Page 10 - Fiber Optic Communications Fund

Contents ix

3.9 Additional Examples 133
Exercises 136
Further Reading 138
References 138

4 Optical Modulators and Modulation Schemes 139
4.1 Introduction 139
4.2 Line Coder 139
4.3 Pulse Shaping 139
4.4 Power Spectral Density 141
4.4.1 Polar Signals 142
4.4.2 Unipolar Signals 142
4.5 Digital Modulation Schemes 144
4.5.1 Amplitude-Shift Keying 144
4.5.2 Phase-Shift Keying 144
4.5.3 Frequency-Shift Keying 145
4.5.4 Differential Phase-Shift Keying 146
4.6 Optical Modulators 149
4.6.1 Direct Modulation 149
4.6.2 External Modulators 150
4.7 Optical Realization of Modulation Schemes 158
4.7.1 Amplitude-Shift Keying 158
4.7.2 Phase-Shift Keying 160
4.7.3 Differential Phase-Shift Keying 162
4.7.4 Frequency-Shift Keying 163
4.8 Partial Response Signals ∗ 163
4.8.1 Alternate Mark Inversion 169
4.9 Multi-Level Signaling ∗ 172
4.9.1 M-ASK 172
4.9.2 M-PSK 174
4.9.3 Quadrature Amplitude Modulation 178
4.10 Additional Examples 182
Exercises 185
Further Reading 186
References 187

5 Optical Receivers 189
5.1 Introduction 189
5.2 Photodetector Performance Characteristics 190
5.2.1 Quantum Efficiency 193
5.2.2 Responsivity or Photoresponse 197
5.2.3 Photodetector Design Rules 199
5.2.4 Dark Current 200
5.2.5 Speed or Response Time 201
5.2.6 Linearity 202
5.3 Common Types of Photodetectors 202
5.3.1 pn Photodiode 203