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Attention deficit hyperactivity disorder (ADHD) is a serious condition that may affect life and lead to significant disruption of functional and brain pathways and psychological state. It is important to find effective therapeutic strategies to overcome this disease and effective ways to treat it. It is better for patients who suffer from this disease to monitor their psychological and health conditions from an early age. As soon as they suspect the possibility of this disease, they should take the initiative to try to see a physician to diagnose the conditions, and then conduct an appropriate brain examination. Recent studies have indicated that functional magnetic resonance imaging (fMRI), which is a special type of magnetic resonance imaging, has an effective role in detecting the disease. It relies on old and familiar electronics as it uses a strong magnetic field and radio waves, and it is increasingly challenged by the push toward stronger magnetic fields and a greater number of channels, which poses major problems for it. These problems can be avoided by using optical techniques. In addition, convolution neural networks (CNNs) are mainly involved in classifying the images captured by fMRI. This approach relies on CNNs for deep feature extraction. An architectural model of a CNN based on residual learning and depth sequencing strategies is proposed in this paper. The proposal consists of 23 layers, and three different algorithms are used to improve performance. A comparison is made between them. They are adaptive momentum (ADAM), stochastic gradient ratios with momentum (SGDM), and an algorithm based on root main square error called (RMSprop), and they are applied on the fMRI dataset. Using these optimization algorithms to classify ADHD cases, it was concluded that the accuracy of ADAM is 95%, SGDM is 96.11%, and RMSprop is 97.78%. The proposed CNN achieves an accuracy of 97.7% compared to the ResNet with 95.83% and the GoogleNet with 91.67%. [ABSTRACT FROM AUTHOR]

The rapid development of emerging technologies observed in recent years, such as artificial intelligence, machine learning, mobile internet, big data, cloud computing, and the Internet of Everything, are generating escalating demands for expanding the capacity density, and speed in next‐generation optical communications. This poses a significant challenge to existing communication techniques. Within this context, the integration of near‐infrared broadband, tunable, and high‐gain luminescent materials into silicon optical circuits or fiber architectures to transmit and modulate light shows enormous potential for advancing next‐generation communication techniques. Here, this review provides an overview of the recent breakthroughs in near‐infrared luminescent epitaxial/colloidal quantum dots, and metal‐active‐center‐doped materials for broadband optical amplifiers and tunable lasers. We also expound on efforts to enhance the bandwidth and gain of these materials‐based amplifiers and lasers, exploring the challenges associate with developing ultra‐broadband and high‐speed optical communication systems. Additionally, the potential applications in Fifth Generation Fixed Networks, integration with 5G and 6G wireless networks, compensation for current Si electronic based CMOS for high computing capability, and the prospects of these light sources for next‐generation optoelectronic devices are discussed. [ABSTRACT FROM AUTHOR]

The characteristics of an Nd:YAG multistage optical amplifier of a laser beam, the spatial parameters of which were corrected by thermal lenses formed in the active elements of each amplifier stage, were studied. Nd:YAG crystals transverse-pumped by laser diode units were used as the amplifier active elements. Removal of lens-compensators was shown to reduce the total optical losses of the amplifier and enhance its compactness. The optical losses of an optical amplifier with five amplification stages and correction of the amplified beam characteristics by thermally induced lenses of active elements were 16%; its linear dimensions, 13% less than similar indicators for a five-stage amplification system with four two-lens compensators between amplification stages. [ABSTRACT FROM AUTHOR]

Expanding gain bandwidth into the L-band for erbium-doped fiber amplifiers (EDFAs) is a crucial strategy to overcome limitations in prevalent C-band focused commercial silica-based EDFAs, significantly boosting optical network transmission capacity. Herein, we synthesized Er3+-doped broadband near-infrared emission tellurite glasses utilizing the melt quenching process, systematically exploring the impact of ZnCl 2 on the glass structure and optical properties. The 82TeO 2 –3Nb 2 O 5 –15ZnCl 2 –3Er 2 O 3 (TNZ15) glass emerged as a standout candidate for broadband amplifiers around wavelength at 1.55 μm. With escalating ZnCl 2 concentration, a discernible red shift in the emission peak wave lines was observed, accompanied by an expansion of the full width at half maximum (FWHM) from 98 nm to 106 nm. Noteworthy characteristics of all samples included exceptional thermal stability and elevated near-infrared (NIR) transmittance. Application of the Judd-Ofelt (J-O) theory facilitated the calculation of J-O parameter intensity, providing deeper insights into the optical behavior of the materials. Finally, the evaluation of TNZ15 planar optical waveguides, employing the vertical top pumping mode of two 980 nm LEDs, encompassed both the C-band (1530–1565 nm) and the L-band (1565–1625 nm). The results underscore the potential of TNZ15 glass as a promising gain material for broadband optical amplifiers and lasers, offering valuable insights into the development of next-generation optical amplification technologies. [ABSTRACT FROM AUTHOR]

