Academic literature on the topic 'Optical fiber communication, optical modulation, Wavelength Division Multiplexing (WDM)'

Dense Wavelength Division Multiplexing (DWDM) is the current area of interest to exploit the bandwidth offered by optical fiber to enhance the data rate requirements. In the present paper analysis of DWDM system using Erbium Doped Fiber Amplifier (EDFA) is carried out in C-band. The 32-channel Wavelength Division Multiplexing (WDM) system, with a high-performanceflowrate of 10 Gbps, has been evaluated. The performance of Return to Zero (RZ) and Non-Return to Zero (NRZ) modulation formats in an optical communication system are investigated by modeling an optical fiber link using software OPTISYS V14. According to the modulated outputs, a comprehensive comparison in terms of Q factor is developed to establish the advantages and disadvantages of the code formats NRZ and RZ in short and long haul optical fiber communication system. Optimum results of Bit Error Rate (BER) and Q-factor are obtained for 60, 80 and 100km of fiber length. Pumping is discussed at 980nm and 1480nm.

Radio over fiber (RoF) techniques are good candidates to create the backbone of the next generation of wireless networks. Many parameters affect RoF communications such as amplified spontaneous emission noise (ASE), four-wave mixing nonlinearity (FWM), the modulation, channel spacing, switching voltage, and phase shifter. In this paper, we propose an improved model of RoF communication systems using subcarrier multiplexing/wavelength division multiplexing (SCM/WDM) technique with unequal channel spacing and 1-km Erbium-doped fiber amplifier (EDFA). Simulation results confirmed that we could obtain the lowest bit error rate and noises when the EDFA is placed at 1 km from the transmitter by using optical single-sideband (OSSB) modulation at frequencies 193.1 THz, 193.2 THz, 193.35 THz, and 193.6 THz.

Nonlinear effects in the optical transmission systems (OTSs) are considered as the major performance limiting factor to provide high transmission rates over ultra-long distances. As the demands for system capacity, transmission range and the number of users is increasing exponentially with the development of mobile broadband, new challenges are being faced by the backbone optical networks. Mainly, the refractive index related non-linearities (RIrNLs) need to be characterized to design an optimal OTS for error-free transmission with provision of wavelength division multiplexing (WDM) to support for multiple channels. This paper provides an estimation technique of RIrNLs for long-haul transmission and their treatment for different channel spacing and the number of channels in a WDM system operating frequency domain multiple in multiple out (FD-MIMO) equalizer based digital signal processing (DSP) receiver and microstrip Chebyshev low pass filter. The main focus of this work is to utilize the existing structure of OTS for RIrNLs treatment with a low cost solution. Thus, by varying the parameters of the third order dispersion parameters, group velocity dispersion parameters, phase modulation dispersion and nonlinear refractive index, the impact of RIrNLs is investigated in detail to enhance the transmission range and capacity of the current OTS. The proposed system is analyzed in terms of range of input power, fiber length and received power for OTS figure of merits including bit error rate (BER) and optical signal-to-noise ratio (OSNR). Using duo-binary modulation, the BER achieved in this work is <10−5 till 500 km range, for maximum number of 32 channels, with 100 Gbps aggregate data rate, which shows the feasibility and effectiveness of our proposed model.

In this paper, we experimentally investigate the turbulence mitigation methods in free-space optical communication systems based on orbital angular momentum (OAM) multiplexing. To study the outdoor atmospheric turbulence environment, we use an indoor turbulence emulator. Adaptive optics, channel coding, Huffman coding combined with low-density parity-check (LDPC) coding, and spatial offset are used for turbulence mitigation; while OAM multiplexing and wavelength-division multiplexing (WDM) are applied to boost channel capacity.

