Mach-Zehnder (MZ) modulator used in CATV system always produces some intermodulation distortion (IMD) that limits the optical transmission performance significantly. In this paper an analytical model of dual parallel Mach-Zehnder (DPMZ)
modulator is proposed to ensure composite second order (CSO) products cancellation and composite third order (CTB) products minimization. We have determined the optimal input optical power splitting ratio with given values of electrode length ratio for a DPMZ modulator. It is found that the effect of CTB is in the allowable range if the input power splitting ratio and electrode length ratio of the primary and secondary MZ modulators are 0.88 and 2.0 respectively.