Incoherent crosstalk model and analysis of fiber bragg grating based optical add/drop multiplexer

Abstract

Wavelength division multiplexing (WDM) optical networks are attracting more and more attention because of their ability to provide increased capacity and flexibility. Optical add-drop multiplexer (OADM) becomes key component for add or drop wavelengths in high bit rate (>10 Gbps) WDM optical networks. Crosstalk arises in OADMs through component imperfection and limits the performance of the optical network. Optical crosstalk at the same wavelength as the information signal is generally referred as homodyne crosstalk. It is particularly serious because it cannot be removed by filtering. Homodyne crosstalk can be incoherent or coherent. Incoherent crosstalk occurs when the signal and interferer are from different optical sources cause rapid power fluctuations and results bit error rate (BER) degradation of the optical transmission system. Incoherent crosstalk also occurs in fiber Bragg grating (FBG) based OADM due to improper reflection. In this research work, analytical models of FBG without and with isolator based OADM have been developed for incoherent crosstalk. Based on these models mathematical expressions have been derived for different performance metrics like- relative intensity noise (RIN), bit error rate (BER) and power penalty. To study the performance limitations of the OADMs, numerical simulation is carried out with large number of crosstalk channel that interfere with the information signal. Results show that amount of crosstalk, RIN and BER of the OADMs are lower and provide better performance than the existing OADMs which uses other technologies. It is also observed that isolator based OADM shows better performance than without isolator because OADM with isolator uses two FBG. Findings of this research work will be helpful to design an efficient WDM system with low crosstalk OADM considering reflectivity, impact of crosstalk and signal wavelengths.