Abstract Free space optics (FSO) is well-competent and premier technology to cater the high speed services in different geographical areas such as hilly areas and inter building network. In this paper, we successfully demonstrated the spectrum sliced wavelength division multiplexed FSO system. In order to make system bandwidth efficient, frequency spacing of 75 GHz is taken among the wavelength division multiplexing (WDM) channels. Carrier spectrum broadening is achieved for spectrum slicing through the nonlinearity called self-phase modulation. Moreover, requirement of multiple laser sources is eliminated. However, in conventional WDM systems, n numbers of lasers are needed to generate n WDM channels. To strengthen the signal in this FSO system, three optical amplifiers are scrutinized such as erbium-doped fiber amplifier (EDFA), semiconductor optical amplifier (SOA) and Raman amplifier in terms of Q-factor and bit error rate (BER). Results revealed that EDFA is best amplifier in proposed SS-WDM-FSO system.

<p>Fiber Raman amplifiers in ultra wide wavelength division multiplexing (UW-WDM) systems have recently received much more attention because of their greatly extended bandwidth and distributed amplification with the installed fiber as gain medium. It has been shown that the bandwidth of the amplifier can be further increased and gain spectrum can be tailored by using pumping with multiple wavelengths. Wide gain of the amplifier is considered where two sets of pumps N_R {5,10} are investigated. The gain coefficient is cast under polynomial forms. The pumping wavelength l_R is over the range 1.40 £ l_R, mm £ 1.44 and the channel wavelength l_s is over the range 1.45 £ l_s, mm £ 1.65. Two multiplexing techniques are processed in long-haul transmission cables where number of channels is up to 10000 in ultra-wide wavelength division multiplexing (UW-WDM) with number of links up to 480. The problem is investigated over wide ranges of affecting sets of parameters.</p>

Optical communication uses light signals for transmitting information from source to destination. Optical fiber communication has been more popular for long-distance data transfer in recent years due to various benefits such as low loss, low cost, simple amplification, minimal interference, and lightweight. A simple optical telecommunication system consists of a transmitter, a medium, and a receiver. Wavelength Division Multiplexing (WDM) is a significant improvement in optical communication. WDM is basically used for improving spectral efficiency and to handle more data from several clients. Normal WDM, CWDM, and DWDM are three types of WDM technology. DWDM uses the most denser optical channels in optical networking. Complete detail about all types of WDM is given. The optical spectrum used in the transmission of light signals is also discussed.

Abstract Analysis of wavelength division multiplexing (WDM) system utilizing erbium-doped fiber amplifier (EDFA) has been carried out by many researchers. In this paper, the performance analysis of 8-channel WDM system utilizing EDFA and fiber Bragg grating (FBG) combination is carried out in a wavelength band 1546–1552 nm at 10 Gbps. The performance of three apodization functions (Uniform, Gaussian and Tanh) of FBG is compared using return-to-zero (RZ) and non-return-to-zero modulation formats at fiber lengths 50, 60, 70 and 80 km. Also, the performance of FBG is compared for both aspects: with chirp and without chirp for grating lengths 5–10 mm. The Gaussian apodized and linearly chirped FBG outperformed the other two in compensating chromatic dispersion. Optimum values of Q-factor are also obtained using linearly chirped FBG with RZ modulation format at 10 mm of grating length.

The discovery of optical fiber cause widespread revolution of communication system. Optical fiber communication has excellency on data transmission speed, security, flexibility, and broadly bandwidth. The applying of WDM network can broaden the bandwidth so that the transmission performance becomes more splendid. Although some factors such as dispersion, attenuation, and scattering can hinder the performance of fiber optic on sending data. Moreover dispersion can wreck data and spread pulse as it travels alongs fiber so that causing interference. There is some methods of dispersion compensation. In this paper, Fiber Raman Amplifier is used on WDM network to strengthen signal which is sent to detector. This research utilize simulation approachment with various bandwidth and length fiber. The results show lowest BER value and highest Q-factor at bandwidth frequency of 30 GHz and fiber length of 20 km.

