Search

In this paper, we investigate the impact of the integrability criterion on mixed-derivative nonlinear Schrödinger equations, specifically focusing on the Rangwala-Rao (R R) equation introduced by A. Rangwala in 1990. Our objective is to enhance our understanding of the dispersion effect by examining innovative soliton wave solutions and their interactions. The tanh method is utilized to generate unique solitary wave solutions for the Rangwala-Rao (R R) equation. The study of the Rangwala-Rao (R R) holds significance as it has the potential to contribute to the development of more efficient optical fiber communication systems. The numerical solutions presented in this research illustrate the dynamic nature of optical fiber pulse propagation, underscoring the distinctiveness of this work compared to previous scholarly endeavors. The study obtained various soliton solutions, including rational, trigonometric, and hyperbolic functions. The results are presented in graphical form with appropriate parameter values to aid visualization. The originality of our computed outcomes, which represent novel achievements that surpass previously derived solutions, becomes evident when we compare our accomplishments with theirs. These newly examined results are innovative and novel, with the potential to significantly propel the realms of nonlinear optics and mathematical physics forward. This study proves that the computational method used is efficient, brief, and widely applicable, making it valuable to engineers who work with engineering models and dynamical models. [ABSTRACT FROM AUTHOR]

In this work, we realised the soliton solutions of nonlinear Schrödinger equation (NLSE) that arise from optical fibers, we considered the modified Sardar sub-equation method (MSSEM) to find solitary solutions analytically. The stability of the retrieved soliton solutions realised from the NLSE are investigated. We demonstrate the soliton solutions that are stable and can last for a very long time without losing its form or energy under specific circumstances and those soliton solutions that are unstable. The MSSEM is a frequently employed technique in research for addressing specific mathematical modeling or physical phenomena problems. Its selection in this specific study might stem from its proven efficacy in handling the particular problem under investigation. The decision to utilize MSSEM could be driven by several considerations, including its precision, computationally efficient, effectiveness, greater accuracy and capability to manage intricate systems. Finally, our method offers greater flexibility in modeling various physical phenomena, which makes it particularly useful in applications in diverse fields such as quantum mechanics and nonlinear optics. The findings have ramifications for the architecture of optical fiber communications and offer significant new insights into the behavior of solitons in optical systems. The NLSE has proven to be an effective tool for understanding wave behavior in fiber optics. Its applications have helped engineers and scientists optimize the design of optical fibers and predict the behavior of various conditions. Moreover, our study provides insights into the fundamental properties of solitary solutions in the NLSEs and their practical implications in physical systems. [ABSTRACT FROM AUTHOR]

In this work we introduce new numerical compact finite-difference algorithms for modeling nonlinear signal propagation in transmission systems based on multimode optical fibers, in the presence of nonlinearity and random linear mode coupling. We compare the computational efficiency of these methods with respect to the standard split-step Fourier method, for different regimes of random mode coupling, such as the weak, the intermediate, and the strong coupling regime. We reveal that, in the intermediate random coupling regime, a non-iterative version of the compact scheme can be twice faster than the standard Fourier method. • Numerical algorithms for modeling signal propagation in multimode transmission links. • Compact finite-difference algorithm of higher order of accuracy. • Different propagation regimes depending on the strength of random linear coupling. • Comparison of the proposed algorithms with the split-step Fourier method. [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]

We present the concept and design of a 100 GHz PIC-based nonlinear frequency division multiplexed transmission system in which four b -modulated spectrally overlapping channels are spectrally stitched without frequency guard bands to obtain a continuous spectrum. Neural network-based equalizers are used at the receiver for improved performance. Simulations show that the proposed system alleviates the problem of nonlinear interaction between neighboring channels, that would, otherwise, be out of reach even for neural network equalization to solve on its own. The system achieves a 960 km transmission distance with a raw data rate of 333 Gbps per polarization and a BER well below the SD-FEC limit for every subcarrier. • New concept and design of a 100 GHz PIC-based nonlinear frequency division multiplexed transmission system. • b -modulated spectrally overlapping channels are stitched to obtain a continuous spectrum without nonlinear interaction between channels. • Neural network-based equalizers are used at the receiver for improved performance. • The system achieves a 960 km transmission distance with a raw data rate of 333 Gbps per polarization and a BER well below the SD-FEC limit for every subcarrier. [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]

