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This study introduces a distinctive LiNbO 3 -based five-ring heptagonal-shaped photonic crystal fiber (PCF) geometry that demonstrates exceptionally high birefringence (Br) and nonlinear coefficient (NLC). Fundamental simulation studies are conducted through the COMSOL software utilizing the finite element method (FEM) with a perfectly matched layer (PML) boundary condition in order to comprehensively explore a variety of relevant optical characteristics, including birefringence, effective area, nonlinearity, core power fraction, dispersion, numerical aperture, confinement loss and so on. The simulation outcomes reveal an ultra-high Br and NLC of 0.081 and 5843.32 W - 1 K m - 1 sequentially, at the operative wavelength of 1.55 μ m. The designed PCF with ultra-high Br and NLC features can be fabricated suitably, which is an advantageous aspect for potential prospective utilization in polarization-maintaining, nonlinear optics, supercontinuum generation, etc. [ABSTRACT FROM AUTHOR]

Organic/polymeric second-order nonlinear optical (NLO) materials, which rely on the poling-induced non-centrosymmetric arrangement of NLO chromophores, have played a very important role in laser technology and optical fiber communication, due to their ultra-fast response speed, excellent machining performance and low dielectric constant. However, the NLO chromophores have the large dipole moments with strong intramolecular charge transfer, which lead to the intermolecular electrostatic interactions to tend to the centrosymmetric arrangement and decrease the poling efficiency. Since the special three-dimensional spatial separation can minimize these strong intermolecular electrostatic interactions during poling process, dendrimers and hyperbranched polymers have been considered as better topology for the next generation of highly efficient NLO materials. In 2013, by the attachment of low generation dendrimers to the hyperbranched backbone, a new dendritic architecture of dendronized hyperbranched polymer (DHP) was proposed for improving the comprehensive performance of NLO materials. Recent results showed many advantages of DHPs in NLO field, such as easy syntheses, large NLO coefficients and high orientation stability, etc. In this review, the latest advancement of DHPs, including the design principle, synthesis, as well as their application as NLO materials is summarized. The new opportunities arising from DHPs are also summarized in the future perspective. [ABSTRACT FROM AUTHOR]

Optical fiber communication has been the most versatile and revolutionary medium of communication that has helped connect millions of people across the globe. These traits have seen tremendous development in the sector of optical fiber communication. There are now many desired qualities expected out of an optical fiber communication such as large transmission capacity and a smaller amount of loss. Communication systems operating with higher transmission rates have found an essential role of non-linear fiber optics. The behavior of light in non-linear media is described by non-linear optics. Cross-phase modulation (XPM) and self-phase modulation (SPM) are a few non-linearities occurring in the optical fiber. Non-linear effects reduce the performance of optical fibers. In this paper, a comparative study of non-linear effects in erbium-ytterbium co-doped fiber is reviewed using simulation. The results are compared with optical systems utilizing normal fiber. The benefits of using Er-Yb fiber have been demonstrated by analyzing effective systems comprising the Er-Yb co-doped fiber and their ability to mitigate the non-linearities. [ABSTRACT FROM AUTHOR]

Nonlinearity is one of the key issues that hinder the development of high-capacity optical short reach systems. This paper proposes three variants of kernel affine projection (KAP) algorithms, all of which combine kernel mapping and affine projection in a reproducing kernel Hilbert space for compensating nonlinear impairments in optical short reach systems. An intensity modulation/direct detection system with a single digital-to-analogue converter, a packaged externally modulated laser and a packaged InP photo-detector is used for experimental demonstration, achieving 238-Gbps (net rate 222-Gbps). Experimental results show that the KAP algorithms can mitigate nonlinear impairments in short-reach communications while maintaining low complexity in reproducing kernel Hilbert space. [ABSTRACT FROM AUTHOR]