Optical communication networks are becoming the backbone of both national and international telecommunication networks. With the progress of optical communication systems, and the constraints brought by WDM transmissions and increased bit rates, new ways to convert the binary data signal on the optical carrier have been proposed. There are different factors that should be considered for the right choice of modulation format, such as information spectral density (ISD), power margin, and tolerance against group-velocity dispersion (GVD) and against fiber nonlinear effects like self-phase modulation (SPM), cross-phase modulation (XPM), four-wave mixing (FWM), and stimulated Raman scattering (SRS). In this dissertation, the several very important modulation formats such as Non Return to Zero (NRZ), Return to Zero (RZ), Chirped Return to Zero (CRZ), Carrier Suppressed Return to Zero (CSRZ), Differential Phase Shift Keying (PSK) and Carrier Suppressed Return to Zero- Differential Phase Shift Keying (CSRZ-DPSK) will be detailed and compared. In order to make performance analysis of such modulation formats, the simulation will be done by using VPItransmissionMakerTM WDM software.

The task of the project was to evaluate a differential phase shift keying demodulation technique by replacing a Mach-Zehnder interferometer receiver with an optical filter (Fiber Bragg Grating). Computer simulations were made with single optical transmission, multi channel systems and transmission with combined angle/intensity modulated optical signals. The simulations showed good results at both 10 and 40 Gbit/s. Laboratory experiments were made at 10 Gbit/s to verify the simulation results. It was found that the demodulation technique worked, but not with satisfactory experimental results. The work was performed at Eindhoven University of Technology, Holland, within the framework of the STOLAS project at the department of Electro-optical communication.

Le réseau d’accès optique est en plein essor, notamment avec le déploiement massif de Fiber to-the-home (FTTH) amenant la fibre jusqu’à l’usager et l’arrivée de la 5ème génération (5G) pour les communications mobiles. Sa démocratisation et l’évolution des usages d’Internet encourage la montée en débit au-delà des 10Gbit/s prévus avec le XG(S)-PON. Il existe de nombreuses solutions pour y parvenir. Dans cette thèse, la montée en débit du réseau d’accès optique passif (PON) sera étudiée sous trois axes :• L’utilisation du format de modulation PAM4 pour réutiliser les composants optiques et électrique sà 10GHz pour atteindre 25Gbit/s. Ce format de modulation à quatre niveaux d’amplitude, en plus d’avoir une meilleure efficacité spectrale que le NRZ couramment utilisé, permet l’introduction d’une structure de PON fonctionnant à deux débits. Au cours du chapitre traitant du PAM4, l’amplification optique sera étudiée pour améliorer les performances de budget optique. La dernière partie traite de l’extrapolation des résultats expérimentaux pour simuler une transmission PAM8.• Les propositions des industriels concernant la montée en débit, à travers trois prototypes. Le premier prototype concerne une application de la norme NG-PON2 et de son option PtP WDM. Le deuxième prototype démontre la faisabilité d’une transmission duobinaire à 25Gbit/s en bande latérale résiduelle. Le troisième et dernier prototype présentera une ébauche de solution pour réaliser le lien fronthaul pour la 5G mobile avec une technologiePtP WDM à 25Gbit/s par canal.• L’implémentation de l’égalisation dans le cadre du PON. Le traitement du signal est très utilisé dans les transmissions optiques du réseau de transport. Avec la montée en débit, son utilisation dans le réseau d’accès semble inévitable. Dans cette partie, les spécificités du PON et des transmissions point-à-multipoints sont étudiées pour proposer une implémentation d’égalisation en accord avec les contraintes de coûts du réseau d’accès et les contraintes liées à la topologie du réseau d’accès
The optical access network is booming, especially with the massive deployment of FTTH connecting clients’ home and antenna sites for the incoming 5G. The fiber’s popularization and the transformation of data consumption drive the bitrate growth. Many solutions are proposed. In this thesis, the passive optical network’s (PON) bitrate growth will be studied along three axes :• PAM4 to reuse 10GHz optoelectronical components to reach 25Gbit/s. This four levels modulation format is more bandwidth efficient than NRZ and it allows to transmit two bitratesas the same time on a PON tree. Within the first chapter, optical amplification is studied to enhance the optical budget for a PAM4 transmission. Last part of the chapter presents asimulation based on the real-time experiment to simulate PAM8.• Three vendors’ solutions for the throughput growth. The first prototype is based on theNG-PON2 standard and its PtP WDM option. The second prototype demonstrates how to transmit 25Gbit/s with duobinary and vestigial side band modulation. The last prototype illustrates a youthful solution for 5G fronthauling with a PtP WDM system transmitting at 25Gbit/s.• Equalization in PON’s context. Signal processing and equalization are common in optical transport links. With the throughput rising, equalization in access network seems indispensable. In the chapter, an implementation of equalization is proposed congruently with point-to-multipoints PON application and compliantly with access network’s cost needs and topology

