Heterodyne optical beat interference limitations on wavelength division multiplexed networks

Abstract

In Wavelength Division Multiplexed (WDM)/Subcarrier Multiplexed (SCM) networks, information is transmitted by modulating a radio frequency subcarrier, which in turn is used intensity modulated an optical signal. When the signals from two or more lasers operating in a WDM/SCM system are combined at a detector, optical beat interference occurs at a frequency equal to the difference in optical frequencies of the lasers. If this beat signal occurs at a frequency near a subcarriers frequency, it will interfere with the information being transmitted. This paper reports experimental results of beat interference from two different optical carriers and shows that the results agree with an analytical model. Based on the results, it is suggested that when designing a WDM/SCM network, it is necessary to take into account the optical beat interference of different optical carriers to achieve an acceptable bit error rate.