MXene are a class of metal carbide and metal nitride materials with a two-dimensional layered structure. MXene Ti3C2Tx has the characteristics of good metal conductivity and adjustable chemical composition, which has attracted the attention of scientists. Recently, Mxene have shown strong nonlinear photonics and optoelectronic effect, which can be used to generate ultrashort pulsed laser. However, soliton molecules pulse in laser cavity based on Mxene have not been reported at present. In this article, MXene have been characterized systematically, and the nonlinear optical characters were measured. In addition, we combined MXene with taper fiber to make a saturable absorber device for an erbium-doped fiber laser. The modulation depth and saturation absorption intensity of MXene are 10.3% and 197.5 MW/cm2, respectively. Thanks to the outstanding character of MXene, a three-order soliton molecules pulse were generated in laser cavity. The center wavelength, pulse interval and spectral modulation period of soliton molecules are 1529.4 nm, 15.5 ps and 0.5 nm, respectively. The above experimental results show that MXene have broad application prospects in the fields of optical fiber communication, laser material processing and high-resolution optics. [ABSTRACT FROM AUTHOR]

Free-space optical (FSO) communication, considered as a last-mile technology, is widely used in many urban scenarios. However, the performance of urban free-space optical (UFSO) communication systems fades in the presence of system vibration caused by many factors in the chaotic urban environment. In this paper, we develop a dedicated indoor vibration platform and atmospheric turbulence to estimate the Bifurcated-Gaussian (B-G) distribution model of the receiver optical power under different vibration levels and link distances using nonlinear iteration method. Mean square error (MSE) and coefficient of determination ($R^2$) metrics have been used to show a good agreement between the PDFs of the experimental data with the resulting B-G distribution model. Besides, the UFSO channel under the effects of both vibration and atmospheric turbulence is also explored under three atmospheric turbulence conditions. Our proposed B-G distribution model describes the vibrating UFSO channels properly and can easily help to perform and evaluate the link performance of UFSO systems, e.g., bit-error-rate (BER), outage probability. Furthermore, this work paves the way for constructing completed auxiliary control subsystems for robust UFSO links and contributes to more extensive optical communication scenarios, such as underwater optical communication, etc. [ABSTRACT FROM AUTHOR]

Regenerative wavelength conversion at 80 Gb/s using distributed Raman gain and cross-phase modulation (XPM) in 1 km of highly nonlinear dispersion-shifted fiber is demonstrated. Raman gain greatly enhances the fiber nonlinearity by changing the power evolution along the fiber and meanwhile maintains the signal-to-noise ratio of the wavelength converted signal due to the effect of distributed gain on optimizing cross-phase versus self-phase modulation. Bit-error-rate measurements were performed both before and after wavelength conversion, with a negative power penalty of 2 dB at 10(-9) bit-error rate for return-to-zero formats. The reshaping properties of this wavelength converter were clearly demonstrated in both the frequency and time domain.

The regular perturbation (RP) series used to analytically approximate the solution of the nonlinear Schrodinger equation has a serious energy-divergence problem when truncated to the first order. The enhanced RP (ERP) method can improve the accuracy of the first-order RP approximation by solving the energy divergence problem. In this paper, we propose an ERP-based nonlinearity compensation technique, referred to as ERP-NLC, to compensate for the fiber nonlinearity in a polarization-division multiplexed dispersion unmanaged optical communication system. We also propose a modified perturbation-based NLC (PB-NLC) technique by simple phase-rotation (PR) of the nonlinear coefficient matrix, referred to as the PR-PB-NLC. The PR-PB-NLC can be considered as a by-product of the ERP-NLC technique. We show through numerical simulation that, for a 256 Gb/s single-channel system, the proposed ERP-NLC technique improves the $Q$ -factor performance by $\sim$ 1.2 dB and $\sim$ 0.6 dB when compared to the electronic dispersion compensation (EDC) and the PB-NLC techniques, respectively, at a transmission distance of 2800 km. Also, the result for a 1.28 Tb/s wavelength-division multiplexed five-channel transmission system at the same transmission distance shows that the $Q$ -factor performance of the ERP-NLC technique is improved by $\sim$ 0.6 dB and $\sim$ 0.4 dB when compared to the EDC and the PB-NLC techniques, respectively. The simulation results for the PR-PB-NLC technique for a single- or five-channel transmission system show an improved $Q$ -factor performance when compared to the EDC and PB-NLC techniques. Finally, we show that the proposed performance enhancement comes with a negligible increase in the computational complexity for the ERP-NLC and PR-PB-NLC techniques when compared to the PB-NLC technique. [ABSTRACT FROM AUTHOR]

