Effects Of Fiber Dispersion Research Articles

High-birefringence negative dispersion effect of novel rectangular lattice photonic crystal fiber

A novel rectangular lattice photonic crystal fiber is proposed which is composed of a central defect core and a cladding with square mesh structure by introducing another air hole row between two air hole rows for every other line into a conventional rectangular lattice photonic crystal fiber. Its dispersion, birefringence and confinement loss are numerically investigated by full vector finite element method with anisotropic perfectly matched layers. Numerical results indicate that the proposed fiber shows higher birefringence negative dispersion effect and stronger confinement ability of guided mode, in which the confinement loss is lower than 10-2 dB ·m-1. The wavelength for high birefringence negative dispersion can be optimized by adjusting the parameters of proposed fiber, such as Λ and d/Λ. The dispersion and the dispersion slope are both negative, the birefringence is higher than 10-2, and nonlinear parameter is close to 55 km-1W-1 over C band (i.e. 1.53—1.565 μm) under the condition of Λ=2.0 μm and d/Λ=0.4. This fiber will have important applications in the fields of polarization maintaining transmission system and dispersion compensation, and also in the design of widely tunable wavelength converter based on four-wave mixing.

Analysis of High-Speed Optical Wavelength/Time CDMA Networks Using Pulse-Position Modulation and Forward Error Correction Techniques

This paper presents a comprehensive analysis of an optical code-division multiple access (OCDMA) network based on two distinct modulation formats, namely ON-OFF keying (OOK) and pulse-position modulation (PPM). We also investigate how each of these modulation formats performs under two distinct 2-D coding schemes, i.e., single-pulse per row (SPR) and multiple-pulse per row (MPR). For both cases, we have accounted for the simultaneous effect of many different dispersion and noise mechanisms (including multiple access interference (MAI) that impair the overall system performance. We have included the laser relative intensity noise at the transmitter side, the fiber dispersive effects (group velocity dispersion (GVD), and first-order polarization-mode dispersion (PMD), and beat, avalanche photodiode (APD), and thermal noises at the receiver side. The effect of GVD and PMD, as well as the influence of noises, on the performance of SPR and MPR codes is also investigated. Another effect studied in this paper is the influence of the APD photodetector on the beat noise of an incoherent OCDMA network. To mitigate systems noises and bit error rate (BER), we have adopted a forward error correction (FEC) RS(255, 239) algorithm in both networks investigated here. New expressions for the BER with all noises and dispersion mechanisms were also derived for the SPR and MPR code schemes. Results indicated that OOK and PPM modulation schemes without additional mechanisms to mitigate MAI and other noise effects are not sufficient to accommodate 32 simultaneous users in an error-free environment (BER < 10-12). This occurs due to the already high BER at the FEC input, which severely affects FECs at the receiver side.

Numerical analysis of supercontinuum generation in highly nonlinear photonic crystal fibers with ultrashort pulses

We have numerically investigated supercontinuum generation in photonic crystal fibers with zero-dispersion wavelengths in the vicinity of 800 nm by using an input pulse with a peak power of about 20 kW and a width of about 10 fs. The effects of fiber dispersion and the input pulse parameters on the generated optical spectra are quantitatively analyzed. The propagation length necessary for the generation of a soliton in the anomalous dispersion region is found to depend on the zero-dispersion wavelength of a fiber. For the generation of a sufficiently broad spectrum, the photonic crystal fiber should be longer than the soliton-generation length. In addition, a spectral recoil effect appears when a solitary wave splits the dispersive wave into two parts.

Impact of Optical Transmission on Multiband OFDM Ultra-Wideband Wireless System With Fiber Distribution

Multiband (MB) orthogonal frequency-division multiplexing (OFDM) ultra-wideband (UWB) wireless, which provides high data rate access, is required to be distributed by using optical fiber. The performance of MB-OFDM UWB over fiber transmission system is investigated considering optical modulation and demodulation impact. Theoretical analysis of the effect of fiber dispersion, optical transmitter, and optical receiver response on system performance is carried out considering amplitude and phase distortion. Experiments are conducted and verified by our theoretical analysis and good agreement is obtained. It is found that RF modulation index of ~4% is optimum for optical transmitter with Mach-Zehnder modulator, and optical receiver with Chebyshev-II response is the best for MB-OFDM UWB over fiber. Compared to back-to-back UWB over fiber, optical transmission is mainly limited by laser phase noise converted relative intensity noise and phase distortion induced by fiber dispersion when optimum modulation index is used. Higher modulation index is limited by amplitude and phase distortion to OFDM signal induced by optical transmitter and receiver response nonlinearities and fiber dispersion and the spectral mask. It is also found that highly received optical power is required for transmission of MB-OFDM UWB signal over fiber.

