@AdamTogether Thanks for the reply.  I am using only One layer BLSTM. First, I have tried 2 BLSTM layers in encoder, it was worse then 1 layer BLSTM.
So how we can be sure that the particualr problem is overfitting problem?  As from the graph the validation loss is not increasing.
secondly, What does these spikes actaully represents? Why we are getting these spikes?