In Telecommunication Network there is issue of speed for usage of triple service/voice, data and video/ related with bandwidth bottleneck problem. So to fill this gap fiber optics technology is taken as a solution due to its high bandwidth capacity. At the beginning fiber Technology uses different Multiplexing Techniques such as Peripheral Digital Hierarchy/PDH/ synchronous Digital Hierarchy/SDH/ and Time division multiplexing/TDM/ for the capacity of Mbps to maximum few Gbs. To increase the bandwidth capacity wave length multiplexing/WDM/and Dense wave length multiplexing/DWDM/ Technology are applied with the capacity of 10Gbs for single channel, but the link transmission capacity is needed to enhance beyond this to improve bandwidth utilization and good spectrum efficiency. Currently the increment of single channel to multi and advance modulation techniques are deployed as a solution for bandwidth increment up to 100Gbs and beyond. In this thesis work I perform the bandwidth enhancement from existing 100 & 200Gbs to 400Gbs Multi-channel (with 4-channel capacity) using DP-QSPK/16QAM advanced modulation techniques. Opt system simulation is done for Link performance analysis using the effect of BER, OSNR and Q-Factor for both Modulation schemes at different Distance and Input power mostly 80-200km Distance and 0,5 and 10dbm power is considered in simulation circuit. From the result obtained the diagrams are piloted and mathematically analyzed the comparison is done between the two Techniques and the better power rate and modulation scheme is recommended through my analyzations. Keywords: BER, DP-QPSK, DP-16QAM, Gbs, Modulation, OSNR, Q-Factor