WDM Systems Research Articles

Effect of saturation tone on spectral EDFA gain spectrum

Accurate characterization of spectral gain of C-band EDFAs in WDM system design is crucial; however, traditional methods often require expensive WDM equipment. This study presents a cost-effective alternative, validated through both experimental measurements and simulations, that utilizes a weak signal probe and a carefully selected saturation tone. By comparing results with a 32-channel WDM reference, we demonstrate that the proposed method achieves high accuracy. The optimal saturation tone wavelength depends on the pump wavelength (980 nm or 1480 nm) and configuration (forward or bidirectional). Nevertheless, a good fit with the reference can be obtained in all scenarios, especially at higher saturation levels. This work provides valuable insights for developing affordable and efficient EDFA gain measurement techniques.

Asymmetric demodulation using decision trees in gridless WDM systems

Asymmetric demodulation using decision trees in gridless WDM systems

Toward Seven-Band Coherent WDM System Covering T to U Bands: Predictions of Transmission and BER Performance

Toward Seven-Band Coherent WDM System Covering T to U Bands: Predictions of Transmission and BER Performance

Minimization of dispersion and non-linear effects in WDM based long-haul high capacity optical communication systems

Abstract Chromatic dispersion and nonlinear impairments pose challenges in high-capacity optical transmission systems, leading to signal distortions, channel interference and diminished the transmission performances. This paper explores the utilization of dispersion compensating fibers (DCF) using different schemes to mitigate the dispersion that accumulates along the length of a fiber in a 16 × 10 Gbps high-capacity long haul WDM system over a range of 500 km. When different wavelengths of light pulses are transmitted through an optical fiber, they experience varying speeds due to the refractive index’s wavelength dependency. As a result, the light pulses become temporally spread out as they travel through the fiber, and this dispersion persists throughout the fiber’s length. Considering non-linear effects such as self-phase modulation (SPM) and cross-phase modulation (XPM), this paper analyze and compare the three compensation schemes of DCF in a 16 channel WDM system. Moreover the impact of non-linearities based on fiber length are also analyzed and compared. The results are evaluated by comparing metrics such as Q-factor, bit error rate (BER) and eye height. The analysis concludes that the symmetrical compensation scheme of DCF outperforms the pre- and post-compensation scheme. This finding suggests that the symmetrical compensation method offers a promising solution for high-capacity access networks, providing high spectral efficiency, cost-effectiveness, and improved flexibility.

Wavelength multiplexing system based on ring resonators

Wavelength Division Multiplexing, WDM, is a technology developed for applications in telecommunications with the purpose of combining numerous wavelength signals into one single fibre. The aim of this research is the characterization of WDM systems of ring resonators with planar optical waveguides. The optical responses for different configurations, dimensions, and materials are analysed by doing a parametric study both considering analytical expressions and a Finite Element Tool. The results are from add-drop topologies with one, two and three rings. The main difference between topologies with the same parameters is the number of resonance wavelengths, which is higher due to the increase in the number of ring-shaped waveguides. It is concluded that adjusting the rings’ dimensions, the resonant wavelengths are tuned. Furthermore, the higher the rings’ radius the lower is the free spectral range, that can take values from 40 nm to 90 nm. Then, the number of resonant peaks in a wavelength range may change. Also, 1500–5000 describes the values computed for the quality factor, whereas the full width at half maximum varies within some units of nanometres. For models with different core materials, the higher transmittances decrease with lower core refractive indexes and the resonance width increases. These are new degrees of freedom to tune the response of the device that can definitely work as optical wavelength multiplexer, having losses from 20% to 40% considering the transmitted optical power.

Performance Investigation of 400 × 100 Gb/s Ultra-Dense WDM System Using Different Modulation Techniques with Varying Channel Spacing

Performance Investigation of 400 × 100 Gb/s Ultra-Dense WDM System Using Different Modulation Techniques with Varying Channel Spacing

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%.

