Free-Space Laser Communications (eBook)
XII, 418 Seiten
Springer New York (Verlag)
978-0-387-28677-8 (ISBN)
This is a comprehensive tutorial on the emerging technology of free-space laser communications (FSLC). The book offers an all-inclusive source of information on the basics of FSLC, and a review of state-of-the-art technologies. Coverage includes atmospheric effects for laser propagation and FSLC systems performance and design. Free-Space Laser Communications is a valuable resource for engineers, scientists and students interested in laser communication systems designed for the atmospheric optical channel.
Arun K. Majumdar Ph.D., is Director of Research at LCResearch, Inc. in California. He has more than 23 years of experience from Industry, University and National Laboratory settings in the areas of atmospheric turbulence effects on laser propagation, imaging and communications. He received his Ph.D. in Electrical Engineering from the University of California, Irvine.
Jennifer C. Ricklin received her Ph.D. in electrical engineering from the Johns Hopkins University. She has been with the Army Research Laboratory since 1983. Since that time her research interests have included a number of topical applications of laser beam propagation in the atmosphere. She is now a Program Manager at DARPA / ATO.
Free-space laser communications, also referred to as optical communica- tions, is a popular subject in today's technological marketplace. A number of conferences on this subject have been organized by professional societies such as SPIE (the International Society of Photo Optical and Instrumenta- tion Engineering), OSA (Optical Society of America), and IEEE (Instituteof Electrical and Electronics Engineers). The evolving technology of free-space laser communications is emerging as an appealing alternative to RF com- munications for links between satellites, as well as a promising addition to terrestrial applications such as video or computer linkups between buildings. There is a pressing need for more information on laser communications that is comprehensive enough to provide in-depth knowledge of free-space com- munications, and that can satisfy the current demands of the research and commercial needs. This book has been designed to provide a comprehensive, unified tutorial to further understanding of the fundamental techniques for laser communi- cations through the earth's atmosphere. The driving force behind free-space laser communications is the continuous demand for higher bandwidth to deliver high-capacity voice, data, and images to the customer. Free-space propagation distances include ranges that encompass a few millimeters (for example between optical interconnects in a computer using photonics to replace metal interconnects), a fewmeters (such as indoor communications), a fewkilometers (between buildings, campuses, and hospitals), and even up to thousands of kilometers (such as from an aircraft or satellite to the ground).
Arun K. Majumdar Ph.D., is Director of Research at LCResearch, Inc. in California. He has more than 23 years of experience from Industry, University and National Laboratory settings in the areas of atmospheric turbulence effects on laser propagation, imaging and communications. He received his Ph.D. in Electrical Engineering from the University of California, Irvine.Jennifer C. Ricklin received her Ph.D. in electrical engineering from the Johns Hopkins University. She has been with the Army Research Laboratory since 1983. Since that time her research interests have included a number of topical applications of laser beam propagation in the atmosphere. She is now a Program Manager at DARPA / ATO.
Preface 6
Contributors 10
Table of Contents 12
Introduction 13
1. Introduction 13
1.1. Brief History 14
1.2. Applications 15
1.3. Advantages and Challenges 15
1.4. Limitations 15
1.5. Basics of Operation 16
2. Understanding Free-Space Laser Communications Systems Performance 17
2.1. Bit Error Rate 17
2.2. Fundamental Limit of Light Detection 17
2.3. BER for a Random Stochastic Communication Channel 18
2.4. Wavelength Selection Criteria 19
2.5. Adaptive Optics for Free-Space Laser Communications 19
