Performance analysis of single sideband modulation technique using Mach Zehnder Modulator based on different phase angles of electrical hybrid coupler

Abstract

This paper provides an insight on the generation and the performance analysis of two different optical single sideband (OSSB) modulation techniques depending on the phase angle of the electrical hybrid coupler. It takes into account the problem of the chromatic dispersion in the single mode fibers in Passive Optical Networks (PON), which severely degrades the performance of the system. The RF signal at the input of a dual drive Mach Zehnder Modulator (MZM) is divided in two parts equally with an electrical hybrid coupler providing a phase difference of 90° and 120° respectively to generate two different SSB techniques. The conventional OSSB generation technique with 90° phase difference suppresses either lower or upper first order sideband but 2nd order harmonics still exists in the spectrum. The 2nd and higher order harmonics generated due to non-linearity of the MZM depends upon the modulation index. The increase in modulation index leads to increased harmonic distortion at the receiver. The SSB with 120° hybrid coupler suppresses lower first order and upper second order sideband (or upper first order and lower second order sideband). It is shown that, the amount of suppression of the second order sideband (lower or upper) increases with the increase in the Extinction Ratio (ER) of the MZM. Comparing with the conventional OSSB technique, the suppression of second order sideband in the SSB with 120° hybrid coupler reduces the effect of chromatic dispersion in single mode fibers thereby increasing the transmission distance.