mironclaw,

Yes, the key piece at the moment is completion of 400G Tx in order to have the complete TxRx solution. From there it's straight forward progress to 800 and 1.6T.  Basically a slam dunk, or as slam dunky as one can expect.

I'm not sure the statement that the DML platform is more difficult is the primary reason for the parallel development paths.  There are likely other reasons for wanting both platforms (DML vs EML) fully developed.

Advantages of the DML platform are that it's lower power, simpler design, and not dependent on development of advanced modulation technologies (ie TFLN or others such as polymers).  Generally speaking, I suspect the principle challenge with advancing signaling speed using DML platform is the DMLs themselves.  No surprise here, an evolution in laser technology is common in the optical industry. Leading-edge interfaces start with EMLs which are then followed with lower-cost same-rate DML technologies.  DML's are simpler and smaller, therefore ideal for integration into POET's platform.

From my understanding, current DML technology limits signaling to 100G/lane, which at 16 lanes will provide up to 1.6T (4X400G) on a single device using POET's DML platform.  It's possible they may be working on upgrading their original DML platform with 3rd party lasers capable of 100G/lane speeds.  SV indicated they were anticipating completion of this activity in Q4.