I see a lot of optical module especially gpon which are sfp but seem to exceed the speed of a traditional sfp port are the speed realistic in real world usage
Speeds as we are used to (1Gbps, 2.5Gbps, 5Gbps, 10Gbps, etc.) are standard speeds for ethernet (over fiber). Other technologies (GPON, CPRI, etc.) standardize other speeds.
Mind that speed over fiber (or UTP cable) doesn’t relate directly with speed of SFP interface (which is 1Gbps for SFP or 10Gbps for SFP+ or 25Gbps for SFP28).
So would a 1.2Gb GPON module in a 1Gb SFP port max at 1Gb
It doesn’t work like that. The SFP Transceiver specification https://members.snia.org/document/dl/26184 details the mechanical dimensions, electical connections and read-only serial information which describes the module capabilities. Whilst you can plug any ethernet, fibre channel, SONET or GPON SFP module into an SFP cage it won’t work unless the equipment supports the data encoding and rate(s) for that type of SFP module.
There are a number of active GPON-to-ethernet SFP modules which incorporate a processor, memory and storage to handle the ITU-T GPON to IEEE ethernet 1000BASE-X protocol conversion which will be limited to 1Gb ethernet - basically packing the functionality of an ONT into the SFP module. There are even a few which support 2.5GBASE-X but the equipment has to support this too.
Many of these active SFP modules run hot, have proprietary management interfaces and poor/nonexistent documentation. You also have to configure them with authentication information to establish a GPON connection, often ISPs will not provide this as the network demarcation point is the ONT they supply. In some cases you can reverse-engineer the necessary information but the module almost certainly will not support any proprietary OAM the ONT vendor has implemented, the ISP may detect this as a fault condition.
There are a number of threads in the forum discussing these modules.
Thanks for the detailed response this is the break down i was looking for 