We present a novel method to estimate chromatic dispersion with ultra-low sampling rate based on training sequence. The under-sampling can be equivalent to over-sampling by splicing points with periodic sequence. The functional relationship between equivalent over-sampling rate and symbol rate, actual sampling rate and sequence period is deduced. To demonstrate the feasibility of the method, the simulation of a 28 GBaud QPSK optical fiber communication system is carried, in which 76 MSa/s sampling rate is equivalent to 66.5 GSa/s sampling rate. The results show that maximum estimation error is less than 160 ps/nm after 100 km to 2300 km SSMF transmission. We also demonstrate the robustness of the proposed method to amplified spontaneous emission and nonlinear noise in a three-channel optical fiber communication system. Moreover, the proposed method has been experimentally verified with a 20.5 GBaud QPSK system, 1.25 GSa/s sampling rate is equivalent to 51.25 GSa/s sampling rate, and estimation error is less than 100 ps/nm and 150 ps/nm after 100 km and 200 km SSMF transmission, respectively. The proposed method eliminates the requirement of high speed ADC and is cost effective, which can be used for optical performance monitoring. [ABSTRACT FROM AUTHOR]

Radio-on-Free-Space Optical systems constitute a very attractive option for interconnecting central base stations with remote antenna units. Nonetheless, the optical signal propagation through the atmosphere is tremendously affected by turbulence- and misalignment-induced fading. In the present study, we investigate the transmission of code division multiple access signals over a free-space optical (FSO) link. The atmospheric turbulence is modeled by the M (Malaga) distribution, which acts as a unifying statistical model encompassing all the well-known distributions that have been proposed in the FSO area. In addition, nonzero boresight pointing errors (PEs) are employed, which are described by an accurate approximation of the Beckmann distribution. Novel mathematical expressions are extracted regarding the average bit error rate and the outage probability of the forward and the reverse link. Moreover, appropriate numerical results are depicted for various turbulence and PE scenarios, along with their associated corroborative outcomes. [ABSTRACT FROM AUTHOR]

A high-gain, dispersion-tolerant, and linear phase-modulated analog photonic link is proposed and demonstrated based on full spectrum optical sideband processing (FSOSP). In the proposed link, upper sidebands and lower sidebands are transmitted separately in different optical paths. By suppressing the optical carrier, this link can be linearized. Moreover, it can be dispersion-tolerant due to single-sideband modulation, and it can be high-gain due to reflected spectrum reuse and power enhancement of upper and lower optical sidebands as the suppression power of optical carrier is compensated. Additionally, gain and spurious-free dynamic range are experimentally improved by 15.52 and 25.06 dB, respectively, in the proposed dispersion-tolerant link, as compared to that in a conventional phase-modulated link without FSOSP. [ABSTRACT FROM PUBLISHER]

A mathematical framework is presented to study the evolution of multi-point cumulants in nonlinear dispersive partial differential equations with random input data, based on the theory of weak wave turbulence (WWT). This framework is used to explain how energy is distributed among Fourier modes in the nonlinear Schrödinger equation. This is achieved by considering interactions among four Fourier modes and studying the role of the resonant, non-resonant, and trivial quartets in the dynamics. As an application, a power spectral density is suggested for calculating the interference power in dense wavelength-division multiplexed optical systems, based on the kinetic equation of the WWT. This power spectrum, termed the Kolmogorov-Zakharov (KZ) model, results in a better estimate of the signal spectrum in optical fiber, compared with the so-called Gaussian noise model. The KZ model is generalized to non-stationary inputs and multi-span optical systems. [ABSTRACT FROM PUBLISHER]

