Low Driving Voltage Operation of MZI-Type EA Modulator Integrated With DFB Laser Using Optical Absorption and Interferometric Extinction

We have developed a novel electroabsorption modulator (EAM)-integrated distributed feedback laser (EA-DFB laser), in which an EAM functioning as an external modulator is integrated in a Mach–Zehnder interferometer (MZI). The MZI-type EAM (MZEA) modulates light intensity by both optical absorption and interferometric extinction. As a result, it improves the extinction ratio (ER) of a conventional EAM, which allows us to reduce the modulation voltage ( $V_{{\rm m}}$ ), and thus reduce the power consumption of the driver circuit. A fabricated MZEA-integrated DFB laser (MZEA-DFB laser) exhibited high-ER operation and an output power of about 8 dBm, which is comparable to that of a conventional EA-DFB laser, with a 100-mA laser current. Thanks to the high ER and sufficient output power, the MZEA-DFB laser operating at half the $V_{{\rm m}}$ of a conventional EA-DFB laser is able to generate optical signals with a given optical modulation amplitude, and we achieved a 25.8-Gb/s 40-km transmission with the novel laser at a $V_{{\rm m}}$ of $1 {\rm V_{pp}}$ .