Wavelength Division Multiplexing Research Articles

Ultra-compact and high-performance four-channel coarse wavelength-division (de)multiplexing filters based on cascaded Mach-Zehnder interferometers with Bezier-shape directional couplers

Using cascaded Mach-Zehnder interferometers (CMZIs) provides an attractive option for realizing coarse wavelength-division (de)multiplexing (CWDM) filters with low losses, low crosstalk, flat tops, and high scalability. However, they usually have large footprints and insufficient fabrication tolerances, due to the inferior performance of conventional directional couplers (DCs) used for MZIs. Here, a four-channel CMZI wavelength-division (de)multiplexer based on novel Bezier-shape DCs with compact footprints, broad bandwidths and decent fabrication tolerances. For the fabricated (de)multiplexer with 20-nm channel spacing, the excess loss is less than 0.5 dB and the crosstalk is lower than −19.5 dB in the 1-dB bandwidth of 12.8 nm. For the case with a core-width deviation of ±20 nm, the device still performs very well with low losses and low crosstalk. Compared to the state-of-the-art MZI-based CWDM filters, the present device has slightly high performances and a footprint of 0.012 mm2 shrunk greatly by ∼3-folds. This work can be extended for more channels and other material platforms.

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.

Simultaneous generation of wavelength multiplexing and polarization multiplexing from a wavelength-tunable ultrafast fiber laser

A wavelength-tunable mode-locked erbium-doped all-fiber laser delivering both wavelength multiplexing and polarization multiplexing asynchronous pulses is experimentally demonstrated, which is challenging in previous studies. The numerical simulations validate the experimental observations and reveal that the cavity birefringence and polarization dependent loss (PDL) induced by the wavelength division multiplexer play a significant role in the formation of different types of asynchronous pulses. Our results not only provide insights into the physical mechanism of the asynchronous pulses generation, but also offer a potential low-complexity light source for dual-comb applications.

Performance analysis of hybrid optical amplifiers for multichannel wavelength division multiplexed (WDM) optical networks

Abstract Hybrid Optical Amplifier (HOA) has made a significant change in Wavelength Division Multiplexed (WDM) optical networks. We have proposed diverse hybrid optical amplifier configurations for the better performance of WDM optical networks. These configurations are SOA-EDFA, EDFA-EDFA and EDFA-Raman amplifier for 24 channels WDM optical networks at 10 Gbps with channel spacing of 0.8 nm. The performance of the systems is evaluated on the behalf of different parameters such as, quality factor, eye diagram, bit error rate and output power. The efforts are made to optimize these parameters. From the results, it is assessed that EDFA-Raman configuration gives superior results as compared to EDFA-EDFA configuration and SOA-EDFA hybrid optical amplifier configuration for long distance. Further it is also observed that EDFA-Raman hybrid optical amplifier configuration is suitable for high data rates up to 20 Gbps.

Erbium/Ytterbium-Doped Waveguide Amplifier (EYDWA) for extended reach of Wavelength Division Multiplexing based free space optics system (WDM/FSO)

Abstract This work is focused to carry out the investigation of wavelength division multiplexing (WDM) approach on free space optical (FSO) transmission systems using Erbium Ytterbium Doped Waveguide Amplifier (EYDWA) integrated as post-or pre-amplifier for extending the reach to 30 Km for the cost-effective implementation of FSO system considering weather conditions. Furthermore, the performance of proposed FSO-wavelength division multiplexing (WDM) system is also evaluated on the effect of varying the FSO range and results are reported in terms of Q factor, BER, and eye diagrams. It has been found that, under clear rain the post-amplification was performed and was able to reach transmission distance over 27 Km, whereas, the FSO distance has been limited at 19.5 Km by using pre-amplification.

Transmission challenges in metropolitan area optical networks

Abstract For implementing wide/metropolitan area network in optical fiber communication system the key technology that can be utilized is wavelength division multiplexing (WDM). We discuss the use of WDM in metropolitan networks along with its special feature of using optical add drop multiplexers and also design issues in implementing these systems. The issue of nonlinear crosstalk induced in metropolitan networks is considered in terms of power penalty. Also, the effect of dispersion induced in optical fibers is considered by using two types of transmission systems. One is considering the non-zero dispersion shifted fiber (NZDSF) in dispersion effected environment and second is, implementing dispersion compensation after normal single mode fiber (SMF + DCF). The effect of nonlinear cross talk which can limit transmission performance is discussed in both cases in context with different parameters like power penalty, frequency difference between signal & crosstalk and transmission distance etc.

