Binh Engineering – Electrical SECOND EDITION SECOND EDITION Carefully structured to instill practical knowledge of fundamental issues, Optical Fiber Communication Systems with MATLAB® and Simulink® Models describes the modeling of optically amplified fiber communications systems using MATLAB® and Simulink® This lecture-based book focuses on concepts and interpretation, mathematical procedures, and engineering applications, shedding light on device behavior and dynamics through computer modeling Supplying a deeper understanding of the current and future state of optical systems and networks, this Second Edition: • Reflects the latest developments in optical fiber communications technology • Includes new and updated case studies, examples, end-of-chapter problems, and MATLABđ and Simulinkđ models Emphasizes DSP-based coherent reception techniques essential to advancement in short- and long-term optical transmission networks Solutions manual available with qualifying course adoption Optical Fiber Communication Systems with MATLAB® and Simulink® Models, Second Edition is intended for use in university and professional training courses in the specialized field of optical communications This text should also appeal to students of engineering and science who have already taken courses in electromagnetic theory, signal processing, and digital communications, as well as to optical engineers, designers, and practitioners in industry K22108 Optical Fiber Communication Systems with MATLAB ® and Simulink ® Models Optical Fiber Communication Systems with MATLAB® and Simulink® Models Optical Fiber Communication ® Systems with MATLAB ® and Simulink Models XXXXXXXXXXXXXXXXX "The authors are the foremost authorities in the subject area … If you want to develop, manage, and be very successful with your professional group, then this book is a must." —Gavriel Salvendy, Purdue University, West Lafayette, Indiana, USA The authors draw on their many years of experience in the field of management science to lay out procedures, tools, and techniques that address each step of the life cycle of an engagement—from definition of the services to be delivered, to evaluation of the results with the client The book guides you—starting with the Rules—through the maze of delivering your professional service Here’s What You Get: • The steps for how to develop your niche in the marketplace • A structure for how to manage professional service delivery, from start to finish • Tips on how to set up an environment and develop a culture that will result in superior service delivery—such that the delivery process incorporates rigorous internal discipline and control • Discussion of rapid implementation and deployment concepts that can be attained without compromising internal discipline and control • Examples of documentation standards for professional service proposals and deliverables (reports) • Discussion of application of the Rules for Success in two engagements conducted by the authors The authors draw on their many years of experience in the field of management science to lay out procedures, tools, and techniques that address each step of the life cycle of an engagement—from definition of the services to be delivered, to evaluation of the results with the client The book guides you—starting with the Rules—through the maze of delivering your professional service SECOND EDITION Le Nguyen Binh SECOND EDITION Optical Fiber Communication ® Systems with MATLAB ® and Simulink Models Optics and Photonics Series Editor Le Nguyen Binh Huawei Technologies, European Research Center, Munich, Germany Digital Optical Communications, Le Nguyen Binh Optical Fiber Communications Systems: Theory and Practice with MATLAB® and Simulink® Models, Le Nguyen Binh Ultra-Fast Fiber Lasers: Principles and Applications with MATLAB® Models, Le Nguyen Binh and Nam Quoc Ngo Thin-Film Organic Photonics: Molecular Layer Deposition and Applications, Tetsuzo Yoshimura Guided Wave Photonics: Fundamentals and Applications with MATLAB®, Le Nguyen Binh Nonlinear Optical Systems: Principles, Phenomena, and Advanced Signal Processing, Le Nguyen Binh and Dang Van Liet Wireless and Guided Wave Electromagnetics: Fundamentals and Applications, Le Nguyen Binh Guided Wave Optics and Photonic Devices, Shyamal Bhadra and Ajoy Ghatak Digital Processing: Optical Transmission and Coherent Receiving Techniques, Le Nguyen Binh 10 Photopolymers: Photoresist Materials, Processes, and Applications, Kenichiro Nakamura 11 Optical Fiber Communication Systems with MATLAB® and Simulink® Models, Second Edition, Le Nguyen Binh SECOND EDITION Optical Fiber Communication ® Systems with MATLAB ® and Simulink Models Le Nguyen Binh H U A W E I T E C H N O L O G I E S C O , LT D , E U R O P E A N R E S E A R C H C E N T E R MUENCHEN, GERMANY Boca Raton London New York CRC Press is an imprint of the Taylor & Francis Group, an informa business MATLAB® and Simulink® are trademarks of The MathWorks, Inc and are used with permission The MathWorks