In the MZI, the splitter and combiner are connected together by using two optical waveguides. These waveguides are characterized by their lengths and propagation constants. So, defining \(L_1\) and \(\beta_1\) as the length and propagation constant in the first waveguide and, \(L_2=L_1+\Delta L\) and \(\beta_2\) the length and propagation constant in the second waveguide, the output's combiner will present an electric field: