Optical devices for high speed optical communications

Date of Completion

January 2000


Physics, Optics




For high speed optical communications, we need lasers and modulators that can operate at high speeds. In lasers and modulators used for high speed communications, various properties, such as, the spectral width under modulation, and relaxation oscillation frequency, determine the high speed performance of these devices. It is also important to study the various multiplexing and demultiplexing techniques used to make these already fast devices operate at even higher rates. This thesis reports a study of sources for high speed communication systems and their application in very high speed time division multiplexed transmissions. ^ Semiconductor sources with integrated electroabsorption modulators and distributed feedback lasers (EML) are important for high speed (2.5 Gb/s and higher) transmission systems. These devices have very low spectral width under modulation which reduces the effect of fiber chromatic dispersion. Various properties, such as, the linewidth enhancement factor (α-factor) and relative intensity noise (RIN) of EMLs are extensively studied. Modulation doping of a multi-quantum-well laser, can reduce the α-factor and the relative intensity noise, and increase the relaxation oscillation frequency. We have investigated theoretically these various properties of a modulation doped InGaAsP quantum well (QW) laser emitting at 1.55 μm. Rational harmonic mode-locking is potentially an important source for generation of high frequency pulse trains needed for ultra-high speed networks. But in order to use these pulses in optical communication we need to stabilize them. We have studied a new method to stabilize a fiberlaser. ^ Ultrahigh-speed optical time-division-multiplexed (TDM) transmission technologies are essential to construct the ultrahigh-speed all-optical networks needed in the multimedia era. The demultiplexing technique will be realized using the LiNbO3 Mach-zender modulators. ^