Optical 1.56 Tbps coherent 4-QAM transmission across 60 km SSMF employing OFC scheme

We propose a cost proficient approach to generate Optical Frequency Comb (OFC) lines with Intensity Modulators (IM) in cascaded configuration. The proposed OFC setup utilizes a Directly Modulated Laser (DML) source instead of a conventional approach of using continuous wave laser. A single phase modulator and two Mach Zehnder modulators are used in cascaded connectivity and configured with best parametric values to generate the maximum amount of flat comb lines. The RF source is determined by a sine wave with a signal frequency of 25 GHz where the driving force of the source is 26.9 dBm. The DML is directed by a pseudorandom bit sequence generator and a non-return-to-zero pulse generator having a frequency of 193.1 THz. 78 Comb lines have been achieved successfully having high tone to noise ratio, which is an enormous number of comb lines given the scenario. The proposed scheme is then applied at the OLT side of a coherent 4-Quadrature Amplitude Modulation (QAM) transmission system where 20 Gbps data is transmitted across each carrier frequency for downlink transmission. Overall, 1.56 Tbps data has been successfully transmitted across 25 km, and 60 km SSMF having minimum power penalties, good optical signal to noise ratio with neat and clear constellation diagrams ensuring the transmission.