광 이중 측파대 변조 방식과 16 QAM 신호를 이용한 부반송파/파장 분할 다중화 시스템의 성능 분석에 대한 연구

본 논문에서는 광 이중 측파대역 변조 방식과 16 QAM(Quadrature Amplitude Modulation) 신호를 이용한 부반송파/파장 분할 다중화 시스템의 성능을 부반송파 채널 간격, 누화 전력 량(crosstalk power), BER(Bit-Error Rate) 특성을 통해 연구하고 있다. 광 전송 링크에서 분산 특성과 자기 위상 변조, 상호 위상 변조와 같은 비선형 현상을 고려하였을 때 BER특성을 살펴보았다. 컴퓨터 시뮬레이션 결과, 부반송파/파장 분할 다중화 시스템의 성능을 결정짓는 주도적인 인자는 마흐-젠더 변조기의 비선형 특성과 부반송파 채널 간격으로 관찰되었다. 광섬유의 분산에 의한 영향만 고려했을 때는 전송거리가 증가함에 따라 높은 주파수에 있는 부반송파 채널의 BER 성능이 나빠졌으나, 분산과 비선형 효과를 함께 고려되었을 경우 광섬유에 입사하는 전력이 클 때 높은 주파수에 있는 부반송파 채널에서 약간의 BER 성능 향상을 확인할 수 있었다. In this paper, we investigate the performance limitations of SubCarrier Multiplexed(SCM) WDM systems using optical Double-Side Band(DSB) modulated 16 QAM signals. The Bit-Error Rate(BER) performance is evaluated under various optical transmission links including the effects of the dispersion and fiber nonlinearities such as SPM(Self-Phase Modulation) and XPM(cross-phase modulation). After simulation of SCM-WDM systems, the dominant factors determining the entire system performance are appeared to be the nonlinearity of MZ(Mach-Zehnder) modulator and the SCM channel spacing. The BER performance of subcarrier channels in the higher frequencies was degraded with the large dispersion effect only, however, the performance was improved a little with a combined effect of fiber dispersion and nonlinear effect when the hish fiber launching power was applied.

Effects of the Vector Combinatorial Codeconnection Parameters on the Performance of an OCDMA System for High-Speed Networks

In this paper, we study the performance of optical code-division multiple access (OCDMA) systems using vector combinatorial (VC) code under various link parameters. The impact of the fiber dispersion effects on the multi-user interference (MUI) is reported using a commercial optical systems simulator, Virtual Instrument Photonic (VPITM). The VC code is compared mathematically with other codes which use similar techniques. We analyzed and optimized the data rate, fiber length, and channel spacing in order to reduce the BER without the need to deploy dispersion compensating devices. The performance and optimization of VC code in OCDMA system is reported. We have demonstrated that, for a high data rate (higher than 2.5 Gb/s), even if dispersion compensated devices are not deployed, the BER can be significantly improved when the VC code desired parameters are selected. We have shown that when compensation dispersion devices are not deployed in the system, there is a tradeoff between the limited dispersion effects and the MUI.

Effects of the Random Diagonal code link parameters on the performance of an OCDMA scheme for high-speed access networks

In this paper, we study the performance of optical code-division multiple access (OCDMA) systems using Random Diagonal (RD) code under various link parameters. This code which can be constructed using address segment and data segment. One of the important properties of this code is that the cross correlation at data level is always zero, which means that Phase Intensity Induced Noise (PIIN) is reduced. The impact of the fiber dispersion effects on the MAI is reported using a commercial optical systems simulator, OptSim TM . The RD code is compared mathematically with other codes which use similar techniques. We analyzed and optimized the data rate, fiber length, and channel spacing in order to reduce the BER without the need to deploy dispersion compensating devices. The performance and optimization of RD code in OCDMA system is reported. We have demonstrated that, for a high data rate (higher than 2.5 Gb/s), even if dispersion compensated devices are not deployed, the BER can be significantly improved when the RD code desired parameters are selected. We have shown that when compensation dispersion devices are not deployed in the system, there is a trade off between the limited dispersion effects and the MAI.

