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Random fiber lasers (RFLs), a new variety of random lasers, have become a vigorous research spot over the past decades. RFLs possess superiorities in efficiency, structural flexibility, directionality, cost, etc. Particularly, RFLs are discovered to be good platforms for the construction of various forms of high‐performance lasers. Herein, recent progress in the spectral manipulation of RFLs and the applications of spectral‐tailored RFLs are reviewed. Both theoretical and experimental investigations of the unique spectral properties of RFLs up to now are presented. The superior wavelength flexibility of RFLs which can achieve any desired lasing wavelength in the 1–2.1 µm band is highlighted. Via spectral manipulation, RFLs have shown the capability of high‐spectral‐purity, narrow‐bandwidth, and multi‐wavelength output. Furthermore, the RFLs featuring unique spectral properties can lead to various promising applications, which are concisely summarized, including optical fiber communication, optical fiber sensing, imaging, supercontinuum generation, nonlinear‐frequency conversion, mid‐infrared lasing pump sources, and laser‐driven inertial confinement fusion motivation. The challenges and prospects for RFLs are also discussed. [ABSTRACT FROM AUTHOR]

Midinfrared photonic devices are used as lasers and photodetectors in optical gas sensors and fiber‐optic communications. Herein, the pair number dependence and strain compensation dependence of the InAsSb/InAsP superlattice structure to increase luminescence intensity and reduce crystal defects is investigated. InAs substrates are used to demonstrate various effects of strain compensation, including its role in increasing luminescence intensity and improving the surface flatness. Furthermore, the photoluminescence spectra of a grown superlattice between the InAs substrate and GaAs substrate with two‐temperature‐step growth are shown. [ABSTRACT FROM AUTHOR]

Given the ever‐increasing demand for transmission capacity in optical fiber communication systems, there is a growing focus on developing active fibers and devices with an optical response across a wider spectrum. Bismuth (Bi)‐doped photonic glasses have attracted significant interest for their exceptional ultra‐broadband optical response, particularly within telecommunication bands. However, developing advanced Bi‐activated materials with robust optical response, high compatibility with commercial transmission systems, and low processing temperature remains a huge challenge. Herein, an anion hybridization strategy is proposed to overcome the aforementioned limitations. The anion hybridization significantly enhances the broadband optical response (≈10 times) of the Bi center following the introduction of fluorine ions, and reduces the transition temperature of the photonic glass (≈200 °C). Moreover, the near‐infrared optical response bandwidth experiences significant broadening, a result attributed to the larger inhomogeneous broadening. Furthermore, successful fabrication of the anion‐hybridized Bi‐activated glass fiber is achieved, demonstrating excellent compatibility with commercial transmission fibers. Additionally, the fabricated fiber exhibits an amplified spontaneous emission and on‐off gain across a broad waveband, further validating its efficacy. These results indicate that anion hybridization offers an effective strategy to optimize the optical and thermal properties of photonic materials to develop novel advanced photonic devices. [ABSTRACT FROM AUTHOR]

With the rapid development of 5G networks, the Internet of Things, and new‐generation of AI, there are considerable demands on expanding the capacity of contemporary optical fiber communication systems. One of the most effective avenues involves the extension of the bandwidth of Er‐doped fiber amplifiers, but with limited success. Herein, an Er‐activated hybridized glass fiber are reported, which can help realize broadband telecommunication. The effect of element hybridization on the bandwidth of Er‐activated fiber is clarified and the structure‐optical response relationship is established. A two‐step deposition approach is proposed to overcome the immiscibility barrier of different hybridized elements, and Er‐activated fiber with uniform doping is constructed. The activated fiber presents excellent compatibility with commercial telecommunication systems, providing a small signal gain of >13 dB in the whole L‐band range and a maximum gain of 28 dB. Furthermore, the Er‐activated fiber amplifier device is successfully developed. It exhibits outstanding optical amplification performance with gain >24 dB in the range of 1580–1624 nm, gain fluctuation less than ±0.9 dB, and noise figure <6.5 dB. The results not only provide a new strategy for developing novel active broadband optical fibers, but a valuable solution for new‐generation large‐capacity optical fiber communication systems. [ABSTRACT FROM AUTHOR]

In this study, we endeavored to create and simulate a D‐type flip‐flop utilizing two‐dimensional photonic crystals featuring a square lattice. This flip‐flop, composed of just two intersecting waveguides, is both compact and straightforward. Constructed from 10 × 10 dielectric rods suspended in air, it boasts low output power in logic mode 0, creating a significant distinction between optical powers in modes 0 and 1, lending it a logical aspect. Optimized for operation at a communication wavelength of 1.55 µm, this flip‐flop proves suitable for optical communication systems. The third window optical fiber communication system is suitable for 1.55 μm wavelength because the fiber has the lowest loss. Our analysis involved calculating the band structure via the plane wave expansion method and determining the optical power distribution using the finite difference time domain method. [ABSTRACT FROM AUTHOR]