Multichannel Nonlinear Equalization in Coherent WDM Systems Based on Bi-Directional Recurrent Neural Networks

Multichannel Nonlinear Equalization in Coherent WDM Systems Based on Bi-Directional Recurrent Neural Networks

Enhancing Gain Uniformity in WDM Networks Across C and L Bands Through Hybrid Optical Amplifier Integration

This study explores strategies for optimizing EDFA gain in the context of (WDM and DWDM systems. By reviewing recent literature, we investigate various approaches to enhance EDFA performance, considering factors such as input power, pump power, and fiber length. Our analysis covers optimization algorithms, gain flattening techniques, adaptive gain equalization methods, and hybrid amplifier configurations. Additionally, we examine studies addressing nonlinear effects and the allocation of pump power to maximize gain efficiency. Recent advancements, including machine learning-based approaches and novel gain equalization techniques using phase-shifted fiber Bragg gratings, are also discussed. The findings underscore the significance of tailored EDFA gain optimization methods for improving the overall performance and efficiency of WDM and DWDM systems in optical communication networks.

Physics-based Modeling for Hybrid Data-Driven Models to Estimate SNR in WDM Systems

Physics-based Modeling for Hybrid Data-Driven Models to Estimate SNR in WDM Systems

Twelve-channel LAN wavelength-division multiplexer on lithium niobate

Abstract A twelve-channel local-area-network (LAN) wavelength-division multiplexing (LWDM) filter is proposed and demonstrated with a uniform channel spacing of 4.5 nm (800 GHz) in the O-band of 1270–1330 nm by using x-cut lithium-niobate-on-insulator (LNOI) photonic waveguides for the first time. The present LWDM filter consists of twelve single-channel bandpass filters based on multimode waveguide gratings (MWGs) assisted with a TE0/TE1 mode (de)multiplexer. In particular, two stages of MWGs in cascade are introduced for each single-channel bandpass filter, in order to achieve high sidelobe suppression ratios, thus reducing interchannel crosstalk. For the fabricated twelve-channel LWDM filter, all the channels have very excellent box-like spectral responses with low excess losses of ∼0.6 dB, broad 1-dB bandwidths of ∼2.9–3.4 nm (which is close to 75 % of the channel spacing), and ultra-low interchannel crosstalk of <−40 dB in experiments. In addition, the present device is highly tolerant to the random variations of the etching depth (±20 nm) and the grating waveguide width (±20 nm) of the LNOI photonic waveguides, showing great potential for high-capacity WDM systems.

Impact of various optical amplifiers on the performance of duobinary and modified duobinary modulated 460 channels ultra-dense WDM system

Impact of various optical amplifiers on the performance of duobinary and modified duobinary modulated 460 channels ultra-dense WDM system

S-Band WDM Transmission Using PPLN-Based Wavelength Converters and 400-Gb/s C-Band Real-Time Transceivers

Multi-band WDM transmission beyond the C+L-band is a promising technology for achieving larger capacity transmission by a limited number of installed fibers. In addition to the C- and L-band, we can expect use the S-band as the next band. Although the development of optical components for new bands, particularly transceivers, entails resource dispersion, which is one of the barriers to the realization of multi-band systems, wavelength conversion by transparent all-optical signal processing enables new wavelength band transmission using existing components. Therefore, we proposed a transmission system including a new wavelength band such as the S-band and made it possible to use a transceiver for the existing band by performing the whole-band wavelength conversion without using a transceiver for the new band. As a preliminary verification to demonstrate multi-band WDM transmission including S-band, we investigated the application of a novel wavelength converter between C-band and S-band, which consists of periodically poled lithium niobate waveguide, to the proposed system. We first characterized the conversion efficiency and noise figure of the wavelength converter and estimated the transmission performance of the system through the wavelength converter. Using the evaluated wavelength converters and test signals of 64 channels arranged in the C-band at 75-GHz intervals, we constructed an experimental setup for S-band transmission through an 80-km standard single-mode fiber. We then demonstrated error-free transmission of real-time 400-Gb/s DP-16QAM signals after forward error correction decoding. From the experimental results, it was clarified that thewavelength converter which realizes the uniformlossless conversion covering the whole C-band effectively achieves the S-band WDM transmission, and it was verified that the capacity improvement of the multi-band WDM system including the S-band can be expected by applying it in combination with the C+L-band WDM system.

Design and Analysis of Holmium-Doped Fiber Amplifier for WDM System in 1990 – 2100 nm Wavelength Range at Higher Bit Rates

Design and Analysis of Holmium-Doped Fiber Amplifier for WDM System in 1990 – 2100 nm Wavelength Range at Higher Bit Rates

Nonlinear Interference Noise in Raman-Amplified WDM Systems

Nonlinear Interference Noise in Raman-Amplified WDM Systems

Joint timing recovery and adaptive equalization based on training sequences for PM-16QAM faster-than-Nyquist WDM systems.

