Modern Optical Communication Systems Research Articles

Plasmonic electro-optic modulators on lead zirconate titanate platform

Abstract The advancement in material platforms exhibiting strong and robust electro-optic effects is crucial for further progress in developing highly efficient and miniaturized optoelectronic components with low power consumption for modern optical communication systems. In this work, we investigate thin-film lead zirconate titanate (PZT) substrates grown by a chemical solution deposition technique as a potential platform for on-chip plasmonic electro-optic modulators. A high modulation depth (>40 %) is achieved with 15 μm-long electro-optic directional coupler modulators. An unusual cutoff in the modulation frequency response at ∼200 kHz is observed and further studied with respect to possible reorientation effects. Second-harmonic generation signals are found influenced by the externally applied electric field, indicating that the domain reorientation effect can be responsible for the unusual frequency response observed.

THE NARROW-BAND FILTER BASED ON A MAGNETOPHOTONIC CRYSTAL INVOLVING LAYERS WITH HYPERBOLIC DISPERSION LAWS

Subject and Purpose. Narrow-band filters are among the basic components of modern communication systems, instruments for spectros- copy, high-sensitivity sensors, etc. Photonic crystal structures open up broad possibilities for creating compact-sized, narrow-band filters in the optical and terahertz ranges. Tuning of spectral characteristics of photonic crystal filters is usually carried out through introduction of certain elements into their structure that are sensitive to external electric and magnetic fields. This work has been aimed at investigating electrodynamic characteristics of one-dimensional magnetophotonic crystals with structural layers characterized by "hyperbolic" disper- sion, and suggesting a multichannel, narrow-band filter on their base. Methods and Methodology. The dispersion equation for excitations in an infinite magnetophotonic crystal has been obtained within the framework of the Floquet-Bloch theory, with the use of fundamental solutions of Hill’s equation. The transfer matrix approach has been used to obtain an analytical expression for the transmission coefficient. Results. The band diagram of the one-dimensional magnetophotonic crystal has been analyzed for the case where one of the layers on the structure’s spatial period is characterized by a hyperbolic dispersion law. The areas of existence of surface wave regimes have been found for such layers for the case of normal incidence of the wave upon the finite-seized magnetophotonic crystal. Frequency dependences of the transmission coefficient are characterized by a set of high-Q resonant peaks relating to Fabry-Perot resonances in a periodic struc- ture of finite length. Conclusions. Application of a finite-seized, one-dimensional magnetophotonic crystal is considered as of a means forachieving mul- tichannel optical filtering and formation of a frequency comb. Expressions for the dispersion equation and transmission coefficient have been obtained within the framework of the Floquet-Bloch theory and with the use of the transfer matrix. The feasibility of surface mode excitation has been shown for gyrotropic layers of the periodic structure characterized by a hyperbolic dispersion law, for the case of nor- mal incidence upon the magnetophotonic crystal. The spectral response of the filter contains narrow-band peaks with a high transmission efficiency. By increasing the number of the structure’s periods it is possible to form a frequency comb, which effect can be useful for appli- cations in metrology and modern optical communication systems.

Novel Optical Kerr Switching Photonic Device Based on Nonlinear Carbon Material.

In the context of current communication systems, there is an urgent demand for more efficient and higher-speed optical signal processing technologies. Researchers are actively exploring new materials and devices to harness nonlinear optical phenomena, seeking advancements in this field. Nonlinear carbon materials, especially promising 2D materials, have garnered attention for their potential interaction with light and have become integral to the development of all-optical signal processing devices. This study focuses on utilizing a photonic device based on a nonlinear Au/CB composite material for optical Kerr switching. The application of Au/CB as a nonlinear material in the Kerr switch represents a noteworthy advancement, demonstrating its capability to modulate optical signals. By appropriately applying a pump light, the study achieves optical Kerr switching with an extinction ratio of approximately 15 dB in the fully off state of the signal light carrying a 10 GHz analog signal, marking a pioneering achievement in the field to the best of our knowledge. The experimental results, encompassing extinction ratios, signal control, and stability, not only validate the feasibility of this technology but also underscore its potential applicability within optical communication systems. The successful modulation and control of a 10 GHz analog signal showcase the practicality and effectiveness of the Au/CB-based optical Kerr switch. This progress contributes to the continuous evolution of optical Kerr switching, a crucial component in modern optical communication systems. Therefore, we believe that the Au/CB-based optical Kerr switch is an exceptionally promising and stable all-optical signal processing device. As the contemporary communication landscape evolves, the integration of this technology holds the potential to enhance the efficiency and speed of optical signal processing.

