Chirp Effect of Semiconductor Diode Lasers and Its Application and Impact on Lightwave Transmission

Semiconductor laser change the output light intensity with an modulated voltage or current. However, the signal output phase or frequency also changes to give a dynamic chirp effect. Combined with chromatic dispersion, chirp effect typically limits the transmission distance of an optical signal.
In this thesis, we focus on the chirp effect of directly-modulated semiconductor laser (DML) and external modulators such as Electro-Absorption Modulator (EAM) and Mach-Zenhder Modulator (MZM). The analyzed and measured results are used to investigate the impact of chirp to a lightwave transmission system.
From experimental measurement, directly-modulated semiconductor has severe chirp effect that limits the transmission dispersion when interacting with fiber chromatic dispersion. The chirp effect is suppressed by passing a directly-modulated signal through a narrow-band optical filter to convert the frequency-modulated signal to on-off keying signal. The transmission distance is extended from 20 to over 60 km.