Visible light communication is seen as a crucial technology within optical wireless communication systems. The technology of vehicular visible light communication holds significant importance in the context of connected vehicles. This technology can serve as a supplementary solution to vehicular systems that are based on radio frequency. In this paper, the authors conduct an analysis of the performance of both line-of-sight and non-line-ofsight vehicle-to-vehicle visible light communication systems under the effect of artificial light source and weather conditions, including clear, hazy, and foggy weather. A practical vehicular laser diode, a street lamp, and an avalanche photodiode are used to design the proposed system model. Performance enhancement for the proposed system is achieved using an optical amplifier at the receiving end. An artificial light source of light-emitting diode Corn-type is used to represent an ambient artificial light source. Different metrics such as quality factor and bit error rate are used to assess the system performance of the non-lineof-sight-vehicular communication system. The proposed line-of-sight model achieves a data rate of 25 Gbps, supporting a distance of 80 m under clear sky and hazy atmospheric conditions. For foggy weather, an attainable link distance of 70 m is achieved. The achieved results emphasize the suitability of the suggested models for vehicular applications in real world environment. [ABSTRACT FROM AUTHOR]

Abstract The rapid development of emerging technologies observed in recent years, such as artificial intelligence, machine learning, mobile internet, big data, cloud computing, and the Internet of Everything, are generating escalating demands for expanding the capacity density, and speed in next‐generation optical communications. This poses a significant challenge to existing communication techniques. Within this context, the integration of near‐infrared broadband, tunable, and high‐gain luminescent materials into silicon optical circuits or fiber architectures to transmit and modulate light shows enormous potential for advancing next‐generation communication techniques. Here, this review provides an overview of the recent breakthroughs in near‐infrared luminescent epitaxial/colloidal quantum dots, and metal‐active‐center‐doped materials for broadband optical amplifiers and tunable lasers. We also expound on efforts to enhance the bandwidth and gain of these materials‐based amplifiers and lasers, exploring the challenges associate with developing ultra‐broadband and high‐speed optical communication systems. Additionally, the potential applications in Fifth Generation Fixed Networks, integration with 5G and 6G wireless networks, compensation for current Si electronic based CMOS for high computing capability, and the prospects of these light sources for next‐generation optoelectronic devices are discussed.

This paper presents an all-optical time-extended optical code division multiplexing (TE-OCDM) system using two different optical en/decoders (E/Ds). The proposed system configuration alleviates the rigorous requirement for transmitter specifications in TE-OCDM systems. We numerically evaluate the use of PAM-4 with TE-OCDM for the first time by optimizing chip period to reduce inter-symbol interference (ISI). We utilize an analytical model and simulations to investigate the bit error rate (BER) in back-to-back scenario as a function of extinction ratio (ER) and total power contrast ratio (PCR). The fiber simulation with inline amplifications shows that 8 TE-OCDM PAM-4 signals at 12.5 Gbaud using 1274 nm could reach up to $8\times 30$ km. The total bit rate is equivalent to 200 Gbps (8 TE-OCDM users $\times 12.5$ Gbaud $\times 2$ bits/symbol) per wavelength. Further analysis of the scalability of TE-OCDM over the entire O-band through the optical E/D spectral periodicity, suggests that the feasible total bit rate that can be achieved is approximately 3 Tbps.

This paper explores, through the utilization of analytical models and simulations, the bit error rate (BER) of 400GBASE-LR8/ER8 in back-to-back configuration, considering various extinction ratio (ER) values and photodetector types. Simulation of transmission over fiber is carried out to measure chromatic dispersion (CD) penalty in each scenario. To increase the distance, we simulated a multi-span transmission with inline optical amplifiers (OAs). We mitigated the effects of CD-induced power fading by employing equalization such that the channel under test (CUT) at 1274 nm could reach $7\times 30$ km. The effects of fiber nonlinearity were also investigated for both single-channel and 3 wavelength division multiplexing (WDM) at various channel spacings. Moreover, the relationship between ER and peak-to-average-power ratio (PAPR) at different distances was investigated. An ER optimization for a highly accumulated CD multi-span fiber link with amplification was effective in improving the BER. Finally, we successfully transmitted a 26.56 GBaud 4-level pulse amplitude modulation (PAM-4) signal up to $8\times 30$ km with the optimal ER of 5 dB.

