Very Sorry for the delay. I am designing all optical Gray code to binary code conversion using Mach- Zehndr Interferometer. By adjusting the delay between the arms of the MZI i am getting the BER as zero for all bits. For one of the bit i dint get it as zero but was reaching to zero very very small value so i added an EDFA before combining the outputs of the MZI and i got the BER as zero for that bit also.