Chromatic Dispersion Research Articles

Using ADTS and CNN methods to effectively monitor CD, crosstalk, and OSNR in an optical network

The article presents the results of a method based on asynchronous delay-tap sampling (ADTS) and convolutional neural network (CNN) for determining simultaneously occurring disturbances described using the chromatic dispersion (CD), crosstalk and optical signal-to-noise ratio (OSNR) parameters. The ADTS method was used to generate training and test data for the convolutional network, which in turn was used to learn to recognize interference from said data. The tests were carried out for a transmission speed of 10 Gbit/s and for on-off keying (OOK) and differential phase shift keying (DPSK) modulation. Very good results were obtained in recognizing simultaneously occurring phenomena. Accuracy of over 99% was achieved for CD and crosstalk for DPSK modulation and over 98% for OOK modulation. In the case of amplified spontaneous emission (ASE) noise, slightly weaker results were obtained, above 95–96% for both modulations. Based on the conducted research, it was determined that the use of ADTS and CNN methods enables monitoring of simultaneously occurring CD, crosstalk, and ASE noise in the physical layer of the optical network, while maintaining the requirements for modern monitoring systems.

On the optical soliton solutions of the perturbed Fokas–Lenells equation having parabolic law of self-phase modulation in the presence of spatio-temporal dispersion

In this study, we aimed to obtain optical soliton solutions of the perturbed Fokas–Lenells equation having the parabolic law of self-phase modulation in the presence of spatio-temporal dispersion. The Fokas–Lenells equation is significant in nonlinear optics, particularly for modeling femto-second pulse propagation. By implementing the enhanced Kudryashov method, we derive dark, bright, and kink optical solitons for the investigated model. Visualizing the obtained results supported by 3D and 2D simulations and examining the effects of the parameters within the model on the soliton behavior constitute the other branches of the study. Considering that the interaction of various self-phase modulation forms with the chromatic dispersion term is different and its effects on soliton behavior are different, the parabolic law nonlinearity form is examined in the study and the results obtained are aimed at contributing to studies on both the model and nonlinear optics.

Optical fiber with varied flat chromatic dispersion

This paper investigates the design and properties of the conventional all-solid silica based flat dispersion specialty optical fiber. The design utilizes depressed-clad type of refractive index profile which allows for precise control of the optical fiber modal properties, particularly the chromatic dispersion. Specifically designing the dopants concentrations and depressed clad to core diameter ratio allows to obtain optical fibers with flat chromatic dispersion ranging from anomalous to normal dispersion regime. The regime and the values of chromatic dispersion in optical fibers is obtained through the change of the core diameter with the refractive index profile being the same in all optical fibers. The influence of the dopant choice on the mechanical and optical properties is shown using finite element method (FEM) studies. The study demonstrates that fluorine is a better candidate than boron for optical fiber designs that require precise chromatic dispersion characteristics. Six optical fibers were manufactured with the same refractive index profile differing with core radius. This allowed to obtain optical fibers that have chromatic dispersion in anomalous region (17.82 ps/(nm∙km) at 1.96 µm) for the fiber DCFDF1 and normal region (−115.14 ps/(nm∙km) at 1.57 µm) for the fiber DCFDF6.

Theory of particle beams transport over curved plasma-discharge capillaries

We present a new approach that demonstrates the deflection and guiding of relativistic electron beams over curved paths by means of the magnetic field generated in a plasma-discharge capillary. The active bending plasma (ABP) represents a promising solution that has been recently demonstrated with a proof of principle experiment. An ABP device consists of a curved capillary where large discharges (of the order of kA) are propagated in a plasma channel. Unlike conventional bending magnets, in which the field is constant over the bending plane, in the ABP, the azimuthal magnetic field generated by the discharge grows with the distance from the capillary axis. This features makes the device less affected by the beam chromatic dispersion so that it can be used to efficiently guide particle beams with non-negligible energy spreads. The study we present in the following aims to provide a theoretical basis of the main ABP features by presenting an analytical description of a single-particle motion and rms beam dynamics. The retrieved relationships are verified by means of numerical simulations and provide the theoretical matrix formalism needed to completely characterize such a new transport device. Published by the American Physical Society 2024

Method for Controlling Dispersion in Order to Maintain a Quasi-Soliton Pulse Propagation Mode in High-Speed Fiber-Optic Communications System