Optical amplifiers are developed to boost up the performance of the communication systems. Amplifiers such as erbium doped fiber amplifier (EDFA), RAMAN and semiconductor optical amplifier (SOA) are used for this purpose. It is mandatory to use optical amplifiers for signal transmission to long distances. In this paper, the hybrid optical amplifier EDFA-RAMAN-EDFA is proposed to enhance the signal quality received at receiver end and to initiate the efficient transmission of 8 × 10 Gbps transmission speed for wavelength division multiplexed (WDM) system. The proposed mechanism is evaluated with respect to various parameters such as quality factor, eye-height, and bit error rate (BER) and eye diagram considering various values of transmission distance ranging from 100 to 200 km. The analysis shows that the proposed mechanism has better quality factor value and minimum BER value than the traditional approach. Wider eye opening for proposed technique represents that the distortions produced in the system are least. [ABSTRACT FROM AUTHOR]

In this paper, the major aim is to enhance the bandwidth and therefore increase the capacity of the optical fibre communication system by reducing the dispersion in the fibre. Dispersion compensation is necessary to reduce losses and cost of the system. In this paper, we are basically focusing on reducing or decreasing chromatic dispersion. Chromatic dispersion is a type of dispersion in which pulse broadening occurs due to delay in different spectral components. We here make use of dispersion compensated fibre (DCF) for reducing the dispersion in the WDM system. Here, we basically use three dispersion compensated techniques (pre-compensation, post-compensation and mix compensation). The comparison in the three models of dispersion compensated technique is made in terms of transmission power vs. Q factor and also transmission power vs. Bit Error Rate. [ABSTRACT FROM AUTHOR]

In this paper, design of erbium-doped fiber amplifiers (EDFA) based 16 channel wavelength-division multiplexing (WDM) system for different pump powers and input signal levels using counter propagating pumping scheme is reported. Wavelength range between 1548 and 1560 nm in C-band with channel spacing of 0.75 nm at a bit rate of 10 Gbps are used. Input power given to all the channels is taken between −20 and −35 dBm with 3 dBm variation. Pump power levels between 100 and 500 mW at 980 nm wavelength are used. Low gain flatness with high gains and low noise figures are achieved with the proposed scheme. [ABSTRACT FROM AUTHOR]

This paper proposes a creative (3 × 3) MIMO transmission system employing multimode fibers MMF and MGDM spatial multiplexing technology. Based on spatial injection and spatial detection of light beams, the MGDM approach allows the MMF fiber to benefit from its entire bandwidth and increase its transmission capacity. To increase the quality and transmission capacity, the injection and detection parameters have been optimized. The transmission and reception conditions on the optical fiber are adjusted to ensure the transfer of high-speed services. Thus, ideal injection and detection conditions increase the quality of signals received on an MMF fiber. The proposed transmission chain decreases the modal and chromatic dispersions during transmission, for this reason, three subsystems interconnected by spatial connectors are created. To decrease interference between the modes of the same groups and to correct for attenuation of the signal on a 1200 m cable, two EDFA optical amplifiers were integrated. The simulation of the proposed chain (3 × 3) MIMO of distance 1.2 Km is realized to transmit data with a total rate of about 4.5 Gb/s (1.5 Gb/s for each user). Then, the comparison between the BER and quality factor Q performance was done for a system with and without optical amplifier.

The use of multiple transmitters in a turbulent free-space optical (FSO) communication link can enhance the systems performance because greater received power can improve receiver sensitivity. Nevertheless, the effect of having more power at the receiver can be severe. This paper investigates the impact of using multiple transmitters in preamplified FSO communication links limited by strong atmospheric turbulence (AT), amplified spontaneous emission noise, fixed path loss and pointing errors (PEs) using different preamplifier operating modes and different decision thresholding schemes. Results obtained show that regardless of the number of transmitters used, the best bit error rate (BER) performances are obtained with normalised decision threshold levels of about 0.2 and 0.5 when the decision thresholding scheme at the receiver is non-adaptive and adaptive, respectively. Also, in the strong AT regime, an additional transmitted power of about 7dB is required for the FSO communication systems under minimal PE effects to have the same performance as FSO communication systems without PE. The results also show that when the effects of PE are absent or minimal, a larger receiver would require about 15dB less transmitted power to record the same performance as a smaller receiver. However, with a non-adaptive decision threshold, smaller receivers perform better than larger receivers when the PE effects are severe. Additionally, it is shown in this paper that when the effects of PE is severe, the BER performances consistently get better with more transmitters regardless of the decision thresholding scheme employed at the receiver. However, in the absence of PEs, increasing the number of transmitters indefinitely will not always guarantee improved BER performances when the receiver decision threshold is non-adaptive. The use of multiple transmitters is particularly advantageous for applications where it is either necessary or unavoidable to use lower transmitted power.

Abstract The Gaussian approximation is commonly used to evaluate the performance of free space optical communication systems. However, other performance evaluation methods such as the saddle point approximation, Chernoff bound and the modified Chernoff bound have also been used. This paper investigates the performance of fixed and gain saturated optically preamplified communication systems limited by factors such as strong atmospheric turbulence and pointing errors using various evaluation methods. Average bit error rate results are obtained over a range of average transmitted powers for free space optical communication systems without pointing error and those with pointing error using different saturation regimes, normalised beam widths and pointing error standard deviations. Results obtained in this paper show over a propagation distance of 1500 m, a receiver diameter of 0.15 m performed better than a receiver diameter of 0.03 m when the pointing error standard deviation is 0.1. Also, a receiver diameter of 0.03 m performed better than a receiver diameter of 0.15 m when the pointing error standard deviation is 4. These results show that while larger receiving lenses performed better when pointing error effects are minimal or absent, smaller receiving lenses are better when pointing error effects are dominant. Additionally, it is shown in this paper that while fixed and gain saturated optical preamplifiers produced similar performances when the decision threshold at the receiver is adaptive, the saddle point approximation is not useful for gain saturated optically preamplified receivers. Also, results in this paper showed optimal and near-optimal adaptive decision thresholds for the modified Chernoff bound and Gaussian approximation, respectively.

