Power penalty for optical signals due to dispersion slope in WDMfilter cascades

We calculate the receiver power penalty due to the accumulated dispersion slope of optical filter cascades in wavelength-division-multiplexed optical networks. For flat-top fiber Bragg grating and thin-film filters, dispersive rather than amplitude filter effects dominate the cascade power penalty, which increases with dispersion slope and signal frequency detuning from the cascade zero-dispersion point. The dispersion slope of these filters varies as the inverse cube of their bandwidth, using increased penalties for narrow filters in systems with small channel spacing, For a 60-GHz-wide Bragg grating filter with a 1.3-ns/nm² dispersion slope, a cascade of 26 filters can be tolerated at 10 Gbit/s with ±5 GHz allowed detuning. Optically preamplified receivers have significantly larger dispersion penalties than thermal-noise-limited receivers     

Synthesized Structure of Amplitude—sampled FBG by Simple Inverse FT Technology and Its Application

Using the simple inverse Fourier transformation(FT), the index modulation structure with the sampled period for the sampled fiber Bragg gratings was designed. In this method, the enable channels are operated at identical wavelength while the unable channels are almost suppressed completely. The enable and unable channels can be established based on the applications. This technique is very useful to design the optical devices such as optical add and drop multiplexers (OADMs), and interleavers with dispersion and dispersion slope compensation.     

Impact of fiber dispersion on the performance of entanglement-based dispersive optics quantum key distribution

Dispersive optics quantum key distribution (DO-QKD) based on energy-time entangled photon pairs is an important QKD scheme. In DO-QKD, the arrival time of photons is used in key generation and security analysis, which would be greatly affected by fiber dispersion. In this work, we established a theoretical model of the entanglement-based DO-QKD system, considering the protocol, physical processes (such as fiber transmission and single-photon detection), and the analysis of security tests. Based on this theoretical model, we investigate the influence of chromatic dispersion introduced by transmission fibers on the performance of DO-QKD. By analyzing the benefits and costs of dispersion compensation, the system performance under G.652 and G.655 optical fibers are shown, respectively. The results show that dispersion compensation is unnecessary for DO-QKD systems in campus networks and even metro networks. Whereas, it is still required in DO-QKD systems with longer fiber transmission distances.     

Impact of Fiber Dispersion on Performance of Entanglement-Based Dispersive Optics Quantum Key Distribution

Dispersive optics quantum key distribution (DO-QKD) based on energy-time entangled photon pairs is an important QKD scheme. In DO-QKD, the arrival time of photons is used in key generation and security analysis, which would be greatly affected by fiber dispersion. In this work, we establish a theoretical model of the entanglement-based DO-QKD system, considering the protocol, physical processes (such as fiber transmission and single-photon detection), and the analysis of security tests. Based on this theoretical model, we investigate the influence of chromatic dispersion introduced by transmission fibers on the performance of DO-QKD. By analyzing the benefits and costs of dispersion compensation, the system performance under G.652 and G.655 optical fibers are shown, respectively. The results show that dispersion compensation is unnecessary for DO-QKD systems in campus networks and even metro networks. Whereas, it is still required in DO-QKD systems with longer fiber transmission distances.     

Performance engineering and topological design of metro WDM opticalnetworks using computer simulation

This paper demonstrates the use of computer simulation for topological design and performance engineering of transparent wavelength-division multiplexing metropolitan-area networks. Engineering of these networks involves the study of various transport-layer impairments such as amplifier noise, component ripple, chirp/dispersion, optical crosstalk, waveform distortion due to filter concatenation, fiber nonlinearities, and polarization effects. A computer simulation methodology composed of three main simulation steps is derived and implemented. This methodology obtains performance estimations by applying efficient wavelength-domain simulations on the entire network topology, followed by time-/frequency-domain simulations on selected paths of the network and finally Q-budgeting on an identified worst case path. The above technique provides an efficient tool for topological design and network performance engineering. Accurate simulation models are presented for each of the performance impairments, and the computer simulation methodology is used for the design and engineering of a number of actual metro network architectures     

Performance evaluation of very long span direct detection intensityand polarization modulated systems

