Performance Evaluation of Different QAM Modulation Schemes in a VCSEL Based Single Mode Optical Link

Abstract

Vertical Cavity Surface Emitting Laser (VCSEL) is first demonstrated by K.Iga in 1979. Since then it creates a new era for high speed optical communication system. The most important feature of this optical device is that it can emit light vertically from its substrate surface rather than emitting from its side edge. This special feature of VCSEL provides capability of high speed data transmission very efficiently. That is why today in applications for long range and short range high speed optical communication VCSELs have replaced edge-emitting lasers. VCSELs are now widely used in analog broadband signal transmission, absorption spectroscopy, laser printers, biological tissue analysis, optical fiber data transmission and so many applications. From the beginning of VCSELs introduction, temperature variation always remains dominant contributor to performance degradation and instable output. As VCSEL is a rapid growing field for optical communication, it has to copewith very high temperature, which makes the design of VCSEL based system more complicated and challenging. As increasing temperature reduces a major portion of output power of VCSEL, meeting up the temperature variation issue is prime need for VCSEL based optical communication system. In this thesis, we analyzed and comparedthe temperature dependence, power consumption, BER and Q factor ofM-QAM modulation schemes at 1550nm wavelength for VCSEL based optical link. We further analyzed the performance of VCSEL by designing a long range data transmission system. It is found that at bias current of 2mA the working temperature range extends up to 1250C for 1550 nm. And at a bias current of 12mA, theminimum power dissipation is found to be 1.96mW at room temperature for 1550nm VCSEL based optical data transmission system at 10Gbps.