A major limitation to achieving acceptable system performance in free space optical (FSO) communication systems is the presence of atmospheric turbulence (AT), which results in received signal power fluctuations. In addition to the signal power fluctuations at the receiving end, pointing errors (PEs) can also significantly impair system performance. While achieving reliable communication over long distances is desirable, it is challenging because the AT effects and PEs are more pronounced at longer communication distances. Using Monte Carlo simulation methods, the impact of amplified spontaneous emission noise, AT, PE and geometric spread on cascaded gain saturated and fixed gain optical amplifier (OA) FSO communication systems is investigated in this paper. Results are obtained for different AT regimes, normalised PE standard deviations and normalised beam widths employing non-adaptive and adaptive decision thresholding schemes at the receiver. Results obtained show that increasing the size of the receiver aperture does not have any impact on the average bit error rate (BER) when the PEs are minimal. Also, the BER performances obtained with systems using a smaller receiver aperture are better than those obtained with systems using a larger receiver aperture when PEs are significant. Results obtained also show that even though unacceptable BER performances were obtained under moderate and strong atmospheric regimes when the decision threshold of the receiver is non-adaptive, the advantage of using gain saturated OAs is still evident as gain saturated OAs performed better than fixed gain OAs when the decision threshold of the receiver is non-adaptive.

A novel promoted parallel erbium doped fiber amplifier (PP-EDFA) is numerically demonstrated and investigated, for high capacity 95 × 40 Gb/s dense wavelength division multiplexing (DWDM) transmission system. The proposed PP-EDFA is used to achieve a flat gain over wideband within communication window. The amplifier consists of two sections of erbium-doped fiber (EDF) with a total length of 6 m and requires a total pump laser power of 195 mW. The results reveal that the amplifier has flat gain of 19.8 dB with a ripple of less than 1 dB, over broad bandwidth of 80 nm. The noise figure (NF) of proposed amplifier fluctuates between 3.1 and 5.2 dB, within bandwidth of 1520–1600 nm. In contrast with parallel EDFA (P-EDFA), the proposed PP-EDFA contributes to a higher and flatter gain, as well as it requires shorter EDFs and lower pumping power. The acceptable bit error rate (BER) and signal quality results prove the feasibility of proposed PP-EDFA for applications in broadband DWDM transmission systems. The PP-EDFA can achieve a maximum transmission distance of 90 km for 95-channel DWDM transmission system. [ABSTRACT FROM AUTHOR]

This paper introduces a novel metric and approach for link quality measurement and a new algorithm for human-intervention-free optical link balancing, specifically designed for optical fiber transfer systems that require bidirectional amplification. Bidirectional amplification, essential for reciprocal optical paths to compensate fluctuations for new non-data applications like accurate time transfer and ultrastable coherent frequency transfer, introduces complexities such as feedback loops and phase inconsistencies. Our work ensures that amplified signals maintain precise time alignment, a critical aspect of any bidirectionally amplified system. Amplification processes often introduce phase noise and frequency fluctuations, which are disruptive, especially for non-data applications, necessitating a delicate balance between amplification and signal integrity. Our approach aims to provide a comprehensive solution for these complexities. Our algorithm's effectiveness is demonstrated through rigorous testing on real-world infrastructure. It successfully balances several optical links, indicating robustness when handling bidirectional amplification complexities. Furthermore, an extended use case involving a cascade of four balanced optical amplifiers demonstrates the algorithm's efficiency in more intricate scenarios. This concept has been successfully deployed and tested on one fiber segment of the Czech national research and education network. We discuss the substantial benefits observed in the newly balanced links, highlighting significant advancements in mitigating the challenges of bidirectional amplification. Our findings represent a significant step forward in optical network technologies, addressing critical issues in modern open optical communication systems. [ABSTRACT FROM AUTHOR]

This paper proposes an optimized 16-chip multi-level phase-shifted optical code division multiplexing (OCDM) en/decoder for 4-level pulse amplitude modulation (PAM-4) format by using an amplitude-shaping (AS) technique. The optimized en/decoder can efficiently suppress the crosstalk and the primary beat noise (PBN). The code detection performance for 4-OCDM PAM-4 becomes the lowest to our knowledge. The numerical bit error rate analysis and the back-to-back simulation are shown. We also successfully demonstrate by computer simulation a 100 Gbps/ $\lambda $ enabling by 12.5 Gbaud 4-OCDM PAM-4 transmission in O-band over $6\times 30$ km with in-line optical amplifiers.