Since the timing error detectors sensitivity (TEDS) of the timing recovery algorithm is close to zero under the singularity condition of azimuth θ about ±π/4 and differential group delay (DGD) about n × 1/2T (n is an odd number, T is the symbol period), it makes the squared Gardner phase detector (SGPD) timing recovery algorithm fail to achieve timing synchronization. What's worse, in the faster-than-Nyquist wavelength division multiplexing (FTN-WDM) systems, the tight filtering introduces inter-symbol-interference (ISI) so severe that the convergence cost of the SGPD timing recovery algorithm is extremely large even under the non-singularity condition. This paper proposes a joint timing recovery and adaptive equalization scheme for FTN coherent systems based on training sequences that could calculate channel matrix and indicate polarization characteristics, thereby avoiding the influence of azimuth on adaptive equalization and polarization demultiplexing (AEPD) embedded in the timing recovery feedback loop. Since embedded AEPD could compensate for most of DGD, the TEDS could be restored and timing synchronization could be achieved under the above adverse conditions. Thanks to the innovative scheme, which equalizes ISI and DGD during the feedback process of the loop, the convergence cost of timing recovery could be reduced with similar computational complexity compared with the conventional one. The simulation results of 128 GBaud polarization multiplexing (PM) 16-quadrature amplitude modulation (QAM) FTN-WDM transmission systems demonstrate that the proposed scheme could stably achieve timing synchronization under the singularity condition. And compared with the conventional scheme, the convergence cost is reduced by at least 42% @ 0.9 acceleration factor. In addition, 40 GBaud PM-16QAM FTN experiment results show that the proposed scheme could not only achieve timing synchronization stably but also exhibit an optical signal-to-noise ratio tolerance gain of 0.8 dB compared with the conventional scheme under 800 km transmission.

Performance evaluation of a 2.56 Tbps DP-16QAM WDM system under various channel spacings and weather conditions using MIMO configurations

Abstract This paper proposes a 16 × 160 Gbps DP-16QAM-WDM-FSO system with 100 and 25 GHz channel spacing, utilizing coherent detection with digital signal processing to enhance the receiver sensitivity. The system’s performance is evaluated under different climate circumstances, such as dust, rain, and fog. The MIMO technique with 2 × 2, 4 × 4, and 8 × 8 configurations are suggested to mitigate weather attenuation effects. Performance metrics, including bit error rate (BER), error vector magnitude (EVM %), quality factor (Q-factor), and optical signal-to-noise ratio (OSNR), are utilized to evaluate the system’s performance. Results show that the proposed system increases the maximum transmission distance by 12.67 %–49.33 %, 19.17 %–78.66 %, and 25.68 %–108 % for all weather circumstances when utilizing 2 × 2 MIMO, 4 × 4 MIMO, and 8 × 8 MIMO, respectively. Moreover, while reducing channel spacing improves the system’s spectral efficiency from 1.6 to 6.4 bits/s/Hz, it also degrades the link range and requires an increased OSNR. A performance comparison between our work and related works is also considered in this paper.

Nonlinear wave equation for wavelength/polarization multiplexed signals in fiber transmission

Wavelength/polarization division multiplexing (WDM/PDM) schemes are standardly employed in trunk transmission systems, for which fiber nonlinearity is a serious problem. Generally, the signal transmission characteristics suffering from fiber nonlinearity have been analyzed using the nonlinear Schrödinger equation or the Manakov equation, which was originally presented for single-channel transmission. Therefore, when they are applied to WDM systems, the polarization states of each wavelength light are assumed to be identical, which is not fit to long-haul transmissions wherein the polarization states of WDM signals randomly and independently vary during the fiber transmission. Considering such conditions in WDM/PDM transmission systems, this paper presents a nonlinear wave equation for WDM/PDM signal transmission, which describes the signal behavior in systems where the polarization states of each WDM light are fully random and independent. A formula modified from the Manakov equation is derived using the polarization state coordinate of each signal light in WDM/PDM systems.

Review of FBG and DCF as dispersion management unit for long haul optical links and WDM systems

Review of FBG and DCF as dispersion management unit for long haul optical links and WDM systems

Demonstration of 5.12-Tbps THz-over-fiber transmission in 80 channel WDM system

Demonstration of 5.12-Tbps THz-over-fiber transmission in 80 channel WDM system