This paper proposes an efficient optical fiber communication scheme for an optical metro access network (OMAN) based on an optical multicarrier (OMC) generator. The central office (CO)'s foundation is a novel, cost‐effective OMC‐generating technique. The OMC is designed from a pulsed laser source and three cascaded electro‐optic modulators (EOMs) driven by an amplified RF source of 20 GHz signal that has generated more than 60 frequencies with excellent tone‐to‐noise ratio (TNR) ~ 40 dB and amplitude excursions from zero to 3 dB. The conventional CO is replaced with a cost‐effective OMC‐based source with an effective switching mechanism, which is necessary and equally important to be handled reliably. The downstream data of 20 Gbps per carrier is transmitted using a duo‐binary coding scheme. Six remote nodes (RNs) supported by the suggested OMC source, at each RN 10 optical network units (ONUs), can be deployed having distance laps of 5 km between the RNs, the distance between the RNs and the ONUs is kept at 2 km, the ONUs were tested w.r.t the bit error rate (BER) and the power penalties for the proposed transmissions. The BER for different fiber lengths from 5 to 25 km at various RNs and ONUs ranges were calculated and demonstrated from 1e−3 to 1e−13, showing the feasibility of the proposed OMAN. [ABSTRACT FROM AUTHOR]

Light beams possess various dimensions, such as wavelength, spin angular momentum (SAM), and orbital angular momentum (OAM), which are indispensable in numerous optical applications. However, traditional techniques entail multiple attempts to disclose desired optical information, utilizing unwieldy multi‐pass systems or mechanically moving parts that are cumbersome to integrate into compact and integrated optical systems. Here, a single‐layer dielectric metasurface platform is proposed that enables multi‐dimensional demultiplexing and decoding, circumventing the need for conventional bulk optical elements. The platform can demultiplex 3D light parameters (wavelength, SAM, and OAM) and focus them at distinct spatial positions on a designated focal plane, providing a superior alternative to far‐field beams for integration with optical fiber and communication chips. The study verifies 132‐bit independent channels for a multi‐dimensional demultiplexer and demonstrates the metasurface‐based component's ability to function as an elliptic polarization decoder through a 4‐bit elliptic polarization coding transmission experiment. This work provides a compact and efficient platform for demultiplexing multi‐dimensional SAM and OAM states over a broad wavelength range, with potential implications for optical communications, optical data storage, optical information encryption, and quantum information sciences. [ABSTRACT FROM AUTHOR]

The near‐infrared (NIR) light polarization metrology is crucial in a broad area of applications, such as optical sensing, imaging, and communications. The conventional measurement of NIR light polarization requires bulky polarization optics by the spatial or temporal splitting of the input light beam with expensive infrared detectors. Here, an intelligent fiber‐integrated NIR polarimeter based on upconversion nanoparticles (UCNPs) is demonstrated. Er‐doped UCNPs are synthesized in core–shell structures for bright upconversion luminescence (UCL), and the tapered multimode fiber (MMF) is designed for random Rayleigh‐distributed speckles. It is demonstrated for the first time that spectra‐polarization‐dependent upconverted speckle patterns captured by a cost‐effective visible image sensor can be accurately decoded via a deep neural network (ResNet50). The experimental results show that ResNet50 has a recognition accuracy of over 99.5% for the full‐Stokes parameters of NIR light polarization, along with 100% accuracy for the light wavelength ranging from 1535 nm to 1565 nm. The developed intelligent optical sensors provide a new design paradigm for fiber‐integrated multi‐dimensional NIR light field detection and can be applied in fiber‐optic sensors and communications networks. [ABSTRACT FROM AUTHOR]

The attenuation of ocean surface waves during seasonal ice cover is an important control on the evolution of Arctic coastlines. The spatial and temporal variations in this process have been challenging to resolve with conventional sampling using sparse arrays of moorings or buoys. We demonstrate a novel method for persistent observation of wave‐ice interactions using distributed acoustic sensing (DAS) along existing seafloor fiber optic telecommunications cables. DAS measurements span a 36‐km cross‐shore cable on the Beaufort Shelf from Oliktok Point, Alaska. DAS optical sensing of fiber strain‐rate provides a proxy for seafloor pressure, which we calibrate with wave buoy measurements during the ice‐free season (August 2022). We apply this calibration during the ice formation season (November 2021) to obtain unprecedented resolution of variable wave attenuation rates in new, partial ice cover. The location and strength of wave attenuation serve as proxies for ice coverage and thickness, especially during rapidly evolving events. Plain Language Summary: Coasts globally are susceptible to erosion by ocean waves. In the Arctic, sea ice near the coast can serve as protection for much of the year. It is particularly challenging to measure waves and ice in this environment, which is necessary to understand the degree of buffering and project future changes. Typical ways of observing waves (e.g., buoys and underwater moorings) have lower success in coastal ice. We show a new way to observe waves and ice in these coastal regions using cables at the seabed deployed for internet connection. With the use of an instrument called an interrogator on shore, fibers in these cables can act like a series of hundreds of wave buoys. This allows us to see that waves are reduced at a variable rate throughout the ice. There are significant opportunities to learn more about the coastal Arctic using this novel technology and method. Key Points: Seafloor fiber optic cables can be used to quantify surface waves in seasonally sea ice‐covered oceansHigh spatial‐resolution wave observations may be used to study wave attenuation in ice at much finer resolution than previously possibleThe rapid evolution of the location and strength of attenuation serves as proxy for the evolution of ice itself [ABSTRACT FROM AUTHOR]