does not warrant the accuracy of the text or exercises in this book The book’s use or discussion of MATLAB® and Simulink® software or related products does not constitute endorsement or sponsorship by The MathWorks of a particular pedagogical approach or particular use of the MATLAB® and Simulink® software CRC Press Taylor & Francis Group 6000 Broken Sound Parkway NW, Suite 300 Boca Raton, FL 33487-2742 © 2015 by Taylor & Francis Group, LLC CRC Press is an imprint of Taylor & Francis Group, an Informa business No claim to original U.S Government works Version Date: 20141003 International Standard Book Number-13: 978-1-4822-1752-0 (eBook - PDF) This book contains information obtained from authentic and highly regarded sources Reasonable efforts have been made to publish reliable data and information, but the author and publisher cannot assume responsibility for the validity of all materials or the consequences of their use The authors and publishers have attempted to trace the copyright holders of all material reproduced in this publication and apologize to copyright holders if permission to publish in this form has not been obtained If any copyright material has not been acknowledged please write and let us know so we may rectify in any future reprint Except as permitted under U.S Copyright Law, no part of this book may be reprinted, reproduced, transmitted, or utilized in any form by any electronic, mechanical, or other means, now known or hereafter invented, including photocopying, microfilming, and recording, or in any information storage or retrieval system, without written permission from the publishers For permission to photocopy or use material electronically from this work, please access www.copyright.com (http:// www.copyright.com/) or contact the Copyright Clearance Center, Inc (CCC), 222 Rosewood Drive, Danvers, MA 01923, 978-750-8400 CCC is a not-for-profit organization that provides licenses and registration for a variety of users For organizations that have been granted a photocopy license by the CCC, a separate system of payment has been arranged Trademark Notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation without intent to infringe Visit the Taylor & Francis Web site at http://www.taylorandfrancis.com and the CRC Press Web site at http://www.crcpress.com To the memory of my father To my mother, Mrs T H Nguyen To Phuong and Lam Contents Preface xxi List of Abbreviations xxv Introduction 1.1 Historical Perspectives 1.2 Digital Modulation for Advanced Optical Transmission Systems 1.3 Demodulation Techniques 1.4 MATLAB® Simulink® Platform 1.5 Organization of the Book Chapters 10 Optical Fibers: Geometrical and Guiding Properties 13 2.1 Motivations and Some Historical Background 13 2.2 Dielectric Slab Optical Waveguides 15 2.2.1 Structure 16 2.2.2 Numerical Aperture 17 2.2.3 Modes of Symmetric Dielectric Slab Waveguides 17 2.2.3.1 The Wave Equations 18 2.2.4 Optical-Guided Modes 19 2.2.4.1 Even TE Modes 20 2.2.4.2 Odd TE Modes 20 2.2.4.3 Graphical Solutions for Guided TE Modes (Even and Odd) 21 2.2.5 Cutoff Properties 22 2.3 Optical Fiber: General Properties 23 2.3.1 Geometrical Structures and Index Profile 23 2.3.1.1 Step-Index Profile 24 2.3.1.2 Graded-Index Profile 24 2.3.1.3 Power-Law-Index Profile 24 2.3.1.4 Gaussian-Index Profile 25 2.3.2 The Fundamental Mode of Weakly Guiding Fibers 25 2.3.2.1 Solutions of the Wave Equation for Step-Index Fiber 26 2.3.3 Cutoff Properties 31 2.3.4 Single and Few Mode Conditions 32 2.4 Power Distribution and Approximation of Spot Size 35 2.4.1 Power Distribution 35 2.4.2 Approximation of Spot Size r0 of a Step-Index Fiber 36 2.5 Equivalent Step-Index (ESI) Description 37 2.5.1 Definitions of ESI Parameters 38 2.5.2 Accuracy and Limits 39 2.5.3 Examples on ESI Techniques 39 2.5.3.1 Graded-Index Fibers 39 2.5.3.2 Graded-Index Fiber with a Central Dip 39 2.5.4 General Method 40 vii viii Contents 2.6 Nonlinear Optical Effects 41 2.6.1 Nonlinear Phase Modulation Effects 41 2.6.1.1 SPM: Self-Phase Modulation 41 2.6.1.2 XPM: Cross-Phase Modulation 42 2.6.1.3 Stimulated Scattering Effects 43 2.6.1.4 Stimulated Brillouin Scattering (SBS) 44 2.6.1.5 Stimulated Raman Scattering (SRS) 45 2.6.1.6 Four-Wave Mixing 45 2.7 Optical Fiber Manufacturing and Cabling 47 2.8 Concluding Remarks 49 Problems 50 References 52 Optical Fibers: Signal Attenuation and Dispersion 55 3.1 Introduction 55 3.2 Signal Attenuation in Optical Fibers 56 3.2.1 Intrinsic or Material Attenuation 56 3.2.2 Absorption 56 3.2.3 Rayleigh Scattering 57 3.2.4 Waveguide Loss 57 3.2.5 Bending Loss 57 3.2.6 Microbending Loss 58 3.2.7 Joint or Splice Loss 58 3.2.8 Attenuation Coefficient 59 3.3 Signal Distortion in Optical Fibers 60 3.3.1 Basics on Group Velocity 60 3.3.2 Group Velocity Dispersion (GVD) 61 3.3.2.1 Material Dispersion 61 3.3.2.2 Waveguide Dispersion 65 3.4 Transfer Function of Single-Mode Fibers 68 3.4.1 Higher-Order Dispersion 68 3.4.2 Transmission Bit-Rate and the Dispersion Factor 68 3.4.3 Polarization Mode