2.6. Coding for Atmospheric Channel 19
3. Summary 20
Acknowledgement 20
References 20
Atmospheric channel effects on free-space laser communication 21
1. Introduction 21
2. Beam Extinction Due to Atmospheric Aerosols and Molecules 22
2.1. Extinction 22
2.2. Molecular Extinction 23
2.3. Molecular Transmittance Codes 24
2.4. Aerosol Extinction 25
2.5. Mie Theory 27
2.6. Aerosol Models 29
2.7. Atmospheric Attenuation of Laser Power 31
3. Channel Effects Due to Optical Thrbulence 32
3.1. Refractive Index Structure Parameter C2n 32
3.2. Optical Turbulence Models 35
3.2.1. PAMELA Model 35
3.2.2. Gurvich Model 40
3.2.3. SLC-Day Model 42
3.2.4. Hufnagel-Valley Model 42
3.2.5. HV-Night Model 43
3.2.6. Greenwood Model 43
3.2.7. Other Thrbulence Models 44
3.3. Free-Space Laser Communication in Optical Turbulence 45
3.3.1. Free-Space Laser Beam Propagation 45
3.3.2. Laser Beam Propagation in Optical Turbulence 46
3.3.3. Scintillation Index and Aperture Averaging 48
3.3.4. Beam Wander 52
3.3.5. Bit Error Rate Determination for a Direct-Detection Binary Optical Communication Link 52
3.3.6. Reducing Optical Turbulence Effects 56
Acknowledgments 56
Appendix A: Mathcad Version of PAMELA Model 57
PAMELA inputs 57
Calculate Solar Insolation I, Irradiance R, Sensible Heat Flux H 57
Calculate Pasquill Stability Class 57
Calculate Flux Profile Relationships 57
Calculate Cn2 58
Date, time,and location inputs 58
Meteorological and Terrain Inputs 58
Change degrees Fahrenheit to Kelvin 58
Calculate radiation class Cr 59
Calculate wind speed class cw 59
Calculate Monin-Obukhov Length L 59
Estimate dimensionless wind shear .m 60
Estimate dimensionless temperature gradient .h 60
Estimate characteristic temperature Tstar 60
Estimate gradient for refractive index fluctuations 60
Estimate eddy dissipation rate e 61
Appendix B: Calculating Solar Iirradiance and Sensible Heat Flux 61
Appendix C: Calculation of Aperture-Averaged Scintillation Index Using Mathcad 62
Rytov variance 62
focusing parameter 62
diffractive parameter 63
beam size (radius) at the receiver 63
Aperture-averaging Factor A 63
Aperture-averaged scintillation index 64
References 64
Free-space laser communication performance in the atmospheric channel 69
1. Introduction 69
2. Basics of Laser Communication Link Analysis 71
2.1. Communication Channel Characterization 71
2.2. Transmitter and Receiver System 72
2.3. Link Analysis 72
2.3.1. Data Rate 74
2.3.2. Link Margin 74
2.3.3. Bit Error Rate in Presence of Atmospheric Absorption and Scattering 74
2.3.4. Example Numerical Results 76
2.4. Optical Link Reliability 82
3. Laser Communication Performance Prediction and Analysis Under Scintillation Conditions 84
3.0.1. Hufnagel-Valley Model 85
3.1. Scintillation index: Point Receiver and Aperture Averaged Variance 85
3.1.1. Plane Wave 87
3.1.2. Spherical Wave 87
3.1.3. Gaussian beam wave [14] 87
3.2. Probability Density Function (pdf) Models 88
3.3. Received Signal-to-Noise -Ratio (SNR) and Bit-Error-Rate (BER) 91
3.3.1. Relationship between SNR and BER 91
3.3.2. Why Atmospheric Turbulence Increases the Bit Error Rate? 92
3.3.3. Bit-Error Rate Computation for OOK Modulation 93
3.3.4. Bit-Error Rate Computation for Pulse Position Modulation(PPM) : Some Basics 94
3.4. Probability of Fade 95
4. Example Numerical Results 96
4.1. Example I : Uplink (Spherical Wave/OOK) 96
4.2. Example 2: Downlink (Plane Wave/OOK) 99
4.3. Example 3: Horizontal: Terrestrial Link (Gaussian Beam Wave/OOK) 101
4.4. Example 4: Downlink PPM Laser Communication in Presence of Atmospheric Turbulence and Multiple Scattering Media 104
4.4.1. Theory and Formulation of BER for PPM with Stretched Pulses for Pulse Position Modulation 104
4.4.2. BET-Error-Rate (BER) and Slot Count Statistics 107
4.4.3. The Impulse Response Function in the Case of Multiple Scattering 108
4.4.4. Numerical Results 109
4.4.5. BER Computation for Both Turbulence and Multiple Scattering Media 110
5. Other Examples/Scenariosof Free-Space Optical and Laser Communications 112
5.1. Ground to Space Shuttle Link 112
5.2. UAV-to-Ground Lasercom Link 112
5.2.1. Indoor Optical Communication 112
5.2.2. Free-space Optical Interconnect 113
6. Multiple Transmitters/Receivers Approach for Lasercomm 114
