This paper focus on improvement bit error rate (BER) performance due to atmospheric turbulence effect in free space optical communication (FSOC) using new modulation technique that is dual diffuser modulation (DDM) technique. This technique uses two transmitter and differential mode detection at the receiver. The combination of dual diffuser with differential detection mode at receiver produce the superior modulation against the turbulence especially reducing the scintillation index, overcome the signal detection with fix zero threshold and improve the power received. These three element factors are important in order to improve the overall performance of free space optical system. The analysis result shows that under strong turbulence condition, the BER can improve 42 percent in term of FSO distance propagation.