Abstract: A method and apparatus is provided for controlling the bias point of a Mach-Zehnder modulator. The method begins by applying a dither signal to a DC bias that is applied to a Mach-Zehnder modulator. A component of an optical output signal provided by the Mach-Zehnder modulator that is synchronous with the dither signal is detected. The dither signal is adjusted to maintain the detected component of the optical output signal at a substantially constant value.

Abstract: A filtered three-level transmitter is provided by filtering a binary electrical drive signal to produce a unit modulation pulse spanning four-bit-periods and describable by three parameters. One or more of the three parameters of the unit modulation pulse are adjusted to optimize a figure of merit associated with performance of an optical transmission system. A three-level electrical drive signal is then generated from the unit modulation pulse for input to a Mach-Zehnder modulator. The three parameters of the unit modulation pulse are each defined over a half-bit period and together are sufficient to describe a line-coded transmission eye diagram. The parameters are adjusted so that an optical transmission system in which the inventive transmitter is utilized is optimized with a set level of net chromatic dispersion.

Abstract: Photocurrent suppression is achieved without deleteriously affecting modulation performance in a surface normal, electro-absorption, quantum well modulator by introducing a sufficient number of non-radiative recombination centers in the quantum well region of the modulator. The presence of the non-radiative recombination centers significantly shortens the lifetime of photogenerated carriers and, thereby, suppresses the photocurrent. Modulation performance characteristics such as contrast ratio are maintained at acceptable levels even though exciton broadening occurs in the quantum wells. The present modulator exhibits a careful balance between defect density in the quantum wells and the acceptable degree of exciton broadening necessary to preserve quantum effects.