Frequency chirping in external modulators

A general formula is given that expresses frequency chirping in some types of external intensity modulators, such as the loss modulator, directional-coupler-type modulator, Mach-Zehnder interferometry-type modulator, and total-internal-reflection-type modulator. The chirping phenomenon treated is caused by the phase modulation due to an accompanied refractive index change. It is uniquely expressed in terms of an alpha -parameter that contributes to frequency chirping in the same manner as in the direct modulation of a semiconductor laser. In addition, the transmission bandwidth of a single-mode fiber system using an external modulator is discussed and compared with the results obtained utilizing direct laser modulation.<>