Fracture of fiber-reinforced cement composites: effects of fiber dispersion

Short-fiber reinforcement is commonly used to improve various properties of cement-based materials, including their resistance to shrinkage cracking, post-cracking strength, and toughness. The spatial distribution of fibers within a structural component exhibits local variations that depend on many factors, including the methods of production. Local measures of fiber volume fraction can be much lower than the global average and such regions can act as flaws within the composite material. In addition, fiber orientation is restricted by any near surfaces of the structural component. Such non-uniformities of the fiber distribution can significantly affect fracture behavior and complicate the interpretation of fracture test results. This paper concerns the computational modeling of fiber- reinforced cement composites (FRCC), with attention to the effects of non-uniform fiber distributions. The simulations utilize lattice models of the matrix phase of the composite, based on the Voronoi tessellation of irregularly positioned nodes within the structural domain. A crack band approach provides energy-conserving, mesh-insensitive descriptions of fracture through the irregular lattice. Each fiber is explicitly modeled within the lattice framework. The fiber distributions are synthetically constructed within the structural domain, although experimentally determined fiber positions could be used. Models of simple tensile tests demonstrate a dependence of post-cracking strength and toughness on the spatial distributions of the fibers.

Maximum-Likelihood Phase and Channel Estimation for Coherent Optical OFDM

We present a channel model for a coherent optical orthogonal frequency-division-multiplexed (CO-OFDM) system including linear fiber dispersion effects and noises from optical amplifiers and intercarrier interference induced by laser phase noise. Based upon this model, we derive maximum-likelihood (ML) phase estimation and channel estimation for the CO-OFDM system. Both computer simulation and transmission experiment of the CO-OFDM system show that the ML decision-feedback following pilot-assisted phase estimation gives the optimal performance.

Practical Design Model of DnPSK Systems using direct BER Counting and Rigorous BER Modeling

Summary We present a design model for practical 100 Gb/s transmission DnPSK systems which accounts for imperfections in system components i.e. fiber attenuation, dispersion and non-linear effects, electrical drive circuitry for optical modulators, optical amplifiers including amplified spontaneous emission ASE noise and a realistic Rx description with non-ideal Low Pass Filtering (LPF). The model uses direct error-counting combined with an analytical rigorous BER model. An example 50 Gs/s DQPSK transmission system with 240 km transmission is considered for a specified 6 2 PRBS symbolsequence as well as for a 14 2 PRBS symbol-sequence where a selected 6 2 symbol-sequence is used in the theoretical results. We demonstrate excellent agreement between the two methods over two orders of magnitude for the Bit-Error-Rate (BER) in a system regime where the signal interaction with ASE noise during fiber transmission is not significant. The analytical BERresults are extended over ten orders of magnitude.

Analyses of constraints on high speed optical code division multiplexing access (OCDMA) link parameters due to fiber optic chromatic dispersion

In direct sequence-optical code division multiplexing access (DS-OCDMA) system networks, data rate and data spreading technique involved in such systems require a high chip rate. Transmission link in these systems is significantly affected by the fiber chromatic dispersion. In this study, we have developed and employed a simple model to estimate the G652 fiber dispersion effects. OCDMA technique has been employed to investigate fiber chromatic dispersion effects on multiple access interference (MAI). We have found that, at a short optical fiber length, the optical fiber dispersion has a significant impact on the high data rate transmission systems (higher than 750Mbit/s). The performance and optimization of optical orthogonal code (OOC) in the OCDMA system is reported. We have demonstrated that, for a high data rate, even if dispersion compensated devices are not deployed, the BER can be significantly improved when the OOC desired length is selected. We have shown that when compensation dispersion devices are not deployed in the system, there is a trade off between the limited dispersion effects and the MAI.