Analysis the flat gain/noise figure using RAMAN-Reflective Semiconductor Hybrid Optical Amplifier in C + L + U triple band for super dense wavelength division multiplexing system

Abstract Nonlinearity, flat gain and noise figure are the prime concern for super dense wavelength division multiplexing (SD-WDM) systems which have been resolved from RAMAN-RSOA hybrid optical amplifier (HOA) for the first time in this paper. Channel capacity is taken up to 400 with data rate of 10 Gbps. Performances are evaluated with respect to C + L + U band for 1520–1680 nm and 1520 to 1640 nm. RSOA is operated at 40–120 mA bias current to attain best rating flat gain of 34.07 dB with variation of 3.5 dB than the others HOAs (RAMAN-EDFA, RAMAN-SOA and EDFA-SOA). Moreover, the impact of EDFA-SOA is not acceptable in terms of noise figure for SD-WDM optical communication system.

Compact Morpho‐Molecular Microscopy for Live‐cell Imaging and Material Characterization

AbstractThe Compact Morpho‐Molecular Microscopy (CM3) is proposed and demonstrated for multi‐functional imaging and characterization of living cells and material structures by simultaneously offering quantitative phase imaging (QPI), dispersion characterization, and fluorescence imaging. The compactness and stability of CM3 are realized by propagating lasers of different wavelengths in specially treated optical fibers and fiber‐based beam splitters and wavelength division multiplexers, as well as simplifying the detection scheme through Fourier‐space multiplexing and implementing a single camera for both QPI and fluorescence imaging. Quantitative phase maps of two wavelengths are retrieved from a multiplexed interferogram, and a synthesized wavelength phase map is derived to guide the height profiling of samples with extended depth. With the wavelength resolved phase maps, a physical model is derived to obtain sample dispersion parameters, which further enables us to quantify the hemoglobin concentration of red blood cells in real time. By inserting an appropriate emission color filter, fluorescence imaging is realized using the same camera, which significantly broadens the cell imaging applications of CM3. As a cost‐effective and multifaceted imaging method, CM3 may find many promising applications in live‐cell imaging and material characterization.

Power evolution prediction of bidirectional Raman amplified WDM system based on PINN.

We propose using physical-informed neural network (PINN) for power evolution prediction in bidirectional Raman amplified WDM systems with Rayleigh backscattering (RBS). Unlike models based on data-driven machine learning, PINN can be effectively trained without preparing a large amount of data in advance and can learn the potential rules of power evolution. Compared to previous applications of PINN in power prediction, our model considers bidirectional Raman pumping and RBS, which is more practical. We experimentally demonstrate power evolution prediction of 200 km bidirectional Raman amplified wavelength-division multiplexed (WDM) system with 47 channels and 8 pumps using PINN. The maximum prediction error of PINN compared to experimental results is only 0.38 dB, demonstrating great potential for application in power evolution prediction. The power evolution predicted by PINN shows good agreement with the results simulated by traditional numerical method, but its efficiency is more suitable for establishing models and calculating noise, providing convenience for subsequent power configuration optimization.

Performance analysis of a hybrid optical amplifier based 480-Gbps DWDM-FSO system under the effect of different atmospheric conditions