Dispersion 71 3.4.4 Fiber Nonlinearity 74 3.5 Advanced Optical Fibers: Dispersion-Shifted, -Flattened, and -Compensated Optical Fibers 77 3.6 Effects of Mode Hopping 77 3.7 Numerical Solution: Split-Step Fourier Method 78 3.7.1 Symmetrical Split-Step Fourier Method (SSFM) 78 3.7.2 MATLAB® Program and MATLAB® Simulink® Models of the SSFM 79 3.7.2.1 MATLAB® Program 79 3.7.2.2 MATLAB® Simulink® Model .83 3.7.3 Modeling of Polarization Mode Dispersion (PMD) 83 3.7.4 Optimization of Symmetrical SSFM 84 3.7.4.1 Optimization of Computational Time .84 3.7.4.2 Mitigation of Windowing Effect and Waveform Discontinuity 84 3.8 Concluding Remarks 85 Appendix E: Problems on Optical Fiber Communication Systems 837 • Now if setting the delay time Tb is that of a bit period, transform the structure into the z-transform diagram and hence obtain the transfer function of the coder in the z-domain, thence the frequency response of this coder Plot the frequency response of the transfer function of the filter in continuous domain • Find the impulse response of the coder, hence the term partial response • Sketch a block diagram that shows the functionality of precoding, coding, trilevel conversion (offset), and decoding • A binary sequence d(k) = {0 1 0 1} is applied to the input of the duobinary coder Determine the data sequences b(k), c(k), and c′(k) in the electrical domain, which can be used to modulate an optical modulator • Assuming that there is no dispersion in the transmission of the duobinary data sequence, find the output pulse sequence at the output of the decoder What is the physical realization of the decoder? Thence, sketch the sequence at the output of a decision circuit Now the electrical signals are applied to a microwave amplifier that would condition the signals to appropriate signal levels so as to modulate the optical modulator The measured spectra are recorded as shown in the following diagrams Determine where in the block diagram (Figure E.2) that each of the spectrum belongs to the points of the diagram of the transmission system Question 13: Differential quadrature phase-shift keying (DQPSK) DQPSK is a 2-bit per symbol modulation, that is, 2 bits/symbol; thus, the scheme is spectral efficient (i) Give a brief account of the modulation schemes DPSK and DQPSK (ii) Give a structure of a precoder for DPSK, which gives a differential phase modulation as the codes for “1” and “0.” (iii) Now extend this precoder and the phase quadrature modulation technique for the structure of a DQPSK optical transmitter Question 14: Single-sideband (SSB) and double-sideband (DSB) modulations Referring to Figure E.2a through c for generation of optical signals with SSB, (a) State the functionality of the Hilbert transformer Hence, could you deduce a general principle for suppression of a sideband to generate SSB signals? (b) What is the role of the phase shifter π/2? (c) Explain the operation of the optical SSB transmitter, in both time and frequency domain Confirm that the spectrum is correct Question 15: Coherent optical communication systems Sketch a structure of an optical coherent receiver Give a brief description of the roles of each component in your system What is the typical modern linewidth of the laser that acts as the local oscillator? Give a distinction between the homodyne and heterodyne coherent system 838 Appendix E: Problems on Optical Fiber Communication Systems RF amplifier T Pules pattern generator RF Laser Data Data Mach–Zehnder modulator Divider LT Bias Mach–Zehnder modulator π/2 RF Hilbert transformer (a) Pulse pattern generator Data Coupler Optical SSB signal APOC 03 Bias RF amplifier DSB Mach–Zehnder modulator Laser Data RF RF amplifier Phase modulator Optical SSB si RF Bias ˆ m(t) m(t) Hilbert transformer Bias RF amplifier Single sideband modulation: transmitter setup Pulse pattern generator Data Laser Phase modulator MZ modulator Data RF 10 Gb/s Back to back eye diagram RF Bias RF amplifier Hilbert transformer RF amplifier Transfer characteristic of Mach–Zehnder modulator P U E P +1 E (b) t Extinction ratio: 4.9 dB Power spectral density of the optical signal (simulation) +1 SBS: precautions to avoid signal degradation are necessary P: optical power E: electrical field (c) Figure E.2 SSB modulation and generation using (a) transform in optical domain, (b) transform in electrical domain, and (c) realization of an SSB optical transmitter Appendix E: Problems on Optical Fiber Communication Systems 839 A homodyne optical receiver has the following parameters: a A photodetector with a responsibility of 0.9 is followed by an electronic preamplifier whose total equivalent noise spectral density is pA/(Hz)1/2 and an electrical bandwidth of 15 GHz The transmission bit rate is 10 Gb/s b The local oscillator is a tunable laser source with a linewidth of 100  MHz The  wavelength in vacuum of both the signals and the local oscillator is 1550.92 nm The average optical power of the local oscillator coupled to the photodetector is dBm Sketch the structure