Bismuth (Bi)-doped aluminosilicate, phosphosilicate, germanosilicate and high (⩾50 mol%) germanosilicate fibers have shown luminescence around 1.15 μm, 1.3 μm, 1.45 μm and 1.7 μm, respectively. Bi-doped fibers have paved the way for developing optical amplifiers and fiber lasers in the wavelength region of 1150–1500 nm and 1600–1700 nm, where it can serve a wide range of applications in astronomy, imaging, medicine and advanced optical communications. However, spectroscopic study is required to understand the nature of near-infrared (NIR)-emitting Bi active centers (BACs) to improve the efficiency of Bi-doped fiber amplifiers and lasers. In this paper, we review the luminescence properties of Bi-doped glasses as well as Bi-doped fibers with aluminosilicate, phosphosilicate, and germanosilicate glass hosts. Absorption and emission cross-sections of Bi-doped phosphosilicate fibers are reported. In addition, we review the current state of the art of Bi-doped fiber amplifiers development in the second telecom window (O-band) and in the E-band and S-band for the next-generation high-capacity optical communications.

The Gaussian approximation is commonly used to evaluate the performance of free space optical communication systems. However, other performance evaluation methods such as the saddle point approximation, Chernoff bound and the modified Chernoff bound have also been used. This paper investigates the performance of fixed and gain saturated optically preamplified communication systems limited by factors such as strong atmospheric turbulence and pointing errors using various evaluation methods. Average bit error rate results are obtained over a range of average transmitted powers for free space optical communication systems without pointing error and those with pointing error using different saturation regimes, normalised beam widths and pointing error standard deviations. Results obtained in this paper show over a propagation distance of 1500 m, a receiver diameter of 0.15 m performed better than a receiver diameter of 0.03 m when the pointing error standard deviation is 0.1. Also, a receiver diameter of 0.03 m performed better than a receiver diameter of 0.15 m when the pointing error standard deviation is 4. These results show that while larger receiving lenses performed better when pointing error effects are minimal or absent, smaller receiving lenses are better when pointing error effects are dominant. Additionally, it is shown in this paper that while fixed and gain saturated optical preamplifiers produced similar performances when the decision threshold at the receiver is adaptive, the saddle point approximation is not useful for gain saturated optically preamplified receivers. Also, results in this paper showed optimal and near-optimal adaptive decision thresholds for the modified Chernoff bound and Gaussian approximation, respectively. [ABSTRACT FROM AUTHOR]

The Japanese National Institute of Information and Communications Technology (NICT) is currently developing a high-performance laser-communication terminal for CubeSats aimed at providing a high-datarate communication solution for LEO satellites requiring transmission of large volumes of data from orbit. A key aspect of the communication system is a high-power optical amplifier capable of providing enough gain to the transmitted signals to be able to close the link on its counterpart's receiver with the smallest impact in terms of energy and power on the CubeSat's platform. This manuscript describes the development of a miniaturized 2-W space-grade 2-stage erbium-doped fiber amplifier (EDFA) compatible with the CubeSat form factor, showing the best power-to-size ratio for a space-qualified EDFA to the best of the authors' knowledge. Performance results under realistic conditions as well as full space qualification and test are presented, proving that this module can support short-duration LEO-ground downlinks as well as long-duration intersatellite links. [ABSTRACT FROM AUTHOR]

The ever increasing capacity demand on optical networks and the slowdown of improving spectral efficiency lead to the solution of utilizing more wavelength band in existing optical fibers. More and more operators will extend from C band to C+L bands, or plan to deploy C+L systems, and in future they may utilize more of other bands. This paper firstly discusses different optical layer architectures for multi-band system. Using optical components that can natively support multi-band is attractive to us, because in this way the multi-band system can be planned and operated similarly with the single-band system, which is customer friendly and potentially more economical. We address mainly three technical challenges in this paper. The first one is the wide-band fiber optical amplifier (OA). After a short review of recent research progress, we propose a hybrid erbium-doped fiber (EDF) and bismuth-doped fiber (BDF) based OA approach, and demonstrated single-stage amplification over 100 nm in extended C+L bands. The second challenge is the optical cross connect based on wavelength selective switch (WSS). It is not trivial to realize a C+L-band WSS while preventing the key optical parameters (filtering bandwidth, loss, channel isolation, etc.) to be degraded. We analyze different technical schemes, and propose an optical design based on an LCoS with a large panel size and a high-dispersion diffraction grating. The optical design and simulation on a 2×35 WSS reveals this approach can support 100-nm extended C+L spectrum and is promising for commercialization. The third challenge is the SRS induced WDM channel power inequality, which is more severe for multi-band system. We propose a solution by using OAs with a novel optical spectrum processor (OSP). Simulation and experiment showed that the power of the WDM channels can be equalized on a per span basis, which can prevent accumulation of stimulated Raman scattering (SRS) induced wavelength division multiplexing (WDM) channel power transfer and can meanwhile keep the optical signal to noise ratio (OSNR) of WDM channels well equalized. [ABSTRACT FROM AUTHOR]

Wavelength Division Multiplexing (WDM) system has been evolving and upgrading in the direction of high speed, long distance and large capacity. In recent years, with the maturity of high-speed optoelectronic devices, the research and application of beyond 400 Gbit/s has made a rapid progress. Based on the technical status and requirements of 800 Gbit/s transmission systems, this paper discusses the key technical problems, sorts out the latest developments in standardization research. The evolution and application of 800 Gbit/s optical systems is further discussed.

