Chapter 9 - Planar lightwave circuits

Abstract

This chapter focuses on planar lightwave circuits which are used by silica-based optical waveguides. These are fabricated on silicon or silica substrate by a combination of flame hydrolysis deposition (FHD) and reactive ion etching (RIE). Fine glass particles are produced in the oxy-hydrogen flame and deposited on the substrates. After depositing under cladding and core glass layers, the wafer is heated to a high temperature for consolidation. The circuit pattern is fabricated by photolithography and reactive ion etching. The core ridge structures are then covered with an over cladding layer and consolidated again. The chapter describes the various kinds of planar lightwave circuit devices for optical wavelength division multiplexing (WDM) systems and subscriber networks. It summarizes the waveguide parameters and propagation characteristics of four kinds of waveguides. Since the typical bending radius of silica waveguide is around 2–25 mm, the chip size of the large-scale integrated circuit becomes several centimeters square. Therefore, reduction of propagation loss and the uniformity of refractive indices and core geometries throughout the wafer are strongly required. Various kinds of waveguides are utilized depending on the circuit configurations.