© 2015 IEEE. The chirp factor of optical modulators is an important parameter that relates how the induced phase varies with the instantaneous power of a generated optical pulse, from which the dynamic chirp can be obtained. The two most common modulators are Lithium Niobate Mach-Zehnder and electroabsorption modulators. This paper describes simple models of the modulator response and uses a linear pulse characterization method to measure pulse intensity and phase. The experimental chirp measurements are used in conjunction with the models to determine modulator chirp factor.