A method of OSNR calculation considering an incoherent coupling-noise and instability of optical filters transfer-function in ROADM cascade

A high accuracy of optical signal to noise ratio (OSNR) calculation is a key factor in optical transmission system design improvement. This assures constant maintenance of the required bit error rate (BER) in an operating communication system and serves as an important guideline for its further expansion. In various standards for OSNR calculations, coupling noise is considered as an assigned value to the transceiver equipment. An analytical method of the OSNR calculation for cascaded connections of optical cross-connects (OXC) is presented in this paper. This method is based on the International Telecommunication Union (ITU) recommendation and considers major trends of cross-talk noise estimation using the power penalty approach. OSNR calculations were performed with MathCad . The results obtained show OSNR reduction by increasing the number of OXCs and spans. Achieved results are in agreement with the results presented in the literature for OSNR coupling noise calculations in a Reconfigurable Optical Add/Drop Multiplexers (ROADMs) cascade.