Abstract : https://www.youtube.comLinearity is an important property of optical devices in analog communication systems. In this paper, we study the 3rd-order intermodulation distortion (IMD3) of an InP/InGaAsP multiple-quantum- well (MQW) traveling-wave type electroabsorption modulator (TW-EAM). We observe that dips in the measured IMD3 results are different from those by general transfer curve of electroabsorption modulators (EAMs). In order to verify it, we analyse the phenomena by using the absorption coefficients according to a wavelength and a bias voltage. Thus, we can see that the dips result from the quantumconfined Stark effect (QCSE). We propose the method to enhance linearity of MQW-EAMs by using this effect in addition to the E/O response.