Abstract Among various fibre nonlinearity compensation schemes, digital backpropagation (DBP) is considered a benchmark because it can eliminate all deterministic linear and nonlinear impairments. The so-called nonlinear Shannon limit in optical fibre transmissions with DBP origins from nondeterministic effects, mainly nonlinear signal–noise interaction (NSNI) via the Kerr effect. Previous analysis of the nonlinear transmission performance is generally based on an assumption of weak NSNI. In this paper, we extend the theoretical analysis to the strong NSNI. We analyse the accumulation of NSNI along the whole fibre link and derive closed-form expressions of SNR and other important parameters. Subsequently, we verify our theoretical analysis in simulation and show that our expression still provides a good prediction well beyond the SNR peak, where the nonlinear phase shift is much larger than unity and the NSNI is strong. Our solutions provide more accurate amendments to the established ones, and we extend them to optical fibre transmission systems with polarization-multiplexing, wavelength-division multiplexing and finite transceiver noise. [ABSTRACT FROM AUTHOR]

The modeling of the simultaneous propagation of high-power and bidirectional data along the same 10-km-long single-mode fiber is discussed. The intense signal carries the energy needed to supply an instrument in the context of cabled submarine observatories. The considered mathematical description takes into account the fiber’s nonlinear behavior in terms of Raman and Brillouin scattering to describe spectral propagation in the static regime. By testing our model against measurements, its validity is evaluated. Preliminary results are promising and reveal the path to follow for its improvement. [ABSTRACT FROM AUTHOR]

We analytically and numerically investigate the propagation dynamics of initially chirped symmetric Airy pulses in an optical fiber. The results show that the positive chirps act to promote the interference in generating a focal point on the propagation axis, while the negative chirps tend to suppress the focusing effect, as compared to conventional unchirped symmetric Airy pulses. The numerical results demonstrate that the linear propagation of chirped symmetric Airy pulses depend considerably on the chirp parameter and the primary lobe position. In the anomalous dispersion region, positively chirped symmetric Airy pulses first undergo an initial compression, and reach a foci due to the opposite acceleration, and then experience a lossy inversion transformation, and come to the opposite facing focal position. The impact of truncation coefficient and Kerr nonlinearity on the chirped symmetric Airy pulses propagation is also disclosed separately. [ABSTRACT FROM AUTHOR]

A novel full-duplex hybrid passive optical network/radio over fiber (PON/RoF) link with 10-Gbit/s 4-ary quadrature amplitude modulation (4-QAM) signal for alternative wired and wireless converged access is proposed. In the central station (CS), optical frequency multiplication (OFM) is implemented to generate millimeter- wave (mm-wave) band optical carrier with three tones via a dual-electrode Mach-Zehnder modulator (DE-MZM). The downlink QAM baseband signal is modulated on one sideband via an optical I/Q modulator. At the hybrid optical network unit (HONU), the downlink converged signal is routed into different receiver modules to achieve wired or wireless access. Moreover, the centralized lightwave separated from the downlink is reused as the uplink optical carrier for either wired or wireless access, and modulated by the baseband or mm-wave data of the uplink alternatively. Since the HONU is free from the laser source, the system complexity and cost are reduced. The simulation results show that our proposed full-duplex hybrid PON/RoF link for the alternative wired and wireless access maintains good performance even when the transmission link with standard single mode fiber (SSMF) is extended to 30 km. [ABSTRACT FROM AUTHOR]

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]

An arsenic tri-selenide-based strip/slot hybrid waveguide with a single horizontal silica slot is proposed to achieve an extremely low and flat dispersion with three zero dispersion wavelengths. By adjusting the geometrical structural parameters of the hybrid waveguide, dispersion tailoring is fully obtained. The flat group velocity dispersion varying between ±0.08 ps2/(m) is obtained over a 1253 nm bandwidth. The parameters of effective area, nonlinear coefficient, and third-order dispersion are all investigated. Moreover, a compact on-chip all-optical wavelength converter is designed based on degenerate four-wave mixing in this waveguide. The dependencies of conversion efficiency and conversion bandwidth on the pump wavelength are discussed. The impact of pump power and signal power on the conversion efficiency is also investigated. The results show that a maximal conversion efficiency of −0.46 dB, and a 3-dB conversion bandwidth of 830 nm in the mid-infrared is achieved. [ABSTRACT FROM AUTHOR]