Relevance: Every year, there is an increasing need to enhance the bandwidth and range of fiber-optic communication systems. The study of methods to control dispersion is relevant and helps maintain a quasi-soliton regime, which is essential for ensuring high-speed, reliable data transmission. Conducted modeling and calculations make this research practical and applicable. This will enable engineers to accurately predict the system's behavior and optimize its performance before implementing it in real-world networks.Problem statement: Investigation of the processes of maintaining a quasi-soliton regime in fibers with decreasing chromatic dispersion and alternating fibers with different signs of chromatic dispersion, both with and without initial chirping.Goal of the work: The development and analysis of techniques to control dispersion in order to maintain a quasi-soliton mode of light propagation in single-mode optical fibers.Methods: The study of the processes of maintaining a quasi-soliton regime was carried out by mathematical and numerical modeling. To substantiate the methods, theoretical analysis and calculations were carried out and schemes for a quasi-soliton fiber-optic communication system were developed and modeling was carried out.Result: The analysis of the results demonstrated the effectiveness of the proposed method and showed the efficiency and stability of the solutions in conditions that were close to real-world scenarios. Novelty: Models for maintaining a quasi-soliton regime and methods for studying them have been developed. The most effective ways to preserve quasi-soliton pulses over long distances have been analyzed.Practical significance: The developed models and research methods can be applied in the educational process and the development of real fiber-optic communication systems.

A tutorial on the physics of light and image shading.

This paper provides an overview of the many different ways that light interacts with surfaces in the natural environment to provide useful information for visual perception. It begins with a discussion of how the concept of light has evolved over the course of human history. It then considers a wide variety of optical phenomena including Lambert's laws of illumination, the effects of microscopic surface structure on patterns of reflection, the bidirectional reflectance distribution function, the refraction of transmitted light, chromatic dispersion, thin film interference, sub-surface scattering, the Fresnel effects, indirect illumination from multiple reflections, caustics, and the structure of the light field. The primary goal of this discussion is to provide the necessary background information to help students and young researchers more easily understand the scientific literature on the perception of 3D shape and material properties from patterns of image shading.

Impact of dispersion-shifted fiber on optical communications link through orthogonal channels

Dispersion-Shifted Fiber (DSF) is essential for reducing chromatic dispersion in high-speed optical communication systems. This study investigates the influence of Four Wave Mixing (FWM) on the quality of signals in orthogonal channels. We examine the advantages of DSF technology and analyze the impact of modulation formats such as On-Off Keying with Return-to-Zero (OOK-RZ) and Duo Binary Modulation class-1 (DBM-1) on transmission performance at different distances. This research assesses the efficacy of orthogonal channels in mitigating four-wave mixing (FWM) effects and improving the overall performance of eight-channel systems at distances of 100 km and 200 km through computer simulations. The results of our study show notable enhancements, namely in optimizing the Q-factor (a metric for signal quality) and reducing bit error rates when employing orthogonal channels compared to previous work. By integrating orthogonal channels with OOK-RZ modulation, we achieved higher performance and reduced nonlinear impairments in a simulated eight-channel system with 50 GHz spacing and 80 Gb/s data rates. This effect was particularly pronounced at high input power levels. At an input power of 20 dBm and a distance of 200 km, this particular combination yielded a maximum Q-factor of 27.25 and a minimum FWM power of −54 dBm. In comparison, under the same conditions, the use of OOK-RZ alone resulted in an FWM power of −24 dBm and a Q-factor of only 1.63. This research provides vital insights into enhancing the efficiency and dependability of optical communication systems, hence facilitating breakthroughs in high-speed data transfer and network scalability.

Advancing on-chip Kerr optical parametric oscillation towards coherent applications covering the green gap

Optical parametric oscillation (OPO) in Kerr microresonators can efficiently transfer near-infrared laser light into the visible spectrum. To date, however, chromatic dispersion has mostly limited output wavelengths to >560 nm, and robust access to the whole green light spectrum has not been demonstrated. In fact, wavelengths between 532 nm and 633 nm, commonly referred to as the “green gap”, are especially challenging to produce with conventional laser gain. Hence, there is motivation to extend the Kerr OPO wavelength range and develop reliable device designs. Here, we experimentally show how to robustly access the entire green gap with Kerr OPO in silicon nitride microrings pumped near 780 nm. Our microring geometries are optimized for green-gap emission; in particular, we introduce a dispersion engineering technique, based on partially undercutting the microring, which not only expands wavelength access but also proves robust to variations in resonator dimensions. Using just four devices, we generate >150 wavelengths evenly distributed throughout the green gap, as predicted by our dispersion simulations. Moreover, we establish the usefulness of Kerr OPO to coherent applications by demonstrating continuous frequency tuning (>50 GHz) and narrow optical linewidths (<1 MHz). Our work represents an important step in the quest to bring nonlinear nanophotonics and its advantages to the visible spectrum.