The coordinated multipoint transmission/reception aided collocated antenna system (CoMP-CAS) and the mobile relay assisted fractional frequency reuse distributed antenna system (MR-FFR-DAS) constitute a pair of virtual-MIMO-based technical options for achieving high spectral efficiency in interference-limited cellular networks. In practice, both techniques have their respective pros and cons, which are studied in this paper by evaluating the achievable cell-edge performance on the uplink of multicell systems. We show that, assuming the same antenna configuration in both networks, the maximum available cooperative spatial diversity (or the multiplexing gain) inherent in the MR-FFR-DAS is lower than that in the CoMP-CAS. However, when the cell-edge mobile stations (MSs) have a low transmission power, the lower complexity MR-FFR-DAS relying on the simple single-cell processing may outperform the CoMP-CAS by using the proposed soft-combining-based probabilistic data association (SC-PDA) receiver, despite the fact that the latter scheme is more complex and incurs a higher cooperation overhead. Furthermore, the benefits of the SC-PDA receiver may be enhanced by properly selecting the MRs' positions. Additionally, we show that the performance of the cell-edge MSs roaming near the angular direction halfway between two adjacent remote antennas (i.e., the “worst-case direction”) of the MR-FFR-DAS may be more significantly improved than that of the cell-edge MSs of other directions by using multiuser power control, which also improves the fairness among cell-edge MSs. Our simulation results show that, given a moderate MS transmit power, the proposed MR-FFR-DAS architecture employing the SC-PDA receiver is capable of achieving significantly better bit error rate (BER) and effective throughput across the entire cell-edge area, including even the worst-case direction and the cell-edge boundary, than the CoMP-CAS architecture. [ABSTRACT FROM AUTHOR]

A ( 3 + 1 ) -dimensional coupled nonlinear Schrödinger system is investigated, which describes the pulses in an optical fiber and transverse effects in a nonlinear optical system. With the aid of symbolic computation and Hirota method, bright one- and two-soliton solutions of the system are derived. On the basis of the soliton solutions, we will graphically discuss the head-on collisions which include the elastic and inelastic collisions between the two bright solitons. After an elastic collision, two colliding solitons keep their shapes, amplitudes and velocities unchanged except for some phase shifts, while inelastically, the intensity of one soliton is enhanced, while the other gets suppressed. [ABSTRACT FROM AUTHOR]

In this paper, we propose a novel detector for single-channel long-haul coherent optical communications, termed stochastic digital backpropagation (SDBP), which takes into account noise from the optical amplifiers in addition to handling deterministic linear and nonlinear impairments. We discuss the design approach behind this detector, which is based on the maximum a posteriori (MAP) principle. As closed-form expressions of the MAP detector are not tractable for coherent optical transmission, we employ the framework of Bayesian graphical models, which allows a numerical evaluation of the proposed detector. Through simulations, we observe that by accounting for nonlinear signal—noise interactions, we achieve a significant improvement in system reach with SDBP over digital backpropagation (DBP) for systems with periodic inline optical dispersion compensation. In uncompensated links with high symbol rates, the performance difference in terms of system reach for SDBP over DBP is small. In the absence of noise, the proposed detector is equivalent to the well-known DBP detector. [ABSTRACT FROM PUBLISHER]

A novel all-fiber low-pedestal spectral compression scheme is proposed and demonstrated. The scheme is based on an anomalously dispersive single-mode fiber (SMF) cascading a nonlinear optical loop mirror with a highly nonlinear fiber (HNLF) in the loop. Both numerical and experimental results show that the spectral pedestal after spectral compression in the HNLF can be efficiently suppressed by the nonlinear optical loop mirror through the chirp-related intensity filtering effect. The measured spectral pedestal energy ratio is 9.59% using the proposed scheme, which is nearly a quarter of that using the conventional alternative based on an anomalously dispersive SMF followed by a feedthrough HNLF. [ABSTRACT FROM PUBLISHER]

Motivated by the looming capacity crunch in fiber-optic networks, information transmission over such systems is revisited. Among numerous distortions, interchannel interference in multiuser wavelength-division multiplexing (WDM) is identified as the seemingly intractable factor limiting the achievable rate at high launch power. However, this distortion and similar ones arising from nonlinearity are primarily due to the use of methods suited for linear systems, namely WDM and linear pulse-train transmission, for the nonlinear optical channel. Exploiting the integrability of the nonlinear Schrödinger (NLS) equation, a nonlinear frequency-division multiplexing (NFDM) scheme is presented, which directly modulates noninteracting signal degrees-of-freedom under NLS propagation. The main distinction between this and previous methods is that NFDM is able to cope with the nonlinearity, and thus, as the signal power or transmission distance is increased, the new method does not suffer from the deterministic crosstalk between signal components, which has degraded the performance of previous approaches. In this paper, emphasis is placed on modulation of the discrete component of the nonlinear Fourier transform of the signal and some simple examples of achievable spectral efficiencies are provided. [ABSTRACT FROM AUTHOR]

