1. Introduction ................................................ 1
1.1. An Overview of Fusion Splicing and Its Applications ....... 1
1.2. The Fusion Splicing Process ............................... 3
1.3. Essential Optical Fiber Concepts .......................... 8
1.3.1. Optical Characteristics ............................ 8
1.3.2. Material and Mechanical Characteristics
of Silica Fibers .................................. 13
1.4. Alternatives to Fusion Splicing .......................... 15
1.5. Fusion Splices in the Optical Network .................... 17
1.6. A Brief History of Fusion Splicing ....................... 21
1.7. The Frontiers of Fusion Splicing ......................... 23
1.8. Summary .................................................. 25
2. Fiber Preparation and Alignment ............................ 27
2.1. Stripping ................................................ 27
2.1.1. Fiber Coatings .................................... 28
2.1.2. Mechanical and Thermo-Mechanical Stripping
Techniques ........................................ 31
2.1.3. Chemical Stripping Techniques ..................... 33
2.1.4. Vaporization Stripping Techniques ................. 34
2.2. Cleaving ................................................. 35
2.2.1. Cleaving Techniques and Hardware .................. 36
2.2.2. Basic Cleaving Principles ......................... 36
2.2.3. Cleave Defects .................................... 39
2.2.4. The Importance of Cleave Quality .................. 40
2.3. Alignment ................................................ 42
2.3.1. Passive Alignment ................................. 43
2.3.2. Image-Based Active Fiber Alignment ................ 43
2.3.3. Transmitted-Power Based Active Fiber Alignment .... 44
2.3.4. Light-Injection and Detection (LID) Technology .... 46
2.4. Summary .................................................. 47
3. Mechanics of Fusion Splicing ............................... 49
3.1. Heat Transfer During Fusion Splicing ..................... 49
3.1.1. Arc-Discharge Heating ............................. 50
3.1.2. Heat Flow ......................................... 52
3.2. Mechanical Forces During Fusion Splicing ................. 57
3.2.1. Compressive, Tensile, and Bending Forces .......... 58
3.2.2. Surface Tension and Viscosity ..................... 62
3.2.3. Implications for Core Alignment ................... 65
3.2.4. Fusion Splice Duration ............................ 67
3.2.5. Neckdown, Dissimilar Fiber Diameters,
and Dissimilar Fiber Viscosities .................. 68
3.2.6. Bubbles, Airlines, and Air Holes .................. 70
3.3. Dopant Diffusion ......................................... 73
3.3.1. Theory of Dopant Diffusion ........................ 74
3.3.2. Dopant Diffusion Coefficients ..................... 79
3.3.3. Diffusion Examples ................................ 80
3.4. Stress and Strain ........................................ 82
3.4.1. Source of Stress and Strain in Optical Fibers ..... 83
3.4.2. Fusion Splicing and Its Relationship
to Residual Stress and Strain ..................... 86
3.5. Summary .................................................. 88
4. Optics of Fusion Splicing .................................. 91
4.1. Modal Description of Fusion Splices ...................... 93
4.1.1. The Scalar Wave Equation .......................... 93
4.1.2. Modes ............................................. 96
4.1.3. The Scattering Matrix ............................. 99
4.1.4. The Overlap Integral ............................. 104
4.1.5. The Reflectance of Fusion Splices ................ 106
4.2. The Optics of Single-Mode Fiber Fusion Splices .......... 108
4.2.1. The Mode Field Diameter .......................... 110
4.2.2. The Gaussian Approximation ....................... 1ll
4.2.3. Reflectance of Single-Mode Fusion Splices ........ 116
4.2.4. Modal Noise and Single-Mode Fiber Splices ........ 116
4.3. The Optics of Multimode Fusion Splices .................. 119
4.3.1. Propagation Characteristics ...................... 119
4.3.2. Splice Loss Approximation Formulae ............... 121
4.3.3. Reflections from Multi-Mode Fusion Splices ....... 123
4.3.4. Fusion Splices Between Single- and Multimode
Fibers ........................................... 123
4.4. The Beam Propagation Method (BPM) ....................... 124
4.4.1. Introduction to BPM .............................. 124
4.4.2. The Transparent Boundary Condition ............... 128
4.4.3. Mode Solving with BPM ............................ 129
4.4.4. Computing Splice Loss with BPM ................... 130
4.4.5. A Practical BPM Example .......................... 131
4.5 Summary ................................................. 134
5. Splice Loss Estimation and Fiber Imaging .................. 137
5.1. Fusion Splice Imaging and Image Processing .............. 139
5.1.1. The Imaging System ............................... 139
5.1.2. Introduction to Fiber Imaging .................... 141
5.1.3. Characteristics of Fiber Images .................. 141
5.1.4. Basic Image Processing ........................... 146