7. Conclusion 116
Acknowledgments 117
References 117
Laser communication transmitter and receiver design 121
1. Introduction 121
1.1. Background 123
1.2. Scope 127
1.3. Historical Perspective 127
2. General Wavelength Considerations 129
2.1. Carrier Characteristics 129
2.2. Electromagnetic Signaling Options 131
2.2.1. Overview of FSO Modulation Formats and Sensitivities 132
2.2.1.1. On-Off-Keying (OOK) 133
2.2.1.2. Differential-Phase-Shift-Keying (DPSK) 134
2.2.1.3. Phase-Shift-Keying (PSK) 135
2.2.1.4. M -ary Orthogonal Modulation 135
2.2.1.5. M-ary Pulse-Position Modulation (M-PPM) 137
2.2.1.6. M-ary Frequency-Shift Keying (M-FSK) 139
2.2.1.7. Polarization-Shift-Keying (PoISK) 140
2.3. Comparison of RF and Optical Properties 140
2.3.1. Diffraction 140
2.3.2. Optical Detection 141
2.3.3. Technology Limitations 142
2.3.4. Average and Peak Power Limited Transmitters 143
2.3.5. Quantum Noise Limitations 144
2.3.6. Quantum-limited Direct Detection (DD) 147
2.3.7. Thermal Noise 150
2.4. Example Sensitivities and Link Budget 153
3. Transmitter Technologies 154
3.1. Direct Modulation and Semiconductor Laser Sources 155
3.1.1. Spectral Shaping 156
3.2. Semiconductor Laser Structures 158
3.3. Laser Wavelength Control 159
3.4. Cavity-Dumped and Q-Switched Lasers 161
3.5. Master Oscillator Power Amplifier (MOPA) 162
3.5.1. Modulation 162
3.5.2. Mach-Zehnder Modulator (MZM) 163
3.5.2.1. MZM Phase Elements 165
3.5.2.2. MZM Bias Control 166
3.5.2.3. Extinction Ratio (ER) 166
3.5.2.4. Extinction Ratio Characterization and Optimization 167
3.5.2.5. MZM Drive Powerand Chirp Considerations 169
3.5.2.6. Pulsed Waveform Generation 171
3.5.3. High Power Optical Amplifier 173
3.5.3.1. Average Power Limited (APL) Properties 175
3.5.3.2. Amplifier Gain, Saturation, and Noise 175
3.5.3.3. Amplifier Efficiency 177
3.5.3.4. Polarization-Maintaining (PM) Fiber Amplifier Designs 180
3.5.4. High-Efficiency Semiconductor Optical Amplifiers 182
3.5.5. Arbitrary Waveforms and Variable-Duty-Cycle Signaling 184
3.5.5.1. Low Duty Cycle Limitations 186
3.5.5.2. A) Limited TX Modulation Extinction 186
3.5.5.3. B) Transmitter ASE 186
3.5.5.4. C) Nonlinear Impairments 188
4. Receiver Technologies 193
4.1. Direct Detection-PIN 193
4.2. Direct Detection Avalanche-Photodiode (APD) 195
4.3. Direct Detection-Photon Counting 196
4.4. Coherent Homodyne Receivers 197
4.5. Optically Preamplified Direct Detection 198
5. Performance and Implementation Considerations 201
5.1. Waveform and Filtering Considerations 202
5.1.1. Symmetric Filtering 204
5.1.2. Gaussian Waveforms and Matched Optical Filtering 205
5.1.2.1. Relaxed Filter Tolerances 205
5.1.2.2. Reduced Sensitivity to Timing Jitter 207
5.1.2.3. Combined Optical and Postdetection Filtering 209
5.1.3. Optimized Multi-Rate Transceivers 211
5.2. Differential Phase Shift Keying (DPSK) 212
5.2.1. DPSK Wavelength Alignment Considerations 213
5.2.2. Interferometer Stabilization 215
5.2.3. Multi-Wavelength DPSK Receiver Options 218
5.2.4. Reconfigurable DPSK Demodulators 221
5.3. Hybrid Modulation Formats 222
5.4. Demonstrated Communication Performance 223
5.5. Applications: to the Moon and Beyond 227
Acknowledgments 230
Acronyms andAbbreviations 232
References 234
Symbols 231
Free-space laser communications with adaptive optics: Atmospheric compensation experiments 259
1. Introduction 260
2. Adaptive Optics Architectures for Free-Space Optical Communication Systems 261
3. Experimental System Arrangement and Components 264
4. Compensation of Low-Order Distortions 267
4.1. Tracking and Fast Beam Steering System 267
4.2. Compensation of Atmospheric Wave-Front Tilt Distortions 269
4.3. Laser Communication with Tip/Tilt Control 270
5. SPGD High-Resolution Wave-Front Control 272
5.1. SPGD Adaptive Optics System 272
5.2. Temporal Behavior of the Received Power in the Tip/Tilt-Compensated Receiver System 273
5.3. Wave-Front Control with the SPGD AO System 274
5.4. SPGD Adaptive Transceiver System 279
6. Summary and Conclusion 280
Acknowledgment 281
References 281
Optical networks, last mile access and applications 285
1. Optical Networks 286
1.1. Types of FSO Systems for Different Network Architectures 286
