Wavelength Division Multiplexing Technique Research Articles

Tbps wide-field parallel optical wireless communications based on a metasurface beam splitter

Optical wireless communication (OWC) stands out as one of the most promising technologies in the sixth-generation (6G) mobile networks. The establishment of high-quality optical links between transmitters and receivers plays a crucial role in OWC performances. Here, by a compact beam splitter composed of a metasurface and a fiber array, we proposed a wide-angle (~120°) OWC optical link scheme that can parallelly support up to 144 communication users. Utilizing high-speed optical module sources and wavelength division multiplexing technique, we demonstrated each user can achieve a communication speed of 200 Gbps which enables the entire system to support ultra-high communication capacity exceeding 28 Tbps. Furthermore, utilizing the metasurface polarization multiplexing, we implemented a full range wide-angle OWC without blind area nor crosstalk among users. Our OWC scheme simultaneously possesses the advantages of high-speed, wide communication area and multi-user parallel communications, paving the way for revolutionary high-performance OWC in the future.

Single-detector multiplex imaging flow cytometry for cancer cell classification with deep learning.

Imaging flow cytometry, which combines the advantages of flow cytometry and microscopy, has emerged as a powerful tool for cell analysis in various biomedical fields such as cancer detection. In this study, we develop multiplex imaging flow cytometry (mIFC) by employing a spatial wavelength division multiplexing technique. Our mIFC can simultaneously obtain brightfield and multi-color fluorescence images of individual cells in flow, which are excited by a metal halide lamp and measured by a single detector. Statistical analysis results of multiplex imaging experiments with resolution test lens, magnification test lens, and fluorescent microspheres validate the operation of the mIFC with good imaging channel consistency and micron-scale differentiation capabilities. A deep learning method is designed for multiplex image processing that consists of three deep learning networks (U-net, very deep super resolution, and visual geometry group 19). It is demonstrated that the cluster of differentiation 24 (CD24) imaging channel is more sensitive than the brightfield, nucleus, or cancer antigen 125 (CA125) imaging channel in classifying the three types of ovarian cell lines (IOSE80 normal cell, A2780, and OVCAR3 cancer cells). An average accuracy rate of 97.1% is achieved for the classification of these three types of cells by deep learning analysis when all four imaging channels are considered. Our single-detector mIFC is promising for the development of future imaging flow cytometers and for the automatic single-cell analysis with deep learning in various biomedical fields.

High-Capacity Coherent WDM Networks Empowered by Probabilistic Shaping and End-to-End Deep Learning

To optimize the functionality of coherent optical fiber communication (OFC) systems and enhance their capacity related to long-haul transmissions, wavelength-division multiplexing (WDM) and probabilistic constellation shaping (PCS) techniques have been used. This paper develops an end-to-end (E2E) deep learning (DL)-based PCS algorithm, i.e., autoencoder (AE) for a high-order modulation format WDM system that minimizes nonlinear effects while ensuring high capacity and considers system parameters, in particular those related to the OFC channel. Only the AE of the central channel is trained to meet the specified performance objective, as the system design employs identical AEs in each WDM channel. The simulation results show that the architecture should consist of two hidden layers, with thirty two nodes per hidden layer and a ”32×modulation order” batch size to obtain optimal system performance, when designing AE using a dense layer neural network. The behavior of the AE is examined to determine the optimum launch-power ranges that enhance the system's performance. The developed AE-based PCS-WDM provides a 0.4 shaping gain and outperforms conventional solutions.

Stable and wavelength-tunable multiwavelength laser for high-rate measurement device independent quantum key distribution

Measurement device independent quantum key distribution (MDI QKD) has attracted growing attention for its immunity to attacks at the measurement unit, but its unique structure limits the secret key rate. Utilizing the wavelength division multiplexing (WDM) technique and reducing error rates are effective strategies for enhancing the secret key rate. Reducing error rates often requires active feedback control of wavelengths using precise external references. However, for a multiwavelength laser, employing multiple references to stabilize each wavelength output places stringent demands on these references and significantly increases system complexity. Here, we demonstrate a stable, wavelength-tunable multiwavelength laser with an output wavelength ranging from 1270 to 1610 nm. Through precise temperature control and stable drive current, we passively lock the laser wavelength, achieving remarkable wavelength stability. This significantly reduce the error rate, leading to an almost doubling of the secret key rate compared to previous experiments. Furthermore, the exceptional wavelength stability offered by our multiwavelength laser, combined with the WDM technique, has further boosted the secret key rate of MDI QKD. With a wide wavelength tuning range of 5.1 nm, our multiwavelength laser facilitates flexible operation across multiple dense wavelength division multiplexing channels. Coupled with high wavelength stability and multiple wavelength outputs simultaneously, this laser offers a promising solution for a high-rate MDI QKD system.