Tailored Dispersion and Nonlinear Effects in Flint Glass Honeycomb PCF for Optical Communication

This paper describes a highly nonlinear flint glass-based honeycomb photonic crystal fiber (FGH-PCF) with a wavelength of 1550 nm. The PCF’s distinctive honeycomb lattice structure, combined with the nonlinear capabilities of flint glass, enables a wide range of nonlinear optical applications. To adjust the PCF's dispersion and nonlinear effects, numerical simulations and optimization approaches were used. To achieve maximum performance, fabrication procedures were carefully regulated. Dispersion values of −436.6 ps/(nm.km) for x polarization and −448.1 ps/(nm.km) for y polarization were verified by experimental characterization. The PCF displayed low confinement losses of 2.289 dB/cm (x polarization) and 4.935 dB/cm (y polarization), as well as birefringence of 2.202×10-3. The PCF measured 558.8 and 547.9 W-1 km-1 for x and y polarization, respectively, indicating a high nonlinear coefficient. The highly nonlinear FGH-PCF shows promising potential for nonlinear optical applications such as four-wave mixing, supercontinuum generation, frequency conversion, and parametric amplification. This research paves the way for compact and efficient nonlinear devices in modern optical communication systems and other cutting-edge technologies.

Modelling and numerical analysis of combined dual impact of SRS and FWM on the performance of upstream and downstream channels of a novel UDWDM/DWDM-PON

Wavelength division multiplexing (WDM) is an important method in modern optical communication systems for both long-haul and access networks. Particularly, after being standardized by Telecommunication Standardization Sector of International Telecommunication Union (ITU-T), WDM passive optical network (WDM-PON) becomes a considerable choice for fronthaul implementations of 5G networks. Stimulated Raman scattering (SRS) and four-wave mixing (FWM) are crucial nonlinear impacts that significantly limit the performance of WDM-based optical fiber communication systems. In this paper, an ultra-dense/dense WDM-PON (UDWDM/DWDM-PON) architecture has been proposed and combined dual impact of SRS and FWM on performances of upstream channels (USCs) and downstream channels (DSCs) of the proposed UDWDM/DWDM-PON has been numerically analyzed. USCs have been assumed to operate in 1310 nm region while operating wavelength region of DSCs has been taken as 1550 nm. Simulations have been performed on both UDWDM-PON architectures with 3.125 GHz and 6.25 GHz channel spacings and DWDM-PON architectures with channel spacings between 12.5 GHz and 100 GHz. 2x15-channel and 2x63-channel system structures have been considered in simulations. Signal-to-crosstalk ratio (SXR) has been chosen as performance parameter and its variation with channel input powers, channel spacings and channel lengths have been simulated for both USCs and DSCs of 2x15- and 2x63-channel UDWDM/DWDM-PONs. Results show that the proposed UDWDM/DWDM-PONs using single G.652 fiber can exhibit a reliable communication with minimum 23 dB SXR performance under combined dual impact of SRS and FWM unless some highlights about input powers and channel lengths mentioned in the paper are neglected.

Ferroelectrically Modulated and Enhanced Photoresponse in a Self-Powered α-In2Se3/Si Heterojunction Photodetector.