Optical soliton solutions of the nonlinear complex Ginzburg-Landau equation with the generalized quadratic-cubic law nonlinearity having the chromatic dispersion

In this study, we consider the complex Ginzburg-Landau equation with the generalized quadratic-cubic law of self-phase modulation. This model finds applications in various fields, such as the study of superconductivity, nonlinear optical phenomena, pattern formation, and designing photonic devices and systems. This manuscript successfully employs the new Kudryashov method to derive analytical solutions for complex Ginzburg-Landau equations with the generalized quadratic-cubic law of self-phase modulation. The 3D, contour, and 2D graphical representations of the acquired solutions are represented. Therefore, W-shaped, bright, and dark soliton structures are derived. Through rigorous analysis and interpretation, valuable insights into the influence of the parameters of the presented model on the soliton behavior are achieved.

A facile route to fabricate transparent and mechanically robust glass-fabric reinforced composites via refractive index matching and tow-spreading technique

There are challenges to fabricate GFRPs with high optical clarity and mechanical performance due to the inevitable chromatic dispersion and yarn crimp in the fabric. Herein, a facile route to fabricate transparent glass-fabric reinforced composites is reported using refractive index matching and tow-spreading technique. By introducing different amount of BMA, the epoxy matrix could match the refractive index of glass fibers at different wavelength. The fabricated composites exhibit intriguing pale blue/blue, dark blue/ purple, purple-pink/pink chromatic dispersion, respectively. Among them, the 0.2 mm-thick GFRP with 4 % BMA (fiber volume fraction ≈ 50.4 %) exhibits the highest total transmittance (89.5 %) and lowest haze (3.4 %). Compared with commercial standard-tow fabric, composites with spread-tow fabrics exhibits less chromatic dispersion and transparency loss. Moreover, simultaneously reinforcing and toughening effect could be observed in the composites with BMA modified matrix. The optimized composites possess tensile strength of 289 MPa and flexural strength of 416 MPa.

Efficient multiphoton microscopy with picosecond laser pulses.

Multiphoton microscopes employ femtosecond lasers as light sources because the high peak power of the ultrashort pulse allows for multiphoton excitation of fluorescence in the examined sample. However, such short pulses are susceptible to broadening in a microscope's highly dispersive optical elements and require careful dispersion management, otherwise decreasing excitation efficiency. Here, we have developed a 10 nJ Yb:fiber picosecond laser with an integrated pulse picker unit and evaluated its performance in multiphoton microscopy. Our results show that performance comparable to femtosecond pulses can be obtained with picosecond pulses only by reducing the pulse repetition rate and that such pulses are significantly less prone to the effect of chromatic dispersion. These findings proved that the temporal pulse compression is not always efficient, and it can be omitted by using a smaller and easier-to-use all-fiber setup.

Chromatic dispersion measurement of optical fiber using spectroscopic optical coherence tomography

Chromatic dispersion (CD) in optical fibers results in the broadening and overlapping of transmitted lights, and thus reduces the capacity of information transmission and increases the bit-error-rate of communication system. Hence it needs to be accurately measured and then compensated. There have been various methods for fiber CD measurement, but most of them are complicated to obtain wavelength components and require adjustment during measurement, and thus have the drawbacks of being time-consuming, and susceptible to system stability and environmental influences. In this work, a measurement method of fiber CD based on the principle of spectroscopic optical coherence tomography (OCT) was proposed by using a swept-source OCT system to capture interference signal, and using Wigner-Villy distribution as time-frequency analysis method to extract spectral − spatial distribution. Wavelength − OPD curve could be obtained from the distribution, where the OPD (optical path difference) is the spatial delay induced by the fiber CD, and the CD profile varying with the wavelength was finally obtained from the curve. One fiber sample was measured with 1060 and 1310 nm band systems, and another different type of fiber sample was measured with 1310 nm band system. The measured results are agreement with the claimed or theoretical results, demonstrating the feasibility of this method. It has some significant advantages and is a promising method for fiber CD measurements.