Free space optical (FSO) systems offer a desirable and affordable way of providing communication services in remote locations. They provide secure wireless transmission without the requirement for licensing and with lower implementation costs. However, due to the impact of atmospheric turbulences on the effectiveness of FSO systems, their implementation faces significant challenges. Dense wavelength division multiplexing (DWDM) has shown promise in addressing the growing bandwidth needs in optical networks. This paper introduces a hybrid optical amplifier based system, combining DWDM and FSO technology. Energy conservation in such a system involves optimizing various aspects to reduce power consumption while maintaining or improving performance. The proposed DWDM-FSO system operates at a rate of 480 Gbps and consists of 12 channels, each capable of transmitting data at 40 Gbps. The system's performance is evaluated and compared by determining the Q-factor and bit error rate (BER) for both the cases when hybrid amplifier is employed and with no hybrid amplifier within the C-band, specifically focusing on wavelengths around 1550 nm. Moreover, the length of the FSO link is increased to assess the corresponding Q-factor and BER. Resultantly, the maximum distance for the FSO link is determined, ensuring that it remains within acceptable Q-factor and BER thresholds. Furthermore, the FSO system's effectiveness is assessed and compared across various atmospheric conditions. The findings reveal that, in clear weather conditions, the FSO system achieves a maximum distance of 510 meters while maintaining satisfactory Q-factor and BER values when not utilizing a hybrid amplifier. However, by integrating a hybrid amplifier, the system's reach significantly extends to 1700 m under clear weather conditions, still maintaining acceptable Q-factor and BER values.

Nonlocal Metasurface with Chiral Exceptional Points in the Telecom-Band.

The exceptional point (EP) is the critical phase transition point in parity-time (PT) symmetry systems, offering many unique physical phenomena, such as a chiral response. Achieving chiral EP in practical applications has been challenging due to the delicate balance required between gain and loss and complicated fabrication, limiting both working band and device miniaturization. Here, we proposed a nonlocal metasurface featuring orthogonal gold nanorods, where loss modulation is achieved through rod size and lattice pitch. By tuning the coupling strength, we experimentally observed the PT symmetry phase transition and chiral EP in the telecom-band. The experimental and simulated circular conversion dichroism at EP reach 0.79 and 0.99, respectively. We also demonstrated an abrupt phase flip of a specific component near EP theoretically. This work provides a feasible scheme for exploring EP in polarized space within the telecom-band, which may find applications in polarization control, wavelength division multiplexing, ultrasensitive sensing, imaging, etc.

The application of optical fiber in network communication

In recent years, optical fiber communication has gained widespread use in daily life due to its robust communication and transmission capabilities, strong confidentiality, anti-interference properties, and the availability of convenient and accessible materials. This technology has made remarkable strides in network communication and integrated device design, among other areas. This article will commence by discussing the fundamental structure of optical fibers and illustrating the propagation of optical signals within them. It will then analyze the benefits, such as higher transmission rates, wider frequency bands, and the low loss characteristics of optical fibers. Subsequently, the article will enumerate two of the most commonly utilized Optical Fiber Communication (OFC) technologies: Wavelength Division Multiplexing (WDM) technology and optical amplifier technology. It will summarize their principles and strengths. Finally, the article will showcase the practical applications of optical fiber communication, particularly focusing on its role in 5G mobile communication, military operations, and radio and television communication.

Wavelength-tunable Tm:Y2O3 ceramic vortex laser with a changeable orbital angular momentum state.

Wavelength-tunable orbital angular momentum (OAM) lasers with controllable topological charges have the potential for serving as light sources for large-capacity optical communication by combining conventional wavelength division multiplexing (WDM) with OAM mode-division multiplexing (OAM-MDM). In this study, we demonstrate a wavelength-tunable Tm-bulk laser that can control OAM states in the 2-µm spectral range. The excitation conditions for different Laguerre-Gaussian (L G 0,l ) modes in a bulk laser cavity are theoretically determined by measuring the spatial propagation dynamics of the annular pump beam. As a proof-of-principle study, we experimentally generate OAM states of |ℏ| and |2ℏ| from a T m:Y 2 O 3 ceramic laser with a tunable emission wavelength using a Lyot filter (LF). The spatial properties of the scalar optical vortices are well conserved during wavelength tuning, indicating the feasibility of our approach for producing wavelength-tunable structured light. These OAM laser sources, which are characterized by their robustness and compactness, have potential applications in various areas such as optical communications, quantum optics, super-resolution microscopes, and more.