In this paper, numerical methods are suggested to compute the discrete and the continuous spectrum of a signal with respect to the Zakharov-Shabat system, a Lax operator underlying numerous integrable communication channels including the nonlinear Schrödinger channel, modeling pulse propagation in optical fibers. These methods are subsequently tested and their ability to estimate the spectrum are compared against each other. These methods are used to compute the spectrum of various signals commonly used in the optical fiber communications. It is found that the layer peeling and the spectral methods are suitable schemes to estimate the nonlinear spectra with good accuracy. To illustrate the structure of the spectrum, the locus of the eigenvalues is determined under amplitude and phase modulation in a number of examples. It is observed that in some cases, as signal parameters vary, eigenvalues collide and change their course of motion. The real axis is typically the place from which new eigenvalues originate or, are absorbed into after traveling a trajectory in the complex plane. [ABSTRACT FROM AUTHOR]

In this paper, a post digital linearization technique is proposed and demonstrated for a conventional intensity-modulation direct-detection analog photonic link. Instead of precisely emulating the transfer function of the whole nonlinear system in the digital domain, the key distortion information is directly acquired from hardware. By low biasing the Mach-Zehnder modulator, linearization can be achieved through simply multiplying the distorted signal by the coreceived low-pass band. Theory analysis shows that only the bias angle should be known by the algorithm, whereas the simulation shows adequate tolerance. The low bias angle also results in an improved link gain. The experiment shows a well-suppressed third-order intermodulation distortion (IMD3). With the optical down conversion, we demonstrate a spurious-free dynamic range increasing from 103.2 to 123.3 dB in a 1-Hz bandwidth. [ABSTRACT FROM PUBLISHER]

We analyze, in theory, simulation, and experiment the spurious-free dynamic range (SFDR) for a radio-over-fiber (RoF) system using a polarization-dependent electro-absorption modulator (EAM) that is linearized using mixed polarization. The mixed-polarization EAM makes use of a polarization-dependent EAM, where a linear polarizer is placed in front of and behind the optical modulator. It is found that improvements of more than 8.1 and 9.5 dB in SDFR for back to back and after 20 km of fiber transmission, respectively, are predicted in theory and simulation and verified experimentally. Suppression of second-order nonlinear distortion is also investigated by simulation and experiment. Moreover, closed forms of the adjacent channel power ratio and third-order intermodulation distortion to carrier power ratio of an orthogonal frequency division multiplexing (OFDM) ultra-wideband (UWB) signal are presented for an RoF link using mixed-polarization EAM. Finally, mixed-polarization EAM is verified for improving the error vector magnitude of the OFDM UWB signal over fiber by more than 3 dB. [ABSTRACT FROM PUBLISHER]

We derive closed-form expressions for nonlinear transmission performance of dual-polarization closely spaced coherent optical orthogonal frequency-division multiplexing (CO-OFDM) systems. We find that the fiber nonlinear noise exhibits a signature of the flicker noise or 1/f noise beyond the corner frequency that is inversely proportional to the total participating bandwidth. We derive a noise enhancement factor that captures the interference effect of nonlinear noises among different spans. For a 10 \times 100-km standard single-mode-fiber (SSMF) link with no dispersion compensation at an optimal launch power density of - 15.9 dBm/GHz, the spectral efficiency of 9.90 b/s/Hz can be achieved for dual-polarization transmission, which is about 93% increase over single-polarization transmission. The closed-form expressions are also applicable to the closely spaced coherent single-carrier systems where the symbol rate is much larger than the dispersion walk-off bandwidth, and the optical dispersion is uncompensated. [ABSTRACT FROM PUBLISHER]

This paper describes a multistandard fiber fed wireless system, which provides low-cost and enhanced performances regarding laser nonlinearity and RF transmitted power. Experimental results demonstrate that the proposed scheme provides not only optimized performances for low cost coming both from plastic optical fiber and vertical cavity surface emitting lasers (VCSELs), but also optimization of RF modulation power by complementary cumulative distribution function analysis and enhanced linear behavior by a whole new quasi-static approach of the VCSEL. With the help of those features, we successfully demonstrate minimization of error vector magnitude for simultaneous ultra-wideband multiband-orthogonal frequency division multiplexing and wireless local area network 802.11g optically transmitted signals and the possibility to use this system under conditions for symmetrical wireless communication. [ABSTRACT FROM PUBLISHER]