碩士
中華大學
電機工程學系碩士班
88
The wavelength-division-multiplexing (WDM) optical fiber communication system with incomplete dispersion compensations are studied. During signal transmission, signal pulse width of each channel may be compressed or broadened by the combined effect of the dispersion, self-phase modulation and cross-phase modulation. A formula is derived to estimate the root-mean-square (rms) pulse width of WDM system in the absence of amplifier noise during signal transmission. Exact rms pulse width is numerically solved to compare with the rms pulse width estimated by the formula. Using the derived formula, the effect of the cross-phase modulation on the WDM system is clearly understood. With amplifier noise, system performance is evaluated by Q factor. By proper post dispersion compensation, the improvement of system performance in each channel is studied, and the design rules of the WDM system are found.

Chong, Kin Man.
Thesis (M.Phil.)--Chinese University of Hong Kong, 2009.
Includes bibliographical references (p. 58-63).
Abstract also in Chinese.
Acknowledgement --- p.i
Abstract --- p.ii
摘要 --- p.iv
Table of contents --- p.vi
List of figures and tables --- p.viii
Chapter Chapter 1 --- Introduction --- p.1
Chapter 1.1. --- Overview of optical regeneration --- p.1
Chapter 1.1.1. --- O-E-O regeneration --- p.3
Chapter 1.1.2. --- All-optical regeneration --- p.5
Chapter 1.2. --- Motivation of this thesis --- p.7
Chapter 1.3. --- Outline of this thesis --- p.9
Chapter Chapter 2 --- Previous schemes of all-optical regeneration --- p.10
Chapter 2.1. --- Introduction --- p.10
Chapter 2.2. --- Fiber-based all-optical regeneration --- p.12
Chapter 2.2.1. --- SPM-based regeneration --- p.12
Chapter 2.2.2. --- FWM-based regeneration --- p.15
Chapter 2.3. --- Semiconductor-based all-optical regeneration --- p.18
Chapter 2.3.1. --- XGM-based regeneration --- p.18
Chapter 2.3.2. --- XAM-based regeneration --- p.20
Chapter 2.4. --- Multi-wavelength regeneration --- p.22
Chapter 2.5. --- Summary --- p.23
Chapter Chapter 3 --- Multi-wavelength optical 2R regeneration utilizing self-phase modulation and inter-channel walk-off control in fiber --- p.25
Chapter 3.1. --- Introduction --- p.25
Chapter 3.2. --- System architecture of the regenerator --- p.27
Chapter 3.3. --- Experimental setup --- p.28
Chapter 3.4. --- Results and discussions --- p.32
Chapter 3.4.1. --- Effects of the improper inter-channel walk-off --- p.35
Chapter 3.4.2. --- Effects of the improper filter offset --- p.36
Chapter 3.5. --- Summary --- p.39
Chapter Chapter 4 --- Investigation of the scalability and cascadability of our proposed multi-wavelength regeneration scheme --- p.40
Chapter 4.1. --- Introduction --- p.40
Chapter 4.2. --- Simulation models and results --- p.41
Chapter 4.2.1. --- 10x10-Gb/s scenario --- p.41
Chapter 4.2.2. --- 4x40-Gb/s scenario --- p.47
Chapter 4.3. --- Discussions --- p.51
Chapter 4.4. --- Summary --- p.53
Chapter Chapter 5 --- Conclusion and future works --- p.54
Chapter 5.1. --- Summary of the thesis --- p.54
Chapter 5.2. --- Future works --- p.55
List of publications --- p.57
Bibliography --- p.58

