Guided-wave Digital Optics
As pointed out in the previous chapter, guided-wave optics is an important field of digital optics. Guided-wave digital optics refers more to integrated waveguides rather than fiber optics (systems that are fabricated through digital lithographic means rather than the conventional fiber perform drawing process).
However, integrated waveguide technology is closely related to fiber optics technology, for applications such as sensors, telecom modulators, DWDM devices and so on (especially to provide input and output interfaces for the digital waveguide device). Such systems are also known in industry as Planar Lightwave Circuits (PLCs) or planar integrated optics.
As it is an intrinsic part of the realm of digital optics, this chapter will introduce the concept of guided-wave optics, define the various modes that can in optical waveguides, and explain the fundamentals of optical couplers and optical modulators. It will also show how free-space planar optics can be used in PLCs in order to integrate novel and complex optical functions.
3.1 From Optical Fibers to Planar Lightwave Circuits (PLCs)
As early as 1870, John Tyndall in the United Kingdom demonstrated light guiding in a thin water jet. Ten years later, Alexander Graham introduced for the first time the notion of an optical waveguide, and in the early 1930s the first patents on ‘optical tubing’ appeared. As early as 1950, a patent for a two-layer glass waveguide (two different indices of refraction) ...