Multifunctional optical logic device based on nanoscale rectangular ring resonator

Integrated optical logic devices are essential building blocks for implementing all-optical arithmetic and logic unit. In this paper, an ultra-compact multifunctional optical logic device consisting of a rectangular ring resonator coupled with two parallel metal–insulator–metal waveguides is presented. The transmission characteristics of the structure are analyzed in detail via temporal coupled-mode theory. The finite-difference time-domain simulation results reveal that multiple logic functions can be implemented with the aid of the wavelength division multiplexing technique at different output ports. Specifically, all seven basic types of logic gates, half-adder, half-subtractor, and 2*4 decoder can be implemented by monitoring the transmission of through and drop ports at different wavelengths. More importantly, among these functions, six logic gates (OR, XNOR, NAND, NOR, XOR, and AND) and half-adder functions can be performed simultaneously; the NOT logic operation is performed with controllable output ports and selectable working wavelengths; the half-subtractor and 2*4 decoder functions can be operated simultaneously. The proposed logic device is characterized by a small area overhead, multifunctionality, fast response time, and ultrahigh-speed information processing. It may potentially be applied in on-chip universal and parallel photonic computing units.

Evaluation of resource efficiencies for the non-symmetric dynamic wavelength allocation method applied in the P2MP WDM-PON network design

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

Integrated long reach and energy-efficient NGPON-VLC system with OCDM/WDM for smart green buildings

Smart green buildings (SGBs) are composed of numerous services and offer hopeful solutions to the world's continuous and rapid urbanization. Conventional data transmission systems are insufficient to deliver acceptable services because to the sudden surge in high-quality information transmission requirements over long distance for numerous linked residents in SGBs. Consequently, a hybrid next generation passive optical network (NGPON) along with visible light communication (VLC) indoor/outdoor broadcast network is presented in this work to increase the reliability with intelligence, exalted overall efficiency, cost efficiency, and security of SGBs. Bidirectional PON-VLC system incorporates the time and wavelength division multiplexing (TWDM), wavelength division multiplexing (WDM) and optical code division multiplexing (OCDM) techniques. In order to improve system performance, various OCDM codes are used in this work at 10/2.5 Gbps per channel throughput via fiber-VLC channels. According to the simulation results, the modified new zero cross-correlation (MNZCC) code performs better than previous codes and supports 200 active residents at reliable 100 km fiber along with 5 m VLC range. Furthermore, by expanding the received aperture diameter to 25 cm, VLC coverage may be increased till 10 m. Moreover, it provides adequate receiver sensitivities of − 13 to − 12 dB in uplink with − 9.8 to − 6 dBm in downlink for 200 to 600 fields of view angles compared to 00 view angle having sensitivity of − 15 dBm. Additionally, the numerical analysis and comparison performance show that PON-VLC outperforms fiber-VLC link-based scenarios when it comes to noise and channel impairments.

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.

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.

Optimization of the Decision Criterion for Increasing the Bandwidth Utilization by Means of the Novel Effective DBA Algorithm in NG-PON2 Networks

In this paper, the reasons for the bandwidth and wavelength utilization in future next-generation passive optical networks are presented, and the possibilities for realization and utilization of extended dynamic wavelength and bandwidth algorithms for the second next-generation passive optical networks (NG-PON2) are analyzed. Next, principles of the effective dynamic bandwidth allocation are introduced in detail, focused on the importance of the decision criterion optimization. To achieve a better bandwidth utilization of dedicated wavelengths in NG-PON2 networks, this paper is focused on the novel effective dynamic bandwidth allocation algorithm with adaptive allocation of wavelengths to optical network units as well as the optimization of the decision criterion. The algorithm and the proposed method are tested and evaluated through simulation with actual traffic data. For analyzing novel extended dynamic wavelength and bandwidth algorithms used for various cases of wavelength allocation in NG-PON2 networks, the effective dynamic bandwidth allocation algorithm analysis is realized in the enhancement of simulation program. Finally, an optimization of the decision criterion defining a minimum bandwidth utilization of the actual wavelength is executed for NG-PON2 networks based on the hybrid time and wavelength division multiplexing technique.

