Hi Gokul,
I suggest you contact Optiwave via mail and ask them this question. Otherwise, since this is a prototype system, you can most probably find it in William Shieh’s book “OFDM for Optical Communications” when various forms of DDO-OFDM are presented. I work on CO-OFDM, but remember reading about DDO-OFDM in the aforementioned.
Regards