in the C-band wavelength range. A comparative analysis of various optical amplifiers revealed that EDFA exhibited the highest gain variation, making it an optimal choice for gain flattening. The key parameters to achieve optimal EDFA gain flattening include the wavelengths of the channels, EDFA length, noise figure (NF), and the number of cascaded FBGs. Simulation experiments are conducted using Optisystem software (ver. 14.2) and the obtained results reveal that EDFA gain flatness can be achieved within the wavelength range of 1531 to 1533 nm, utilizing an EDFA length of 6 m and 12 cascaded FBGs. These findings contribute to the advancement of gain flattening techniques in optical WDM systems, enhancing their performance and reliability.

Ultra-Wide Bandwidth Brillouin-Raman Random Fiber Laser With Augmented Synergistic Nonlinearity

We propose a Brillouin-Raman random fiber laser with enhanced synergistic nonlinearity for ultra-wide bandwidth Brillouin comb generation. The augmented synergistic nonlinearity, including enhanced Rayleigh scattering (RS) effect, stimulated Brillouin scattering (SBS) and stimulated Raman scattering (SRS), is achieved in a hybrid fiber (a fiber combination of a 7.2-km dispersion compensation fiber and a 10-km single-mode fiber) under a strong Raman pumping condition. Under the strong Raman pumping condition, more Stokes lines are generated due to the enhanced RS-induced oscillations of Brillouin Stokes lines at short wavelength band, thus suppressing self-lasing cavity mode oscillations at long wavelength band. In the experiments, the multi-wavelength Brillouin comb with an ultra-wide bandwidth of 63.5 nm (1513 nm-1576.5 nm) with frequency spacing of double Brillouin frequency shift, which is the largest bandwidth from Brillouin fiber lasers, to the best of our knowledge, has been achieved. The proposed ultra-wide bandwidth Brillouin-Raman fiber laser has potential applications in optical communication, optical wavelength division multiplexing, and fiber sensing.

Multi-Wavelength Photonic Neuromorphic Computing for Intra and Inter-Channel Distortion Compensations in WDM Optical Communication Systems

Digital signal processing (DSP) has been widely applied in optical communication systems to mitigate various signal distortions and has become one of the key technologies that have sustained data traffic growth over the past decade. However, the strict energy budget of application-specific integrated circuit-based DSP chips has prevented the deployment of some powerful but computationally costly DSP algorithms in real applications. As a result, fiber nonlinearity-induced signal distortions impede fiber communication systems, especially in wavelength-division multiplexed (WDM) transmission systems. To solve these challenges in DSP, there has been a surge of interest in implementing neural networks-based signal processing using photonics hardware (i.e., photonic neural networks). Photonic neural networks promise to break performance limitations in electronics and gain advantages in bandwidth, latency, and power consumption in solving intellectual tasks that are unreachable by conventional digital electronic platforms. This work proposes a photonic recurrent neural network (RNN) capable of simultaneously resolving dispersion and both intra and inter-channel fiber nonlinearities in multiple WDM channels in the photonic domain, for the first time to our best knowledge. Furthermore, our photonic RNN can directly process optical WDM signals in the photonic domain, avoiding prohibitive energy consumption and speed overhead in analog to digital converters (ADCs). Our proposed photonic RNN is fully compatible with mature silicon photonic fabrications. We demonstrate in simulation that our photonic RNN can process multiple WDM channels simultaneously and achieve a reduced bit error rate compared to typical DSP algorithms for all WDM channels in a pulse-amplitude modulation 4-level (PAM4) transmission system, thanks to its unique capability to address inter-channel fiber nonlinearities. In addition to signal quality performance, the proposed system also promises to significantly reduce the power consumption and the latency compared to the state-of-the-art DSP chips, according to our power and latency analysis.

