Looking at the recent financials, I don't know that they really require anything more than tranches 1 and 2 to get them to September.

In my layman's (non accountant) read of the Q1 financials, negative cash flow was very approximately USD$1.6M per quarter (see pages 6, 24-27 from condensed financials), includes POET plus Denselight (discontinued operation).  So, in order to get through to end of Q3 (september) from end of Q1, they need ~$3.2M USD.

As of end of March they had ~$950K USD in the bank, add in the $4.3M CAD (~$3.2M USD) raised in the debentures so far, plus the credit facility with $2.5M CAD (~$1.85M USD) accessible to-date, gives us a total of ~$6M USD.  IMO, this appears to be plenty to get them through September.  Of course, someone should probably check my math to confirm I've got a correct read on this.

I suppose they still may want additional tranches for various reasons, but I'm not so sure they absolutely must.  IMO of course!