Photonic MMW Generation Using PM-DPMZM for Full Duplex 32×10 Gbps RoF-WDM System

Abstract This paper presents a study of a 32×10 Gbps Radio over Fiber and Wavelength Division Multiplexing (RoF-WDM) full-duplex system that uses Phase Modulators and a Dual-Port Mach-Zehnder Modulator (PMs-DPMZM) for bidirectional data transfer. The system employs Millimeter-Wave (MMW) signaling over optical fiber and focuses on selecting a technology that provides high transmission capacity per wavelength, improved spectral efficiency, and resistance against optical transmission impairments. The proposed method was validated using simulation results to confirm the efficiency of the proposed system in generating a 40 GHz signal and efficiently detecting and modulating the RF signals. The results demonstrate that the system exhibits strong resistance against dispersion, non-linear effects, and noise, delivering satisfactory performance for distances of up to 220 km. By analyzing the input power, the paper establishes a relationship between input power and signal quality, revealing that an optimal power of 0 dBm leads to an improved Quality Factor (QF) and reduced transmission errors. Furthermore, the evaluation of received optical power indicates the power level required to maintain an acceptable error rate, approximately -20.9690 dBm for downstream data transfer and -20.7245 dBm for upstream data transfer at the BER limit. The simulation performance also demonstrates the transmission efficiency achieved through a high Polarization Mode Dispersion (PMD) coefficient of up to 0.8. The analytical calculations conducted in this work provide valuable insights for optimizing and enhancing the performance of RoF-WDM networks.

Design of a high-precision current source system for tunable laser driving

Fiber Bragg Grating (FBG), which is an Optical Fiber Sensor with high sensitivity, light weight, and strong anti-interference ability, can realize the measurement of physical quantities, such as temperature and strain. The sensor network formed by FBG sensors is through wavelength division multiplexing, which greatly reduced the difficulty of sensor wiring. Therefore, FBG sensors are widely used in sensing fields such as aerospace, bridges and tunnels. As a wavelength-modulated Optical Fiber Sensor, FBG’s sensing accuracy depends not only on the performance of the laser, but also on the stability of the driving current. In this paper, a high-precision current source system for laser S7500 modulation drive is designed, with a resolution of output current is higher than 2uA. and the laser S7500 is continuously linearly scanned at 20pm intervals in the wavelength range of 1527nm to 1567nm. The wavelength accuracy of the output optical signal is better than 2pm. The test results prove that the system has the advantages of high modulation speed, good stability and high reliability, and can be applied to high-precision FBG sensor networks.

Performance Analysis of Subcarrier Index Modulation OFDM in a DWDM-FSO link

Free Space Optics (FSO) is a wireless optical communication system using light to establish high-capacity links between points without the need for physical cables. However, its susceptibility to atmospheric conditions such as fog, rain, and turbulence presents challenges to signal quality maintenance. To address this, Dense Wavelength Division Multiplexing (DWDM), traditionally employed in fiber optics, is leveraged to optimize bandwidth utilization and scalability in high-capacity communications. The integration of DWDM into FSO systems offers redundancy and resilience against signal degradation induced by atmospheric conditions. To the best of our knowledge, this is the first time a paper explores the performance of the Subcarrier Index Modulation Orthogonal Frequency Division Multiplexing (SIM-OFDM) technique within a DWDM-FSO system. The objective is to reinforce FSO link robustness and improve transmission rates. Through a comparative analysis with conventional OFDM in an Additive White Gaussian Noise (AWGN) channel, the study reveals a notable Signal-to-Noise Ratio (SNR) gain of at least 3dB with enhanced SIM-OFDM (ESIM-OFDM). Simulations, conducted with realistic parameters within the DWDM-FSO architecture, demonstrate that ESIM-OFDM modulation enables a transmission range of 2 km with an aggregated rate of 10.1 Gb/s. These results underscore the potential of SIM-OFDM in enhancing FSO system performance through the integration of DWDM technology. The proposed ESIM-OFDM DWDM-FSO scenario could represent a highly interesting solution for establishing 5G Backhaul links.

Joint intra and inter-channel nonlinear compensation scheme based on improved learned digital back propagation for WDM systems.