Effect of carbon fiber dispersion on the mechanical properties of carbon fiber-reinforced cement-based composites

The preparation of carbon fiber-reinforced cement-based composites involved two-step dispersions of carbon fibers. Both steps affected greatly the mechanical properties of the composites. With the aid of ultrasonic wave, a new dispersant hydroxyethyl cellulose was used to help fiber dispersion in the first step. The fracture surface of the composites was observed by scanning electron microscopy. The distribution of major elements was analyzed by the energy dispersive spectroscopy and the composition was analyzed through X-ray diffraction. The flexural strength, tensile strength, modulus, and compression strength were measured. Results showed that the distribution of major elements varied with the variation of the fiber dispersion status. The compressive strength increased by 20%, the tensile strength was 2.4 times that of the material without carbon fibers, the modulus increased by 26.8%, whereas the flexure stress decreased by 12.9%.

Externally Modulated Optical Minimum Shift Keying Format

This paper presents the generation and the performance evaluation of optical minimum shift keying (MSK) for high-speed and high-spectral-efficiency wavelength-division multiplexing systems. The detailed principle on optical MSK generation and detection is derived and analyzed. Optical MSK data (10.7 Gb/s) are successfully generated by an experiment using the proposed scheme. The results show that the optical MSK signal exhibits a very compact optical spectrum. The performance of the optical MSK modulated system is evaluated and compared with those of 50% duty-cycle return-to-zero differential phase shift keying (RZ-DPSK) and 50% duty-cycle return-to-zero on-off keying (RZ-OOK) modulated systems, via both simulation and experiment, in terms of dispersion tolerance, linear crosstalk, self-phase modulation (SPM) tolerance, stimulated Brillouin scattering (SBS) threshold, optimal receiver filter bandwidth, and optimal link launch power into single-mode fibers and dispersion compensation fibers. Experimental and simulation results show that the MSK signal exhibits the largest tolerance against fiber dispersion and SPM effect as compared with RZ-DPSK and RZ-OOK. Experimental results also confirm the negative penalty against the SPM effect. The SBS threshold of both the MSK and RZ-DPSK systems is more than 10 dB higher than that of the RZ-OOK system. The MSK that is generated with conventional carrier-suppressed return-to-zero (CSRZ) pulses exhibits a narrower optimal optical filter bandwidth but a wider electrical filter bandwidth compared with those of RZ-OOK and RZ-DPSK. The MSK signal that is generated with pure dual-mode pulses has a similar optimum range to RZ-OOK and RZ-DPSK at a high optical signal-to-noise ratio (OSNR) but has a narrower optimal optical filter bandwidth at a low OSNR. The optimum fiber launch power study shows that the MSK signal that is generated using the conventional CSRZ pulses exhibits higher optimum launch power, which agrees with the SPM tolerance study.

Simultaneous Cancellation of Fiber Loss, Dispersion, and Kerr Effect in Ultralong-Haul Optical Fiber Transmission by Midway Optical Phase Conjugation Incorporated With Distributed Raman Amplification

An alternative application of distributed Raman amplification (DRA) for ultralong-haul optical fiber transmission is proposed. In our study, the DRA is employed in a transmission system using midway optical phase conjugation (OPC) for amplifying an optical signal and, at the same time, for constructing signal power evolution, which is symmetrical with respect to the midpoint of the system where the OPC is performed. Then, the nonlinear signal waveform distortions that are caused by the Kerr effect, as well as fiber dispersion, are almost completely compensated by the OPC, whereas the fiber loss is compensated by the DRA. Three possible symmetrical signal power maps - a power map that has a reverse sign of the power map that is caused by lump amplification, a flat signal power map, and an arbitrary symmetrical signal power map - are numerically designed by using appropriate Raman pump powers. We show that the flat power map exhibits smaller difference from the target and a higher optical signal-to-noise ratio and requires lower pump power than the other two power maps. Numerical simulation results demonstrate that, by employing the flat power maps with a span of 40 km, a single-wavelength signal whose data rate is 160 Gb/s can be successfully transmitted over 5000 km, and the Kerr effect is sufficiently suppressed near limitation due to the nonlinear accumulation of noise. Finally, we study the feasibility of expanding our method to wavelength-division-multiplexed signal transmission by designing a DRA gain with multiple-wavelength pumping to simultaneously obtain a flat power map and a wide-and-flat gain bandwidth. By using four-wavelength Raman pumps while carefully choosing pump wavelengths and their powers, we achieve the DRA gain that simultaneously gives a fluctuation of the signal power of only 3.5%, a gain ripple of only 5.3%, and, at the same time, a gain bandwidth of as wide as 46 nm.