of the receiver and then its equivalent small-signal circuit, which includes the generated electronic signal current at the output of the photodetector and the total noise currents looking from the input of the electronic preamplifier What is the dominant noise source in this receiver? For an optical signal with an average power of −20 dBm, estimate the signal-to-noise ratio (SNR) at the output of the photodetector Recalculate the SNR of the receiver if the frequency of the local oscillator is 20 GHz away from that of the signal carrier frequency E.14 Problems on Digital Optical Receiver for Optical Communications Systems and Networks E.14.1  Optical Communications Systems Design: Mini Project Network Distribution Transmission link distance Transmission techniques BER Network configuration Total capacity Wavelength regions Optical channel frequency spacing Transmission medium Fault monitoring systems Optical amplifiers Photonic components Transmitters and receivers Australian Ultra-Wideband Optical Fiber Backbone Networks Melbourne–Sydney (air km x 1.25); Sydney–Brisbane; Brisbane Alice Springs (NT)–Port Headland (WA); Port Headland–Perth; Perth–Kalgoorlie–Port Augusta–Adelaide; Adelaide–Melbourne; and Melbourne–Hobart Hanoi–HCM City–Can Tho (underseas or terrestrial routes) DWDM techniques with SDH technology STM-64 9953 Mb/s NRZ format T X(ω) = 2T sinc(ωt) t T –T π X(ω) = ω , |ω | < ωo o π , |ω | = ω o 2ωo O , | ω | > ωo x(t) = sinc(ωot) π ωo x(t) = 1–|t|/T,|t| T x(t) = exp π T π/ωo –ωo 2π 3π t ωo ωo 2π 3π T T ωo X(ω) = T sinc2 ωT –T T T t –t2 2T2 2T 2π T X(ω) = 2π T exp 2 –ω T t 2π T 4π T 841 Appendix E: Problems on Optical Fiber Communication Systems Table of Fourier Transform Pairs x(t) = exp – |t| T 2T X(ω) = + ω2T 2T ≤ t T |t| > T x(t) = + cos πt 2 T ω t X(ω) =T sin c(ωT) + T sin c(ωT + π) T + T sin c(ωT – π) T –T 2π 3π 4π T T T t ω j X(ω) = – ω x(t) = sin(t) –1 t T = T δ(t) x(t) = δ ω t X (ω) =T T T t ω E.14.3  Problems on Optical Transmitters Question 1: Direct modulation (a) Sketch a diagram on how to connect the laser source and the electrical data generator for direct modulation (b) A laser has a threshold current of 10 mA and output power of 10 mW at a driving current of 40 mA Data sequence is assuming a perfect square wave Sketch the laser P-I relationship and then a diagram on how to drive the laser using the time-amplitude scale of the input current Make sure that there would be no turn-on delay (c) If the rise time of the laser is 10 ps and the data bit rate is 10 Gb/s, sketch the output optical pulse sequence Question 2: Direct modulation (a) State the advantages and disadvantages of FP lasers and DFB lasers in terms of optical linewidth, output power, spectrum under modulation, and bias conditions (b) Give reasons why direction modulation of lasers cannot work for bit rates greater than Gb/s 842 Appendix E: Problems on Optical Fiber Communication Systems Question 3: External modulation A bit pattern “1 1 0 1 1” with a bit rate of 10 Gb/s is input into two separate modulators to generate ASK and BDPSK modulation format (a) Sketch the modulated bit pattern including the carrier which can be drawn with two or three periods within the duration of a bit period Hence the phase distribution or the scatter diagram of the modulated sequence (b) An MZIM is used as an optical modulator, its Vπ is V Show how the data sequence can be conditioned to feed into the electrode port of the modulator so that ASK or BDPSK signals can be generated Make sure that you show the biasing voltage (c) Repeat (b) for the case that the modulator is a dual-drive type of optical modulator (d) Give a structure of a precoder for DPSK modulation, that is, the precoder that would generate the differential codes which are then used to drive the optical modulator with signal conditioning to appropriate level for driving the electrodes Question 4a: Optical modulator and phasor diagram (a) Sketch the schematic diagram of an intensity optical modulator which consists of an optical waveguide as the input light guide which is then split into two parallel paths whose refractive indices would be modulated by an electrode, hence a phase modulation of the lightwaves that pass through these waveguides This type of optical modulator can be termed as an interferometric intensity modulator (b) For a single-drive modulator, only one path of the lightwave is modulated What is the total phase change exerted on the lightwaves if the following parameters are employed for the optical modulation: electro-optic coefficient: r = 10−11 m/V, electrode length = 10  mm Separation between active electrode and earth electrode = μm (c) Estimate the change in the refractive index due to the applied voltage via the electro-optic effect, then (d) The change in the velocity of the lightwave (e) The total phase change over the electrode length, note that a phase change of 2π is equivalent to the slowing down of one wavelength You may confirm that the c∆n 2π phase change can be given by ∆φ = L n λ (f) Estimate the voltage required for applying to the electrode so that a π phase change occurs on the lightwave carrier passing through it (g) Write down an expression that represents the lightwave at the input Thence those for the split waves propagating in the two parallel lightpaths of the interferometer Represent their phasors in a plane (h) Then find the sum of the two phasors and hence project this total phasor vector on the real axis and obtain the equation of the lightwave at the output of the modulator as a function of the applied voltage V Appendix E: Problems on Optical Fiber Communication Systems 843 Question Optical modulator and phasor diagram—dual-drive MZM (a) Repeat Question with a bias voltage of Vb = Vπ/2 and Vπ and a time-varying signal of vs(t) = Vπ/2 cosωst with ωs = 2πfs and fs = 20 GHz (b) Now the modulator is a dual-drive MZM, repeat Question with a bias voltage of Vb = Vπ/2 and Vπ and a time-varying signal of vs(t) = Vπ/2 cosωst with ωs = 2πfs and fs = 20 GHz Question 6a An optical fiber communication system consists of an optical transmitter using a 1550 nm DFB laser with a linewidth of 10 pm (pico-meters), an external optical modulator whose bandwidth is 20 GHz, and a total insertion loss of dB The modulator is driven with a bitpattern-signal generator with a 10 dBm electrical power output into a 50 Ω line A microwave amplifier is used to boost the electrical data pulse to an appropriate level for driving the optical modulator The data bit rate is 10 Gb/s and its format is NRZ An 80 km standard single-mode fiber is used for the transmission of the modulated signals (a) Sketch the block diagram of the transmission system (b) If the Vπ of the external modulator is V, what is the gain of the microwave amplifier so that an extension ratio of 20 dB can be achieved for the output pulses of “1” and “0” at the output of the modulator Make sure that you sketch the amplitude and power output of the modulator versus the driving voltage into the modulator What type of connector that you would use for connecting the microwave amplifier to the modulator and that to the bit pattern generator (c) If the DFB laser emits dBm optical power at its pigtail output then what is the average of optical power contained in the signal spectrum You may assume that the pulse sequence generated at the output of the bit pattern generator is a perfect rectangular shape (d) What is the effective dB bandwidth of the signal power spectrum Thence estimate the total pulse broadening of the pulse sequence at the end of the 80 km fiber length Similarly, estimate the pulse sequence if the bit rate is 40 Gb/s (e) Now if a dispersion compensating fiber of 20 km is used to compensate for the signal distortion in the 80 km fiber, what is the required dispersion factor of this fiber so that there would be no distortion If the loss of the dispersion compensating fiber is 1.0 dB/km at 1550 nm, estimate the average optical power of the signal at the output of the dispersion compensating fiber (f) Based on the dispersion limit given in the following, plot the dispersion length as a function of the bit rate for NRZ format The dispersion limit, under linear regime operation, can be estimated in the following equation (Ref Forgheti et al.* 1997): Note : LD = c ρ λ BR 2D * Forghieri et al., RZ versus NRZ in nonlinear WDM systems, IEEE Photonics Technology Letters, vol 9, No.7, July 1997, pp 1035–1037 844 Appendix E: Problems on Optical Fiber Communication Systems where BR is the bit rate D is the dispersion factor (s/m2) ρ is the duty cycle ratio, that is, the ratio between the “ON” and “OFF” in a bit period LD is in meters Question 6b Repeat Question for return-to-zero (RZ) format and ASK modulation Sketch the structure of the RZ optical transmitter, note that an extra optical modulator must be used and coupled with the data modulator of Question 1, the optical pulse carver Give details of the pulse carver including driving voltage, driving signal, and synchronization with the data generator Question 6c: Spectral efficiency (a) A DWDM optical transmission system that can transmit optical channels whose channel spacing is 100 GHz What is the spectral efficiency if the bit rate of each channel is 40 Gb/s and the modulation is NRZ-ASK (b) Repeat (a) for RZ-ASK modulation format (c) Repeat (a) and (b) for the channel spacing of 50 GHz Question (a) Give a structure of an optical transmitter for generation of RZ-ASK modulation format Make sure that you assign the optical power of lightwaves generated from the light source and that at the output of the optical modulators so that a maximum of 10 dBm of optical power is launched into the standard single-mode fiber so that it is below the nonlinear SPM effect limit (b) Describe the operation of the optical modulator, the pulse carver, so that it can generate periodic pulse sequence before feeding into the data generator Make sure that you provide the amplitude and intensity levels versus the driving signal