In this paper long distances very high capacity NRZ optical transmission systems adopting direct detection are considered in links with a low average chromatic dispersion. Particular attention is devoted to polarization modulated (PM-DD) systems. Polarization modulated systems results to he more degraded with respect to intensity modulated (IM-DD) systems by the light depolarization induced by the interplay among the Kerr effect, the ASE noise of the optical amplifiers and the polarization mode dispersion. The light depolarization is particularly strong in conditions of large spectral broadening that are met when the chromatic dispersion value is maintained very low along the link. On the other hand the use of a fluctuating chromatic dispersion with a mean value equal to zero, whereas the local dispersion is different from zero, shows the double advantage to reduce the chromatic dispersion impairments and to limit the spectral broadening. The advantages offered by this dispersion management technique have been already shown in several experiments for IM-DD systems: in this work we show that this technique is very important also for PM-DD systems since the limitation in the spectral broadening reduces the light depolarization. We show that adopting a suitable dispersion management and an opportune preamplifier optical filter transmissions at 5 Gb/s can be attained in transoceanic links by means of FM-DD systems     

Tunable optical filters for dense WDM networks

WDM is currently taking over as the leading technology in point-to-point transmission links. For optical implementation of WDM networks, logical functionalities such as wavelength (channel) selection should be carried out in the wavelength domain; thus, the development of dynamic optical devices is required. One key device is a tunable optical filter. Important features of such a filter include low insertion loss, narrow bandwidth, high sidelobe suppression, large dynamic range, fast tuning speed, a simple control mechanism, small size, and cost effectiveness. Here, an extensive overview of the different technologies used to produce tunable optical filters is presented. Among them, fiber filters such as fiber Bragg gratings and fiber Fabry Perot are the most commercialized, yet inherently limited in their dynamic speeds. For high demanding dynamics, micro-machined and acousto-optic filters can offer a good solution for microsecond tuning speeds. Faster tunable devices, in nanosecond tuning speeds, might emerge out of microresonators, electrooptic filters, and active DBR filters     

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.     

薄膜干涉型光学全通滤波器的设计与分析

设计并分析了用于多信道色谱补偿的薄膜Gires-Tournois干涉仪（GTI）型光学全通滤波（OAPF），讨论了反射镜的膜层结构对器件 的群延迟谱和反射谱的影响，。以及大角度入射引起的偏分离现象和幅度畸变现象，给出了单级和多级串拉OAPF的初步设计结果。     

Autocorrelation pulse distortion in optical fiber CDMA systemsemploying ladder networks

This paper extends a pulse propagation previously developed by Marcuse for the characterization of pulse transmission in single mode fibers to the case of pulsed optical code-division multiple-access (CDMA) systems that employ encoders and decoders based on ladder networks. The model accounts for important degradation factors such as fiber dispersion, source linewidth (coherence), chip time duration and phase and delay mismatch between the source encoder and the destination decoder. Although results are only presented for the autocorrelation signal, the model can be employed to analyze the impact of the above mentioned     

The realization of all-pass filters for third-order dispersioncompensation in ultrafast optical fiber transmission systems

Thin film (TF)-based coupled cavity all-pass filters (CCAP) have the potential for providing compact, low-loss, and highly stable third-order dispersion (TOD) compensation in ultrafast optical fiber transmission systems employing optical time-division multiplexing (OTDM). In this paper, a methodology for designing CCAP filters for TOD compensation is presented, First, we develop a theory necessary for designing the cavity structure, that is, mirror reflectivity and cavity spacing, of CCAP filters. As a next step, we discuss how we can represent such filters as TF devices and demonstrate several TF-layer design examples. Finally, a coupled two-cavity filter is constructed and tested. The filter has a center wavelength that can be varied over a range of 8 nm and can compensate for fiber TOD between 2.0 and 15.5 ps ³ over a bandwidth between 3.6 and 1.2 nm, respectively. The peak spectral ripple of the filter is 1.0 dB, The experimentally measured dispersion curves of the filter agree well with the theory     

