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The vacuum field energies and their connection to the force between two plates are presented while deriving the Casimir force. Thermal radiation and the Planck spectrum are introduced and the Einstein A and B coefficients and their properties under thermodynamic equilibrium examined. Microwave cavities and wave guides are considered and their general properties derived with special consideration given to conducting waveguides and transmission lines. Optical waveguides are analyzed using the ray optic picture. Topics include planar waveguides, variable index circular waveguides, single mode fibers, and dispersion. Finally, photonic crystals are discussed and photonic band structures are shown to be analogous to electronic bands.

This chapter describes the communication revolution based on the introduction of fibre optic links during the period 1970-90. The breakthrough required silica optical fibre waveguides with ultra-low loss, allowing long distance transmission of digital signals. Minimum loss occurred at wavelengths near 1.5 μm, a spectral region lacking suitable sources and detectors. Minimising dispersion demanded the development of single mode IR lasers and the demand for large bit rates, that of high speed detectors, challenges met by the use of epitaxial layers of the material GaInAsP grown by MOVPE. More recently, wavelength-division multiplexing required sources operating at many well-defined wavelengths, a problem solved by development of tuneable single mode lasers. The pressure for ever higher bit rates led to the development of high speed semiconductor optical modulators. Current trends favour the development of opto-electronic integration, following the lead of electronic integration.

In a quantum cascade laser, the light is confined both vertically, by the sequence of the epitaxial layers, as well as horizontally, by the ridge structure that also confines laterally the current. Because the epitaxial growth allows the tighter control of layers thicknesses as compared to the lateral one, optical confinement is usually stronger in the vertical direction. As a result, the simplest model of the one-dimensional dielectric slab model correctly predicts the propagation index and overlap factor of the waveguide, and is usually a good starting approximation for a more complete computation. This chapter discusses the dielectric slab waveguide, interface plasmon mode, optical properties of doped layers, two-dimensional confinement, large optical waveguides, and thermal properties.

In covering the fundamentals and ideal implementation of integrated multi-port interferometers and waveguide meshes, we saw that solutions with larger integration density of programmable unit cells enables the synthesis of more complex circuits. However, photonic integrated circuits (PICs) generally suffer from design and fabrication errors and other non-ideal working conditions, which compromises performance and scalability. In addition, PICs require the development of two additional tiers (electronic hardware and software) to allow their programmability, optimisation and (re)configuration. This chapter introduces basic practical considerations of programmable PIC design and reviews experimental demonstrations of both multi-port interferometers and waveguide mesh arrangements. It analyses the main error sources and their impact on circuit performance and investigates the most challenging evolution obstacles for very large-scale programmable PICs. It introduces an analytical method for arbitrary waveguide mesh analysis. Finally, it presents a general architecture for the control subsystem and introduces the software framework and main algorithms.

Integrated waveguide meshes are the third evolutionary step in programmable photonics, and rely on the large-scale repetition of interferometric waveguide elements and phase actuators conceived and designed to implement a common hardware platform that enables the programming of arbitrary photonic circuit topologies and design parameters by suitable setting of its control signals. In contrast to linear feedforward-only programmable circuits, these circuits enable the synthesis of optical cavities, optical loops and feedbackward paths. Their improved versatility entails a paradigm shift regarding the development of application-specific photonic integrated circuits. Here, the long and costly test cycles can be potentially substituted by off-the-shelf ready-to-use circuits. This allows them to be applied to myriad systems requiring optical linear processing and dynamic configuration. This chapter introduces the basic design principles and the implementations of the most popular designs. It then provides a comparative analysis of alternative waveguide mesh arrangements and their performance evaluation.