5.2. Loss Computation ........................................ 147
5.2.1. Introduction to Coupled-Mode Theory .............. 148
5.2.2. Coupled-Mode Theory in a Single-Mode Fiber:
Microbend Theory ................................. 151
5.2.3. Coupled-Mode Theory for Loss Computation ......... 154
5.3. Summary ................................................. 160
6. Splice Strength, Reliability, and Packaging ............... 161
6.1. Introduction to Splice Strength and Reliability ......... 162
6.2. Crack Growth Theory ..................................... 165
6.3. Characterizing Splice Failure Strength: Weibull
Statistics .............................................. 168
6.4. Theory of Proof Testing for Long-Term Reliability ....... 172
6.5. Proof Testing Methods and Hardware ...................... 176
6.6. Splice Packaging ........................................ 177
6.6.1. Splice Recoating Technology ...................... 178
6.6.2. Rigid Splice Protectors and Splints .............. 180
6.7. Summary ................................................. 181
7. Splice Measurement and Characterization ................... 183
7.1. Transmission Measurements ............................... 184
7.1.1. Insertion Loss and Cutback Measurements .......... 184
7.1.2. The- "Pre-Splice" Technique ...................... 187
7.1.3. The Two-Splice Technique ......................... 187
7.1.4. Spectral Splice Loss Measurements ................ 189
7.2. Reflection Measurements ................................. 189
7.2.1. Optical Continuous Wave Reflectometers
(OCWRs) .......................................... 190
7.2.2. Optical Time-Domain Reflectometer (OTDR)
Measurements ..................................... 191
7.2.3. High Resolution Reflection Measurements .......... 197
7.3. Refractive Index Profiling of Fibers and Fusion
Splices ................................................. 199
7.4. Summary ................................................. 202
8. Splice Process Optimization and Special Splicing
Strategies ................................................ 203
8.1. Design of Experiments for Splice Optimization ........... 204
8.1.1. The Splice Parameter Space ....................... 205
8.1.2. Orthogonal Arrays ................................ 206
8.1.3. Example Splice Optimization ...................... 210
8.2. Special Splicing Strategies ............................. 214
8.2.1. Fire Polishing and Arc Scanning .................. 214
8.2.2. Bridge Fibers .................................... 215
8.2.3. Dopant Diffusion and TEC Splices ................. 217
8.2.4. Low-Temperature Splices .......................... 220
8.2.5. Offset Heating ................................... 221
8.2.6. Tapered Splices .................................. 222
8.2.7. Fattened Splices ................................. 226
8.3. Summary ................................................. 226
9. Fusion Splicing of Specialty Fiber ........................ 229
9.1. Non-Zero Dispersion Shifted Fibers ...................... 229
9.1.1. Introduction to NZ-DSF ........................... 230
9.1.2. Special Splicing Considerations for NZ-DSF ....... 230
9.2. Polarization-Maintaining Fibers ......................... 231
9.2.1. Introduction to PM Fibers ........................ 232
9.2.2. Cleaving Considerations for PM Fibers ............ 233
9.2.3. Polarization Crosstalk and Polarization
Extinction Ratio ................................. 234
9.2.4. PM Fiber Alignment ............................... 237
9.3. Erbium-Doped Fibers ..................................... 240
9.3.1. Introduction to Erbium-Doped Gain Fibers ......... 241
9.3.2. Strategies For Low-Loss EDF Fusion Splicing ...... 242
9.3.3. Loss Measurement of Erbium-Doped Fiber Splices ... 244
9.4. Dispersion-Compensating Fibers .......................... 244
9.4.1. Introduction to Dispersion-Compensating Fibers ... 245
9.4.2. Splicing Strategies for Dispersion-
Compensating Fibers .............................. 246
9.5. Microstructured Fibers .................................. 248
9.5.1. Types of Microstructured Fibers .................. 248
9.5.2. Fusion Splicing Microstructured Fibers ........... 249
9.6. Summary ................................................. 253
10.Splicer Hardware: State of the Art ........................ 255
10.1.Introduction to Splicer Hardware ........................ 256
10.2.Field Splicers .......................................... 256
10.3.Factory Splicers ........................................ 259
10.4.Research and Laboratory Splicers ........................ 264
10.5.Summary ................................................. 266
Appendix A: List of Mathematical Symbols ..................... 267
Appendix B: List of Abbreviations ............................ 275
Appendix C: List of Relevant Published Standards
and Requirements ................................. 277
References ................................................... 279
Index ........................................................ 301
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