In this paper, we improve the learned digital back propagation (LDBP) and propose a novel joint intra and inter-channel nonlinearity compensation scheme for polarization division multiplexing wavelength-division multiplexed (PDM-WDM) systems. From the perspective of interpretable neural network, the scheme realizes the alternating compensation of chromatic dispersion (CD) and nonlinearity based on physical models. The chromatic dispersion compensation (CDC) adopts one-dimensional convolution operation in the time domain. Moreover, the pulse-broadening effect is introduced into the overlap-and-save method. For nonlinear compensation, the improved joint model is applied, and the impact of the intra-channel pulse broadening and the walk-off effect between different channels caused by CD on the nonlinear effect is considered. To validate the effectiveness of the proposed scheme, we construct an 11-channel simulation system of 36 GBaud PDM uniform 16 quadrature amplitude modulation (PDM-16QAM) 1600 km and 64 GBaud PDM-64QAM 400 km, as well as a 5-channel experimental system of 28 GBaud PDM-16QAM 806.4 km. The simulation results show that the performance of PDM-16QAM with 0.5 steps per span and PDM-64QAM with 2 steps per span improve the Q-factor by approximately 0.75 dB and 0.54 dB at the optimal launch power, compared with the linear compensation scheme. The transmission performance of PDM-16QAM is higher than that of digital back propagation with 5 steps per span (DBP-5StPS), and the complexity is only 31.36% of that of DBP-5StPS. The performance of PDM-64QAM is higher than that of DBP-10StPS, with a complexity of 62.72%. The experimental results show that the performance of PDM-16QAM with 0.5 steps per span is improved with 0.86 dB Q-factor improvement compared with the linear compensation scheme at the optimal launch power, and the performance of the proposed scheme is higher than that of DBP-5StPS with a complexity of only 23.68%.

Generalized Rayleigh quotient optimization method for inter-channel nonlinearity compensation in coherent optical communication systems.

Inter-channel nonlinearity compensation plays a crucial role in wavelength division multiplexing (WDM) systems for improving transmission capacity and distance. In this work, we propose a novel, to the best of our knowledge, inter-channel nonlinearity compensation method called generalized Rayleigh quotient optimization (GRQO) method with two different working modes. In an 8 × 64 GBaud 16-ary quadrature amplitude modulation (16-QAM) experimental system over 1600 km standard single-mode fiber (SSMF), the proposed method shows a 0.40 dB Q2 factor improvement over nonlinear polarization cross talk canceller (NPCC) with a moderately low computational complexity of about 2000 real multiplications per bit (RMb).

Sub-volt high-speed silicon MOSCAP microring modulator driven by high-mobility conductive oxide

Silicon microring modulator plays a critical role in energy-efficient optical interconnect and optical computing owing to its ultra-compact footprint and capability for on-chip wavelength-division multiplexing. However, existing silicon microring modulators usually require more than 2 V of driving voltage (Vpp), which is limited by both material properties and device structures. Here, we present a metal-oxide-semiconductor capacitor microring modulator through heterogeneous integration between silicon photonics and titanium-doped indium oxide, which is a high-mobility transparent conductive oxide (TCO) with a strong plasma dispersion effect. The device is co-fabricated by Intel’s photonics fab and our in-house TCO patterning processes, which exhibits a high modulation efficiency of 117 pm/V and consequently can be driven by a very low Vpp of 0.8 V. At a 11 GHz modulation bandwidth where the modulator is limited by the RC bandwidth, we obtained 25 Gb/s clear eye diagrams with energy efficiency of 53 fJ/bit.

Earthquake-Tolerant Energy-Aware Algorithm for WDM Backbone Network

Traffic on backbone communication networks is growing significantly every year. This results in an increase in both energy consumption and the carbon footprint they leave on the environment. As a response, research efforts are focused on reducing energy consumption in telecom networks. Wavelength division multiplexing (WDM) optical networks are key for addressing rising bandwidth demands in backbone networks, but this leads to a concurrent surge in energy usage. Additionally, regions with high seismic activity risk damage to backbone networks from earthquakes, causing significant bandwidth loss and service disruptions. This paper aims to reduce the energy consumption in a backbone network by implementing an algorithm that optimizes energy efficiency while preserving network connectivity and resistance to earthquake phenomena. The proposed algorithm redesigns and modifies a backbone network by deactivating the unnecessary links without affecting the network performance. The scheme is extensively evaluated through simulations using real seismic data from the Geodynamic Institute of the National Observatory of Athens, confirming earthquake resilience and energy efficiency goals, with an energy saving of up to 9% compared to existing solutions.