Photodetectors have been applied to pivotal optoelectronic components of modern optical communication, sensing, and imaging systems. As a room-temperature ferroelectric van der Waals semiconductor, 2D α-In2Se3 is a promising candidate for a next-generation optoelectronic material because of its thickness-dependent direct bandgap and excellent optoelectronic performance. Previous studies of photodetectors based on α-In2Se3 have been rarely focused on the modulated relationship between the α-In2Se3 intrinsic ferroelectricity and photoresponsivity. Herein, a simple integrated process and high-performance photodetector based on an α-In2Se3/Si vertical hybrid-dimensional heterojunction was constructed. Our photodetector in the ferroelectric polarization up state accomplishes a self-powered, highly sensitive photoresponse with an on/off ratio of 4.5 × 105 and detectivity of 1.6 × 1013 Jones, and it also shows a fast response time with 43 μs. The depolarization field generated by the remanent polarization of ferroelectrics in α-In2Se3 provides a strategy for enhancement and modulation of photodetection. The negative correlation was discovered because the enhancement photoresponsivity factor of ferroelectric modulation competes with the photovoltaic behavior within the α-In2Se3/Si heterojunction. Our research highlights the great potential of the high-efficiency heterojunction photodetector for future object recognition and photoelectric imaging.

Effect of Some Parameters on Optical Soliton Pulses in Photonic Crystal Fibers

Fiber optics have been greatly enhanced by photonic crystal fibers based on microstructured air-glass designs. On the one hand, such fibers enable very tight light confines in a small mode shape region, resulting in significantly improved alternative options between light and dielectric medium. Photonic crystal fibers, on the other hand, allow light to be guided via air core instead of glass. As a result, the latter form of fiber decreases optical nonlinearities in ways that classic fiber designs cannot. The chirp effect and dispersion of photonic crystal fibers with super-Gaussian pulses during various pulses durations are examined in this paper in both normal and anomalous dispersion patterns. The chirp effect and fiber dispersive nonlinear effects are investigated. For this study, a mathematical model of the solution of a nonlinear equation involved the split-step Fourier method. Peak power was reduced for broad pulses. When the magnitude of the super-Gaussian pulse increased proportionally, pulse constriction was also noticeable, Furthermore, the results reveal that an anomalous dispersion system was superior to a regular dispersion system for pulse . The experimental findings will facilitate further research into more understanding of photonic crystal fibers, and to improve data speeds in modern optical communication systems

High-responsivity dual-frequency hot-electron photodetectors with magnetic polaritons beneath metal grating strips

In this work, near-infrared Au-grating/MoS2/Au hot-electron photodetectors (HEPDs) with magnetic polaritons (MPs) beneath the top Au grating strips are designed and proposed. The MPs are formed by the near-field coupling between the grating and the bottom Au film, which achieves a light absorption greater than 99.5% at 1550 nm for the HEPDs. The simulations show that the absorption wavelength can be tuned independently and widely to cover the whole short wavelength infrared band by adjusting width of the grating strips, and the near-perfect absorption characteristics can be maintained. Then, dual-frequency HEPDs with two different grating strip widths in one cycle of the Au-grating are designed. Without external bias, the theoretical responsivities as high as 11.2 mA W−1 at 1200 nm and 6.2 mA W−1 at 1550 nm are achieved for the HEPDs by a three-step electrical model. In addition, a modulation distance between the two absorption peak positions of the HEPDs could be larger than 1100 nm. This provides a new idea for the realization of high-responsivity near-infrared HEPDs for arbitrary dual-band detection, which has great potential in modern optical communication systems.

Formation of double-hump solitons and their applications in optical communication systems

Optical communication system with optical solitons has the characteristics of low relay cost, low bit error rate and long relay distance. The modern optical communication system is developing towards large capacity, long distance and high speed. The width of optical pulse has been increased to femtosecond. With the increase of signal frequency, the effects of dispersion and nonlinear involved in it become more and more complex. Therefore, using femtosecond soliton communication to overcome these problems has urgent practical significance. In this paper, starting from the coupled nonlinear Schrödinger equation describing soliton transmission, we use the bilinear method to study the transmission characteristics and interaction of double-hump solitons under the interaction of dispersion and nonlinear effects, solve the problem of mutual interference between adjacent optical solitons, and realize the non-interaction transmission between adjacent solitons. This conclusion lays a theoretical foundation for the optical soliton propagation without distortion and interference in optical communication systems.