Wireless sensor networks is a comprehensive intelligent information system which integrates information acquisition, information transmission and information processing. It has been widely used in many fields. How to guarantee the quality of service is an important topic to make effective use of wireless sensor networks. Additionally, the applications of wireless sensor networks also put forward new requirements which are different from traditional networks. This paper adopts an energy‐efficient routing protocol with QoS guarantee for real‐time communication in wireless sensor networks. The energy‐efficient routing protocol transforms the real‐time requirements of application communication into the speed requirements of data packets and dynamically adjusts the transmission power and routing decision of nodes according to the data packet speed and network state. When the real‐time requirement of communication is high, it increases the transmission power of nodes and switching speed with increasing energy consumption and reducing system throughput. When the real‐time requirement of communication is low, it saves energy consumption and increases system throughput by reducing the transmission power of nodes. The associated structure includes dynamic speed allocator, delay estimator, forwarding policy, queue manager and neighbor manager. Experimental results show that the energy‐efficient routing protocol greatly reduces the loss rate and energy consumption of real‐time data communication delay. [ABSTRACT FROM AUTHOR]

Micro‐optical components exhibit significant potential applications in various fields such as imaging, optical fiber communication, and aerospace owing to their small size, light weight, and flexible design. It is imperative to fabricate micro‐optical components on hard brittle materials to improve stability and broaden the optical transmission range. Therefore, femtosecond laser processing technology is demonstrated to be an efficient processing strategy for preparing refractive/diffractive micro‐optical components on hard brittle materials compared to other established micromachining techniques. This study reviews recent advances in refractive/diffractive micro‐optical components using femtosecond laser processing technologies. The applications of refractive/diffractive micro‐optical components with high accuracy, efficiency, and quality in the fields of imaging, sensing, display, and integration are also summarized. Moreover, the challenges of femtosecond laser processing technologies and the outlook of micro‐optical components are highlighted. [ABSTRACT FROM AUTHOR]

The generation and evolution of soliton molecules are investigated theoretically with the coupled nonlinear Schrodinger equations based on a vector field. The formation of second‐and third‐order soliton molecules is investigated. Besides this, various‐order soliton molecules from the 6th order to the 13th order have been observed by adjusting small‐signal gain and phase delay. Finally, we analyze the reason for the soliton molecule generation. Exploring soliton molecules is helpful for optical communication as well as for fiber laser design. [ABSTRACT FROM AUTHOR]

We built the cross‐spectral density matrix elements analytical expression of random electromagnetic Gaussian vortex (REGV) beam propagating in gradient‐index (GRIN) fiber, which is used to study the polarization properties of the beam. The distribution of spectral degree of polarization (SDOP) and state of polarization (SOP) show the same periodicity and symmetry. The distribution law of SDOP and SOP is unchanging with the topological charge m changing and is changed by adjusting the spatial self‐correlation length σxx. The research results have guiding significance for the propagation of random electromagnetic vortex beams in optical fibers, which could be considerable value in high‐speed and large‐capacity optical fiber secure communication. [ABSTRACT FROM AUTHOR]

In this paper, a novel algorithm based on logistic regression digital backpropagation (LR‐DBP) is proposed to mitigate the effect of dispersion and nonlinearity in a long‐distance optical transmission system. The LR‐DBP can evaluate nonlinear effects by estimating the cross‐entropy error and adjusting the structure of DBP. The experiment is setup to demonstrate an 80 Gbit/s 16QAM signal transmitted across 1000 km single‐mode fiber. The results show that LR‐DBP achieves a 1.8 dB launch power improvement over the dispersion compensation algorithm and a 0.6 dB launch power gain with DBP. The proposed algorithm could obtain with 19.2% computational complexity decrease and 19.6% central processing unit (CPU) running time decrease by calculating the average numbers of real multiplications and CPU running times. [ABSTRACT FROM AUTHOR]

As the fundamental building block of optical fiber communication technology, thermally drawn optical fibers have fueled the development and prosperity of modern information society. However, the conventional step‐index configured silica optical fibers have scarcely altered since their invention. In recent years, thermally drawn multifunctional fibers have emerged as a new yet promising route to enable unprecedented development in information technology. By adopting the well‐developed preform‐to‐fiber manufacturing technique, a broad range of functional materials can be seamlessly integrated into a single fiber on a kilometer length scale to deliver sophisticated functions. Functions such as photodetection, imaging, acoustoelectric detection, chemical sensing, tactile sensing, biological probing, energy harvesting and storage, data storage, program operation, and information processing on fiber devices. In addition to the original light‐guiding function, these flexible fibers can be woven into fabrics to achieve large‐scale personal health monitoring and interpersonal communication. Thermally drawn multifunctional fibers have opened up a new stage for the next generation of information technology. This review article summarizes an overview of the basic concepts, fabrication processes, and developments of multifunctional fibers. It also highlights the significant progress and future development in information applications. [ABSTRACT FROM AUTHOR]

The authors investigate and demonstrate an all‐optical hybrid fiber‐free space optical (FSO)‐fiber communication system based on optical code division multiple access (OCDMA). Under different turbulence effects, the interception probability and interception distance are used as security metrics, and optimal parameters are obtained when the system meets the requirements of reliability and security simultaneously. The interception probability increases with the enhancement of turbulence effect, and decreases as the number of interfering users increases. In the case of strong turbulence, the maximum interception probability is 4.14 × 10−4. The authors design and build a 10 Gb/s all‐optical hybrid fiber‐FSO‐fiber CDMA communication system. It is shown that, under the soft‐decision forward‐error‐correction threshold of 2 × 10−2, this scheme can guarantee physical layer security in the second 20‐km optical fiber link under different turbulence conditions, while the interception distance is 8 km in the first optical fiber link. Under the hard‐decision forward‐error‐correction threshold of 3.38 × 10−3, the whole system can ensure the physical layer security. [ABSTRACT FROM AUTHOR]

