OPCPA systems are capable of delivering high peak and average power pulses, consisting of only a few oscillation cycles of the electric field. The development of these systems are motivated by attosecond pulse generation and the examination of ultrafast physical processes. During my work I was using a 4D numerical code for the modelleding of OPCPA. I have examined a few OPA arrangements, which can increase the efficiency of the amplification process and the bandwidth of the amplified pulses. I have numerically optimized the OPCPA of the ELI-ALPS SYLOS system and carried out a comparative study of a mid-IR OPCPA system.