Preface

Generally the term photonic crystal refers to two dimensional (2-D) and three dimensional (3-D) structures. Using 2-D and 3-D photonic crystals it is possible to control the propagation of light at arbitrary angles of incidence and not only the light normally incident as is the case for conventional optical films. Further, using photonic crystals, it is possible to achieve optical functionality not possible using conventional optical materials. This book provides a complete overview about photonic crystals including properties, applications, approaches and methods for the study.

This book is structured into four main sections:

*1. Introduction of Photonic Crystals.* Many organisms have photonic crystals as part of their 'bodies'. Recent research into the diversity of photonic crystals in nature has led us to question how such precise nanostructures form, with the hope that answers may lead to breakthroughs in their engineering. In a study of structural colors in nature, a remarkable convergence emerged in the nanoscale architecture of 2-D and 3-D periodic photonic crystals between species, families, phyla, and even kingdoms of organisms. Of the many types developed engineers, living organisms possess only four. These, however, occur in many unrelated species. It is possible that a combination of intra-cellular engineering and molecular self-assembly— as opposed to proportional genetic mutation—is the major factor in the evolution of photonic crystals in nature. In this section are reported examples of photonic crystals observed in nature and some examples of layouts such as gratings and guided waves.

*2. Photonic crystals and applications.* Applications such as optical logic devices, MEMS and bio-sensors are presented. Photonic crystals are promising technology in future optical signal processing and optical computing. In this direction optical logic gates are the fundamental components in optical digital information processing. In recent years, researchers have proposed other applications as photonic crystal MEMS based, and biosensors for bio-molecular detection systems (deoxyribonucleic acid (DNA) chips detectors). The listed topics are discussed in this section.

*3. Photonic crystal fiber:* Photonic-crystal fiber (PCF) confine slight in hollow cores or with confinement characteristics not possible in conventional optical fiber. PCF are used for applications in fiber-optic communications, fiber lasers, nonlinear devices,

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high-power transmission, highly sensitive gas sensors, and other areas. More specific categories of PCF include photonic-bandgap fiber (PCFs that confine light by band gap effects), holey fiber (PCFs using air holes in their cross-sections), hole-assisted fiber (PCFs guiding light by a conventional higher-index core modified by the presence of air holes), and Bragg fiber (photonic-bandgap fiber formed by concentric rings of multilayer film). This section shows some important applications of the PCF.

*4. Design and Modeling*: Photonic crystals are described exactly by Maxwell's Equation systems. Much of our research, however, is directed at achieving a higher level of understanding of these systems, so that it is possible to predict and explain their behaviour. This section discusses an overview about computational methods for photonic crystals including coupled mode and plane wave expansion theory.

**Alessandro Massaro** 

Italian Institute of Technology IIT Center for Bio-Molecular Nanotechnology, Lecce Italy

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high-power transmission, highly sensitive gas sensors, and other areas. More specific categories of PCF include photonic-bandgap fiber (PCFs that confine light by band gap effects), holey fiber (PCFs using air holes in their cross-sections), hole-assisted fiber (PCFs guiding light by a conventional higher-index core modified by the presence of air holes), and Bragg fiber (photonic-bandgap fiber formed by concentric rings of

*4. Design and Modeling*: Photonic crystals are described exactly by Maxwell's Equation systems. Much of our research, however, is directed at achieving a higher level of understanding of these systems, so that it is possible to predict and explain their behaviour. This section discusses an overview about computational methods for

**Alessandro Massaro** 

Italy

Italian Institute of Technology IIT

Center for Bio-Molecular Nanotechnology, Lecce

multilayer film). This section shows some important applications of the PCF.

photonic crystals including coupled mode and plane wave expansion theory.

**Part 1** 

**Introduction to Photonic Crystals** 

**Part 1** 

**Introduction to Photonic Crystals** 

**1** 

*France*

**How Nature Produces Blue Color** 

*Institut des Nanosciences de Paris (INSP), University Pierre et Marie Curie, Paris,* 

Today, blue is a very fashionable color in European countries. This has not always been the case (Pastoureau, 2000), as cultural perceptions have slowly evolved since prehistoric times. In cave paintings, white, red and black have been the only available tones and these colors remained basic for Greek and Latin cultures, where blue was neglected or even strongly devalued. The word *caeruleus*, which is often used for brightly blue species, in naming plants and insects, is etymologically related to the word *cera*, which designates wax (not to the world *caelum* – sky – as often believed): it meant first white, brown or yellow (André, 1949), before being applied to green and black, and much lately, to a range of blues. Latin and Greek philosophers were so diverted from blue that they even did not notice its presence in the rainbow: for *Anaximenes* (585-528 BC) and later for *Lucretius* (98-55 BC), the rainbow only displayed red, yellow and violet; *Aristotle* (384-322 BC) and *Epicurus* (341-270 BC) described it as red, yellow, green and violet. *Seneca* (ca. 4 BC - 65 AD) only mentioned red, orange, green, violet but, strangely, also added purple, a metameric color not found in the decomposition of white light. Later in the Middle-Ages, *Robert Grosseteste* (ca. 1175-1253) revisited the rainbow phenomenon in its book "*De Iride*" and still did not find there any blue color (Boyer, 1954). Blue emerged slowly in minds and art, only after the advent of technological breakthroughs in stained glass fabrication (as introduced in the 12th century rebuild of St Denis Basilica) and after the progressive use of blue dyes, which followed the

Another slow emergence of blue has been observed in the development of an efficient blue light-emitting diode. Red, yellow and green solid-state diodes appeared early after the development of the first device by Nick Holonyak Jr and S. Bevacqua in 1962, but the blue diode did not become practical until the work of Shuji Nakamura, in 1993. Since then, the blue and ultraviolet diodes have gained maturity and give rise to the emergence of powerful

If the blue color has been slow to emerge in human culture and technology, it was not so in nature. Blue flowers, birds, fishes, reptiles, insects, spiders, shrimps… have been observed very frequently. Blue colored structures have even been found on fossil beetles. The objective

A classification of *natural* photonic structures is not straightforward: these structures are complex, with multiscale effects and disorder. A useful classification requires some mathematical idealization of the structures. Our scheme is based on the number of dimensions

of this chapter is to discover how blue colorations are achieved in living organisms.

extension of woad cultivation, all after the 13th century.

white sources that appear to be the future of all lightening devices.

**1. Introduction** 

Priscilla Simonis and Serge Berthier
