A 1G interface on a Nexus 5500 connected to a Juniper device was not coming up. Various optics were tested (both 1G and 1/10G) with the same issue.
On the Juniper side the link RX/TX light levels were fine and there was no reported issue.
The Nexus 5500 series is not auto speed sensing. To allow the 1G port to work, the speed needs to be hard set to 1000:
int e1/1
speed 1000