I am a engineer in Optical transceiver for over 10+years in a CM manufactory(OEM SFP+/QSFP+/QSFP28/CFP basiclly from 1G to 100G) in China for CISCO, HW, ZTE, Nokia plus ALU, Ericsson. Probablly from most of the equipment vendors you know. And also been widely adapted by white box switches from Mega datacenter in Google...
These companies does not make optical transceiver themself but instead they make multi-source agreement to define this optical transceiver so the whole industry suply chain manufature the same components to reduce the costs. Further to this MSA, each company define the specs of transceivers, contents in EEPROM(which makes the transceiver to be identical to the swithes) and send the specs to the factory that meets their standards in terms of quality, cost, capacity, R&D ability and financial states.
Take CISOC 10G SFP+ multi-mode 850nm SR for example, the annual volume they purchase from manufactory is 5million pcs with around $12.00/pcs. it is basiclly the same hardware in this optical transceivers we supply to HW, Nokia, ZTE and other equipments with different EEPROM content for the switches to read.
All SFP, SFP+, CFP, QSFP+, QSFP28 modules contain a number of recorded values by the buyer in their EEPROM and include:
l Vendor Name
l Vendor ID
l Serial Number
l Security Code
l CRC
There are a bunch of so called compatible transceiver online claim to be functional in your switches. the chances are, they are probably some junk hardware assembly in a hand workshop.
Let me know if you have any question.