In a 100G coherent optical fiber communication system, the equalization algorithm of polarization effects in fibers is generally integrated in digital signal processing (DSP) using a multiple input/multiple output (MIMO) equalizer to overcome the impairment due to the polarization effects in fiber. However, it was found in some extreme scenarios, such as the lightning strikes near the fiber cables, the Kerr effect and Faraday effect would induce very fast time‐varying state‐of‐polarization (SOP) and transient variation of principal‐state‐of‐polarization (PSP) of polarization mode dispersion (PMD) which would result in the coherent receivers unlocking. Faced with the difficulty, we propose a 3‐parameter RSOP model and design a window‐split structured Kalman filter equalization scheme instead of conventional MIMO equalizer to cope with this extreme scenario of large PMD combined with ultra‐fast rotation of SOP in presence of residual chromatic dispersion (RCD). The proposed equalization method has an excellent performance and can cope with RCD in the range of ±820 ps/nm under RSOP from 100 krad/s to 3 Mrad/s and DGD = 200 ps. [ABSTRACT FROM AUTHOR]

Further attenuation of Rayleigh scattering of silica glass is required to extend the capacity of long‐distance optical fiber communication. To theoretically examine the effect of aluminum and fluorine co‐doping on the density fluctuations of silica glass, which is related to Rayleigh scattering, a set of force‐matching potentials (FMP) for simulating F‐doped aluminosilicates was developed using Bayesian optimization based on density functional theory calculations. Molecular dynamics (MD) simulations with the new FMP could evaluate the densities of silica glasses to which a small amount of fluorine was doped and those of aluminosilicate glasses with a wide range of aluminum contents within reasonable accuracy. The FMP successfully represents the changing role of aluminum from a network former without a compensating cation (threefold coordination) to that with a compensating cation and a charge compensator in the aluminosilicates. Indeed, relative concentrations of four, five, and sixfold‐coordinated aluminum observed by NMR measurements were reproduced better than the original Teter potential at a high aluminum content. At an aluminum content lower than 1 mol%, threefold‐coordinated aluminum was observed, which is consistent with ESR measurements. After careful validations of the FMP, the effect of the co‐doping of alumina and fluorine on the density fluctuations of silica glass was computationally examined. Consequently, it was expected that the co‐doping might not sufficiently attenuate the Rayleigh scattering, even though 1 wt% fluorine would be able to reduce the density fluctuations of aluminosilicate glasses for some extent. This is because more alumina‐doping increases density fluctuations of silica glass if the drawing temperature and procedure are the same with those for silica glass fiber. Thereby, a possible fabrication process to sufficiently attenuate the Rayleigh scattering of the F‐doped aluminosilicate glass was proposed, according to the density fluctuation analysis at high temperature. [ABSTRACT FROM AUTHOR]

A neural network (NN)‐assisted probabilistic shaping (PS) distribution matcher is proposed, in which the model is simplified by a structured optimization method. The NN algorithm can encode the information sequence, making the signal obey the Gaussian distribution, and can directly restore the received signal. In addition, the algorithm uses the novel training method at both ends of the transmitter and receiver so that the system performance is significantly improved. PS system verification experiments have been carried out under 16QAM‐DMT modulation format. Under the hard decision forward error correction (FEC) threshold of 3.8*10−3 BER, the proposed system achieves 1.1 dB improvement compared to the traditional 16QAM‐DMT system. [ABSTRACT FROM AUTHOR]

A novel fast‐adaptive weighted hybrid‐shaped M‐ary quadrature amplitude modulation (HS‐MQAM) format is proposed in this paper. By introducing a fast‐adaptive weighting factor array related to geometric shaping and probabilistic shaping, the non‐linear impairment is mitigated and the bit error rate (BER) and mutual information (MI) performances are further improved. The simulation results show that the proposed HS‐61QAM outperforms both geometric‐shaped 61 quadrature amplitude modulation (GS‐61QAM) and regular 64QAM, and has more obvious advantages in the long‐haul optical transmission system. For a 120‐Gb/s optical communication system over 10 × 75 km fiber transmission link, compared with GS‐61QAM and regular 64QAM, the proposed approach can achieve about 4.2 and 8 dB OSNR gain at the BER of 10−2, and 0.21 and 0.55 bits/symbol MI gain at the OSNR of 22 dB. [ABSTRACT FROM AUTHOR]

Transition metal nitride materials exhibit unique optical characteristics and have attracted much interest for various applications, including waveguiding, photovoltaics, and nonlinear optical devices. Herein, titanium nitride (TiN), as a typical representative of biocompatible transition metal nitrides, is prepared and modified with gold nanoclusters (Au NCs) for promoting the carrier mobility, and the corresponding physical characteristics are systematically characterized. The TiN‐based saturable absorber (SA) on microfiber is fabricated and its nonlinear optical absorption property is also studied experimentally. Furthermore, the TiN‐decorated SA is applied in an ultrafast fiber laser at the communication bands. The fiber laser can generate the stable ultrashort pulses with a pulse width of 1.66 ps, a fundamental repetition rate of 7.49 MHz, and a spectral bandwidth of 2.61 nm. More importantly, the chaotic multiple pulses can be obtained, which is reported for the first time in the fiber laser based on the TiN SA on microfiber as far as it is known. The chaotic multiple pulses show many interesting characteristics, including high average pulse energy, varying pulse separations, and pulse intensities. These results have proved that the TiN shows great potential in many fields, such as advanced optical‐intensity modulator, ultrafast pulse dynamics, and optical fiber communications. [ABSTRACT FROM AUTHOR]

High-viscosity, low-crosslinked poly(butylene terephthalate) (PBT) from organic chain extenders and inorganic particles are prepared. PBT modification adopted from multifunctional, commercially available chain extension containing nine epoxy groups (ADR9) occurs in the first-step chain extension; hydroxyl addition modified dioxazoline (BOZ) serves as the second step. Anion stratiform inorganic hydrotalcite (HT) is used to adjust the crystallization behavior and damp-heat aging properties of PBT. The reaction between the chain extender and PBT end-groups such as carboxyl (-COOH) and hydroxyl (-OH) enhances the interfacial bonding between the PBT matrix and dispersed HT phases. With a fraction of chain extenders in the PBT matrix, the chain-extended PBT exhibits higher mechanical properties, intrinsic viscosity, average molecular weight, and melt viscosity than those of unmodified PBT. Damp-heat aging resistance measurements show correlation with initial carboxyl content in the resin. Reducing the concentration of carboxyl endgroups in the resin is shown to increase hydrolytic stability. The modified PBT resin can be used in optical fiber communication cable industry for its high level of damp-heat aging resistance as well as good mechanic properties. [ABSTRACT FROM AUTHOR]

Metal–inorganic semiconductor–metal photodetectors (MSM‐PDs) have received great attention in many areas, such as optical fiber communication, sensing, missile guidance, etc., due to their inherent merits of high speed, high sensitivity, and easy integration. This review focuses on MSM‐PDs with the semiconductor layer made of inorganic materials including traditional semiconductors (such as GaAs and Si), the third‐generation wide bandgap semiconductors (such as GaN, ZnO, and SiC), as well as several emerging semiconductors (such as perovskites and 2D materials). First, the basic structures of MSM‐PDs, including the planar and vertical configurations, are presented. Then, their working principles of MSM‐PDs are discussed. Subsequently, the research progresses on MSM‐PDs consisting of different photosensitive semiconductor materials are described in detail. Additionally, the efforts to optimize MSM‐PDs from the aspects of dark current, response speed, responsivity, spectral adjustment, etc., are also introduced. Finally, the review is concluded with the perspectives of MSM‐PDs from the authors' vision. [ABSTRACT FROM AUTHOR]

In fiber‐optic communications using diverse spatial modes for sustainable capacity scaling, the intelligent recognition of different mode bases is of great importance to enhance the flexiblity and compatibility of mode management. Here a convolutional neural network (CNN) model is introduced to recognize the four mode bases with the azimuthal index ℓ= 5, namely the LP5,1 mode group, the linearly and circularly polarized OAM±5,1 mode group, and the vector EH4,1 or HE6,1 mode group in a ring‐core fiber. A camera is first used to capture intensity profiles of mode bases as training and testing data sets of the neural network. The CNN‐based deep learning successfully recognizes different mode bases with an overall recognition rate of close to 100%. Furthermore, an alternative compact and cost‐effective approach is considered toward practical applications by replacing the camera with a photodetector (PD) array for intelligent mode bases recognition. A 1 × 5 PD array can perfectly recognize different mode bases with a recognition rate of close to 100%. Even a 1 × 2 PD array with only two PDs can obtain a high recognition rate of close to 93.3%. The demonstrations may open up new perspectives for deep learning enabled robust and intelligent optical communications exploiting spatial modes. [ABSTRACT FROM AUTHOR]

Silicon‐based photodetectors show attractive prospects due to their convenient preparation, high detectivity, and complementary metal–oxide–semiconductor compatibility. However, they are currently limited by low responsivity and sharp decay at sub‐bandgap wavelength. Although the aforementioned limitation can be partly solved by femtosecond laser processing, the surface defects and carrier activation rates result in a large dark current and narrow spectral response, which are unsatisfactory. Herein, rapid thermal annealing and hydrogenated surface passivation are introduced to elevate the broad‐bandgap responsivity and signal to noise ratio and to suppress the dark current. At optimal conditions, a sub‐bandgap responsivity of 0.80 A W−1 for 1550 nm at 20 V at room temperature is obtained, comparable with commercial germanium photodiodes and much higher than previously reported silicon photodiodes. Moreover, the prepared photodetector responded to spectral range from 400 to 1600 nm, with responsivity reaching 1097.60 A W−1 for 1080 nm at 20 V, which is the highest in reported silicon photodetectors. Simultaneously, the device shows competitive detectivity (1.22 × 1014 Jones at −5 V) due to the post‐processing procedures and suppressed dark current (7.8 μA at −5 V). The results show great prospects for black silicon in infrared light detection, night vision imaging, and fiber‐optic communication. [ABSTRACT FROM AUTHOR]

