This book consists of a total of nine chapters. Chapter 1 discuss the general introduction about the subject including a brief review of optical waveguides and switches as well as a brief outline of the objectives. Chapter 2 aim the study and design of optical gates such as NOT gate, AND gate, OR gate, universal gates (NAND/NOR) and XOR/XNOR gates. In Chapter 3, multiplier and comparator device based on Mach-Zehnder Interferometers (MZIs) have been discussed. Chapter 4 consists of full adder/subtractor and reversible adder using MZIs. Chapter 5 describes the pseudorandom binary sequence generator, bit pattern recognition, sequence generator, parity generator/checker and binary to BCD converter device. Chapter 6 consists of the D-flip flop, T-flip flop, synchronous up counter, twisted ring counter, and optical universal shift register device. Chapter 7 elaborates the various signal routers based on MZIs. Chapter 8 deals with a temperature sensor and a sensor for bio-medical applications and Chapter 9 describes the factors affecting the performance of devices. These mentioned optical WDM components exhibit wide commercial applications in DWDM optical network area.