Optical Nonlinearities in Chalcogenide Glasses and their Applications (eBook)

Preface 6
Contents 8
1 An Introduction to Chalcogenide Glasses 11
1.1 Introduction 11
1.2 Structure of Chalcogenide Glasses 11
1.3 Electronic Properties of Chalcogenide Glasses 16
1.4 Chalcogenide Glasses for Near-Infrared Optics 20
1.5 Chalcogenide Glasses for Mid-IR and Far-IR Applications 22
1.6 Bulk Chalcogenide Glasses, Composition, and Optical Constants 24
1.7 Chalcogenide Thin Films and Comparison with the Bulk 27
1.8 Photoinduced Changes in Chalcogenide Glasses 31
1.9 Summary 37
2 Basic Concepts of Nonlinear Optics 39
2.1 Polarization 39
2.2 Wave Equation 40
2.3 The Harmonic Oscillator Model in Linear Optics 47
2.4 The Anharmonic Oscillator Model in Nonlinear Optics 50
2.5 Properties of Anisotropic Media 52
2.6 Second-Harmonic Generation 53
2.7 Self-Phase Modulation and Soliton Generation 54
3 Experimental Techniques to Measure Nonlinear Optical Constants 65
3.1 Introduction 65
3.2 Degenerate Four-Wave Mixing 65
3.3 Nearly Degenerate Three-wave Mixing 69
3.4 Z-Scan 71
3.5 Third-Harmonic Generation 73
3.6 Optical Kerr Gate and Ellipse Rotation 74
3.7 Self-Phase Modulation 77
3.8 Spectrally Resolved Two-Beam Coupling 79
3.9 Mach-Zehnder Interferometry 80
3.10 Summary 83
4 Measurement of Nonlinear Optical Constants 85
4.1 Measurements of Nonlinear Refractive Index 85
4.2 Measurements of Nonlinear Absorption Coe.cient 101
4.3 Determination of Three Photon-Absorption and Multiphoton Absorption 104
4.4 Second-Harmonic Generation, Phase Conjugation, Self-Phase Modulation, etc. 105
4.5 Comparison of Chalcogenide Nonlinearities with Silica 112
5 Optical Nonlinearities in Chalcogenide Fibres 117
5.1 Fabrication of Chalcogenide Fibers and Their Linear Optical Properties 117
5.2 Nonlinear Optical Properties of Fibers 121
5.3 Pulse Propagation in Fibers 124
5.4 Group-Velocity Dispersion Compensation by Fiber Gratings 131
5.5 Applications 132
6 Optical Switching in Chalcogenide Glasses 139
6.1 Criteria of Material Properties for All-optical Switching 139
6.2 Design Issues for All-Optical Switching 141
6.3 All-Optical Switching in Chalcogenide Glasses 141
6.4 All-Optical Switches, AND Gate, NOR Gate, etc. 155
6.5 Limitations of All-Optical Switches 159
6.6 Summary 159
7 Issues and Future Directions 161
7.1 Optical Limiting 161
7.2 Second-Harmonic Generation and Electro-Optic Effects 163
7.3 Fabrication of Rib and Ridge Waveguides and of Fiber Gratings 165
7.4 All-Optical Nonlinear Integrated Circuits 176
7.5 Inclusion of Metal Nanoparticles to Enhance Nonlinearity 178
7.6 Other Applications 179
7.7 Summary 185
References 187
Chapter 1 187
Chapter 2 190
Chapter 3 191
Chapter 4 192
Chapter 5 195
Chapter 6 198
Chapter 7 199
Index 205

1 An Introduction to Chalcogenide Glasses (p. 1-2)

1.1 Introduction

Chalcogenide glasses are based on the chalcogen elements S, Se, and Te. These glasses are formed by the addition of other elements such as Ge, As, Sb, Ga, etc. They are low-phonon-energy materials and are generally transparent from the visible up to the infrared. Chalcogenide glasses can be doped by rareearth elements, such as Er, Nd, Pr, etc., and hence numerous applications of active optical devices have been proposed. Since chalcogenide-glass .bers transmit in the IR, there are numerous potential applications in the civil, medical, and military areas. Passive applications utilize chalcogenide .bers as a light conduit from one location to another point without changing the optical properties, other than those due to scattering, absorption, and re.ection. These glasses are optically highly nonlinear and could therefore be useful for all-optical switching (AOS). Chalcogenide glasses are sensitive to the absorption of electromagnetic radiation and show a variety of photoinduced e.ects as a result of illumination. Various models have been put forward to explain these effects, which can be used to fabricate diffractive, waveguide and fiber structures. For recent reviews, see [1–4]. Next-generation devices for telecommunication and related applications will rely on the development of materials which possess optimized physical properties that are compatible with packaging requirements for systems in planar or fiber form. This allows suitable integration to existing fiber-based applications, and hence requires appropriate consideration as to material choice, stability, and long-term aging behavior.

1.2 Structure of Chalcogenide Glasses

Solids are a particular state of condensed matter characterized by strong interactions between the constituent particles (atoms, molecules). Solids can be found or prepared either in an ordered (crystalline) state or in a disordered (noncrystalline) state. While the ordered state of a solid is limited to only de.ned. An ideal crystal corresponds to a regular arrangement of atoms in a lattice with well-de.ned symmetry, and a structural unit called the unit cell can be de.ned. Translation of the unit cell along the three coordinate axes reproduces the whole assembly of atoms. A real crystal does not exhibit perfect periodicity in space and contains various kinds of imperfections or defects. Solids which lack the periodicity of the atoms are called noncrystalline solids or amorphous, vitreous or glassy solids. While crystals possess long-range order (LRO), in amorphous materials short-range order (SRO) still exists.

Although the first and second nearest-neighbor coordination shells are wellde fined, atoms in the third coordination sphere start to become uncorrelated with those in the first one. In other words, the limit of short- and mediumrange order is the first 3–4 interatomic distances. The price to be paid for the loss of LRO is the appearance of .uctuations in angles and distances between the bonds. The ideal noncrystalline network is di.cult to define. Particularly, different thermal treatments lead to various noncrystalline arrangements of atoms. A continuous random network [5] might be considered to be an ideal noncrystalline network for covalent solids.