Capacity Region Bounds for Optical WDM Channels Based on First-Order Regular Perturbation

It is known that fiber nonlinearities induce crosstalk in a wavelength division multiplexed (WDM) system, which limits the capacity of such systems as the transmitted signal power is increased. A network user in a WDM system is an entity that operates around a given optical wavelength. Traditionally, the channel capacity of a WDM system has been analyzed under different assumptions for the transmitted signals of the other users, while treating the interference arising from these users as noise. In this paper, we instead take a multi-user information theoretic view and treat the optical WDM system impaired by cross-phase modulation and dispersion as an interference channel. We characterize an outer bound on the capacity region of simultaneously achievable rate pairs, assuming a simplified <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$K$</tex-math></inline-formula> -user perturbative channel model using genie-aided techniques. Furthermore, an achievable rate region is obtained by time-sharing between certain single-user strategies. It is shown that such time-sharing can achieve better rate tuples compared to treating nonlinear interference as noise. The achievable rates using the latter strategy are known to exhibit a maximum for an optimum launch power, beyond which a further increase of power leads to a reduction in achievable rates. For the single-polarization single-span system under consideration and a power 3.5 dB above the optimum launch power, treating nonlinear interference as noise results in a rate of 4.25 b/sym, while time-sharing gives a rate of 7.99 b/sym.

Optical Spectral Shaping Based on Reconfigurable Integrated Microring Resonator-Coupled Fabry–Perot Cavity

We demonstrate a multifunctional optical spectral shaper on a silicon photonic chip. The proposed structure is composed of a tunable microring resonator (MRR) and three tunable Sagnac loop mirrors (SLMs), which can be regarded as a large SLM incorporating an MRR-coupled Fabry–Perot (FP) cavity. To realize flexible tuning, thermo-optically tunable Mach-Zehnder interferometer (MZI) couplers are used to replace conventional directional couplers with fixed coupling coefficients. By controlling the tunable MZI couplers, the proposed structure can be reconfigured as various functional structures including an all-pass MRR with tunable coupling regime, a tunable FP cavity, an SLM incorporating FP cavity, and an MRR-coupled FP cavity. This flexible reconfiguration allows for multifunctional optical spectral shaping including tunable comb filtering, Fano and EIT-like resonances. In particular, the complementary flat-top comb filtering responses can be theoretically obtained in the two ports of this device with same free spectral range (FSR) value, which enable the (de)interleaver operation. The experimental results show that the implemented all-pass MRR has a maximum extinction ratio (ER) of 38.9 dB and the corresponding quality factor is 6.5×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> . The comb filter based on configured FP cavity can be switched from narrowband response (0.06 nm) to wideband flat-top response (0.23 nm), with ERs up to 10.6 dB and 22 dB, respectively. Moreover, a dynamic conversion between Lorentz, EIT, and Fano resonance line shapes based on the coupled resonant system can be realized. The demonstrated integrated device holds great potential for various applications such as filtering and switching in optical wavelength-division multiplexing (WDM) communication networks.

DAC/ADC-free 4 × 12.9 Gbit/s 65,536-level quantum noise stream cipher secure optical WDM transmission based on delta-sigma modulation.

We propose and experimentally study a novel, to the best of our knowledge, quantum noise stream cipher (QNSC) secure transmission scheme based on the delta-sigma modulation (DSM) technique. The cooperation of the QNSC and DSM mechanisms makes it possible to transmit an ultrahigh-order encrypted signal in the non-return-to-zero (NRZ) on-off keying (OOK) format. The delivery of the NRZ OOK waveform over the fiber link allows us to send and receive signals using digital ports, instead of high-speed and high-resolution digital-to-analog converters (DACs) and analog-to-digital converters (ADCs)in conventional QNSC systems. Meanwhile, clock synchronization can be achieved by using a simple clock data recovery algorithm. The extra clock signal transmission link in conventional QNSC systems is no longer needed. The proposed scheme is also compatible with wavelength division multiplexing (WDM) systems. In this work, 4 × 12.9 Gbit/s plaintext is encrypted to a 65,536-level QNSC signal and then transmitted over a 10-km standard single-mode fiber. The transmitter and receiver are established by commercial 100G QSFP28 optical modules with clock data recovery. This proposed scheme can be easily deployed in commercial systems due to its minimalist implementation architecture and relatively low hardware cost.

