Provided is a Mach-Zehnder modulator. The Mach-Zehnder modulator comprises an input wave guide and an output wave guide arranged on a substrate, a first branch wave guide and a second branch wave guide connected in parallel between the input and output wave guides, and a connecting region configured to connect the first branch wave guide and the second branch wave guide. Each of the first and second branch wave guides comprises first doped regions doped with a first dopant and second doped regions doped with a second dopant having different conductivity from the first dopant, and the connecting region is doped with the first dopant and arranged between the first regions of the first and second branch wave guides.