The concentration of infiltrated water molecules into polymer matrix of composite materials is an important mechanical and chemical functional parameter of smart composite materials during exploitation in various research, medical, industrial, and security applications and it is important to design a setup as simple and as efficient as possible for measuring and monitoring this important parameter. The paper presents simulation/design results obtained using self‐interference long period grating fiber sensors in measuring and monitoring the concentration of infiltrated water molecules into polymer composite materials. The investigated long period grating fiber sensors are used as they are or mounted in interferometric setups. Self‐interference long period grating fiber sensors are manufactured by inscribing diffraction gratings into or on single mode commercial communication optical fibers and are used in smart composite materials as signal generators of their feedback loop being embedded into the polymer matrix. [ABSTRACT FROM AUTHOR]

Cross-connection is the only point in the communications field that has not been automated. With the many fibre networks that have been built, there is strong demand from operators for an automatic optical distribution frame (AODF) to reduce operational costs and provide high-level services. From the twisting relationships between the fibre patch cords on the main distribution frame (MDF), the relationship between the input lines and output lines on the MDF is reversed to be perpendicular to each other, and one-dimensional arrays of input lines and output lines (1D to 1D) are formed to construct the model. According to the model, the AODF prototype of the 1D to 1D form was fabricated with the smallest Lucent connector connector and verified through several cross-connect experiments. The prototype designed has a simple structure, a three-degrees-of-freedom Cartesian coordinate robot can meet switch requirements, and there is non-winding between the fibres after multiple cross-connects. Compared to the single-layer and double-layer form tests, the switch process requires multiple hand-over operations, and handovers take a long time in the switch process. Further research is needed to optimise the handover method and greatly improves the switching speed. [ABSTRACT FROM AUTHOR]

A split‐step time‐domain modeling is applied to investigate the characteristics of dual‐mode distributed feedback (DFB) laser diode (LD) for terahertz (THz) wave generation. The THz wave generation from 163 to 1,378 GHz by proper thermo‐optic tuning and initial detuning combination is effectively simulated, which is qualitatively analogous to the experimental results. It is shown that the residual facet reflectivity should be below 0.003 to suppress the facet‐to‐facet cavity modes and provide good spectral quality. The time‐domain simulation tool could be incorporated into future THz fiber‐optic communication systems. [ABSTRACT FROM AUTHOR]

This work experimentally shows a transmission path based on standard single‐mode optical fiber and perfluorinated graded‐index plastic optical fiber with the connections between distinct optical fibers being made by fiber collimators using free‐space optical transmission. The data stream consists of a bidirectional 400 Gbps optical transmission using four wavelength channels with quadrature phase‐shift keying modulation format, combined with dual‐polarization and Nyquist pulse‐shaped. The results obtained seeks to study the use of short‐distance cables in plastic optical fiber as a flexible means of interconnection, when inserted between single‐mode optical fibers or as a coupling medium between devices with single‐mode optical inputs/outputs located in data centers/video headends. [ABSTRACT FROM AUTHOR]

Abstract: Expanding the use of physical degrees of freedom to employ spatial multiplexing of data in optical communication is considered to be the most disruptive and effective solution for meeting the capacity demand of the growing information traffic. Development of space division–multiplexing methods stimulated research on spatial encoding, detection, and processing of data, attracting interest from various fields of science. Here a passive all‐dielectric metasurface with near‐unity transmission is demonstrated that engineers spatial mode profiles, potentially of an arbitrary complexity. The broadband response of the metasurface covers all S, C, and L bands of fiber communications. Unlike conventional phase plates, the metasurface allows for both phase and polarization conversion, providing full flexibility for the mode engineering. The dielectric metasurface is employed for mode multiplexing in a free‐space optical communication system with an extinction ratio in excess of 20 dB over the whole C‐band with negligible penalty even for 100 Gb s−1 data transmission. These results merge two seemingly different fields, optical communication and metamaterials, and they suggest a novel approach for an ultimate miniaturization of mode multiplexers and advanced LiFi technologies. [ABSTRACT FROM AUTHOR]

A new multifeature recognition method for optical fiber vibration signals is proposed to solve the difficulty with the present long-distance distributed optical fiber sensing systems based on phase-sensitive optical time-domain reflectometer (φ-OTDR) in effectively distinguishing vibrational intrusions. Firstly, wide-band background noise is reduced by spectral subtraction to enhance time-frequency characteristics of vibration signals. Then, multifeature parameters including short-time energy ratio, short-time level crossing rate, vibration duration, and power-spectrum energy ratio are extracted from the vibration signals. Finally, by utilizing support vector machine classifiers to identify multifeature vectors of different types of vibration signals, patterns of vibration events are recognized accurately. Experiments show that after using this method to process 800 vibration signal samples generated by four different vibration events, namely, taping, striking, shaking, and crushing, the signal-to-noise ratio is enhanced by more than 10 dB and the recognition rates of vibration events are over 90%. The experimental results prove that this method can improve the classification accuracy of vibration events detected by φ-OTDR distributed optical fiber sensing systems with a recognition time below 0.6 s, especially for long distances. [ABSTRACT FROM AUTHOR]

The authors study the performance of pulse-amplitude modulation, with 2, 4 and 8 levels per symbol, for short reach applications with propagation over up to 2 km of standard single mode fibre. They consider the three modulation formats operated both at the same bit-rate of 25 Gbps and at same symbol rate of 25 Gbaud, supposing 3.125% forward error-correction overhead and bit error rate threshold of 10-4. They analyse transmitters (Tx) and receivers (Rx) based on digital signal processing, including a training-driven finite impulse response (FIR) filter equaliser set through the least-mean-square algorithm. They analyse the sensitivity impairments induced by a limited Tx/Rx electrical bandwidth and evaluate the minimum number of taps - and consequent latency - needed by the FIR equaliser to obtain sensitivity benefits. [ABSTRACT FROM AUTHOR]