All-fiber optical nonreciprocity based on parity-time-symmetric Fabry-Perot resonators

Nonreciprocal light transmission in an all-fiber platform is critical in modern optical communication systems, which can avoid the packaging and integration process required in current devices based on magneto-optical or nonlinear materials. Here we propose and demonstrate an all-fiber device with remotely tunable isolation ratio and switchable isolation direction by constructing two mutually coupled Fabry-Perot (FP) resonators with identical geometry and balanced gain and loss. By controlling the pumping power, strong optical nonreciprocity is achieved due to gain saturation nonlinearity that is enhanced by the broken parity-time symmetry. Nonreciprocal light transmission with an isolation ratio of 8.58 dB at 1550 nm and an insertion loss of 2.5 dB is demonstrated. The isolation bandwidth is 125 MHz, which is determined by the bandwidths of the two coupled FP resonators. The proposed approach provides an all-fiber solution for a remotely tunable and optically controlled isolator, which may find applications in software-defined optical networks.

A Class of Tiled Diagonal Zipper Codes With Multiple Chains

Tiled diagonal zipper codes (TDZCs) are shown to be a class of competitive forward error correction codes in modern optical fiber communication systems. This paper introduces the multichain tiled diagonal zipper codes (MC-TDZCs) in which multiple TDZC chains are coupled together in a cyclic manner. Firstly, we present the encoding and decoding algorithms of the proposed MC-TDZCs. Secondly, we analyze the graphical structures of the minimum stall patterns of the MC-TDZCs using directed graphs. Thirdly, we derive the multiplicities of these minimum stall patterns. The analytical results show that the size of the minimum-sized stall patterns of the proposed MC-TDZCs is larger than that of the underlying TDZC counterpart. Finally, we present simulation results to show the performance advantages of the proposed MC-TDZCs under the constraint of equal storage size for decoding. Particularly, a rate 0.94 MC-TDZC with four chains shows more than four orders of magnitude improvement in bit error rates compared to its underlying TDZC counterpart.

Data-Driven Method for Nonlinear Optical Fiber Channel Modeling Based on Deep Neural Network

Recently, data-driven fiber channel modeling methods based on deep learning have been proposed in optical communication system simulations. We investigate a new data-driven method based on the deep neural network (DNN) to model the nonlinear fiber channel with the characteristics of attenuation, chromatic dispersion, amplified spontaneous emission noise, self-phase modulation (SPM), and cross-phase modulation (XPM). Demonstration in multiple dimensions, including constellations, optical waveforms, spectra, and the normalized mean square error, shows that DNN can approach the transfer function of the fiber channel accurately. Additionally, the DNN shows good generalization for modulation formats and wavelength schemes. Besides, the time complexity of DNN-based method for modeling nonlinear fiber channel is reduced significantly (96.5%) compared to the conventional model-driven method, which is based on the split-step Fourier method. This work demonstrates that the DNN can model accurately the nonlinear fiber channel that takes account of both SPM and XPM. Therefore, it can contribute to the application of data-driven methods in modern optical communication system simulations and designs.

ВЛИЯНИЕ ЭФФЕКТА ЧЕТЫРЕХВОЛНОВОГО СМЕШЕНИЯ НА КАЧЕСТВО ПЕРЕДАЧИ ОПТИЧЕСКИХ СИГНАЛОВ

Currently, almost everyone uses information transmission services. To meet all the needs, the power and data transmission rates in modern optical communication systems have reached enormous values. At high transmitted powers, undesirable nonlinear effects occur in the optical fiber, which reduce the efficiency of the entire optical system. Nonlinear effects in optical fibers impose various limitations on the communication channel, and understanding such effects is practically necessary. Four-wave mixing is the dominant nonlinear effect present in optical networks with wavelength-division multiplexing. The general provisions on the mechanism of manifestation of four-wave mixing in an optical fiber are substantiated. The article presents a variant of the classification of nonlinear effects. The types of four-wave mixing are considered. The paper shows the dependence of the FWM effect on the number of signals in the path and the phase ratio between the interacting signals. The authors propose ways to increase the reliability of optical signal transmission in fiber-optic transmission systems.