A fiber-optic sensing scheme of measuring pressure is described here. The high reflective mirror in a laser cavity is replaced by a Sagnac loop in this scheme. The method combining the Sagnac effect with fiber loop ringdown technology fully embodies the advantages of both. The working principle is discussed in detail, and the whole sensing performance is demonstrated by applying sensing force to the sensor area. The sensing force can be obtained by measuring the ringdown time. The pressure measurement range of this device is 40 to 350 N. The detection sensitivity 0.4 ns∕N can be realized in this system. The experimental curve reveals a close relationship between the sensing strain and the ringdown time. [ABSTRACT FROM AUTHOR]

Optical communication system is a kind of communication system using the light wave as the carrier. It has been widely used in recent years with the advantages of the long distance. Optical solitons have some merits for high stability, amenable to generate and low cost, it is an ideal carrier of optical communication system. In this paper, the regulation of pulse characteristics of the optical soliton is studied theoretically. The influence of high-order dispersion and high-order nonlinear effects on the amplitude, shape and other transmission characteristics of the optical soliton is studied by using the bilinear method with the high-order variable coefficient nonlinear Schrödinger (NLS) equation in the nonuniform fibers, and the regulation problems such as the maintenance and excitation of the optical soliton are analyzed. The waveform and amplitude control of the optical soliton and the change of optical soliton characteristics with the dispersion management are studied profoundly, and the nonlinear dynamic processes in their respective intracavity are analyzed. A feasible scheme for avoiding and utilizing the optical soliton is proposed, which has the significance for the investigation of the parameter regulation and dynamic control of the optical soliton in practical inhomogeneous optical fiber communication systems. [ABSTRACT FROM AUTHOR]

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]

We have evaluated that in-line non-linear compensation schemes decrease the complexity of digital backward propagation and enhance the transmission performance of 40/112/224 Gbit/s mixed line rate network. Multiple bit rates, i.e. 40/112/224 Gbit/s and modulation formats (i.e. DP-QPSK and DP-16QAM) are transmitted over 1280 km of Large $$\hbox {A}_{eff}$$ Pure-Silica core fiber. Both grouped and un-grouped spectral allocation schemes are investigated. Optical add-drop multiplexers are used to drop the required wavelength for signal processing in the transmission link. Moreover, hybrid mid-link spectral inversion and in-line non-linear compensation methods are also analyzed. This gives us enhanced system performance and DBP step-size of 400 km in WDM 224 Gbit/s DP-16QAM system, significantly reducing the complexity of digital backward propagation. [ABSTRACT FROM AUTHOR]

Photonic time stretched analog-to-digital converter (PTS-ADC) utilizes a broadband optical source and dispersion medium to expand the capabilities of electrical digitizers, achieving real-time sampling with high resolution. In order to minimize used fiber length and simplify PTS-ADC equipment, large dispersion photonic crystal fiber (PCF) is used as dispersion medium. In this letter we demonstrated the impact of optical nonlinearity on PTS-ADC based on large dispersion PCF performance as compared with single mode fiber (SMF) and dispersion compensation fiber (DCF). It is stimulated that dispersion penalty null frequency of fundamental tone will shift using three fibers when nonlinearity is added. In comparison, SMF is most insensitivity by changing input optical power, then PCF. However PCF is most insensitive by changing pulse width. Meanwhile, PCF is best to suppress 3rd-order harmonic distortion according to carrier-to-interference ratio (CIR) in three fibers. PCF is the most suitable as broadening medium in PTS-ADC. [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]

Coherent-Optical OFDM systems are known to be sensitive to large peak-to-average power ratio (PAPR) at the transmitter output, due to nonlinear properties of some components involved in the transmission link. In this paper, we investigate the impact of an amplification of such signals via a semiconductor optical amplifier (SOA), considering some recent experimental results. An efficient tradeoff between BER performance, computational complexity and power efficiency is performed by a proper design of Wang's nonlinear companding function, considered for the first time in an optical communication context. A BER advantage of around 3 dB can hence be obtained over a standard system implementation not using PAPR reduction. The designed function also proves to be more efficient than μ -law function, considered in the literature as an efficient companding scheme. [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]