voltage levels which are used to drive the optical modulators Question 8: Nonlinear SPM effect The nonlinear refractive index coefficient of silica-based standard single-mode fiber is n2 = 2.5 × 10 −20 m 2/W (a) What is the effective area of the standard single-mode fiber—you can refer to the technical specification of the Corning SMF-28 and its MFD to estimate this area (b) Estimate the change in the refractive index as a function of the average optical power Hence, estimate the total phase change due to this nonlinear effect after propagating through a length L (in km) of this fiber (c) Hence, estimate the maximum length L of the standard single-mode fiber that the lightwaves can travel so that not higher than 0.1 rad of the phase change on this lightwave carrier would be suffered (d) Show how you can generate a format that would have an RZ format and a suppression of the lightwave carrier Show that the width of the RZ pulse on this case is 67% of the bit period Hint: you may represent the lightwaves in the path of the optical modulator, an optical interferometer by using phasors First sketch the Appendix E: Problems on Optical Fiber Communication Systems 845 phasor of the input lightwave Then those of the two paths and then the phase applied onto these paths Then sum up at the output to give the resultant output For the pulse width you can estimate the width over which the amplitude fall to 1/ (2) of its maximum (e) Now show you can generate RZ pulse sequence with 50% and 33% pulse width of the bit period Question 9: Balanced Receiver (a) Sketch the schematic diagram of an optical balanced receiver—a balanced receiver would consist of a delay interferometer and a back-to-back connected pair of photodetector with its output connected to the input of an optical preamplifier (b) What is the functionality of the delay interferometer What is the temporal length of the delay unit? (c) What are the roles of the two optical couplers and their ideal coupling coefficients? (d) What is the relationship between the two output ports of the delay interferometer? (e) Suppose that a sequence of 4 bits of a DPSK 10 Gb/s data channel is presented at the input of a balanced receiver The phases of the lightwave carrier contained within these four bits are π π ο π at the transition of the bit period (f) Sketch the carrier wave and the pulse envelope The lightwave has a wavelength of 1550 nm—however to illustrate the wave you are expected to sketch only a few periods of the waves contained within the bit period at the input of the receiver (g) Sketch the electrical signal at the output of the electronic preamplifier not including noises (h) Now assuming that an optical amplifier is used as an optical preamplifier is placed at the input of the balanced receiver that would give an optical signal power of −10 dBm for the “0” and “1” of the DPSK sequence The responsibility of the photodetector is 0.9 and the electronic preamplifier has a trans impedance of 150 Ω and a total equivalent noise current spectral density of pA/(Hz)1/2 and a bandwidth of 15 GHz Sketch the signal waveform at the output of the electronic preamplifier Question 10: Duobinary modulation format (a) Design a block diagram of a precoder that would generate tri-level modified duobinary format signals Make sure that the coefficients of the filters are specified Hint: you may refer to pages 8–11 of the lecture notes Hence, derive the spectrum of the signals after the precoder of the modified duobinary (b) If possible obtain the precoders for AMI and duobinary and their frequency responses Compare the frequency responses of the three modulation schemes (c) Sketch the structure of the tri-level duobinary precoder with its output of −1, 0, +1 (d) Now then show how to use the coded signals to drive a dual-drive MZIM to generate optical duobinary signals 846 Appendix E: Problems on Optical Fiber Communication Systems Question 11: Duobinary modulation format (a) A modulation format that would allow the detection of the modulated signals is duobinary which is a special case of partial response coding (see Chapter on modeling and optical transmitters) (b) Give a brief account of the principles of operation of this line code (c) A duobinary coder using a delay and add coding structures is shown in the following If a three-level duobinary-coded signals are required, design the precoder for this type of modulation d(k – 1) d(k) Tb Tb a0 d(k – 2) a1 + a2 c(k) (d) Now if setting the delay time Tb is that of a bit period, transform the structure into the z-transform diagram and hence obtain the transfer function of the coder in the z-domain, thence the frequency response of this coder Plot the frequency response of the transfer function of the filter in continuous domain (e) Find the impulse response of the coder, and hence the term partial response (f) Sketch a block diagram that shows the functionality of precoding, coding, tri-level conversion (offset) and decoding (g) A binary sequence d(k) = {0 1 0 1} is