Extraction of newly soliton wave structure of generalized stochastic NLSE with standard Brownian motion, quintuple power law of nonlinearity and nonlinear chromatic dispersion

Stochastic optical solitons are a fascinating phenomenon in nonlinear optics where soliton-like behavior emerges in systems affected by stochastic noise. This study investigates the influence of Brownian motion on wave propagation in optical fibers. The propagation is modeled using a stochastic nonlinear Schrödinger equation incorporating quintuple power-law nonlinearity and nonlinear chromatic dispersion. To explore this, the improved modified extended tanh (IMET) scheme, leveraging the extended Riccati equation, is employed. This technique facilitates the extraction of various stochastic solutions, including bright, dark, and singular solitons. Furthermore, solutions in the shapes of exponential, singular periodic, and Weierstrass elliptic forms are investigated. The study looks at how the strength of noise impacts various solutions, and Matlab software is used to create 2D and 3D graphs that show the results. It has been noted that when noise intensity rises, signal level falls and surface flattens.

Mid-infrared supercontinuum generation in As2S3-circular photonic crystal fibers pumped by 4.5 µm and 6 µm femtosecond lasers

A study on As2S3 chalcogenide photonic crystal fiber (PCF) and its potential in supercontinuum generation (SCG) applications is presented. The designed fibers exhibit near-zero flattened chromatic dispersion, facilitating coherent and broad SCG utilizing femtosecond lasers at 4.5 and 6 µm wavelengths. A continuous spectrum spanning from 1.5 to 8 µm is achieved when the initial fiber is stimulated with an input power of 20 kW. With a pulse width of 100 fs and input power of 6 kW, the second fiber provides soliton-induced SCG with 2 to 15 µm spectral bandwidth. Furthermore, the integration of these large core diameter PCFs with high-power laser pulses guarantees the preservation of optical fiber integrity without damage. Consequently, these fibers hold promise for delivering SC spectra characterized by high power density, catering to a diverse range of practical applications including optical communications, spectroscopy, sensing, metrology, and calibration.

Transceiver impairment robust and joint monitoring of PDL, DGD, and CD using frequency domain pilot tones for digital subcarrier multiplexing systems

Optical performance monitoring is vital for enabling dynamically reconfigurable optical networks. This paper introduces a monitoring scheme that is robust to transceiver impairments for coherent digital subcarrier multiplexing (DSCM) systems that simultaneously monitors polarization-dependent loss (PDL), differential group delay (DGD), and chromatic dispersion (CD). In the proposed scheme, a pair of frequency domain pilot tones (FPTs) are inserted into the X and Y polarizations of the transmitted dual-polarization signal. Both the signal and the FPTs endure identical channel impairments during fiber transmission. At the receiver side, the transmitted FPTs are extracted to monitor the channel impairments. We begin by establishing a simplified system model using a single frequency tone to analyze the effects of system impairments on the frequency domain pilots. Based on this model, CD, PDL, and DGD are jointly and accurately estimated. In addition, the influences of temporal, amplitude, and phase mismatches between in-phase (I) and quadrature (Q) components of transceivers on channel impairment monitoring are completely eliminated. This achieves a channel impairment monitoring scheme that is robust to transceiver impairments. Experimental verification shows that the proposed scheme can jointly and accurately estimate a wide range of CD, PDL, and DGD. Additionally, the proposed monitoring scheme demonstrates strong robustness against transceiver impairments, rapid polarization fluctuations, and amplified spontaneous emission (ASE) noise.

Simulative analysis of carrier suppressed return to zero based symmetrical compensated optical link

Abstract Optical communication systems provide high data rates to fulfil users’ demands. In addition, the modulation format is essential to the system’s transmission quality and spectral efficiency. Furthermore, the effects of chromatic dispersion, which impair the performance and quality of transmitted signals, are mitigated using dispersion compensation techniques. In optical communication systems, dispersion compensation techniques are essential for preserving signal quality, increasing transmission distances, improving system performance, and offering network designers flexibility. These methods seek to improve signal quality and enable transmission at longer distances by reducing or eliminating the distortion brought on by dispersion. This paper uses a symmetrical compensation technique to analyze the performance of the CSRZ modulation format-based optical communication system. The research is conducted within a communication range of 150–350 km. The system is evaluated in terms of input power, filter order, and filter depth. The results indicate that the proposed system performed better at an input power of 4 dBm using a third-order filter and 60 dB filter depth.