Photonics and Optical techniques have advanced recently by a great extend to play an important role in Microwave and Radar applications. Antenna array of modern active phased array radars consist of multiple low power transmit and receive mod- ules. This demands distribution of the various Local Oscillator(LO) signals for up conversion of transmit signals and down conversion of receive signals during various modes of operation of a radar system. Additionally, these receivers require control and clock signals which are digital and low frequency analog, for the synchronization between receive modules. This is normally achieved through RF cables with complex distribution networks which add significantly higher additional weight to the arrays. During radar operations, radio frequency (RF) transmit signal needs to be distributed through the same modules which will in turn get distributed to all antenna elements of the array using RF cables. This makes the system bulky and these large number of cables are prone to Electromagnetic Interference (EMI) and need additional shielding. Therefore it is very desirable to distribute a combination of these RF, analog and digital signals using a distribution network that is less complex, light in weight and immune to EMI. Advancements in Optical and Microwave photonics area have enabled carrying of higher datarate signals on a single fiber due to its higher bandwidth capability including RF signals. This is achieved by employing Wavelength Division Multi- plexing (WDM) that combine high speed channels at different wavelengths. This work proposes, characterizes and evaluates an optical Wavelength Division Multiplexed(WDM) distribution network that will overcome the above mentioned problems in a phased array radar application. The work carries out a feasibility analysis supported with experimental measurements of various physical parameters like am- plitude, delay, frequency and phase variation for various radar waveforms over WDM links. Different configurations of optical distribution network are analyzed for multipoint distribution of both digital and RF signals. These network configurations are modeled and evaluated against various parameters that include power level, loss, cost and component count. A configuration which optimizes these parameters based on the application requirements is investigated. Considerable attention is paid to choose a configuration which does not provide excess loss, which is economically viable, compact and can be realized with minimum component count. After analysing the link configuration, multiplexing density of the WDM link is considered. In this work, since the number of signals to be distributed in radar systems are small, a coarse WDM(CWDM) scheme is considered for evaluation. A comparative study is also performed between coarse and dense WDM (DWDM) links for selection of a suitable multiplexing scheme. These configurations are modeled and evaluated with power budgeting. Even though CWDM scheme does not permit the utilisation of the available bandwidth to the fullest extent, these links have the advantage of having less hardware complexity and easiness of implementation. As the application requires signal distribution to thousands of transmit-receive modules, amplifiers are necessary to compensate for the reduction of signal level due to the high splitting ratio. Introduction of commonly available optical amplifiers like Erbium Doped Fiber Amplifier (EDFA), affect the CWDM channel output powers adversely due to their non-flat gain spectrum. Unlike DWDM systems, the channel separation of CWDM systems are much larger causing significantly high channel gain differences at the EDFA output. So an analysis is carried out for the selection of a suitable wavelength for CWDM channels to minimize the EDFA output power variation. If the gain difference is still significant, separate techniques needs to be implemented to flatten the output power at the antenna end. A CWDM configuration using C-band and L-band EDFAs is proposed and is supported with a feasibility analysis. As a part of evaluation of these links for radar applications, a mathematical model of the WDM link is developed by considering both the RF and digital sig- nals. A generic CWDM system consisting of transmitters, receivers, amplifiers, multiplexers/ demultiplexers and detectors are considered for the modeling. For RF signal transmission, the transmitters with external modulators are considered. Mod- eling is done based on a bottom-top approach where individual component models are initially modeled as a function of input current/power and later cascaded to obtain the link model. These models are then extended to obtain the wavelength dependent model ( spectral response) of the hybrid signal