applied to the input of the duobinary coder Determine the data sequences b(K), c(k), and c′(k) in the electrical domain which can be used to modulate an optical modulator (h) Assuming that there is no dispersion in the transmission of the duobinary data sequence find the output pulse sequence at the output of the decoder What is the physical realization of the decoder? Thence sketch the sequence at the output of a decision circuit (i) Now the electrical signals are applied to a microwave amplifier that would condition the signals to appropriate signal levels so as to modulate the optical modulator The measured spectra are recorded as shown in Figure E.3(c) (j) Determine where in the block diagram (as per attached diagram) that each of the spectrum belongs to the points of the diagram of the transmission system Question 12: DQPSK DQPSK is a 2-bit per symbol modulation, that is, 2 bits/symbol, thus the scheme is spectral efficient (a) Give a brief account of the modulation schemes DPSK and DQPSK (b) Give a structure of a precoder for DPSSK—that gives a differential modulation with phase as the codes for “1” and “0.” (c) Now extend this precoder and the phase quadrature modulation technique for the structure of a DQPSK optical transmitter 847 Appendix E: Problems on Optical Fiber Communication Systems Question 13: SSB and DSB Modulation Referring to Figure E.3a through c for generation of optical signals with SSB, (a) State the functionality of the Hilbert transformer Hence, could you deduce a general principle for suppression of a sideband to generate single sideband signals? (b) What is the role of the phase shifter π/2? (c) Explain the operation of the optical SSB transmitter, in both the time and frequency domain Confirm that the spectrum is correct DSB Pulse pattern generator Data Mach–Zehnder modulator Laser Data RF Phase modulator Optical SSB si Bias RF ˆ m(t) m(t) RF amplifier Hilbert transformer (a) Bias RF amplifier Single sideband modulation: transmitter setup Pulse pattern generator Data Laser Phasemodulator MZ modulator Data RF 10 Gb/s Bias Back to back eye diagram RF RF amplifier Hilbert transformer RF amplifier Transfer characteristic of Mach–Zehnder modulator P U E P +1 E (b) t Extinction ratio: 4.9 dB Power spectral density of the optical signal (simulation) +1 SBS: precautions to avoid signal degradation are necessary P: optical power E: electrical field (c) Figure E.3 SSB modulation and generation using (a) transform in optical domain, (b) transform in electrical domain, (c) realization of an SSB optical transmitter 848 Appendix E: Problems on Optical Fiber Communication Systems Question 14: Coherent Optical Communication Systems (a) Sketch a structure of an optical coherent receiver Give a brief description of the roles of each component in your system (b) What is the typical modern linewidth of the laser that acts as the local oscillator? (c) Give a distinction between the homodyne and heterodyne coherent system (d) A homodyne optical receiver has the following parameters: Absolute maximum ratings (TC = 25°C) Parameter Symbol Storage temperature Operating case temperature Optical output power Forward current Reverse voltage Photodiode reverse voltage Condition Ratings Unit CW CW −40 to +70 −20 to +65 150 20 °C °C mW mA V V Tstg Top Pf IF VR VDR Optical and Electrical characteristics (TL = 25°C, TL : Laser temperature) Limits Parameter Symbol Threshold current Forward voltage Optical output power Threshold optical output power Slope efficiency Monitor Current Ith VF Pf Pth η Im Peak wavelength Side-mode suppression ratio Rise time Fall time Photodiode dark current Photodiode capacitance Tracking error λP Sr tr tf ID Ct TE Cooling capacity Cooler current ∆T IC Cooler voltage Thermistor resistance Thermistor B constant VC Rth B Test Condition CW CW, IF = 30 mA CW CW, IF = Ith CW, Pf = mw CW, Pf = mw VDR = V CW, Pf = mw Ppeak = mW, Ibias = Ith VDR = V VDR = V, f = MHz TC = −20 to +65°C TL = 25°C, Pf = mW at TC = 25°C APC with monitor PD CW, Pf = mw ∆T = 40°C P f = mW Figure E.4 Technical data of a semiconductor laser diode Min Typ Max — — — 0.07 0.05 20 1.1 — 30 0.09 0.08 30 1.5 — 120 — — mA V mW μW mW/mA mA 1530 30 — — — — — 1550 33 0.2 0.4 12 ±5 1570 — 0.5 0.5 100 — — nm dB ns ns nA pF % 40 — — 0.5 — °C A — 9.5 3500 1.2 10 3900 2.1 10.5 4300 V KΩ °K Unit 849 Appendix E: Problems on Optical Fiber Communication Systems TL = 25°C TL = 25°C 140 120 Relative optical output power Forward current, IF (mA) 160 100 80 60 Pf = mW Ibias = Ith 40 Time (0.5 n/div.) 20 0 0.5 Relative intensity (dB) (a) –20 1.5 2.0 2.5 (b) Forward voltage, VF (V) Laser pulse response 20 mV TL = 25°C 500 pS Pf = mW –40 –60 –80 1540 (c) 1.0 1550 Wavelength (nm) 1560 (d) Typical eye diagram at the transmitter output Figure E.5 Laser P–I characteristics and output pulses and eye diagram (a) Forward current versus forward voltage (b) Pulse response (c) Lasing spectrum (d) Eye diagram generated from modulated laser (e) A photodetector with a responsibility of 