Theoretical Analysis of The Super-Gaussian Pulse Propagation in Solid-Core Photonic Crystal Fiber

Fiber optics have been greatly enhanced by photonic crystal fibers based on microstructure air-glass designs. On the one hand, such fibers enable highly tight light confine in a small mode shape region, resulting in significantly improved alternative options between light and dielectric medium. Photonic crystal fibers, on the other hand, allow light to be guided via air cores instead of glass. As a result, the latter form of fiber decreases of optical nonlinearities in ways that classic fiber designs cannot. The chirp effect and dispersion of photonic crystal fibers with super-Gaussian pulses during various pulses durations are examined in this paper. In both normal and anomalous dispersion patterns. As done the chirp effect and fiber dispersive nonlinear effects are investigated. For this study, the mathematical model of the solution of nonlinear equation is split-step Fourier method. The peak power reduces for broad pulses. When the magnitude of the super-Gaussian pulse increasing proportion, the pulse constriction is also noticeable, Furthermore, these results disclose important facts, such as the fact that an anomalous dispersion system is superior to a regular dispersion system for pulse. These findings are incredibly useful in learning more about photonic crystal fiber and improving data speeds in modern optical communication systems.

On the Kurtosis of Modulation Formats for Characterizing the Nonlinear Fiber Propagation

Knowing only two high-order statistical moments of modulation symbols, often represented by the fourth moment called “kurtosis”, the overestimation of nonlinear interference (NLI) in a Gaussian noise (GN) model due to Gaussian signaling assumption can be corrected through an enhanced GN (EGN) model. However, in some modern optical communication systems where the transmitted modulation symbols are statistically correlated, such as in systems that use probabilistic constellation shaping (PCS) with finite-length sphere shaping, the kurtosis-based EGN model produces significant inaccuracies in analytical prediction of NLI. In this paper, we show that for correlated modulation symbols, the NLI can be more accurately estimated by substituting a statistical measure called windowed kurtosis into the EGN model, instead of the conventional kurtosis. Remarkably, the optimal window length for windowed kurtosis is found to be consistent with the self-phase modulation (SPM) and cross-phase modulation (XPM) characteristic times in various system configurations. The findings can be used in practice to analytically evaluate and design NLI-tolerant modulation formats.

Pulse Compressor based on Tunable Etched PM-MZI underwater Communication System

Underwater Optical Communication System (UOWC) has been used nowadays in modern optical communication systems. It has many militaries, industry, and scientific community applications. A compressed laser source was obtained in this experiment after using a pulse duration of 9 ns, peak power of 1.2297 mW, full width half maximum (FWHM) 286 pm, and a wavelength of 1546.7 nm. This work used three designs Single, cascaded, and nested, designed based on polarization-maintaining Mach-Zander interferometer (PM-MZI) this fiber etched. All three designs are tested in two different ways. The first structure consists of three variable lengths of (PMF) (8, 16, and 24) cm with etching 30 min. The Second structure has three constants of (PMF) 10 cm lengths with different etching times (10, 20, and 30) min correspond to (112.3, 86.7, 72.8) μm cladding diameter respectively. Four samples of water (seawater, shallow water, coastal water, distilled water) are regarded. This paper studies the effect of the four water samples placed on the fibers used in two structures within different three designs. The results obtained were single fiber, the compression factor FC = 1.1 when the PMF length is 24 cm and thickness cladding is 72.8 μm under shallow water. The peak power is (0.11) PW, the central wavelength is 1546.427 nm, and FWHM is 256 pm. while the cascaded shows FC = (1.5) in distilled water with variable fiber lengths. Finally, in design nested, FC is (1.2) in shallow water with constant fiber lengths.

