ZR optics are spec'ed to 80km but they're not part of the 10GE standard; they're rather a "Cisco special."

In terms of what actually allows them to transmit light over this distance may be "protected" information from Cisco (both the ZR and ER operate on 1550nm SMF), but they've published some of the optical parameters for the ZR XENPAK here.

ZR optics are spec'ed to 80km but they're not part of the 10GE standard; they're rather a "Cisco special."

In terms of what actually allows them to transmit light over this distance may be "protected" information from Cisco (both the ZR and ER operate on 1550nm SMF), but they've published some of the optical parameters for the ZR XENPAK here.

EDIT: While I thought that 10GBASE-ZR was Cisco-specific, it's not actually. The wikipedia page for the 10Gig standard states "multiple manufacturers" have introduced "ZR" optics which are based on the 80km PHY described in the OC192 SONET specs.