Signal processing for optical communication

Optical communication plays a significant and increasing role in our society. The public demand for higher network speed requires an optical backbone network with larger capacity. Accompanying high transmission-rate optical communications system are severe technical specifications for optical devices and systems. Many popular optical devices could be represented with a digital filter model as described in this article. Use of well-developed signal processing techniques and algorithms to design these optical devices is a wise use of existing technology. The wavelength division multiplexing (WDM) system, which is the dominating optical communication system, is introduced in this article. Three signal processing application examples for optical communications are presented: optical wavelength interleaver, an all-pass filter for chromatic dispersion compensation, and an electronic equalizer. As demonstrated in this article, signal processing could play an important role in the development of advanced optical communication systems. However, as demonstrated in the case of an electronic equalizer, some optical system characteristics may require special attention if signal processing techniques are to be applied successfully. Therefore, interdisciplinary cooperation between researchers in optics and signal processing will be crucial for optical communications to fully benefit from signal processing.     

Enhanced performance of WDM systems using directly modulated lasers on positive dispersion fibers

Cost-effective directly modulated distributed feedback lasers (DML) have attracted much attention recently for operation at the 1.55 μm wavelength band applications in metropolitan area networks. In this paper, we show by simulation that the effect of directly modulated laser chirp can be compensated by a negative dispersion fiber, but this only occurs in a specific range of DML output power, and that a pulse broadened by the positive dispersion fiber can be equalized using self-phase-modulation (SPM) in optical fiber. The majority of metro and access networks are made up of conventional single-mode fibers (SMF) which are positive dispersion fibers. We demonstrated that optimum compensation is always feasible for such fibers, since the magnitude of the SPM can be controlled by changing the optical power in the fiber. Furthermore, simulation suggests that this technique will enable directly modulated wavelength division multiplexed systems to enhance their performance if the power of each channel is appropriate.     

Design of Dispersion Compensation and Nonlinear Distortion Self-compensation in Co-network Transmission Systems

Dispersion and nonlinear distortion have an effect on transmission performances of optical fiber transimission systems,The schemes of dispersion compensation and nonlinear distortion self-compensation in telecom-CATV co-network transmission systems are reported,followed by investigation on (1) the impact of dispersion compensation fiber (DCF) on fiber nonlinear effects with a cascade of erbium-doped fiber amplifiers (EDFAs) and different dispersion compensation schemes,(2) the impact of the complex on the total nonlinear distortion induced by EDFA gain tilt and the light source.As a result,dispersion compensation optimal scheme and EDFA negative gain tilt are suggested as a solution to dispersion compensation optimal scheme and EDFA negative gain tilt are suggested as a solution to dispersion compensation and the nonlinear distortion self-compensation.     

Dispersion Monitoring Techniques in High Bit-rate Optical Communication Systems

For the efficient dynamic dispersion compensation, it is essential to monitor the dispersion accurately. The existing main dispersion monitoring techniques in high bit-rate optical communication systems are presented as well as their operating principles and research progress. The advantages and disadvantages of these methods are analyzed and discussed.     

Optical Performance Monitoring of Phase-Modulated Signals Using Asynchronous Amplitude Histogram Analysis

As optical networks continue to grow towards high capacity and high flexibility, new transmission technologies are being introduced. In order to maintain the quality of signal and control over network in the transparent domains, optical performance monitoring (OPM) systems are becoming a necessity. Phase modulation formats emerge as the solution of choice in transparent domains because of their sensitivity, spectral efficiency, and resilience to optical impairments. In this paper, we demonstrate a flexible OPM method for phase-modulated signals using asynchronous amplitude histogram analysis. We show numerically and experimentally the monitoring of optical signal-to-noise ratio (OSNR), chromatic dispersion (CD), and polarization-mode dispersion (PMD) for differential phase-shift keying (DPSK) and differential quadrature phase-shift keying (DQPSK) signals. The OSNR can be measured within range of 20-35 dB and accumulated chromatic dispersion between 600 and 600 ps/nm. The asynchronous amplitude histogram monitoring method is proved to be a precise and versatile monitoring tool for high-capacity optical networks.     

