Biodetection Using Silicon Photonic Crystal Microcavities

Lord Rayleigh was the first to study electromagnetic wave propagation in one-dimensional (1D) periodic media and to identify the angle-dependent, narrow band in which light propagation is prohibited. However, it was not until a full century later, when Yablonovitch [1] and John [2] in 1987 combined Maxwell’s equations with solid-state physics theorems to introduce the concept of photonic bandgaps in two and three dimensions. Many subsequent developments in fabrication, theory, and applications (e.g., fiber optics, integrated optics, and negative refraction materials) have since followed.

As shown in Fig. 7.1, photonic crystals (PhCs) are periodically structured media [3] in one, two, or three dimensions. PhCs can be designed to produce photonic bandgaps. Light with photon energies or frequencies that fall inside this bandgap cannot propagate through the PhC. The periodicity in length scale is proportional to the wavelength of light inside the bandgap. PhCs are the electromagnetic analog of crystalline atomic lattices, in which interference in the electron wavefunction produces the forbidden bands. Hence, the study of PhCs is also governed by the Bloch-Floquet theorem.