In this work, a novel scheme to realize optical Meyer wavelet filter based on time lenses and Mach-Zehnder modulators in optical domain was proposed and the transfer functions of Meyer wavelet decomposition and reconstruction processed in frequency domain were derived to realize Meyer wavelet de-noising for optical signal. The filter could be used to reduce the nonlinear noise induced by the interaction of EDFA's ASE noise, fiber's dispersion and nonlinearity in high bit rate multi-span optical communication systems without photo-electric conversion. The bit error rate curves of the optical bit sequence without and with optical Meyer wavelet filter were plotted to show the effectiveness of the optical Meyer wavelet filter, which can achieve better result and improve the optical communication quality in dispersion compensation links. [ABSTRACT FROM AUTHOR]

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]

Abstract: We investigated the transient and steady-state processes of a probe field in an optical fiber. It is found that the nonlinear processes can be easily controlled via the coherent field and incoherent pumping field. The underlying mechanisms are much more practical than those in atomic systems, which may provide some possibilities for technological applications in optical-fiber communication. [Copyright &y& Elsevier]

Abstract: A semi-analytical model with three optimizing parameters and a novel non-Gaussian function as the fundamental modal field solution has been proposed to arrive at an accurate solution to predict various propagation parameters of graded-index fibers with less computational burden than numerical methods. In our semi analytical formulation the optimization of core parameter U which is usually uncertain, noisy or even discontinuous, is being calculated by Nelder–Mead method of nonlinear unconstrained minimizations as it is an efficient and compact direct search method and does not need any derivative information. Three optimizing parameters are included in the formulation of fundamental modal field of an optical fiber to make it more flexible and accurate than other available approximations. Employing variational technique, Petermann I and II spot sizes have been evaluated for triangular and trapezoidal-index fibers with the proposed fundamental modal field. It has been demonstrated that, the results of the proposed solution identically match with the numerical results over a wide range of normalized frequencies. This approximation can also be used in the study of doped and nonlinear fiber amplifier. [Copyright &y& Elsevier]

Abstract: Evolution of dual-wavelength fiber laser from continuous wave to soliton pulses is investigated experimentally by using the nonlinear polarization rotation technique. With the increase of pump power, the proposed laser successively delivers the dual-wavelength continuous wave, the single-wavelength soliton pulses, and the dual-wavelength soliton pulses. The dual-wavelength laser operates at the central wavelengths of about 1533 and 1546nm with the separation of ∼13nm. The number of soliton pulses operating in the dual-wavelength state is much larger than that of the single-wavelength state, while the pulse intensity always keeps constant. Experimental results reveal that the dual-wavelength mode locking is determined by the combination of pump strength and the cavity filtering effect. [Copyright &y& Elsevier]

Abstract: We theoretically and numerically study the difference frequency generation and the signal amplification bandwidth together with the pump wavelength acceptance for counterpropagating optical parametric amplifiers. It is shown that the specific advantage of those amplifiers is that the DFG and amplification bandwidth is much narrower than in a co-propagating scheme, thus making it possible to shift spectrally or to amplify selectively a single channel over the several present in WDM optical fiber communications. Moreover, the pump wavelength acceptance is shown to be as broad as in the co-propagating scheme. The implementation of such counterpropagating optical parametric amplifiers in a quasi-phase-matched LiNbO3 waveguide is discussed. [Copyright &y& Elsevier]

Abstract: A multi-fiber architecture is proposed to mitigate the nonlinear impairments in fiber-optic systems. The power launched to each fiber is reduced in multi-fiber architecture as compared to the case of single fiber leading to reduction in nonlinear impairments. The optical pulses propagating in the fibers undergo different amount of phase shifts and timing delays. Optical and electrical equalization techniques to compensate for these channel effects are discussed. Our numerical simulation results show that for unrepeatered systems, the performance (Q factor) is improved by 6.2dB using 8-fiber configuration as compared to single-fiber system. In addition, for multi-span system, the transmission reach at a bit error rate (BER) of 2.1×10−3 is quadrupled in 8-fiber configuration. [Copyright &y& Elsevier]

Abstract: Conventional methods which extract dispersion parameters of an optical fiber using four wave mixing rely on the measurement of optical power in the generated wavelengths, and hence are prone to measurement errors. We propose and demonstrate a power-independent method to extract the dispersion curve of a fiber using four wave mixing (FWM). The analytical equations that have been traditionally used to estimate the phase mismatch in FWM are modified to cater to low-dispersion fibers, and are verified. Experiments to obtain the dispersion curve of a low-dispersion and highly nonlinear fiber are discussed and the results are analyzed. Limitations of any FWM-based method to extract the dispersion curve of a fiber are presented for the first time. [Copyright &y& Elsevier]