Fiber optical WDM multiplexers/demultiplexers with low bending losses

Objectives. One of the topical tasks in the development of radio electronic systems for various purposes is a sharp increase in the volume and data transfer rate between the elements of the system. This problem is most successfully solved using fiber optic technology, which has no alternative to meet a number of indicators. The use of optical fibers (OF) as a physical medium made it possible to transfer large information flows over considerable distances. Increasing the capacity of communication systems is pushing manufacturers to develop new OF brands with improved optical and operational characteristics, which makes it possible to improve various optical components that use an OF as an active information transmission medium. The dual-channel single-mode wavelength division multiplexing (WDM) multiplexers/demultiplexers, which are one of spectral selective splitters types, are most widely used in fiber-optic communication systems. Among the advantages of WDM, it is worth to note the transmission of a large amount of information over one OF by the arrangement of channels at different wavelengths and the ability to transmit signals of several wavelengths simultaneously in both directions via one OF that do not interact with each other (duplex communication). During operation, WDM multiplexers can be subjected to various external influences that affect the operation and stability of the device parameters. Currently, there are no data on the effect of OF bending on the optical characteristics of WDM multiplexers. In this regard, it is important to study this dependence, which includes measuring the parameters of optical isolation and insertion loss. The purpose of the study is to work out the manufacturing technology and investigate the manufactured WDM multiplexers based on certain types of bend-resistant OF.Methods. For the formation of two-channel WDM multiplexers, the technology of fused biconical tapering was used, which makes it possible to achieve low insertion loss along with a high degree of channel isolation in the wide temperature range.Results. In the paper, the possibilities of manufacturing fiber multiplexers based on bend-resistant fiber Corning SMF-28 Ultra were discussed. The results of manufacturing and studying the experimental samples of WDM multiplexers optical characteristics were presented. It was established that the use of SMF-28 Ultra quartz fiber made it possible to significantly reduce the deviation of the channel optical isolation in the event of mechanical stresses in the multiplexers OF structure. Conclusions. The possibility of creating two-channel multiplexers with low bending losses and optical isolation up to 20–22 dB was experimentally shown. Possible mechanisms of the influence of the multiplexer fiber twisting on the optical isolation of channels were considered. The results obtained showed that when mechanical stresses in the fused structure of the multiplexer occur, the change in the optical isolation coefficient at two operating wavelengths does not exceed 1 dB.

1.71 Tb/s Single-Channel and 56.51 Tb/s DWDM Transmission Over 96.5 km Field-Deployed SSMF

We report an industry leading optical dense wavelength division multiplexing (DWDM) field trial with line rates per channel <inline-formula> <tex-math notation="LaTeX">$\ge 1.66$ </tex-math></inline-formula> Tb/s using 130 GBaud dual-polarization probabilistic constellation shaping 256-ary quadrature amplitude modulation (DP-PCS256QAM) in a high capacity data center interconnect (DCI) scenario. This research trial was performed on 96.5 km of field-deployed standard single mode G.652 fiber infrastructure of Deutsche Telekom in Germany employing Erbium-doped fiber amplifier (EDFA)-only amplification. A total of 34 channels were transmitted with 150 GHz spacing for a total fiber capacity of 56.51 Tb/s and a spectral efficiency higher than 11bit/s/Hz. In the single-channel transmission scenario 1.71 Tb/s was achieved over the same link. In addition, we successfully demonstrate record net bitrates of 1.88 Tb/s in back-to-back (B2B) using 130 GBaud DP-PCS400QAM.