Femtosecond Laser-Fabricated Photonic Chips for Optical Communications: A Review

Integrated optics, having the unique properties of small size, low loss, high integration, and high scalability, is attracting considerable attention and has found many applications in optical communications, fulfilling the requirements for the ever-growing information rate and complexity in modern optical communication systems. Femtosecond laser fabrication is an acknowledged technique for producing integrated photonic devices with unique features, such as three-dimensional fabrication geometry, rapid prototyping, and single-step fabrication. Thus, plenty of femtosecond laser-fabricated on-chip devices have been manufactured to realize various optical communication functions, such as laser generation, laser amplification, laser modulation, frequency conversion, multi-dimensional multiplexing, and photonic wire bonding. In this paper, we review some of the most relevant research progress in femtosecond laser-fabricated photonic chips for optical communications, which may break new ground in this area. First, the basic principle of femtosecond laser fabrication and different types of laser-inscribed waveguides are briefly introduced. The devices are organized into two categories: active devices and passive devices. In the former category, waveguide lasers, amplifiers, electric-optic modulators, and frequency converters are reviewed, while in the latter, polarization multiplexers, mode multiplexers, and fan-in/fan-out devices are discussed. Later, photonic wire bonding is also introduced. Finally, conclusions and prospects in this field are also discussed.

Simulation Study of In-Phase and Out-Phase Enhanced Absorption of Graphene Based on Parity–Time Symmetry One-Dimensional Photonic Crystal Structure

In the field of modern optical communication systems and photoelectric detection, new components with complex functions and excellent performance are urgently needed. In this paper, a graphene-based parity–time (PT) symmetry structure is proposed, which is achieved by preparing the graphene layer on the top of a PT-symmetry photonic crystal. The transfer matrix method was used to calculate the absorptance of graphene, and a unique amplified absorption effect was found. Meanwhile, the peak value and wavelength position of the absorption can be modulated via the applied electric field. The results show that by adjusting the negative square-wave electric field from −3.5 × 10−5 to −13.5 × 10−5 V/nm (or the positive square-wave electric field from 2 × 10−5 to 11 × 10−5 V/nm), the proposed structure can achieve in-phase (or out-phase) enhanced absorption for the communication wavelength 1550 nm, with the absorption of graphene from 17 to 28 dB (or 30 to 15 dB) corresponding to the square-wave modulation electric field change. The modulable absorption properties of graphene in the structure have potential in optoelectronic devices and optical communication systems.

High-speed electro-optic modulator based on silicon nitride loaded lithium niobate on an insulator platform.

Electro-optic (EO) modulators, which convert signals from the electrical to optical domain plays a key role in modern optical communication systems. Lithium niobate on insulator (LNOI) technology has emerged as a competitive solution to realize high-performance integrated EO modulators. In this Letter, we design and experimentally demonstrate a Mach-Zehnder interferometer-based modulator on a silicon nitride loaded LNOI platform, which not only takes full advantage of the excellent EO effect of LiNbO3, but also avoids the direct etching of LiNbO3 thin film. The measured half-wave voltage length product of the fabricated modulator is 2.24 V·cm, and the extinction ratio is ∼20dB. Moreover, the 3 dB EO bandwidth is ∼30GHz, while the modulated data rate for on-off key signals can reach up to 80 Gbps.

Simulation of optical triode based on PT symmetric structure under electro-optic modulation

In modern microwave and optical communication systems, it is urgent to develop optical components with the same performance as electronic components. In this paper, a PT-symmetric structure including electro-optical medium is designed to construct optical triode. It is found that the structure has a pole effect of amplification under certain parameters. The frequency of the incident wave at the pole is taken as the carrier frequency, and the electrical signal is modulated into an optical signal. By setting the bias electric field, the modulated optical signal can be amplified in phase and out phase, and even by doubling frequency, and a new optical triode model is obtained. The designed model will play an important role in the design of optical integrated devices.