Fiber Bragg Grating Temperature Sensor and its Interrogation Techniques

In this comprehensive review, our focus centers novel strategies and methodologies in FBG temperature sensors and their interrogation techniques investigated for sensing in different environments. FBG temperature sensors are investigated for cryogenic, ambient, high-temperature and ultrahigh-temperature environments. Interrogation techniques encompasses optical interferometry, optical edge filtering, time division multiplexing, optical spectrum analysis (OSA) and wavelength division multiplexing (WDM), each possessing distinct characteristics and working principles. The optical interferometry technique offers exceptional sensitivity and high resolution but has a relatively lower temperature sensing range. The optical edge filtering technique provides good temperature sensitivity, enhanced resolution and nominal temperature sensing range which are mainly dependent on the span and slope of the edge of the optical filter. TDM interrogation technique has the multiplexing capability and cost-effectiveness but limitations like the requirement of partial reflective matched FBGs, spatial separ¬¬¬¬ation of the FBGs and the potential cross-talk make it less attractive for commercial applications. OSA and WDM techniques excel in multiplexing capabilities and boast the widest temperature sensing range. However, OSA is limited for research applications only. On the other hand, WDM stands out with its cost-effective per-sensor implementation and extensive usage in commercial interrogation systems. The significance of this review lies in its ability to provide researchers, engineers, and practitioners with a coherent understanding of the evolving FBG temperature sensing landscape. By consolidating and highlighting recent breakthroughs, we aim to inspire further research initiatives and foster the development of optimized FBG temperature sensing systems.

Design of Multilayered Ring-Core Fiber With Low-Level Inter-Group Crosstalk

We propose a novel ring-core fiber (RCF) with multilayered ring core and modulated refractive index profile (RIP). The simulated results indicate that such a special fiber design is able to support 5 orbital angular momentum (OAM) mode groups (18 OAM modes) with crosstalk between any two high-order adjacent mode groups (MGs) less than -28 dB/km over the whole C and L band. At the wavelength of 1550 nm, crosstalk between the two highest-order MGs is below -36 dB/km. Besides, with the limitation of the existing manufacturing restriction, the geometric size and doping concentration of the designed fiber are allowable and reasonable, which is promising for practical manufacturing. The designed RCF also shows good bending characteristics. Moreover, ultra-broadband performance is analyzed over the whole C + L band ranging from 1530 nm to 1625 nm. This kind of fiber design could be employed in small-scale multiple-input multiple-output digital signal processing (MIMO-DSP) assisted intra-group modes multiplexing transmission or MIMO-free inter-group modes multiplexing transmission combined with the mature wavelength-division multiplexing technique.

A fully-connected three-user quantum hyperentangled network

Exploiting the fantastic features of quantum mechanics, a hyperentangled quantum network encoded in multiple degree of freedoms (DOF), e.g., polarization and orbital angular momentum DOFs, can encode more qubits per transmitted photon and offers a promising platform for many dramatic applications. Here, we demonstrate such a hyperentangled multiuser network with a fully connected network architecture by using dense wavelength division multiplexing and entanglement transfer technique. Three hyperentangled states in polarization and time-energy DOFs are multiplexed to three single mode fibers to form the fully connected network architecture. Then, three interferometric quantum gates are utilized for transferring quantum entanglement from time-energy to orbital angular momentum DOF. The experimental results reveal a high quality of the hyperentanglement of the constructed network with the entangled state fidelity of higher than 96%. Our approach can provide a novel way to construct a large-scale hyperentangled network that can support various kinds of quantum tasks like superdense coding and teleportation.

Free-space mid-IR communications using wavelength and mode division multiplexing

There has been growing interest in free-space optical (FSO) communications in the mid-infrared (mid-IR) region. In this paper, we review FSO communications in the mid-IR using wavelength division multiplexing (WDM) and orbital angular momentum (OAM)-based mode division multiplexing (MDM). We introduce the effects of mid-IR wavelengths in FSO communication links. The methods available to modulate and detect signals on mid-IR wavelengths are discussed. Subsequently, we introduce WDM and OAM-based MDM techniques in the mid-IR. Finally, we focus on the performance of a mid-IR FSO communication system combining both multiplexing techniques.