Abstract: An approach to convert NRZ signal to Manchester code at 20 Gbit/s based on nonlinear optical fiber loop mirror (NOLM) is demonstrated. Using 20 Gbit/s NRZ data and optical clock as external pumps of the NOLM, the conversion of NRZ to Manchester code is successfully realized. The eye diagrams, waveforms and optical spectra are presented. We investigated the extinction ratio (ER) penalty (5dB) to evaluate the system performance and analyzed the method to improve it. The proposed scheme is potential for applications in future networks. [Copyright &y& Elsevier]

Abstract: This paper presents a multi-functional all-optical device performs simultaneous chromatic dispersion (CD) monitoring, extinction ratio (ER) improvement and tunable wavelength conversion using four-wave mixing (FWM) in a single piece of highly nonlinear optical fiber (HNLF). The multi-functional ability arises from the nonlinear power transfer function (PTF) between the input signal and the output idler wave, which not only maps the CD information of the signal onto the average power of idler wave, but also transfers the data information to the idler wave with ER enhancement, making the device compact and cost effective. Furthermore within the wavelength tuning range the monitoring sensitivity and output ER can be much higher compared to all optical monitors and regenerators proposed before. Numerical simulations are then used to demonstrate the efficiency of this method. [Copyright &y& Elsevier]

Abstract: We present a detailed investigation of all-optical RZ-OOK to RZ-BPSK modulation format conversion at 10Gb/s using cross-phase modulation in a length of highly nonlinear fiber. In particular, we examine the impact of the input RZ-OOK signal characteristics, such as duty cycle, average (peak) power, optical signal to noise ratio, and degradation from residual dispersion and differential group delay on the BER performance of the converted RZ-BPSK signal. We also present results on RZ-OOK to RZ-BPSK modulation format conversion with wavelength multicasting. [Copyright &y& Elsevier]

In this paper, we propose the design of tunable and robust wavelength converters which can perform the polarity-preserved or polarity-inverted wavelength conversion by using the cross-phase modulation (XPM) in a dispersion-flattened highly nonlinear photonic crystal fiber (DF-HNL-PCF). The newly designed wavelength converter consists of a DF-HNL-PCF and an optical band-pass filter in the simple straight-line configuration, where XPM leads to broadening the spectrum of a continuous-wave probe light and the polarity-preserved, tunable wavelength conversion is then implemented by filtering out the blue-chirped or red-chirped spectral component of a probe light. The experimental results show that the polarity-preserved wavelength converter using a DF-HNL-PCF can achieve the error-free conversion of 10 Gbit s-1 optical data signals with the maximum power penalty of less than 2.1 dB over a wavelength range of nearly 34 nm. This wavelength tunability is actually limited by an operational wavelength range of the tunable optical band-pass filter that is used to extract the wavelength-converted signal in our experiment. Moreover, the polarity-inverted wavelength conversion is observed at the XPM-based wavelength converter using a DF-HNL-PCF, for the first time. This is achieved by tuning the central wavelength of an optical band-pass filter to coincide with that of a chirped probe light. [ABSTRACT FROM AUTHOR]

Abstract: We consider the evolution of nonlinear optical pulses in inhomogeneous optical media wherein the pulse propagation is governed by the nonlinear Schrödinger equation with varying dispersion. We adopt the Painlevé analysis in order to obtain the condition for the soliton pulse propagation. We find that there exist two dispersion profiles satisfying this criterion, namely, the constant dispersion and exponentially dispersion decreasing profiles. In the exponentially varying dispersion media, we explain the existence and the formation of chirped optical soliton through the equation for the chirp parameter that results from variational analysis. For further elucidation, we provide the phase-plane diagram in terms of the normalized chirp and intensity (peak power), which explains the physical mechanism of linearly chirped soliton pulse compression in the exponentially dispersion decreasing media. In addition, we discuss the generation of exact chirped higher order solitons using the Bäcklund transformation method. As a special case, we find an oscillatory two-soliton breather pulse, which, at decreasing intervals, evolves into a familiar hyperbolic secant shape whose amplitude is twice that of a fundamental soliton. We highlight on the point that the crux of this work in realizing a compact pulse compressor could possibly result in a myriad of applications in modern optical fiber communications systems. [Copyright &y& Elsevier]

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]