Harmonic and intermodulation distortion modeling in IM-DD multi-band radio over fiber links exploiting injection locked lasers

A comprehensive numerical tool has been developed for the evaluation of the performances of Radio over Fiber (RoF) links intended for wireless signal distribution.At the transmitter end an appropriate set of rate equations allows to model the optical source as a solitary laser or as an appropriately injection locked laser. The optical channel is modeled putting into account the combined effect of fiber dispersion, laser source non ideal performances (e.g. non-linear effects, frequency chirp), and quadratic detection of the receiving photodiode. The simulation model developed can be a useful tool at the design stage allowing a preliminary evaluation of the characteristics of real RoF links.

Double-pass remotely pumped Er3+-doped fiber amplifier embedded with chirped fiber Bragg grating

A highly efficient erbium-doped fiber amplifier configured in double-pass amplification scheme with a chirped fiber Bragg grating is demonstrated in this study. The chirped fiber Bragg grating is used to perform as the reflector and concurrently to compensate the effect of fiber dispersion. The proposed amplifier architecture is able to maintain gain of higher than 20 dB for small signals with 10 mW pump power. It has been successfully tested as the remotely pumped amplifier to compensate a span loss of 62.2 dB with 2.5 Gbps signal in a repeaterless transmission experiment. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 1993–1996, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21847

Dual-function remotely-pumped Erbium-doped fiber amplifier: Loss and dispersion compensator

An efficient Erbium-doped fiber amplifier configured in doublepass amplification scheme with chirped fiber Bragg grating as the reflector is presented in this paper. The proposed amplifier architecture is optimized and designed to work under consideration of low pump powers for remotely-pumped applications. The chirped fiber Bragg grating is used to reflect the amplified signal back to the Erbium-doped fiber and at the same time to compensate the effect of fiber dispersion. The proposed amplifier architecture is able to maintain gain of higher than 20 dB for small signals less than -23 dBm with 10 mW pump power only. The integrated function of loss and dispersion compensator in single black box is an attractive solution to be used as pre-amplifier.

Analysis of CNR penalty of radio-over-fiber systems including the effects of phase noise from laser and RF oscillator

The effect of phase noises from a laser and an oscillator on radio-over-fiber (RoF) systems is analyzed and discussed with a power spectral density (PSD) function. A Mach-Zehnder modulator (MZM) and a phase shifter are employed to externally generate an optical single sideband (OSSB) signal since the OSSB signal is tolerable for power degradation due to a chromatic fiber-dispersion effect. It is shown that a carrier-to-noise ratio (CNR) penalty is deeply related to the bandwidth of a receiver filter and the phase noise from a radio frequency (RF) signal oscillator rather than that from a laser in a small differential-delay environment and a direct detection scheme. The CNR penalty due to the increment of the laser linewidth from 10 to 624 MHz is almost 1.1 dB, while the increase of the RF-oscillator linewidth from 1 to 100 Hz results in about a 20-dB penalty at a 30-GHz 10-km transmission in a standard single-mode fiber (SSMF) with a fiber chromatic dispersion of 17 ps/km/spl middot/nm.

Optical CDMA detection by basis selection

In this paper, we present a novel optical code-division multiple-access (O-CDMA) multiuser detector employing a basis-selection (BS) algorithm called the orthogonal-matching pursuit (OMP) algorithm. The proposed detector is compared with the receiver structures previously proposed in the literature. The effects of fiber dispersion to the various types of CDMA detectors are investigated. It is shown by simulation results that the proposed detection architecture is a very promising candidate, given its low computational complexity and high detection performance. It is also shown to be more robust to low signal-to-noise ratio (SNR) and near-far effect when compared to most of the well-known O-CDMA receiver architectures.

A comparison between optical SSB transmitter/filter in a full-duplex radio-on-fiber transport system

We present the investigation of the fiber Bragg grating (FBG) filter as an optical single sideband (SSB) filter at the receiving site. A comparison is made with an alternative optical SSB generation technique using optical SSB transmitter. The function of the optical SSB filter is employed to replace the optical SSB transmitter, not only to select the appropriate wavelength but also to suppress the fiber dispersion effect. Using simple FBG filter as an optical SSB filter in full-duplex radio-on-fiber (ROF) transport systems is a very attractive option, as it is passive and potentially low cost.