Photonic Crystal Waveguides and Bio-Sensors

Photonic crystals (PCs) are actually implemented as biosensors [Ganesh et al., 2007], optical resonators [Karnutsch et al., 2007] and wavelength filters [D’Orazio et al., 2008; Pierantoni et al., 2006]. Other kinds of photonic crystals can be implemented by considering a periodic structure with defect line and/or central cavities. Several architectures of micro-cavities (see examples in Fig. 1 (a), (b)and (c)) have been studied in the past by using triangular and square lattices layouts [Joannopoulos, 1995] oriented on optoelectronic technology. Optoelectronic technologies are often affected by cost and space problems that prevent them from being used even more widely. The development and implementation of photonic integrated circuits (PICs) could provide a solution to these two major obstacles. Couplers such as tapered waveguides and photonic crystal (PhC) devices can be integrated in the same chip in order to reduce the space, especially concerning complex optical switch systems, and, to provide high transmitted power and high efficiency of the PICs. For example, the use of tapered waveguides is necessary in order couple the light into a W1 PhC waveguide (illustrated in Fig. 1 (a)). This kind of W1 PhC waveguide is object of much interest because of its potential for controlling and manipulating the propagation of light. In particular, sharp bends, junctions, couplers, cavities, add-drop filters, and multiplexers have been experimentally demonstrated or theoretically predicted, thus making these devices very attractive for highly integrated photonic circuits [Mekis et al., 2008; Pottier et al., 2003; Johnson et al., 2002; Sanchis et al., 2002; Chau et al., 2004; Chietera et al., 2004; Xing et al., 2005; Camargo et al., 2004; Talneau et al., 2004; Marki et al., 2005; Camargo et al., 2004; Sanchis et al.,2004; Khoo et al.,2006]. The in-plane coupling of W1 PhC is also an important issue for bio-sensors implemented by microand nanofabrication technologies. In fact, the development of microand nanofabrication technologies, biomolecular patterning and micro-electromechanical systems (MEMS), has greatly contributed to the realization of miniaturized laboratories applied to genomic and proteomic analysis. The application fields of these biochips are extremely broad, and they have been referred as several different terms (gene-chip, gene-array, DNA microarray, protein chip, and lab-on-chip). Essentially, these chips, developed both in simple stand-alone configurations and integrated devices/architectures, consist of planar structures, realized on several substrates such as glass or plastic materials, where (bio)molecules (such as DNA, proteins or cells, which selectively conjugate with target molecules) can be immobilized on them through chemical surface modification or in situ synthesis [Fan et al., 2006] as happens DNA sensors. These chips require the use of suitable micro-reactors and/or capillary systems, and the