High-speed PAM-4 is a promising way for future low-cost short-reach fibre communications. However, for 1550 nm transmission with the lowest attenuation for standard single-mode fibre (SSMF), the fibre dispersion-induced inter-symbol interference (ISI) becomes non-linear in direct detection. Dispersion pre-compensation at the transmitter side is necessary to avoid such non-linear ISI. Different from previous methods to generate the vector signal from dispersion pre-compensation using IQ modulators, in this study a digital dispersion pre-compensation (DDPC) scheme based on an intensity modulator (IM) plus a phase modulator (PM) is studied. Taking into account the digital-to-analogue converter (DAC) bandwidth limit on the vector signal generation, anti-aliasing filtering on both the magnitude signal and the phase signal should be applied. The error rate performance of the IM-PM based DDPC scheme is analysed in detail using numerical simulations. For 50 Gb/s PAM-4 transmission at 1550 nm over SSMF, over 50 km fibre transmission can be supported if the two DACs have enough bandwidth larger than 17.5 GHz. If the DAC bandwidth is limited to 15 GHz, it is also possible to transmit over 20 km SSMF. Meanwhile, it is verified that practical 5-bit DAC resolution is enough for the IM-PM based DDPC scheme to work for a wide range of SSMF lengths. [ABSTRACT FROM AUTHOR]

Modern backbone, optical networks have developed into large, massive networks, which consist of numerous intermediate and terminal nodes as well as final users. These networks serve uninterruptedly multitude of users at the expense of considerable power consumption. Many research efforts are aimed at reducing energy consumption in large-scale optical networks; however, this objective is deemed laborious: the operation of such networks has to continuously remain in good levels without disruptions. One of the most compelling techniques to remedy this situation is to switch off redundant links and devices at specific (short) periods. These links and devices remain idle as long as the network can cope with the underlying traffic demands. Hence, a power mechanism is required to manage how and when underutilized network elements may be silent during network operation. Nevertheless, this management entails fast processing and efficient decision making. While many research efforts neglect this serious factor, the problem of reducing the power consumption still threats the development of today's backbone network. In this work, an effective, cognitive power management technique is proposed by enhancing the decision making with traffic prediction. Traffic capacity is estimated in each link within the network supporting, thus, more efficient decisions on switching off underutilized or even idle network elements a priori. The technique introduced succeeds high accuracy levels, while it offers energy savings up to 30 % lower than other energy-aware schemes. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

ABSTRACT We model a multi-cavity optical device composed of fiber Bragg gratings. The sensitivity of the device for refractive index measurement is extracted from the change in its free-spectral range, rendering the sensor robust to small temperature fluctuations. Remote interrogation compatibility is ensured by the all-fiber design. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:423-428, 2017 [ABSTRACT FROM AUTHOR]

Optically active point defects in SiC are attracting a growing interest thanks to their prospect of emission in the near-infrared (NIR) spectral region (application in optical fiber communications and for in vivo imaging) and also thanks to the possibility to control optically their spin. Most of the results have been obtained for the hexagonal SiC polytypes. In this work, we focus on the optical properties of point defects in the 3C-SiC polytype after ion implantation. Different ions, fluences and postimplantation annealing were performed to optimize the defect formation. Photoluminescence results show that the optimal conditions for intense D1 defect related PL emission in the 600-850 nm range are high temperature annealing (up to 1200 °C) and a displacement density not exceeding 1020 cm-3 at the projected range. The creation of Ky5 defect at 1.12 eV has also been demonstrated for lower temperature annealing (800 °C). [ABSTRACT FROM AUTHOR]

We estimate demand for residential broadband using high-frequency data from subscribers facing a three-part tariff. The three-part tariff makes data usage during the billing cycle a dynamic problem, thus generating variation in the (shadow) price of usage. We provide evidence that subscribers respond to this variation, and we use their dynamic decisions to estimate a flexible distribution of willingness to pay for different plan characteristics. Using the estimates, we simulate demand under alternative pricing and find that usage-based pricing eliminates low-value traffic. Furthermore, we show that the costs associated with investment in fiber-optic networks are likely recoverable in some markets, but that there is a large gap between social and private incentives to invest. [ABSTRACT FROM AUTHOR]

A fibre memory is a serial connection of fibre-switch blocks, each combining fibre delay lines with one optical switch. With enhanced flexibility in processing fluid optical data, fibre memories allow ramified applications in the existing literature. This study concentrates on the implementations of timeslot interchangers (TSIs) by fibre memories based on a special type of low-complexity switches, called rotators, under periodic switching control. The proposed TSI structure achieves an economic tradeoff between control and component complexities in the construction of large-scale optical TSIs. [ABSTRACT FROM AUTHOR]

Light-based technologies are strongly supported by various glass materials in general. This article focuses on glasses containing rare-earth elements, doped fibers, as well as their photonic functions such as optical amplifications in fiber telecommunication. Scientific progress and applications of rare-earth spectroscopy and technologies of doped glasses and fibers in recent 60 years have been more than dramatic. Development of various laser diodes has been strongly linked with realization of novel devices of rare-earth-doped glasses. In addition to many milestones listed in the resolution of International Year of Light, we should notice that 2015 is also the 50th anniversary of the erbium-doped glass laser, which is later transformed into the optical fiber amplifier, the enabler of today's information society. [ABSTRACT FROM AUTHOR]

