LUIS ENRIQUE GARCÍA MUÑOZ, Universidad Carlos III de Madrid, Spain

HANS L. HARTNAGEL, Technische Universität Darmstadt, Germany

SASCHA PREU, Technische Universität Darmstadt, Germany

ANTTI V. RÄISÄNEN, Aalto University, Finland

Preface xiii

Foreword xvii

List of Contributors xix

1 General Introduction 1
Hans Hartnagel, Antti V. Räisänen, and Magdalena Salazar-Palma

2 Principles of THz Generation 3
Sascha Preu, Gottfried H. Döhler, Stefan Malzer, Andreas Stöhr, Vitaly Rymanov, Thorsten Göbel, Elliott R. Brown, Michael Feiginov, Ramón Gonzalo, Miguel Beruete, and Miguel Navarro-Cya

2.1 Overview 3

2.2 THz Generation by Photomixers and Photoconductors 5

2.2.1 Principle of Operation 5

2.2.2 Basic Concepts and Design Rules 7

2.2.3 Thermal Constraints 21

2.2.4 Electrical Constraints 23

2.2.5 Device Layouts of Photoconductive Devices 35

2.2.6 Device Layouts of p-i-n Diode-Based Emitters 47

2.3 Principles of Electronic THz Generation 53

2.3.1 Oscillators with Negative Differential Conductance 54

2.3.2 Multipliers (Schottky Diodes, Hetero-Barrier Varactors) 56

2.3.3 Plasmonic Sources 58

References 61

3 Principles of Emission of THzWaves 69
Luis Enrique Garcya Munoz, Sascha Preu, Stefan Malzer, Gottfried H. Döhler, Javier Montero-de-Paz, Ramón Gonzalo, David González-Ovejero, Daniel Segovia-Vargas, Dmitri Lioubtchenko, and Antti V. Räisänen

3.1 Fundamental Parameters of Antennas 69

3.1.1 Radiation Pattern 69

3.1.2 Directivity 71

3.1.3 Gain and Radiation Efficiency 71

3.1.4 Effective Aperture Area and Aperture Efficiency 72

3.1.5 Phase Pattern and Phase Center 72

3.1.6 Polarization 72

3.1.7 Input Impedance and Radiation Resistance 72

3.1.8 Bandwidth 73

3.2 Outcoupling Issues of THz Waves 73

3.2.1 Radiation Pattern of a Dipole over a Semi-Infinite Substrate 75

3.2.2 Radiation Pattern of a Dipole in a Multilayered Medium 79

3.2.3 Anomalies in the Radiation Pattern 82

3.3 THz Antenna Topologies 84

3.3.1 Resonant Antennas 85

3.3.2 Self-Complementary Antennas 87

3.4 Lenses 90

3.4.1 Lens Design 90

3.5 Techniques for Improving the Performance of THz Antennas 93

3.5.1 Conjugate Matching Technique 93

3.5.2 Tapered Slot Antenna on Electromagnetic Band Gap Structures 99

3.6 Arrays 107

3.6.1 General Overview and Spectral Features of Arrays 107

3.6.2 Large Area Emitters 113

References 157

4 Propagation at THz Frequencies 160
Antti V. Räisänen, Dmitri Lioubtchenko, Andrey Generalov, J. Anthony Murphy, Créidhe O’Sullivan, Marcin L. Gradziel, Neil Trappe, Luis Enrique Garcia Munoz, Alejandro Garcia-Lamperez, and Javier Montero-de-Paz

