"Agreement" is a broader term. For example, it can be short for a "letter agreement," which is typically less formal than a "contract."  Letter agreements can be binding or non-binding. If binding, they can be enforced and are a type of contract. 

But don't forget that contracts can have all kinds of conditions and contingencies. 

Without seeing the document(s) that forms the agreement, it's difficult (impossible) to tell exactly what you have, ie, the obligations of and benefits to each party.

Having said that, the way the above language reads, "Poet has an agreement with Adtran to supply..." certainly implies a binding contract.  If Adtran has need for a photonic module (hopefully Adtran will have lots of need for Poet's module for Adtran's optical transceiver), then it's fair to imply that they will purchase at least a part of the modules they need from Poet (there is no indication that Poet will be the sole supplier of the module, ie, that Poet's module will be in all of Adtran's products which utilize a photonic module.  

The above is just legal word salad  - the good part is that companies sophisticated in the business apparently have serious interest in Poet's offerings. Of that, I have no doubt.