0.9 which is followed by an electronic preamplifier whose total equivalent noise spectral density is pA/(Hz)1/2 and an electrical bandwidth of 15 GHz The transmission bit rate is 10 Gb/s (f) The local oscillator is a tunable laser source with a linewidth of 100  MHz The wavelength in vacuum of both the signals and the local oscillator is 1550.92 The average optical power of the local oscillator coupled to the photodetector is dBm (g) Sketch the structure of the receiver and then its equivalent small-signal circuit which includes the generated electronic signal current at the output of the photodetector, the total noise currents looking from the input of the electronic preamplifier What is the dominant noise source in this receiver? (h) For an optical signal with an average power of −20 dBm, estimate the signal to noise ratio at the output of the photodetector (i) Re-calculate the SNR of the receiver if the frequency of the local oscillator is 20 GHz away from that of the signal carrier frequency (Figures E.4 and E.5) Binh Engineering – Electrical SECOND EDITION SECOND EDITION Carefully structured to instill practical knowledge of fundamental issues, Optical Fiber Communication Systems with MATLAB® and Simulink® Models describes the modeling of optically amplified fiber communications systems using MATLAB® and Simulink® This lecture-based book focuses on concepts and interpretation, mathematical procedures, and engineering applications, shedding light on device behavior and dynamics through computer modeling Supplying a deeper understanding of the current and future state of optical systems and networks, this Second Edition: • Reflects the latest developments in optical fiber communications technology • Includes new and updated case studies, examples, end-of-chapter problems, and MATLAB® and Simulinkđ models Emphasizes DSP-based coherent reception techniques essential to advancement in short- and long-term optical transmission networks Solutions manual available with qualifying course adoption Optical Fiber Communication Systems with MATLAB® and Simulink® Models, Second Edition is intended for use in university and professional training courses in the specialized field of optical communications This text should also appeal to students of engineering and science who have already taken courses in electromagnetic theory, signal processing, and digital communications, as well as to optical engineers, designers, and practitioners in industry K22108 Optical Fiber Communication Systems with MATLAB ® and Simulink ® Models Optical Fiber Communication Systems with MATLAB® and Simulink® Models Optical Fiber Communication ® Systems with MATLAB ® and Simulink Models XXXXXXXXXXXXXXXXX "The authors are the foremost authorities in the subject area … If you want to develop, manage, and be very successful with your professional group, then this book is a must." —Gavriel Salvendy, Purdue University, West Lafayette, Indiana, USA The authors draw on their many years of experience in the field of management science to lay out procedures, tools, and techniques that address each step of the life cycle of an engagement—from definition of the services to be delivered, to evaluation of the results with the client The book guides you—starting with the Rules—through the maze of delivering your professional service Here’s What You Get: • The steps for how to develop your niche in the marketplace • A structure for how to manage professional service delivery, from start to finish • Tips on how to set up an environment and develop a culture that will result in superior service delivery—such that the delivery process incorporates rigorous internal discipline and control • Discussion of rapid implementation and deployment concepts that can be attained without compromising internal discipline and control • Examples of documentation standards for professional service proposals and deliverables (reports) • Discussion of application of the Rules for Success in two engagements conducted by the authors The authors draw on their many years of experience in the field of management science to lay out procedures, tools, and techniques that address each step of the life cycle of an engagement—from definition of the services to be delivered, to evaluation of the results with the client The book guides you—starting with the Rules—through the maze of delivering your professional service SECOND EDITION Le Nguyen Binh ... Germany Digital Optical Communications, Le Nguyen Binh Optical Fiber Communications Systems: Theory and Practice with MATLAB and Simulink® Models, Le Nguyen Binh Ultra-Fast Fiber Lasers: Principles... 11 Optical Fiber Communication Systems with MATLAB and Simulink® Models, Second Edition, Le Nguyen Binh SECOND EDITION Optical Fiber Communication ® Systems with MATLAB ® and Simulink Models Le... Systems 485 12.2.1 Intensity Modulation Direct Detection Systems 485 12.2.2 Loss-Limited Optical Communications Systems 488 12.2.3 Dispersion-Limited Optical Communications Systems