Optimal power allocation in nonlinear MDM‐WDM systems using Gaussian noise model

Mode-division multiplexing (MDM) using few-mode fibre (FMF) has received increasing attention to address the exponential growth of data traffic in long-haul optical communication systems. Also, combining the MDM with wavelength-division multiplexing (WDM) is a promising approach for dramatically growing the transmission capacity in such systems. However, a major barrier in this regard is the FMF nonlinear effects, which can significantly reduce the link performance. In this paper, in order to alleviate the FMF nonlinear effects, we focus on power allocation in FMF links by optimizing the input power of each optical WDM channel of each spatial mode, which leads to maximizing the total capacity transmission and also the minimum signal to noise ratio (SNR) margin. The FMF nonlinearity has been already modelled as the Gaussian noise (GN) for which no closed-form formulation has been developed so far. Here, we derive a closed-form GN model for this problem and verify it by comparing with the integral-form GN model and split-step Fourier method. In this approach, an optimal power is independently determined for each channel of each mode by optimizing a capacity maximization and a minimum SNR margin maximization problem in convex forms. The performance of different links including the single mode fibre-WDM, MDM-single channel, and MDM-WDM are compared using computer simulations. These systems are comprehensively investigated in equal/non-equal required SNR as well as flat/non-flat amplifier gain scenarios. It is shown that optimized power allocation to each channel of each mode has a significant enhancement in the minimum SNR margin maximization scheme compared to the best equal power allocation. Furthermore, this improvement is much more in non-equal required SNR and the non-flat amplifier gain scenarios, showing the efficiency of the established approach in practical communication links.

Design and Performance Thulium Doped Fiber Amplifier in Optical Telecommunication Networks

Thulium-doped optical Fiber enhancers (TDFA) are advanced to cover the optical media transmission Wavelength Division Multiplexing (WDM) information transmission in the envisioned the band (800-1800 nm) with up to 6.5dB increment and noise figure as low as 2.6 dB. We existing the first in-band diode-siphoned thulium-doped fiber amplifier (TDFAs) operational in the wavelength locale and test their appropriateness as high request enhancers in possible coming media transmission frameworks.

Nature-Inspired Hybrid Multi-objective Optimization Algorithms in Search of Near-OGRs to Eliminate FWM Noise Signals in Optical WDM Systems and their Performance Comparison

Nowadays, the multi-objective optimizing algorithms which are inspired by nature are widely used in solving the many objectives of NP-complete engineering and industrial design problems. To eliminate one of the prevailing nonlinear optical noise mechanisms, i.e., four-wave mixing noise signals in the optical wavelength division multiplexing (WDM) systems, several unequally spaced channel-allocation algorithms were found that require increased bandwidth than the equally spaced channel-allocation. One of the bandwidths efficient, a USCA algorithm can be designed by considering the optimal Golomb rulers (OGRs) in optical WDM systems. Two nature-inspired multi-objective optimization algorithms (MOAs), namely multi-objective big bang–big crunch (MOBB-BC) optimization algorithm and multi-objective firefly optimization algorithm (MOFA), to solve NP-complete OGR problem in an optical WDM system are proposed here. Additionally, the algorithms MOBB-BC and MOFA are hybridized by introducing differential evolution (DE) based mutation and random walk features in their standard forms. These two features have the potential to explore new search space for MOAs to search for OGRs in a reasonable time. The algorithms presented here solve the two objectives in optical WDM systems, one is the occupied length by the ruler, and the other is total channel bandwidth obtained by OGRs. The obtained results suggest that the considered nature-inspired MOAs are computationally better than the other algorithms to search near-OGRs. To assert the improvement in the MOAs further, the non-parametric Friedman statistical analysis test is employed. The results conclude that for large mark values, the hybridization of MOFA with both DE mutation and Levy-flight strategies potentially performs better than the MOBB-BC and its hybrid forms to search OGR sequences. The hybrid algorithm MOBB-BC can explore OGRs up to 8-marks and near-OGRs for 9 to 20-marks with a maximum computation time of 27 h, whereas hybrid MOFA can examine up to 16-mark OGRs, but finds 17 to 20-mark near-OGRs with the maximum computation time of 20 h. The success rate of the proposed hybrid MOFA to search best OGRs up to 20-marks is 80%, whereas for hybrid algorithm MOBB-BC is 40%.