A Review–Unguided Optical Communications: Developments, Technology Evolution, and Challenges

This review paper discusses the complete evolution of free-space optical (FSO) communication, also known as unguided optical communication (UOC) technologies, all the way back to ancient man’s fire to today’s machine-learning-supported UOC systems. The principles, significance, and developments that have happened over the past several decades, as well as installation methodologies, technological limitations, and today’s challenges of UOCs are presented. All the subsets of UOC: FSO communication, underwater optical wireless communication (UOWC), and visible light communication (VLC), with their technology/system developments, potential applications, and limitations are reviewed. The state-of-the-art developments/achievements in (i) FSO channel effects and their mitigation techniques; (ii) radio-over-FSO techniques; (iii) wavelength division multiplexing and sub-carrier multiplexing techniques; (iv) FSO for worldwide interoperability for microwave access applications; (v) space optical satellite communication (SOSC); (vi) UWOC; (vii) photoacoustic communication (PAC); (viii) light-fidelity; (ix) VLC; (x) vehicular VLC (V2LC); and (xi) optical camera communication are reviewed. In addition, the current developments on emerging technologies such as artificial intelligence (to improve the performance of UOC systems), energy harvesting (for the effective utilization of UOC channels), and near-future communication network scenarios (mandatory for secured broadband digital links) are covered. Finally, in brief, to achieve the full potential of UOC systems, challenges that require immediate research attention are summarized.

A 40-Gbps fiber-FSO convergent transmission system employing OFCL-based WDM and external modulation technique

We have proposed and demonstrated a 40Gbps fiber-free space optics (FSO) convergent system based on external modulation and wavelength division multiplexing (WDM) technique. In this experiment, 4010×4 Gbps signal is successfully transmitted employing WDM scheme over 50 km single mode fiber plus 2.5 km FSO distance. Optical frequency comb lines (OFCL) are generated using a continuous wave laser diode, a radio frequency signal generator, a dual drive Mach Zehnder modulator, and an electrical attenuator. OFC lines, having a side mode suppression ratio (SMSR) value of ∼40 dB and flatness of ∼0.4 dB, are employed as broadband laser source in the presented convergent system. The performance of the fiber-FSO system is investigated theoretically for different weather conditions. Very low power penalty with low bit error rate (BER), clear eye diagrams, and standard Q-factor are achieved in the proposed system. The power penalty is restricted within 2.5 dB and 5.8 dB at a BER of 10−9 for 50 km SMF plus 2.5 km FSO distance in clear weather and 50-km SMF plus 0.4-km FSO distance in heavy fog condition respectively. Thus, the proposed WDM-convergent system is efficient enough for high data rate transmission along with low BER value of ∼10−9 and high Q-factor for different environmental scenarios.

Neuromorphic Computing Based on Wavelength-Division Multiplexing

Optical neural networks (ONNs), or optical neuromorphic hardware accelerators, have the potential to dramatically enhance the computing power and energy efficiency of mainstream electronic processors, due to their ultra-large bandwidths of up to 10’s of terahertz together with their analog architecture that avoids the need for reading and writing data back-and-forth. Different multiplexing techniques have been employed to demonstrate ONNs, amongst which wavelength-division multiplexing (WDM) techniques make sufficient use of the unique advantages of optics in terms of broad bandwidths. Here, we review recent advances in WDM-based ONNs, focusing on methods that use integrated microcombs to implement ONNs. We present results for human image processing using an optical convolution accelerator operating at 11 Tera operations per second. The open challenges and limitations of ONNs that need to be addressed for future applications are also discussed.

Detailed performance investigation and BER characterization of S+C+L band-WDM transmission system

Recently, ultra-wideband (UWB) wavelength-division multiplexing (WDM) technique has been introduced to increase the data transmission capacity of optical system using the same infrastructure fibers. This capacity increase will raise the effect of fiber nonlinearity and stimulated Raman scattering (SRS) due to the increase of total launch power and operating wavelength band, respectively. This paper presents comprehensive investigation of UWB spectral characteristics of the fiber nonlinear interference (NLI) in dual-polarization (DP)− 16QAM S+C+L system. The investigation is based on enhanced Gaussian noise (EGN) model and takes into account the wavelength dependence of various fiber parameters. The results are used as a guide line to assess the transmission performance of the system under different values of symbol rate Rs (50–80 GBaud). The results reveal that a maximum transmission reach of 13 100 km-spans is achieved for Rs= 50 GBaud and 75 GHz channel spacing.

High speed radiation tolerant optical links based on coarse wavelength division multiplexing

The upgrade of CERN’s accelerator complex requires improved beam instrumentation systems that will generate an increased volume of data to be transferred from the radiation areas to the back-end. A solution that increases the throughput of already deployed fibers, with minimal increase of the system complexity, consists in implementing the coarse wavelength division multiplexing (CWDM) technique where independent optical carriers at properly spaced wavelengths are multiplexed into a single fiber. In this paper we describe the CWDM Link project, whose scope is to design and build a high-speed radiation-tolerant optical link based on four CWDM channels. We will also provide details of commercially-available CWDM components and their radiation resistance.