Hello Gaurav,
If I understand your situation correctly, you are using an electrical signal for modulation. If that is the case, you can always use LiNb modulator, which has electrical ports, where you can apply your modulation signal, and optical ports, where you can apply your signal from laser source. This particular scheme was used in the example “100 Gbps DP-QPSK System with Digital Signal Processing” (which you probably considered already). Hope it will give you some ideas…