Abstract: We numerically investigate the impact of channel baud-rate on the performance of logarithmic step-size based spilt-step Fourier method (SSFM). This algorithm is used to implement digital backward propagation (DBP) to efficiently compensate fiber chromatic dispersion (CD) and non-linearities (NL). The DBP method is implemented in N-channel dual-polarization quadrature phase shift keying (DP-QPSK) transmission over 2000km standard single mode fiber (SMF) with no in-line optical dispersion compensation. We investigate the same-capacity and same-bandwidth transmission systems with 56Gbit/s/ch (14GBaud), 112Gbit/s/ch (28GBaud) and 224Gbit/s/ch (56GBaud). Each system has the bandwidth occupancy of 500GHz with a total transmission capacity of 1.12Tbit/s. Moreover, we have also compared the multiple channel transmission performance with single channel transmission to quantify the impact of inter-channel (cross-phase modulation ‘XPM’ and four-wave mixing ‘FWM’) and intra-channel (self-phase modulation ‘SPM’) non-linearities. The logarithmic step-size based DBP algorithm (L-DBP) depicts efficient mitigation of CD and NL impairments. The benefit of the logarithmic step-size is the reduced complexity and computational time for higher baud-rate transmission systems. [Copyright &y& Elsevier]

Abstract: We demonstrate a tunable and switchable dual-wavelength passively mode-locked fiber ring laser in the anomalous dispersion regime that generates high-energy pulses at a sub-100kHz repetition rate. The nonlinear polarization rotation (NPR) technique is employed in this configuration to allow for passively mode-locked operation. By exploiting the intensity-dependent loss caused by NPR, the mode competition could be efficiently alleviated. Moreover, taking advantage of the intrinsic spectral filter induced by the intracavity birefringence, the dual-wavelength separations as well as the wavelength lasing locations could be flexibly tuned by properly rotating the polarization controller. With a repetition rate of 85.8kHz, the laser delivers the single pulse energy of 198nJ at a pump power of 250mW. The combination of high per-pulse energy and flexible tunability in this fiber laser is useful for practical applications. [Copyright &y& Elsevier]

Abstract: We studied the sharp asymmetric Fano line shape in fiber ring resonator systems and provided an explicit expression for asymmetry parameters using the physical parameters of the system. The fiber ring system was controllable and reconfigurable, allowing us to produce a variety of Fano line shapes in different configurations. Experimentally observed asymmetric spectral structures were fully reproduced using the complex-number asymmetry parameters, validating the approximations used to reduce the analytical expression for the line shape to the phenomenological Fano formula. The results may be useful in the design of on-chip application systems. [Copyright &y& Elsevier]

Abstract: We introduce a new measurement method of the nonlinear coefficient (NC) of a highly nonlinear fiber based on a four-wave mixing (FWM) technique. The NC along with the fiber''s zero-dispersion wavelength (ZDW) was determined from the precise measurement of the pump power dependent optimum pump frequency for peak FWM signal generation conditions. The measurement errors of the NC and ZDW values determined with this method were less than 4.6% and 0.051nm, respectively. [Copyright &y& Elsevier]

Abstract: Simultaneous all-optical multi-channel regeneration based on second-order four-wave mixing (FWM) in a single highly nonlinear fiber (HNLF) is studied. Interchannel crosstalk, especially cross gain saturation and generation of interchannel FWM, is avoided by properly time-interleaved channels. Preliminary experiment of 2ch×10Gbit/s operation shows simultaneous noise reduction of the two channels and good agreement with numerical analysis. Numerical investigation on 2ch×40Gbit/s operation using the same parameters as the experiment shows that the regeneration can improve qualities of both channels. For more number of channels and higher speed of operation, several parameters need to be adjusted to avoid interchannel crosstalks. Time synchronization techniques for the input channels are also discussed. [Copyright &y& Elsevier]

Abstract: Correlated signal and idler photon pairs with small detuning in the telecom band can be generated through spontaneous four-wave mixing in dispersion shift fibers. However, photons originated from other nonlinear processes in optical fibers, such as Raman scattering and self-phase modulation, may contaminate the photon pairs. It has been proved that photons produced by Raman scattering are the background noise of photon pairs. Here we show that photons induced by self-phase modulation of pump pulses are another origin of background noise. After studying the dependence of self-phase modulation induced photons in signal and idler bands, we demonstrate that the quantum correlation of photon pairs can be degraded by the self-phase modulation effect. The investigations are useful for characterizing and optimizing an all fiber source of photon pairs. [Copyright &y& Elsevier]

