SFP ER and ZR are both types of small form-factor pluggable (SFP) transceivers used in fiber optic communications, but they have different specifications and capabilities.

SFP ER (Extended Range) transceivers are designed for long-range optical communication up to 40km over single mode fiber. They typically operate at a transmission speed of 1Gbps and use a 1550nm wavelength. SFP ER transceivers are commonly used in network equipment such as switches, routers, and media converters to extend the reach of the network over longer distances.

On the other hand, ZR transceivers are designed for even longer-range optical communication, typically up to 80km over single mode fiber. They also operate at a transmission speed of 1Gbps and use a 1550nm wavelength. ZR transceivers are used in similar network equipment as SFP ER transceivers, but they are capable of reaching greater distances.

In summary, the main difference between SFP ER and ZR transceivers is their maximum transmission range, with ZR transceivers being capable of reaching longer distances compared to SFP ER transceivers.