1.2. Architectures of FSO Networks (Point-to-Point and Point-to-Multipoint Configurations) 288
1.2.1. Optical Wireless in Ring Architecture 288
1.2.2. Optical Wireless in Star Architecture 289
1.2.3. Optical Wireless in Meshed Architecture 290
1.3. Connecting to the Backbone 290
2. FSO Applications 291
2.1. Short Range Aapplications and Last Mile Access 293
2.1.1. FSO in Combination with Satellite and Wireless LAN 296
2.2. Long Range Applications 296
2.3. Space Applications (Aircraft and Satellites) 299
3. Last Mile 301
3.1. Line of Sight 301
3.2. Reliability and Availability 303
3.3. Different FSO Techniques for the Last Mile 306
3.3.1 Small FSO System for 100 m 307
3.3.2. FSO System for 300 m 307
3.4. FSO network for a Small City and Multimedia Applications 308
3.4.1. Multimedia Applications 308
3.4.2. FSO Network for a Small City 309
4. Summary 312
References 313
Communication techniques and coding for atmospheric turbulence channels 315
1. Introduction 316
2. Modeling of Optical Communication through Atmospheric Turbulence 317
2.1. Modeling of Atmospheric Turbulence 318
2.2. Spatial and Temporal Coherence of Optical Signals through Turbulence 318
2.3. Probability Distributions ofTurbulence-Induced Intensity Fading 320
2.3.1. Marginal Distribution of Fading 320
2.3.2. Joint Spatial and Temporal Distributions of Fading 321
3. Maximum-Likelihood Detection of On-Off Keying in Thrbulence Channels 322
3.1. Symbol-by-Symbol Maximum-Likelihood Detection 323
3.2. Maximum-Likelihood Sequence Detection 325
4. Spatial Diversity Reception 325
4.1. Maximum-Likelihood Diversity Detection on Turbulence Channels 325
4.2. Numerical Simulationfor Dual Receivers 327
4.3. Summary 328
5. Temporal Domain Techniques 329
5.1. Markov Chain Model in Maximum-Likelihood Sequence Detection through Turbulence 329
5.1.1 . Joint Temporal Distribution for Turbulence Induced Fading 329
5.1.2. Single-Step MC Model for Fading Correlations 330
5.1.3. Burst Error Distribution for Symbol-by-Symbol Detection 330
5.1.4. Sub-Optimal Per-Survivor Processing for MLSD 333
5.2. Pilot-Symbol Assisted Detectionfor Correlated Turbulent Free-Space Optical Channels 336
5.2.1. Pilot-Symbol Assisted Maximum-Likelihood Detection 337
5.2.2. Pilot-Symbol Assisted Symbol-by-Symbol Detection with Variable Threshold 339
5.2.3. Numerical Simulation 340
5.3. Experimental Demonstration on Temporal Domain Techniques 340
6. Performance Bounds for Coded Free-Space Optical Communication Through Atmospheric Turbulence 344
6.1. Pairwise Codeword-Error Probability Bound 345
6.2. Error-Probability Bounds for Various Coding Schemes 347
6.2.1. Block Codes 347
6.3. Convolutional Codes 348
6.3.1. Turbo Codes 350
6.4. Numerical Simulation Results 351
6.5. Summary 353
Conclusions 354
Acknowledgment 355
References 355
Optical communications in the mid-wave IR spectral band 359
1. Introduction 360
2. Atmospheric Modeling 361
2.1. Atmospheric Turbulence 364
2.1.1. Rytov Variance 365
2.1.2. Coherence Length 366
2.2. Beam Diameter 367
2.3. Direct Detection SNR 369
2.4. Large Scale and Small Scale Turbulence - Spherical Waves 370
2.5. Bit Error Rate (BER) and Minimum SNR 371
3. The MWIR Optical Sources 374
3.1. Semiconductor Based Lasers 374
3.1.1. Lead-Salt Lasers 375
3.1.2. III-V Strained Quantum-Well Lasers 375
3.1.3. Quantum Cascade Lasers 375
3.1.4. Solid-State Lasers 376
3.1.5. Chemical Lasers 377
3.2. Nonlinear Frequency Converters 377
3.2.1. Performance Modeling of OPOs 381
3.2.2. PPLN OPOs 381
3.2.3. Oscillation Threshold Calculations 382
4. The MWIR Detectors 384
4.1. Dember Effect Detectors 384
5. Data Communications in the Mid-IR 386
5.1. Weapon Code Transmission in MWIR 387
5.1.1. Wavelength Selection 388
5.1.2. Transceiver Design Approach 388
5.1.3. Experimental Results 392
5.2. Image Transmission in MWIR using an OPO 397
6. Summary and Conclusions 401
References 401
Quantum cascade laser-based free space optical communications 405
1. Introduction 405
2. High Frequency Analog and Digital Modulation 406
2.1. Stability for NIR-Laser and a QCL-Based FSO Link Under Strong Scattering 408
3. Experimental Apparatus 408
3.1. Satellite TV Transmission Using a QCL-Based FSO Link 414
Acknowledgments 417
References 417