In a research paper by Jingbo Li and co-workers (202000964), a metal-semiconductor-metal Schottky photodetector was designed with spalling WS SB 2 sb through a wet-transfer technique. The resounding success of two-dimensional (2D) graphene has encouraged extensive research efforts for other novel 2D materials, such as transition metal dichalcogenides (TMDs) and transition metal carbides/nitride (MXene). [Extracted from the article]

This paper is focused on passive optical networks (PONs), especially on increasing their network resilience. Because the most critical components in PONs are usually the optical line termination unit (OLT) and optical fibres connecting all network nodes, the main motivation presented within this paper is to improve the resistance of PON against critical failures of OLT and optical fibres between them. Both presented solutions are based on using dual OLT units and the application of asymmetric splitters in order to balance the attenuation and optical signal levels throughout the entire network, while the main innovation consists in the application of ring and bus topologies. Both bus and ring topologies can be formed easily using only passive splitters with optimum splitting ratios; therefore, no active components are necessary. The next advantage is the opportunity of placing both OLT units in physically diverse location, thus increasing the overall network resilience. Moreover, the presented idea with a bus topology offers an additional resistance against the failures of optical fibres connecting the splitters as well. Because the application of asymmetric passive splitters in both solutions is necessary in order to optimize the optical signal levels in the entire network, the mathematical models for calculating of their optimum splitting ratios are included. To verify the functionality of both topologies and their protection mechanisms, complex simulations were performed and are presented in this article as well. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

ABSTRACT A wideband and high resolution fiber delay line system based on a self-fabricated distributed-feedback (DFB) laser is demonstrated in this article, where the delay time drift due to temperature variance is compensated using the extensibility of the standard single-mode fiber (SMF). The DFB laser with the amplitude bandwidth of 18 GHz and the in-band phase variance within 60° is applied as the optical source to provide wideband microwave signal delay. The temperature-dependence delay variance is measured up to 42.8 ps/km/°C in SMF delay line. A compensation capability of 600 ps is reached with a fiber stretcher acted on a motor-driven 300 m SMF. The proposed system not only provides delay drift compensation for the environmental-sensitive systems, but also a feasible solution to realize continuously tuning of delay for stable systems. The tunable range of the microwave delay could be further extended using longer stretched fiber. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:1219-1222, 2015 [ABSTRACT FROM AUTHOR]

ABSTRACT We investigate the impact of different light sources on the optical correlator based on fiber dispersion that can implement a time-spectrum convolution. Simulation and experiment show that the performance of optical correlator degenerates with the increase of optical source's bandwidth. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:441-445, 2015 [ABSTRACT FROM AUTHOR]

In this paper, we are concerned about optimal ( v, 4, 3, 2)-OOCs. A tight upper bound on the exact number of codewords of optimal ( v, 4, 3, 2)-OOCs and some direct and recursive constructions of optimal ( v, 4, 3, 2)-OOCs are given. As a result, the exact number of codewords of an optimal ( v, 4, 3, 2)-OOC is determined for some infinite series. [ABSTRACT FROM AUTHOR]

ABSTRACT This article presented the design of a large drive current laser diode amplifier for 2.4-GHz radio-over-fiber transmission systems in TSMC 0.18-µm CMOS technology. The proposed drive amplifier adopted a single-ended two-stage amplifier structure with the operating voltages of 1.8 and 3.6 V. The technique of dynamic bias is used to enhance linearity. The measurement results show that the linear amplifier achieves the power gain of 16.9 dB, the output 1-dB compression point of 20.1 dBm at 2.4 GHz. The maximum output modulation current is up to 64 mA. The components are all on chip including the input and output matching network, and the total chip area is 1.0 × 0.73 mm2. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:1971-1974, 2014 [ABSTRACT FROM AUTHOR]

Two new CMOS analog continuous-time equalizers for high-speed short-haul optical fiber communications are presented in this paper. The proposed structures compensate the limited bandwidth-length product of 1-mm step-index polymer optical fiber channels (45 MHz, 100 m) and have been designed in a standard 0.18-µm CMOS process. The equalizers are aimed for multi-gigabit short-range applications, targeting up to 2 Gb/s through a 50-m step-index polymer optical fiber. The prototypes operate with a single supply voltage of only 1 V and overcome the severe limitations suffered by the widely used degenerated differential pair caused by the low supply voltage. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

ABSTRACT A novel 60-GHz optical millimeter-wave access system with 5 Gb/s 64QAM-OFDM downlink signals generated by discrete multitone (DMT) modulation, is proposed and experimentally demonstrated. 5Gb/s 64QAM-OFDM signals are successfully transmitted over 42 km SMF-28 and a 0.5 m wireless channel. The proposed self-mixing down-conversion is adopted in the system, and which can simplify the transmitter and receiver configuration, since it eliminates the need for high-frequency microwave source at the central station and local oscillator at the base station. The experimental results demonstrate 64QAM-OFDM downstream signals has higher spectra-efficiency and lower receiver sensitivity penalty than 16QAM-OFDM using DMT modulation and electrical self-mixing. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:259-262, 2014 [ABSTRACT FROM AUTHOR]