Where to find sfp-10g-er datasheet?

By SFP-10G-ER we understand that You mean Cisco compatible SFP+ 10G 40km module. From our product portfolio this corresponds to Multi-Vendor MSA Compatible 10G-SFP-40 SFP+ Module. In linked page You will find detailed specification and You are welcome to order it. After received Your order our team will contact with You and clarify in what platform You plan to use SFP-10G-ER alternative module, in order to encode 100% compatible firmware.