4.1 Helmholtz Equation and Electromagnetic Modes of Propagation 160

4.2 THz Waveguides 167

4.2.1 Waveguides with a Single Conductor: TE and TM Modes 168

4.2.2 Waveguides with Two or More Conductors: TEM and Quasi-TEM Modes 173

4.2.3 Waveguides with No Conductor: Hybrid Modes 177

4.3 Beam Waveguides 183

4.3.1 Gaussian Beam 183

4.3.2 Launching and Focusing Components: Horns, Lenses, and Mirrors 187

4.3.3 Other Components Needed in Beam Waveguides 193

4.3.4 Absorbers 195

4.3.5 Modeling Horns Using Mode Matching 195

4.3.6 Multimode Systems and Partially Coherent Propagation 199

4.3.7 Modeling Techniques for THz Propagation in THz Systems 201

4.4 High Frequency Electric Characterization of Materials 202

4.4.1 Drude Model 203

4.4.2 Lorentz–Drude Model 204

4.4.3 Brendel–Bormann Model 205

4.5 Propagation in Free Space 205

4.5.1 Link Budget 205

4.5.2 Atmospheric Attenuation 206

References 207

5 Principles of THz Direct Detection 212
Elliott R. Brown, and Daniel Segovia-Vargas

5.1 Detection Mechanisms 212

5.1.1 E-Field Rectification 213

5.1.2 Thermal Detection 215

5.1.3 Plasma-Wave, HEMT, and MOS-Based Detection 220

5.2 Noise Mechanisms 223

5.2.1 Noise from Electronic Devices 223

5.2.2 Phonon Noise 225

5.2.3 Photon Noise with Direct Detection 227

5.3 THz Coupling 230

5.3.1 THz Impedance Matching 230

5.3.2 Planar-Antenna Coupling 231

5.3.3 Exemplary THz Coupling Structures 232

5.3.4 Output-Circuit Coupling 235

5.4 External Responsivity Examples 235

5.4.1 Rectifiers 235

5.4.2 Micro-Bolometers 236

5.5 System Metrics 239

5.5.1 Signal-to-Noise Ratio 239

5.5.2 Sensitivity Metrics 240

5.6 Effect of Amplifier Noise 243

5.7 A Survey of Experimental THz Detector Performance 244

5.7.1 Rectifiers 246

5.7.2 Thermal Detectors 247

5.7.3 CMOS-Based and Plasma-Wave Detectors 249

References 250

6 THz Electronics 254
Michael Feiginov, Ramón Gonzalo, Itziar Maestrojuán, Oleg Cojocari, Matthias Hoefle, and Ernesto Limiti

6.1 Resonant-Tunneling Diodes 254

6.1.1 Historic Introduction 254

6.1.2 Operating Principles of RTDs 255

6.1.3 Charge-Relaxation Processes in RTDs 256

6.1.4 High-Frequency RTD Conductance 259

6.1.5 Operating Principles of RTD Oscillators 260

6.1.6 Limitations of RTD Oscillators 261

6.1.7 Overview of the State of the Art Results 264

6.1.8 RTD Oscillators versus Other Types of THz Sources 265

6.1.9 Future Perspectives 265

6.2 Schottky Diode Mixers: Fundamental and Harmonic Approaches 265

6.2.1 Sub-Harmonic Mixers 267

6.2.2 Circuit Fabrication Technologies 270

6.2.3 Characterization Technologies 272

6.2.4 Advanced Configuration Approach 276

6.2.5 Imaging Applications of Schottky Mixers 277

6.3 Solid-State THz Low Noise Amplifiers 278

6.3.1 Solid-State Active Devices and Technologies for Low Noise Amplification 280

6.3.2 Circuit and Propagation Issues for TMIC 282

6.3.3 Low Noise Amplifier Design and Realizations 284

6.3.4 Perspectives 287

6.4 Square-Law Detectors 288

6.4.1 Characterization and Modeling of Low-Barrier Schottky Diodes 289

6.4.2 Design of Millimeter-Wave Square-Law Detectors 291

6.5 Fabrication Technologies 292

6.5.1 Overview of Fabrication Approaches of Schottky Structures for Millimeter-Wave Applications 293

6.5.2 Film-Diode Process 296

References 299

7 Selected Photonic THz Technologies 304
Cyril C. Renaud, Andreas Stöhr, Thorsten Goebel, Frédéric Van Dijk, and Guillermo Carpintero

7.1 Photonic Techniques for THz Emission and Detection 304

7.1.1 Overall Photonic System 304

7.1.2 Basic Components Description 306

7.1.3 Systems Parameters, Pulsed versus CW 307

7.2 Laser Sources for THz Generation 309

7.2.1 Pulsed Laser Sources 309

7.2.2 Continous Wave (CW) Sources 312

7.2.3 Noise Reduction Techniques 314

7.2.4 Photonic Integrated Laser Sources 315

7.3 Photodiode for THz Emission 320

7.3.1 PD Limitations and Key Parameters 320

7.3.2 Traveling Wave UTC-PD Solution 322

7.4 Photonically Enabled THz Detection 324

7.4.1 Pulsed Terahertz Systems 325

7.4.2 Optically Pumped Mixers 328

7.5 Photonic Integration for THz Systems 331

7.5.1 Hybrid or Monolithic Integrations 332

7.5.2 Monolithic Integration of Subsystems 333

7.5.3 Foundry Model for Integrated Systems 334

References 335

8 Selected Emerging THz Technologies 340
Christian Damm, Harald G. L. Schwefel, Florian Sedlmeir, Hans Hartnagel, Sascha Preu, and Christian Weickhmann

8.1 THz Resonators 340

8.1.1 Principles of Resonators 341

8.1.2 Introduction to WGM Resonators 343

8.1.3 Evanescent Waveguide Coupling to WGMs 345

8.1.4 Resonant Scattering in WGM Resonators 346

8.1.5 Nonlinear Interactions in WGM 349

8.2 Liquid Crystals 350

8.2.1 Introduction 350

8.2.2 Characterization 357

8.2.3 Applications 365

8.3 Graphene for THz Frequencies 367

8.3.1 Theory and Material Properties 367

8.3.2 Applications 373

References 377

Index 383

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