Two-Dimensional Photonic Crystal Micro-Cavities for Chip-Scale Laser Applications

Abstract

1.1 Photonic crystals In this chapter we will focus on two-dimensional photonic crystal devices and emphasize their use as building blocks in photonic integrated circuits with applications in high bandwidth optical communication systems. In particular we will discuss recent progress in designing high quality (Q) factor resonant cavities for building efficient microand nanocavity lasers. The first section will provide a brief overview of two-dimensional photonic crystals and motivate their use in photonic integrated circuits. This will be followed by a first principles derivation of the role of the Q factor in estimating laser threshold. We will then focus on the photonic crystal heterostructure cavity due to its exceptionally large Q factor. Its spectral and modal properties will be discussed, and its use as a high output power edge-emitting laser will be presented. We conclude with remarks on continuous wave laser operation via heat sinking lower substrates and the issue of out-of-plane loss. The term photonic crystal refers to any structure with a periodic variation in its refractive index (John, 1987; Yablonovitch et al., 1991; Joannopoulos et al., 1995). The periodicity can be in one, two or three spatial dimensions and can introduce a photonic bandgap (a range of frequencies for which electromagnetic radiation is non-propagating) with the same dimensionality. The bandgap arises due to Bragg reflection and occurs when the spatial periodicity has a length scale approximately one half that of the incident electromagnetic radiation. This same phenomenon gives rise to the electronic bandgap in semiconducting materials. Examples of photonic crystal structures with periodicity in varying spatial dimensions are shown in Figure 1. One dimensional photonic crystals have found many technology applications in the form of Bragg reflectors which are part of the optical feedback mechanism in distributed feedback lasers (Kogelnik & Shank, 1971; Nakamura et al., 1973) and vertical cavity surface emitting lasers (Soda et al., 1979). Two and three dimensional photonic crystals have been the subject of intense research recently in areas related to sensing (Loncar et al., 2003; Chow et al., 2004; Smith et al., 2007), telecommunications (Noda et al., 2000; McNab et al., 2003; Bogaerts et al., 2004; Notomi et al., 2004; Noda et al., 2000; Jiang et al., 2005; Aoki et al., 2008), slow light (Vlasov et al., 2005; Krauss, 2007; Baba & Mori, 2007; Baba, 2008) and quantum optics (Yoshie et al., 2004; Lodahl et al., 2004; Englund et al., 2005).