Wavelength Division Multiplexing (WDM) system has been evolving and upgrading in the direction of high speed, long distance and large capacity. In recent years, with the maturity of high-speed optoelectronic devices, the research and application of beyond 400 Gbit/s has made a rapid progress. Based on the technical status and requirements of 800 Gbit/s transmission systems, this paper discusses the key technical problems, sorts out the latest developments in standardization research. The evolution and application of 800 Gbit/s optical systems is further discussed.

In this work, the functioning of the Top-Hat Hot-Electron Light Emission and Lasing in a Semiconductor Heterostructure (TH-HELLISH) structure, which is based on InGaN/GaN multiple quantum wells, is investigated to employ it as an optical amplifier and wavelength converter. The heterojunction structure is formed by placing four InGaN quantum wells in the n-type GaN region between the n- and p-type GaN layers. The device with a TH-HELLISH structure was grown on a sapphire (Al 2 O 3) substrate by Metal-Organic Chemical Vapor Deposition (MOCVD) with an indium ratio of 0.16. The TH-HELLISH device was fabricated in Top-Hat HELLISH (THH) geometry with four independent n- and p-channels contacts to create a non-isotropic potential distribution in the heterojunction. The electro-photoluminescence (E-PL) technique was used to obtain light amplification and the converted wavelength. A 370 nm excitation light is absorbed by the TH-HELLISH device, subsequently leading to the emission at 440 ± 1 nm, which fulfills the role of a wavelength converter. It was also observed that TH-HELLISH operates as an optical amplifier with a 1.6-times increase in emission at 370 nm excitation. When the device is illuminated with a wavelength of 370 nm, it is monitored that the threshold electric field decreased from 0.25 kV/cm to 0.18 kV/cm, accompanied by a corresponding decrease in the threshold voltage from 12.5 V to 9.0 V. In addition, the TH-HELLISH device is found to be operated independently of the polarity of the applied voltage, and the absorption and emission regions of the device can be switched by changing the polarity of the applied voltage, therefore behaving as a bi-directional wavelength converter and optical amplifier. • TH-HELLISH device is investigated to employ it as an optical amplifier and wavelength converter at room temperature. • A 370 nm excitation light is absorbed by the TH-HELLISH device, subsequently leading to the modulation of 440 ± 1 nm light. • It was also observed that TH-HELLISH operates as an optical amplifier with a 1.6-times increase in emission at 370 nm excitation. • It is observed that the threshold electric field decreased when the device is illuminated with a wavelength of 370 nm. [ABSTRACT FROM AUTHOR]

Free Space Optics (FSO) is one of the most effective solutions for high-speed wireless communication under air turbulence or environmental hazard, while radio over fiber (RoF) shows better performance for long-distance communication. Wavelength division multiplexing (WDM) is the most effective method for multichannel fiber to the home (FTTH) networks. The main objective of this study is to integrate the system performance with RoF and FSO links in order to improve network flexibility and expand the wireless network's coverage in the presence of weather hazards. The signal is generated by an array of optical lasers in the simulation and propagates through a maximum 3 km WDM-FSO link and a long fiber optic backhaul. As a result, each WDM channel can transmit 2.5 Gb/s data, getting a total data rate of 40 Gb/s using 16 WDM channels with a channel spacing of 100 GHz (0.8 nm). Finally, in order to improve the system performance, different optical amplifiers such as EDFA, SOA, and Raman are used in this hybrid WDM network. [ABSTRACT FROM AUTHOR]

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In this work, Er3+-doped phosphate glass with good flatness of the emission spectrum of the L+ band was prepared by optimizing the content of BaO. The absorption and emission spectra were measured. Increase of BaO content is conducive to the broadening of the emission spectrum in the L+ band. The dependence of flatness with Raman intensity has been shown by linear fitting. The results show that B31 sample has best flatness of the emission spectrum in the L+ band. It is showed that the largest emission cross-section at 1630 nm is 0.0529 × 10-20 cm2 and higher than other Er3+-doped phosphate glass. Decay curves of the 4I13/2 level were measured and the longest fluorescent lifetime is 10.18 ms and longer than other glass except germinate glass. The broadening of the Er3+-doped phosphate glass spectrum of the L+ band has been achieved successfully, which provides a reference for the material of optical amplifiers.

