Contents
Foreword..................................... xiii
Chapter 1 Early developments...........1
1.0 Introduction .......................1
1.1 The birth of the OTDR.......2
1.2 Features, functions, and performance improvements ............4
1.3 Summary............................9
Suggested reading ............11
Chapter 2 Fundamentals of fi ber optics .................................................13
2.0 Introduction .....................13
2.1 Total internal refl ection ...13
2.2 Fiber attenuation..............19
2.3 Numerical aperture..........23
2.4 Multipath (modal) dispersion ................................................24
2.5 Chromatic dispersion ......28
2.6 Wavelength-division-multiplexed systems ............................35
2.7 V-parameter, cut-off wavelength, and spot profi le.................36
2.8 Splices and connectors....42
2.9 Bending loss.....................48
2.10 Coherence ........................52
2.11 Summary..........................55
Suggested reading ............57
Problems...........................57
Chapter 3 Fundamentals of OTDR operation ........................................59
3.0 Introduction .....................59
3.1 OTDR design....................62
3.2 A typical OTDR waveform .....................................................63
3.3 Multiple-wavelength OTDRs..................................................65
3.4 Optical masking...............67
3.5 Evolution of the OTDR ....69
3.6 Rayleigh backscatter ........72
3.7 Dynamic range .................74
3.8 Differences between multimode and single-mode OTDRs ...78
3.8.1 Physical differences....81
3.8.2 Refl ectivity differences between single-mode and
multimode fi ber connectors ..............................................81
3.8.3 Differences in backscatter levels .......................................82
3.8.4 Optical-power differences .................................................83
3.8.6 Operating-wavelength differences ....................................84
3.9 Echoes and ghosts............87
3.10 Other types of OTDR confi gurations......................................91
3.10.1 Standard OTDR with an EDFA..........................................91
3.10.2 Coherent-detection OTDR.................................................93
3.10.3 Correlation OTDR.......95
3.10.4 Short-coherence-length coherent OTDRs (multimode)....96
3.10.5 Photon-counting OTDRs....................................................98
3.11 Summary..........................99
Suggested reading ..........100
Problems.........................101
Chapter 4 Performance characteristics of OTDRs...............................103
4.0 Introduction ...................103
4.1 Figures of merit ..............103
4.2 Historical fi gures of merit.....................................................105
4.3 Detailed fi gures of merit .......................................................107
4.3.1 Refl ective dynamic range ................................................108
4.3.2 Scattering dynamic range................................................109
4.3.3 Derivation of the noise fl oor............................................115
4.3.4 Dynamic-range margin ....................................................121
4.3.5 Usable dynamic range .....................................................123
4.3.6 Measurement range ..124
4.3.7 How offset errors affect dynamic-range and
measurement-range calculations.....................................125
4.3.8 Event resolution........135
4.3.9 Loss-measurement resolution .........................................137
4.3.10 Return loss ................139
4.3.11 Linearity ....................140
4.3.12 Data resolution..........141
4.3.13 Clock accuracy..........143
4.3.14 Cursor resolution ......144
4.3.15 Refractive-index uncertainty ...........................................144
4.3.16 Speed of measurement ....................................................146
4.3.16.1 Fiber length .......146
4.3.16.2 Interleaving .......147
4.3.16.3 Data-processing speed .............................................147
4.3.16.4 Display speed....148
4.3.17 Event-detection accuracy ................................................148
4.4 Standards .......................149
4.5 Summary........................150
Suggested reading ..........151
Problems.........................151
Contents ix
Chapter 5 Measuring nonrefl ective events ..........................................153
5.0 Introduction ...................153
5.1 Sources of nonrefl ective events............................................153
5.2 Cursor placement for manual loss and
distance measurements .156
5.3 Distance-measurement errors of nonrefl ective events ........158
5.3.1 Distance-measurement errors caused by waveform
noise ..........................158
5.3.2 Distance-measurement errors caused by fi ltering ..........167
5.3.3 Other contributions to distance-measurement errors ....170
5.4 Summary .......................176
Suggested reading ..........177
Problems.........................178
Chapter 6 Loss-measurement error ......................................................179
6.0 Introduction ...................179
6.1 Loss-measurement errors caused by waveform noise .........179
6.2 Loss-measurement errors due to mismatch of
single-mode fi bers..........185
6.3 Loss-measurement errors on multimode fi ber .......... ..........190
6.4 Bending loss and stress loss in single-mode fi bers..............196
6.5 Wavelength-dependent loss in fusion splices and
connectors between single-mode fi bers ..............................198
6.6 Intrinsic loss in single-mode fusion splices.........................200
6.7 Summary........................205
Suggested reading ..........206
Problems.........................206
Chapter 7 Measuring refl ective events.................................................209
7.0 Introduction ...................209
7.1 Background ....................209
7.2 Causes of refl ection........212
7.2.1 Refl ections from angled cleaves ......................................212
