Isfahan University of Technology

Department of Electrical and Computer Engineering

Issue date: Januarey , 2013

Degree: MSc

Language: Farsi

Contributor: Zahra Mazaheri

Supervisor: Dr. Asghar Gholami

Abstract

Optical communication had an very high growth through the modern communication systems. Particularly, optical fiber communication plays an important role in development of high-speed telecommunication systems. optical communication systems are divided in to free space and fiber optic communication systems. Free-Space Optics (FSO) is a line-of-sight technology that uses lasers to provide optical bandwidth connections. Fiber-optic communication systems use fiber optic as communication channel and have many applications in high-speed data transmission for short and long haul systems. Today, optical fibers are also used in the Internet and local area networks (LAN) to transfer very high data rates Gigabit Ethernet is a standard for high speed telecommunication systems which is defined in the IEEE802.3z standard. 1000BASED-SX is a part of the Gigabit Ethernet standard which defines short haul multimode optical fiber communication systems. In this thesis, optical transmitter parameters and components for a short haul multi mode optical fiber communication system have been studied and an optical transmitter in accordance with 1000BASE-SX standard has been designed and implemented. The transmitter can send data at 4.25 Gbps bit rate, over 1000m MMF on the 850 nm wavelength. The input electrical signal with 4.25 Gbps have a wideband spectrum. To transfer this high frequency signal from input terminals to the amplifier and from amplifier to the laser input, transmission lines are used. Different transmission lines as differential coupled microstrip and CPWG(Coplanar Waveguide with Ground) lines are designedand optimized using ADS software.

Vertical Cavity Surface Emitting Laser(VCSEL) due to its low cost and high power and coupling efficiency is a good selection as the light source for short haul multimode fiber communication systems. But VCSEL parameters are temperature dependent which cause output optical power be highly sensitive to the temperatur. Therefore a control circuit is designed to keep the VCSEL's average power constant with feedback mechanism. All components are assembled onto a 4-layerd FR-4 printed circuit board (PCB). Finally the parameters of the transmitter are measured and are compared with standard values. Since BER test is the best way to ensure the correct functioning of a transceiver system; this test is performed to ensure the verification system.