This paper demonstrates a wavelength-division-multiplexed passive optical network (WDM-PON) scheme based on novel reconfigurable optical amplifiers (ROAs). The measured switching characteristics of the ROA3 constructed with a 2 × 2 crossbar optical switch and a four-port reversible optical circulator (OC) and a conventional EDFA can meet the requirements of most network management and surveillance. The self-made four-port reversible OC's response time is less than 2 ms, and its insertion losses are about 1 dB or less for all the transmission paths and switching states. An optimal design of ROAs is proposed and evaluated for bidirectional optical amplifier protection, in which ROA3 has an EDF length of 7.5 m long with a 1480 nm pump laser and possesses a backward or forward pumping configuration with the corresponding pump power of 200 mW or 50 mW. We verified the scheme's feasibility through a simulation of WDM-PON systems with 40 downstream and upstream channels. This scheme enables the intelligent protection switching in practical operation scenarios for high-capacity multi-wavelength networks. [ABSTRACT FROM AUTHOR]

In this work, Er3+-doped phosphate glass with good flatness of the emission spectrum of the L+ band was prepared by optimizing the content of BaO. The absorption and emission spectra were measured. Increase of BaO content is conducive to the broadening of the emission spectrum in the L+ band. The dependence of flatness with Raman intensity has been shown by linear fitting. The results show that B31 sample has best flatness of the emission spectrum in the L+ band. It is showed that the largest emission cross-section at 1630 nm is 0.0529 × 10-20 cm2 and higher than other Er3+-doped phosphate glass. Decay curves of the 4I13/2 level were measured and the longest fluorescent lifetime is 10.18 ms and longer than other glass except germinate glass. The broadening of the Er3+-doped phosphate glass spectrum of the L+ band has been achieved successfully, which provides a reference for the material of optical amplifiers. [ABSTRACT FROM AUTHOR]

We investigate the random intensity noises that occur in forward-pumped distributed Raman amplifier systems. First, we show pump-to-signal intensity noise transfer characteristics, which strongly depend on the group velocities of pump light and signal light in optical fiber used as a gain medium. When signal light is in the C-band, dispersion shifted fiber (DSF) transfers much larger noise compared with standard single mode fiber. Next, we discuss the origin of the noise induced in pump light. We define the concept of “synthesized polarization” and show that fluctuation in the state of synthesized polarization (SOSP) can induce a large gain instability even if the relative intensity noise (RIN) of each pump laser source is negligible experimentally. Next, we propose a novel optical depolarizer for pump light. It can simultaneously depolarize pump light generated by multiple laser sources. Moreover, it can manage optical phases precisely to suppress the gain instability induced by the fluctuation in SOSP. Finally, we present a measurement of the Q factor of a 16-QAM signal (32 Gbaud) after 35-km transmission, with and without a forward-pumped Raman amplifier. Two pump laser sources with RINs of –134 to –126 dB/Hz were depolarized by the proposed depolarizer, and the generated on-off gain was 7 dB. Though amplified signal light was in the C-band and the gain medium was DSF, 16-QAM transmission specifications were successfully improved, and acceptable noise was observed for 5 hours operation. [ABSTRACT FROM AUTHOR]

In this paper, the synthesis, structure, and optical analysis of Er3+‐doped antimony‐silica glass system are reported. The hybridization of Si with Sb ions is found to be favorable for reducing the phonon energy of the glass system. The optical properties, including the emission intensity and bandwidth, can be simultaneously improved. Notably, the full width at half maxima (FWHM) of near‐infrared emission from Er3+ can be broadened from 61 to 82 nm. Furthermore, the antimony‐silica glass fiber is successfully prepared, and the luminescence and gain performance of the fiber are characterized. The antimony‐silica glass exhibits excellent fiber‐forming ability, and the obtained fiber shows excellent gain performance. The results suggest that antimony‐silica glass is a promising gain material for fiber amplifier and laser. [ABSTRACT FROM AUTHOR]

Wavelength-dependent power excursions in gain-controlled erbium doped fiber amplifiers (EDFA) is a challenging issue in optical networks. We investigate a launch channel power control method using reinforcement learning (RL) to mitigate the power excursions of EDFA systems. A machine learning engine is developed, trained and evaluated with four different policy-gradient RL algorithms that are compared according to two main criteria: achieved power excursion reduction and learning time. Different scenarios are considered with 12-, 24-, 40- active channels at fixed wavelengths and with variable number of active channels (between 12 and 64) assigned randomly at different wavelengths during RL process. We show 62% power excursion reduction in the 40-channel scenario and 28% in the variable scenario, which demonstrates the promising role of online RL approach for controlling power excursion in EDFA systems. [ABSTRACT FROM AUTHOR]

