Silicon Photonics: Fundamentals and Devices

11.1 Introduction

In the present chapter, we shall discuss the operating principle of some of the planar waveguide devices used in communication. We first develop the theory for mode coupling introduced by a small perturbation in the refractive index (RI) of the material in a waveguide. The coupled mode theory is useful in understanding the theory of two important classes of passive waveguide devices: the directional coupler and the Bragg reflector. As will be explained in this chapter as well as Chapters 12 and 13, both the devices play important roles in optical communication and networking. The general coupled mode theory will be developed first, and it will be applied to the two devices mentioned. A few more devices used in communication will then be introduced. The list includes a splitter, a directional coupler, a Mach–Zehnder type interferometer, filters, in particular a Fabry–Perot filter and a ring resonator, the Bragg grating, a dielectric mirror, and a variable optical attenuator [1–12].