Advanced Neural Network-Based Equalization in Intensity-Modulated Direct-Detection Optical Systems: Current Status and Future Trends

Intensity-modulated direct-detection (IM/DD) optical systems are most widely employed in short-reach optical interconnects due to their simple structure and cost-effectiveness. However, IM/DD systems face mixed linear and nonlinear channel impairments, mainly induced by the combination of square-law detection and chromatic dispersion, as well as the utilization of low-cost non-ideal transceivers. To solve this issue, recent years have witnessed a growing trend of introducing machine learning technologies such as neural networks (NNs) into IM/DD systems for channel equalization. NNs usually present better system performance than traditional approaches, and various types of NNs have been investigated. Despite the excellent system performance, the associated high computational complexity is a major drawback that hinders the practical application of NN-based equalizers. This paper focuses on the performance and complexity trade-off of NNs employed in IM/DD systems, presenting a systematic review of the current status of NN-based equalizers as well as a number of effective complexity reduction approaches. The future trends of leveraging advanced NN in IM/DD links are also discussed.

Multiple-reflections single-shot dispersion scan for fast ultrashort-pulse measurements.

A single-shot non-interferometric ultrashort-pulse measurement method based on the dispersion scan (d-scan) technique with a substantially extended time span for the pulses to be measured is presented. While single-shot d-scan is typically used for rather short femtosecond pulses, the presented multiple-reflections d-scan (MR d-scan) technique allows measurement of both short and long femtosecond pulses. Single-shot d-scan is currently limited to pulses with a maximum duration of 60 fs using a chromatic dispersion, i.e., a group delay dispersion (GDD) of 4400 fs2 at 840 nm provided by customized random nonlinear crystals. MR d-scan achieves a GDD of 31100 fs2 at 820 nm in this work, but can generally achieve an increase in GDD of up to two orders of magnitude. MR d-scan works with commonly available output couplers, does not rely on a homogeneous, precisely imaged beam profile and has an in-line configuration. As an example, long femtosecond double pulses are measured and reconstructed.

Optical soliton solutions of the third-order nonlinear Schrödinger equation in the absence of chromatic dispersion

This research paper is dedicated to the investigation of the optical soliton solutions with the power law of self-phase modulation (SPM) and the third-order dispersion (TOD), completely neglecting the chromatic dispersion (CD). The aim is focused on two main points. First, obtaining the straddled soliton solution which permits us to have bright and singular soliton by applying the new Kudryashov (nKM) scheme which was recently introduced as a simple, effective, and reliable method. Second, to observe the influences of the TOD, SPM, and inter-modal dispersion (IMD) on pure-cubic optical soliton dynamics in the absence of the CD.

Neural network-based electrical dispersion pre-compensation for a 56 Gb/s PAM-4 over an 80 km fiber in intensity-modulation and direct-detection systems.

A neural network (NN)-based electrical dispersion pre-compensation (pre-EDC) scheme in intensity-modulation and direct-detection (IM/DD) systems is proposed and experimentally demonstrated in this Letter. The scheme enables 56 Gbit/s four-level pulse amplitude modulation (PAM-4) generation at a transmitter over an 80 km single-mode fiber (SMF) transmission in the C-band. The NN is utilized to better fit nonlinear phase-amplitude transformation due to the chromatic dispersion (CD) in IM/DD systems, in place of the existing Gerchberg-Saxton (GS) iterative algorithm and linear GS-based finite impulse response (GS-FIR) non-iterative compensation schemes. The experimental results show that the measured bit error ratio (BER) can be reduced to below the 7% hard-decision forward error correction (HD-FEC) threshold of 3.8 × 10-3 with 0 dBm receiver optical power (ROP) by the NN-based non-iterative pre-EDC scheme, which also saves up to 81% of computational complexity compared to the GS-based scheme. The results indicate that our proposed scheme is promising for the CD pre-compensation at the transmitter.