All-weather long-wavelength infrared free spaceoptical communications 419
1. Introduction 419
2. Atmospheric Transmission: The Case for LWIR 420
2.1. Molecular Absorption Model 420
2.2. Smoke Extinction Model 420
2.3. Fog Extinction Model 423
3. Component Development for LWIR Communications 423
3.1. Compact RF-Driven Laser 423
3.2. Stark-Effect Modulator 424
3.3. Dielectric Waveguide Modulator 425
3.4. AC Biasing Method 426
4. Experimental Results 427
References 429
"Communication techniques and coding for atmospheric turbulence channels (p. 303-304)
Abstract. In free -space optica l communication link s, atmo spheri c turbulence causes fluctuations in both the inten sity and the phase of the received light signal, impairing link performance. In this paper , we describe severa l communication techniques to mitigate turbulence-induced intensity fluctuation s, i.e., signal fading . The se techniques are applicable in the regime in which the receiv er aperture is smaller than the correlation length of the fading, and the observation interval is shorter than the correlation time of the fading. We assume that the receive r has no knowledge of the instantaneous fading state . The techniques we con sider are based on the stati stical properties of fading, as functions of both temporal and spatial coordinates. Our approaches can be divided into two categories : temporal domain techniques and spatial domain techniques.
In the spatial domain techniques, one must employ at least two receivers to collect the signal light at different positi ons or from different spatial angle s. Spatial diver sity reception with mult iple recei vers can be used to overcome turbulence-induced fading. When it is not possible to place the receivers sufficiently far apart, the fading at different receivers is correl ated , redu cing the diversity gain . We descr ibe a ML dete ction techn ique to reduce the diver sity gai n penalty caused by such fadin g correl ation.
In the temporal domain techniques, one empl oys a single receiver. When the receiver knows only the marginal statistics of the fading , a symbol-by-symbol ML dete ctor can be used to optimize perform ance. When the receiver also knows the temporal correlation of the fadin g, maximum -likelihood sequence detection (MLSD) can be employed, yielding a further perform ance improvement, but at the cos t of very high complexity. We descri be two reduced-compl exity implementations of the MLSD, which make use of a single-s tep Markov chain model for the fading co rrelation in conjunction with per-survivorprocessing. Next,we also investigate the performance of using error-control codingand pilotsymbol-assisted detectionschemesthroughatmospheric turbulence channels.
1. Introduction
Recently, free-space optical communication has attracted considerable attention for a variety of applications [1-8] . Because of the complexity associated with phase or frequency modulation, current free-space optical communication systems typically use intensity modulation with direct detection (IMIDO). However, in practice, the performance of free-space optical communication systems can be degraded by many effects, such as fog, obstruction of the line-of-sight path, atmospheric turbulence and the nonideal characteristics of optical transmitters and receivers. In this chapter, we focus on communication techniques and coding schemes to counter the degradation caused by atmospheric turbulence in IMIDO links."
| Erscheint lt. Verlag | 5.5.2010 |
|---|---|
| Reihe/Serie | Optical and Fiber Communications Reports | Optical and Fiber Communications Reports |
| Zusatzinfo | XII, 418 p. 101 illus., 1 illus. in color. |
| Verlagsort | New York |
| Sprache | englisch |
| Themenwelt | Naturwissenschaften ► Physik / Astronomie ► Optik |
| Technik ► Elektrotechnik / Energietechnik | |
| Schlagworte | Adaptive optics • Basics • Communication • Communication Systems • Information • Laser • Network • Optical communication • Optical Network • Optics • Quantum Cascade Laser |
| ISBN-10 | 0-387-28677-2 / 0387286772 |
| ISBN-13 | 978-0-387-28677-8 / 9780387286778 |
| Haben Sie eine Frage zum Produkt? |
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