With the advancement of nanoscale semiconductor technology,semiconductor optical amplifiers are used to amplify and process all-optical signals. Inthis paper, with the aim of calculating the gain of quantum dot semiconductor opticalamplifier (QD-SOA), two groups of rate equations and the optical signal propagatingequation are used in the active layer of the device. For this purpose, the relatedequations are presented coherently. In our model, the rate equations that are ordinarydifferential equations (ODE) are solved by the Runge-Kutta method. The rate equationsare based on the occupation probabilities of the energy levels instead of the carrierdensities. On the other hand, the signal propagating equation is a partial differentialequation (PDE) and is solved by using the SLICE technique. Therefore, a suitablesolution for numerical modeling is presented. Based on the presented method, modelingis implemented in the MATLAB environment. The modeling results show a remarkableaccuracy of the model. Also, the proposed model is simple and the runtime is too shortin comparison with other similar models.

Experimental studies on gain and saturation of a Yb-doped double-cladding fiber amplifier accompanied with and interpreted by rigorous numerical simulations are presented. The saturation power, the value, and the spectral asymmetry of the output signal are experimentally characterized in both pulsed and continuous wave (CW) operation, and then, verified and interpreted numerically. Power conversion efficiency and quantum conversion efficiency of the amplifier are measured to be up to 55% and 58%, respectively. It is the first time, to the best of our knowledge, to demonstrate a numerical model for the pulsed operation based on the interaction of vector coupled nonlinear Schrodinger equations and the rate equations of the Yb-doped double-clad fiber taking into account all high-order dispersion parameters and the variation of gain coefficient during pulse propagation. A good agreement between numerical and experimental results is observed providing interpretations to the results. The numerical models and the experimental demonstrations provide guidance for the design and analysis of Yb-doped double-cladding fiber amplifiers both in pulsed and CW operation.

This paper demonstrates a wavelength-division-multiplexed passive optical network (WDM-PON) scheme based on novel reconfigurable optical amplifiers (ROAs). The measured switching characteristics of the ROA3 constructed with a 2 × 2 crossbar optical switch and a four-port reversible optical circulator (OC) and a conventional EDFA can meet the requirements of most network management and surveillance. The self-made four-port reversible OC’s response time is less than 2 ms, and its insertion losses are about 1 dB or less for all the transmission paths and switching states. An optimal design of ROAs is proposed and evaluated for bidirectional optical amplifier protection, in which ROA3 has an EDF length of 7.5 m long with a 1480 nm pump laser and possesses a backward or forward pumping configuration with the corresponding pump power of 200 mW or 50 mW. We verified the scheme’s feasibility through a simulation of WDM-PON systems with 40 downstream and upstream channels. This scheme enables the intelligent protection switching in practical operation scenarios for high-capacity multi-wavelength networks.

We present in this work a thulium-doped fiber laser with ring cavity in continuous wave operation. The pumping is based on Erbium-doped fiber lasers at 1600 nm. The operation with continuous wave pumping and pulsed pumping has been studied, obtaining efficiencies of 35% and 38 % respectively. These efficiencies are higher than the known efficiencies pumping at 1600 nm. The emission spectrum has two peaks located between 1910 nm and 1920 nm. As the same time, we present measurements of the spectral gain of the thulium-doped fiber. As an example, we have implemented a thulium-doped fiber amplifier, demonstrating to be able to amplify a supercontinuum spectrum in the interval between 1800 nm and 2000 nm, which could be used to pump highly nonlinear fibers with a zero-dispersion wavelength in this region. [ABSTRACT FROM AUTHOR]

Optical communications are the key enabler for the ever-increasing traffic growth as they allow multiplexing a number of carriers onto a single optical fiber. However, network deployments are becoming more challenging due to the large bandwidth increments. Indeed, the fiber planning process is a slow, costly, and strategic activity for network operators, who must decide where to rent or deploy additional capacity. Depending on the long-term view, the network operator will define a fiber plan which may require high capital expenditure (CAPEX) investments to deploy additional multiple fiber pairs between central offices. During the last few years, C&L-band technologies have evolved to a point where they are now strong candidates to extend the fiber lifetime of these high capacity links. This article aims to present the evolution of C&L-band systems from a network design perspective, covering transmission and optical amplifier capabilities, demand optimization phase, showing a record demonstration of 56.4 Tb/s C&L-band 800 km transmission using commercial C&L-band system technology. [ABSTRACT FROM AUTHOR]

In this paper, a semiconductor optical amplifier (SOA) based 1064 nm fiber ring laser with 63.56 dB optical signal-to-noise ratio (OSNR) is demonstrated. The stable performance is measured for six hours with lasing peak variation of ≤±0.115 dB and wavelength variation of ≤±0.006 nm. Combining the fiber ring laser with fiber Bragg gratings (FBGs), the SOA based fiber ring laser is applied to sense stretch, squeeze, and temperature variation. The results show high linearity, which is suitable for interpolation method prediction and evaluation. A large dynamic range of up to 10 km is also demonstrated for remote sensing applications. [ABSTRACT FROM AUTHOR]