7.2.2 Refl ections from connectors ............................................214
7.2.3 Refl ections from mechanical splices...............................220
7.3 Measuring refl ective events using an OTDR........................221
7.4 Effects that can reduce the accuracy of
refl ectivity measurements ....................................................226
7.5 Calibrating the OTDR's backscatter coeffi cient ...................229
7.5.1 Calculating the backscatter coeffi cient ...........................230
7.5.2 Measuring the backscatter coeffi cient.............................233
7.5.2.1 Measuring the backscatter coeffi cient with a
calibrated refl ector...................................................233
x Contents
7.5.2.2 Measuring the backscatter coeffi cient using
a CWR ...............235
7.5.2.3 Measuring the backscatter coeffi cient
using an OTDR..237
7.6 Integrated return loss.....240
7.7 Summary........................245
Suggested reading ..........247
Problems.........................247
Chapter 8 Complications caused by refl ective events.........................249
8.0 Introduction ...................249
8.1 Refl ections and the dead zone..............................................249
8.2 Improving the dead zone by optical masking......................252
8.3 Impact of refl ections on transmitters and receivers ............257
8.4 Dead zone box................263
8.5 Summary........................265
Suggested reading ..........265
Problems.........................265
Chapter 9 Measuring the numerical aperture and
mode-fi eld diameter of single-mode fi ber...........................267
9.0 Introduction ...................267
9.1 The far-fi eld scanning method of determining
numerical aperture ........268
9.2 Measuring the numerical aperture of single-mode fi ber
using an OTDR...............272
9.3 Measuring the cut-off wavelength of a single-mode fi ber
using an OTDR...............275
9.4 Summary........................277
Suggested reading ..........277
Problems.........................278
Chapter 10 Analyzing passive networks containing
splitters and couplers ...279
10.0 Introduction ...................279
10.1 Determining the locations of breaks in systems
containing splitters ........284
10.2 OTDR requirements for testing networks with splitters .....287
Suggested reading ..........289
Problems.........................290
Chapter 11 Automatic event-marking algorithms and calibration ......291
11.0 Introduction ...................291
11.1 Types of event markings .......................................................291
Contents xi
11.2 Functionality of different types of event markings..............293
11.3 Optimizing acquisition parameters......................................298
11.4 Measuring individual events................................................304
11.5 Testing event-marking software ...........................................312
11.5.1 Test-fi ber calibration .312
11.5.2 Repeatability testing .314
11.5.3 Summary of testing event-marking software ..................317
11.6 Event-marking features..317
11.7 Remote OTDRs for monitoring networks.............................321
11.8 Summary........................325
Suggested reading ..........326
Problems.........................327
Chapter 12 Test fi xtures....................329
12.0 Introduction ...................329
12.1 Dead zone fi xture...........329
12.2 Fiber circulator...............330
12.3 External-source test fi xture ..................................................337
12.4 Loss calibration with fi ber standard.....................................338
12.5 Summary........................340
Suggested reading ..........341
Problems.........................342
Chapter 13 Polarization mode dispersion .............................................343
13.0 Introduction ...................343
13.1 Measurement techniques .....................................................346
13.2 PMD model of optical fi ber...................................................349
13.3 Mathematical model of a polarization OTDR ......................353
13.4 Summary........................357
Problems.........................358
Chapter 14 Dispersion in optical fi bers .................................................359
14.0 Introduction ...................359
14.1 Intermodal dispersion....361
14.2 Intramodal dispersion ...364
14.2.1 Material dispersion ...364
14.2.2 Waveguide dispersion......................................................366
14.3 Dispersion reduction in optical fi bers..................................368
14.4 Measuring dispersion using an OTDR .................................369
14.5 Measuring chromatic dispersion using
multiple-wavelength OTDRs................................................372
14.6 Summary........................375
Suggested reading ..........376
Problems.........................377
xii Contents
Chapter 15 Considerations when selecting an OTDR ...........................379
15.0 Introduction ...................379
15.1 Durability .......................380
15.2 Display and controls......382
15.3 Human interface ............386
15.4 Optical port ....................387
15.5 Accessories, options, and features .......................................394
15.6 Safety..............................396
15.7 Performing a fi ber-acceptance test .......................................399
15.7.1 Sequential steps of an acceptance test............................400
15.8 Measuring the splice attenuation.........................................402
15.8.1 Corrective actions .....403
15.9 When should OTDR traces be taken? ..................................404
15.10 Span measurements.......405
15.10.1 What measurements are required? ................................405
15.11 Field technician's top-ten list ...............................................406
15.12 Summary........................407
Problems.........................407
Glossary of Terms........................409
Mathematical Glossary ...............425
Answers to Problems ..................431
Index............................................433
