You ask :  However, i really don't get it when you compare POET and plug and the numbers they put out, how Plug can be valued with 28billion and Poet with less then 300 million

PLUG and Poet are in 2 different industries, Hydrogen fuel cells and transportation for Plug, which is a sector that scales up to immense size very quickly, an order of magnitude or more greater than the niche Poet has targeted. Secondly there is an EV and hydrogen bubble across most companies active in that field but not in photonics to that degree. These companies are on orthogonal paths that may have crossed in the past but are unlikely to ever do so again.