Dear Rajkumar,
I think you meant OTDV not OTDR.
It looks to me that the power level at the receiver is too low causing the noise overwhelming the signal. There are many parameters that you need to make sure that you choose correctly. You could do the spreading calculation roughly using dispersion and laser linewidth. The fiber dispersion parameter is given by ps/(km nm). Thus a fiber with length L and laser with linewidth of n cause a spreading of L*n ps.
Regards,
Ahmad