We propose a novel approach to characterize the parabolically-shaped pulses that can be generated from more conventional pulses via nonlinear propagation in cascaded sections of commercially available normally dispersive (ND) fibers. The impact of the initial pulse chirp on the passive pulse reshaping is examined. We furthermore demonstrate that the combination of pulse pre-chirping and propagation in a single ND fiber yields a simple, passive method for generating various temporal wave- forms of practical interest. [ABSTRACT FROM AUTHOR]

Recently, a unique approach has been reported in which optical signal degradation is suppressed by realizing mode-hop isolation. This paper analyzes the mode-hop isolation condition in fiber Bragg grating type external-cavity diode lasers (FBG-ECDL). As a result, it has become possible to determine whether mode-hop isolation could be achieved. Moreover, it was verified experimentally that the mode-hop isolation of FBG-ECDLs was actually achieved with this method. The analytical method described in this paper is very useful for designing the uncooled ECDLs whose mode-hop must be isolated. [ABSTRACT FROM AUTHOR]

This year not only commemorates the 60th anniversary of nonlinear optics with the seminal experiment of second harmonic generation [[1]], but it is also the 30th anniversary of the invention of the photonic crystal fiber (PCF) [[2]]. By contrast with the pressurization of a hollow-core PCF with gas to adjust the dispersion, filling the air channels of a standard solid-core PCF guiding light by modified total internal reflection can drastically affect its guidance mechanism. In particular, by filling a broadband-guiding hollow-core PCF with noble gases and pumping it with near-infrared ultrashort pulses, it is possible to generate tunable UV radiation via soliton self-compression [[38]] and resonant dispersive wave emission [[39]]. 10.1364/OL.41.002811 25 Tyumenev R., Russell P.S.J., Novoa D. Narrowband Vacuum Ultraviolet Light via Cooperative Raman Scattering in Dual-Pumped Gas-Filled Photonic Crystal Fiber. [Extracted from the article]

This paper proposes a hexagonal photonic crystal fiber (H-PCF) structure with all circular air holes in order to simultaneously achieve ultrahigh birefringence and high nonlinearity. The H-PCF design consists of an asymmetric core region, where one air hole is a reduced diameter and the air hole in its opposite vertex is omitted. The light-guiding properties of the proposed H-PCF structure were studied using the full-vector finite element method (FEM) with a circular perfectly matched layer (PML). The simulation results showed that the proposed H-PCF exhibits an ultrahigh birefringence of 3.87 × 10−2, a negative dispersion coefficient of −753.2 ps/(nm km), and a nonlinear coefficient of 96.51 W−1 km−1 at an excitation wavelength of 1550 nm. The major advantage of our H-PCF design is that it provides these desirable modal properties without using any non-circular air holes in the core and cladding region, thus making the fiber fabrication process much easier. The ultrahigh birefringence, large negative dispersion, and high nonlinearity of our designed H-PCF make it a very suitable candidate for optical backpropagation applications, which is a scheme for the simultaneous dispersion and nonlinearity compensation of optical-fiber transmission links. [ABSTRACT FROM AUTHOR]

In this paper we seek a solution for robust broadband communication using high altitude platforms (HAPs). We address the requirements of the backhaul link and propose a hybrid millimeter-wave/optical solution to reduce weather-induced-outage probability and enhance throughput. We explore the concept of analogue-modulated wireless laser communication based on orthogonal frequency-division multiplexing (OFDM) in order to achieve a compact transparent payload onboard the HAP. Laser nonlinearity effects and the adverse effects of turbulence in the optical communication channel are identified as the major challenges to successful implementation of this solution and are analyzed. The dependence of normalized symbol error rate (SER) on signal power and turbulence strength is demonstrated for two modulation schemes. We show the severe performance degradation due to laser nonlinearity resulting from increasing signal power in sharp contrast to SER improvement with signal power when nonlinear distortion is not present. [ABSTRACT FROM PUBLISHER]