Impact of cascaded filters-based OADMs in an all optical backbone network/Influence des multiplexeurs d’insertion-extraction optiques, fondés sur des filtres en cascade, sur un réseau dorsal entièrement optique

In all optical backbone networks, the introduction of Ultra Long Haul (ulh) optical systems associated with Optical Add Drop Multiplexers (oadm) gives rise to new network architectures and also to new engineering constraints, because signals suffer effects which do not exist in networks today. The purpose of this paper is to study, through numerical simulations, the impact on the signal brought by the concatenation of oadms. It is usually predicted that the transmission quality is severely degraded by filtering effects. However, the simulations show that by introducing for example a small amount of non-linearities, degradations do not obligatorily happen. So as to highlight the effects of some parameters, we have built, in the simulation tool, different components having particular properties to vary amplitude, frequency and phase of filter group delay ripple. We show how in some circumstances, the eye widens due to cross phase modulation reduction or due to the interplay between chromatic dispersion and non-linear effects.     

Small signal analysis with higher-order dispersion for dispersive optical communication systems

In this paper an improved small-signal analysis has been presented for analyzing the influence of the higher-order dispersion terms on dispersive optical communication systems operating near zero-dispersion wavelength for single mode fiber. A generalized conversion matrix has been reported that gives the transfer function of intensity and phase from the fiber input to fiber output for laser source including the influence of any higher-order dispersion term. In addition, analysis is applicable to evaluate the impact of combined or independent dispersion terms on small-signal frequency response and relative intensity noise (RIN) response of an ultrafast laser diode including noises due to laser spontaneous emission rate and average photon density. These responses are plotted for second-, third-, and fourth-order dispersion terms and their combinations. It is observed that the higher-order dispersion terms have significant impact on frequency and RIN responses at large modulating frequencies and large propagation distances.     

Dispersion effects of FBG filter and optical SSB filtering in DWDM millimeter-wave fiber-radio systems

We study the optical filtering technique for dense wavelength division multiplexing (DWDM) channel allocation of millimeter-wave fiber-radio signals in the optical double-sideband (DSB) format. First, we investigate both theoretically and experimentally the dispersion effect of fiber Bragg grating (FBG) used as the filter on DWDM millimeter-wave optical signal transmissions. This result suggests that the dispersion effect has to be considered in the DWDM channel allocation for millimeter-wave fiber-radio access systems. Next, we propose a DWDM allocation for millimeter-wave fiber-radio systems, which adopts the optical single-sideband (SSB) filtering technique at the receiver side by using a square response of FBG filter. It can realize the minimum WDM channel interval for optical DSB signals, while it enables the optical frequency interleave between the neighboring channels without any serious signal degradation due to the interchannel interference. Then, we experimentally demonstrate the error-free DWDM transmission of two 60-GHz-band, 155.52-Mb/s differential phase-shift keying (DPSK) fiber-radio signals over 25-km-long single-mode fiber (SMF) with the minimum channel interval of 83.6 GHz (=0.68 nm) by using the test-square response FBGs. Finally, we show that based upon the experimental results, in the micro- or pico-cellular DWDM broad-band millimeter-wave fiber-radio access network 1000 antenna base stations (BSs) under the coverage of the single central office (CO) would be feasible by sectorizing the zone.     

Dispersive properties of optical filters for WDM systems

Wavelength division multiplexing (WDM) communication systems invariably require good optical filters meeting stringent requirements on their amplitude response, the ideal being a perfectly rectangular filter. To achieve high bandwidth utilization, the phase response of these filters is of equal importance, with the ideal filter having perfectly linear phase and therefore constant time delay and no dispersion. This aspect of optical filters for WDM systems has not received much attention until very recently. It is the objective of this paper to consider the phase response and resulting dispersion of optical filters in general and their impact on WDM system performance. To this end we use general concepts from linear systems, in particular, minimum and nonminimum phase response and the applicability of Hilbert transforms (also known as Kramers-Kronig relations). We analyze three different classes of optical filters, which are currently being used in WDM systems and compare their performance in terms of their phase response. Finally, we consider possible ways of linearizing the phase response without affecting the amplitude response, in an attempt to approximate the ideal filter and achieve the highest bandwidth utilization