Abstract: In this paper we report passive harmonic mode-locking of an Erbium/Ytterbium-doped double-clad fiber laser with repetition rates up to 10GHz. The modes synchronization was obtained using Nonlinear Polarization Rotation mechanism. The stable operation at 634th harmonic of the fundamental (15.8MHz) repetition frequency was achieved. Soliton pulses with the duration of less than 900fs and 300mW average output power were obtained. [Copyright &y& Elsevier]

Abstract: We investigate optical rogue waves in nonlinear optical fiber with group-velocity dispersion, cubic nonlinearity and linear gain managements. We present conditions for controlling the dynamics of optical pulses via a lens-type transformation. By properly choosing the distributed coefficients, we demonstrate analytically that rogue waves can be restrained or even be annihilated, emerge periodically and sustain forever. We also figure out the center-of-mass motion of rogue waves. [Copyright &y& Elsevier]

Abstract: This paper presents a semi analytical formulation of modal properties of a non linear optical fiber having Kerr non linearity with a three parameter approximation of fundamental modal field. The minimization of core parameter (U) which involves Kerr nonlinearity through the non-stationary expression of propagation constant, is carried out by Nelder–Mead Simplex method of non linear unconstrained minimization, suitable for problems with non-smooth functions as the method does not require any derivative information. Use of three parameters in modal approximation and implementation of Simplex methods enables our semi analytical description to be an alternative way having less computational burden for calculation of modal parameters than full numerical methods. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a simple index-guiding square photonic crystal fiber (SPCF) where the core is surrounded by air holes with two different diameters. The proposed design is simulated through an efficient full-vector modal solver based on the finite difference method with anisotropic perfectly matched layers absorbing boundary condition. The nearly zero ultra-flattened dispersion SPCF with low confinement loss, small effective area as well as broadband supercontinuum (SC) spectra is targeted. Numerical results show that the designed SPCF has been achieved at a nearly zero ultra-flattened dispersion of 0±0.25ps/(nm·km) in a wavelength range of 1.38μm to 1.89μm (510nm band) which covers E, S, C, L and U communication bands, a low confinement loss of less than 10−7 dB/m in a wavelength range of 1.3μm to 2.0μm and a wide SC spectrum (FWHM=450nm) by using picosecond pulses at a center wavelength of 1.55μm. We then analyze the sensitivity of chromatic dispersion to small variations from the optimum value of specific structural parameters. The proposed index-guiding SPCF can be applicable in supercontinuum generation (SCG) covering such diverse fields as spectroscopy applications and telecommunication dense wavelength division multiplexing (DWDM) sources. [ABSTRACT FROM AUTHOR]

We experimentally demonstrate an all-optical bit error monitoring scheme based on the self-phase modulation occurring during the propagation in a highly nonlinear fiber followed by an optical bandpass filter. Numerical simulations are confirmed by experimental observations performed at a repetition rate of 40 Gb/s. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:392-395, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25711 [ABSTRACT FROM AUTHOR]

Abstract: Simultaneous wavelength conversion of multichannel polarization shift keying (PolSK) signal using four-wave-mixing in highly non-linear fiber is demonstrated. In the proposed wavelength converter, the wavelengths of four 10-Gb/s polarization shift keying channels are simultaneously converted without any performance degradation for the converted channels. We successfully achieved high conversion performances for all the converted channels even though the input PolSK channels have different delay time and state of polarization. [ABSTRACT FROM AUTHOR]

Abstract: A novel bit-rate adaptive method, by varying the optical sampling rates alternatively, is proposed in this paper for optical performance monitoring. Firstly, the theoretical model and the differential software-synchronized algorithm are developed. Then, the results verify that different channel bit-rate can be estimated with high precision irrespective of the modulation formats and signal distortion caused by chromatic dispersion and nonlinearity along the fiber link. Employing the proposed bit-rate adaptive method, the eye diagrams and Q values of 10Gbit/s, 40Gbit/s and even higher bit-rate signal can be monitored by a single optical performance monitoring system without any prior knowledge about bit-rate or signal period. The method we propose in this paper has the advantage that different channel bit-rates can be adaptively estimated and the differential software-synchronized algorithm is much simpler. [ABSTRACT FROM AUTHOR]