Gain/noise figure spectra of average power model Raman optical amplifiers in coarse wavelength multiplexed systems

Abstract This work clarifies the gain/noise figure spectra of average power model Raman optical amplifiers in coarse wavelength multiplexed systems. The proposed model have a total received power of 16.306 dBm, signal gain of 21.68 dB, and noise figure of 3.802 dB at the same operation parameters of the previous model which operated at length 0.2 km at the optical fiber coarse wavelength division multiplexing (CWDM) and transmitted signal power is 20 dBm. So the updates help us to greatly improve the system.

Research on Testing of Optical Fiber Wavelength Division Multiplexing System

In order to meet the requirement of long-distance high-speed data bus for information transmission in vehicles, optical fiber wavelength division multiplexing (FWDM) technology is used to realize the transmission of multiple optical signals by connector. Although wavelength division multiplexing technology has been widely used in the field of communication, the adaptability of the real-time control system needs to be further studied. In this paper, a prototype of the optical fiber wavelength division multiplexing system is tested and the test results are preliminarily studied, which provides a basis for evaluating transmission reliability margin and analyzing system failure.

400 Gb/s Silicon Photonic Transmitter and Routing WDM Technologies for Glueless 8-Socket Chip-to-Chip Interconnects

Arrayed Waveguide Grating Router (AWGR)-based interconnections for Multi-Socket Server Boards (MSBs) have been identified as a promising solution to replace the electrical interconnects in glueless MSBs towards boosting processing performance. In this article, we present an 8-socket glueless optical flat-topology Wavelength Division Multiplexing (WDM)-based point-to-point (P2P) interconnect pursued within the H2020 ICT project ICT-STREAMS and we report on our latest achievements in the deployment of the constituent silicon (Si)-photonic transmitter and routing building blocks, exploiting experimentally obtained performance metrics for analyzing the 8-socket chip-to-chip (C2C) connectivity in terms of throughput and energy efficiency. We demonstrate an 8-channel WDM Si-photonic microring-based transmitter (Tx) capable of providing 400 (8 × 50) Gb/s non-return-to-zero (NRZ) Tx capacity and an 8 × 8 Coarse-WDM (CWDM) Si-AWGR with verified cyclic data routing capability in O-band. Following an overview of our recently demonstrated crosstalk (XT)-aware wavelength allocation scheme, that enables fully-loaded AWGR-based interconnects even for typical sub-optimal XT values of silicon integrated CWDM AWGRs, we validate the performance of a full-scale 8-socket interconnect architecture through physical layer simulations exploiting experimentally-verified simulation models for the underlying Si-photonic Tx and routing circuits. This analysis reveals a total aggregate capacity of 1.4 Tb/s for an 8-socket interconnect when operating with 25 Gb/s line-rates, which can scale to 2.8 Tb/s at an energy efficiency of just 5.02 pJ/bit by exploiting the experimentally verified building block performance at 50 Gb/s line. This highlights the perspectives for up to 69% energy savings compared to the standard QuickPath Interconnect (QPI) typically employed in electronic glueless MSB interconnects, while scaling the single-hop flat connectivity from 4- to 8-socket interconnection systems.

Survivable virtual topology search with impairment awareness and power economy in optical WDM networks

Survivability against the link and light-path failures is essential in the optical wavelength division multiplexing (WDM) network along with impairment awareness (IA) and power economy (PE). In this paper, topology search using: 1) Kruskal's minimal weighted topology search algorithm; 2) Hamiltonian cycle (H-cycle)-based survivable topology search algorithm; 3) k-survivable topologies search algorithms have been carried out to find virtual survivable topologies for India's RailTel network. The integer linear programming (ILP) optimisation followed by the heuristics implementation have been carried out for IA and PE with a channel capacity constraint to achieve the survivability considering the case of a single link and light-path failures. We compare the survivable topologies thus obtained in the event of failures, with respect to terminal-to-terminal (terminal) reliability and choose the survivable topologies having the better terminal reliability. Among all, H-cycle-based survivable topology search algorithm shows lowest connection loss probability (CLP) and highest terminal reliability.