The effect of modulator nonlinearity on measurements of chirp in electroabsorption modulators

Traditional techniques for measuring the chirp in external modulators assume that the optical intensity output of the modulator is a faithful representation of the applied voltage. For electroabsorption modulators, which can have highly nonlinear transmission- vs voltage characteristics, this is a poor approximation, especially when they are operated at high modulation indices. We demonstrate a new technique that makes use of the actual measured T(V) for the device under test, and show that this new technique permits measurement of chirp in modulators generating either NRZ signals or soliton pulses. We apply this technique to both bulk and MQW electroabsorption modulators, and show that traditional measurements significantly underestimate the α values of these devices