distribution link Further mathematical analysis of the developed link model revealed its variable separable nature in terms of the input power and wavelength. This led to significant reduction in the link equation complexity and development of some approximation techniques to easily represent the link behavior. The reduced form of the link spectral model was very essential as the initially developed wavelength model had a lot of parametric dependency on the component models. This mathematical reduction process led to simplification of the spectral model into a product of two independent functions, the input current and wavelength. It is also noticed that the total link power within specific wavelength range can be obtained by the integrating these functions over a specific link input power. After the mathematical modelling, an experimental prototype physical link is set up and characterized using various radar signals like continuous wave (CW) RF, pulsed RF, non linear frequency modulated signal (NLFM) etc. Additionally a proof of concept Radio-Over-Fiber (RoF) link is established to prove the superior transmission of microwave signal through an optical link. The analysis is supported with measurements on amplitude, delay, frequency and phase variations. The NLFM waveforms transmissions are further analysed using a matched _ltering process to confirm the side lobe requirement. Further a prototype WDM link is built to study the performance when digitally modulated channels are also multiplexed into the link. The link is again validated for signal levels, delay, frequency and phase parameters. Since amplitude and delay are deterministic, it is proposed that these parameter variations can be compensated by using suitable components either in the electrical or the optical domain. Radar systems use low frequency digital signals of different duty-cycles for synchronization and control across various transmit-receive modules. In the proposed link, these digital signals also modulate a WDM channel and hence the link is called a hybrid system. As the proposed link has EDFA to compensate for the splitting losses, there are chances of transient effects at the EDFA output for these low bitrate channels. Owing to the long carrier lifetime, low bitrate digital channels are prone to EDFA transient effects under specific signal and pump power conditions. Additionally, the synchronization signals used in radar application vary the duty-cycle over time, which is found to introduce variations in transient output. This practical challenge is further studied and the thesis for the first time, includes an analysis of EDFA transient e_ects for variable duty-cycle pulsed signals. The analysis is carried out for various parameters like bitrate, input power, pump power and duty-cycle. Investigations on EDFA transients on variable duty-cycle signals help in proposing a viable method to predict the lower duty-cycle transients from higher duty-cycle transients. The predicted transients were again validated against simulated transients and experimental results. As these transient effects are not desirable for radar signals, we propose a novel transient suppression techniques in optical and electrical domain which are validated with simulation and experimental measures. One suppression technique tries to avoid transient effect by keeping the optical input to EDFA always constant by feeding an inverted version of the original pulse into the EDFA along with the actual pulse. It is observed that as the wavelength of the inverted pulse is closer to the original input pulse, the transient effect settles faster. These EDFA transients are evaluated with WDM link configurations, where both high and low bitrate signals are co-propagated. Another challenging aspect of the link operation is the non-at gain spectrum of EDFA. i.e., EDFA provides unequal power level for various signals at WDM link output. This is especially true in the case of local oscillator signals, where it is preferable to have the same amplitude signals before feeding it to the mixer stages. But in the radar applications, this will require additional hardware circuits to equalize the signal level within a phased array antenna. This work also proposes some of the power equalization methods that can be used along with the WDM links. This part of the work is also supported with simulation model and experimental results. The analytical and experimental study of this thesis aids the evaluation process of a suitable optical Wavelength Division Multiplexed(WDM) distribution network that can be used for the distribution of both RF and digital signals. The optical WDM links being superior with its light weight, less loss and EMI/ EMC immunity provides a better solution to future class of radars.