Performance Investigation of 400 × 100 Gb/s Ultra-Dense WDM System Using Different Modulation Techniques with Varying Channel Spacing

In this work, we have designed an ultra-dense wavelength division multiplexing (UD-WDM) system for 400 channels with a bit rate of 100 Gb/s per channel based on the high spectral efficient modulation techniques such as differential phase shift keying (DPSK), differential quadrature phase shift keying (DQPSK) and dual-polarized quadrature phase shift keying (DP-QPSK). The performance of all the three modulation techniques has investigated for varying channel spacings of 25 GHz, 50 GHz, 75 GHz and 100 GHz. The performance parameters such as bit error rate (BER), quality factor (Q-factor), received cross-talk and eye closure have analyzed with variation in transmission distance and applied input power. It has also observed from the simulation results that the DP-QPSK modulation technique serves the best performance among all three modulation techniques in terms of BER, Q-factor, received cross-talk and eye closure due to its high tolerance towards linear and nonlinear effects for all the four channel spacings of 25 GHz, 50 GHz, 75 GHz and 100 GHz. Although, the DP-QPSK modulation techniques outperformed for all the four channel spacings but the maximum performance has reported for channel spacing of 100 GHz. The maximum Q-factor of 19.6 dB, the minimum BER of around 10^–15 and minimum eye closure of 0.94 dB have reported for DP-QPSK modulation technique for a distance of 100 to 800 km for 100 GHz channel spacing. Also, the maximum quality factor of 18.3 dB and minimum received cross-talk of −9 dB is reported when analyzed for applied input power for 100 GHz channel spacing.