Below are the steps, I would recommend for troubleshooting:
1. Make sure the correct fiber cables are being used between the two segments (MM or SM),
2. Make sure to test the fiber the link running between the two segment using devices such as OTDR, to verify there is no significant amount of loss or cable breaks.
3. Check for the output of the Receiver signal average optical power, make sure the value is higher than 0 mW. Value of 0 indicates the receiving end is not receiving any optical signal from the remote end.
show interfaces diagnostics optics ge-0/0/4
Physical interface: ge-0/0/4
Laser bias current : 12.920 mA
Laser output power : 0.2140 mW / -6.70 dBm
Module temperature : 35 degrees C / 95 degrees F
Module voltage : 3.2820 V
Receiver signal average optical power : 0.2452 mW / -6.10 dBm
Laser bias current high alarm : Off
Laser bias current low alarm : Off
Laser bias current high warning : Off
Laser bias current low warning : Off
Laser output power high alarm : Off
Laser output power low alarm : Off
Laser output power high warning : Off
Laser output power low warning : Off
Module temperature high alarm : Off
Module temperature low alarm : Off
Module temperature high warning : Off
Module temperature low warning : Off
Module voltage high alarm : Off
Module voltage low alarm : Off
Module voltage high warning : Off
Module voltage low warning : Off
Laser rx power high alarm : Off
Laser rx power low alarm : Off
Laser rx power high warning : Off
Laser rx power low warning : Off
Laser bias current high alarm threshold : 45.000 mA
Laser bias current low alarm threshold : 0.000 mA
Laser bias current high warning threshold : 40.000 mA
Laser bias current low warning threshold : 0.400 mA
Laser output power high alarm threshold : 0.7940 mW / -1.00 dBm
Laser output power low alarm threshold : 0.0700 mW / -11.55 dBm
Laser output power high warning threshold : 0.6310 mW / -2.00 dBm
Laser output power low warning threshold : 0.0890 mW / -10.51 dBm
Module temperature high alarm threshold : 93 degrees C / 199 degrees F
Module temperature low alarm threshold : -10 degrees C / 14 degrees F
Module temperature high warning threshold : 88 degrees C / 190 degrees F
Module temperature low warning threshold : -5 degrees C / 23 degrees F
Module voltage high alarm threshold : 3.565 V
Module voltage low alarm threshold : 3.035 V
Module voltage high warning threshold : 3.500 V
Module voltage low warning threshold : 3.100 V
Laser rx power high alarm threshold : 0.5010 mW / -3.00 dBm
Laser rx power low alarm threshold : 0.0063 mW / -22.01 dBm
Laser rx power high warning threshold : 0.3980 mW / -4.00 dBm
Laser rx power low warning threshold : 0.0080 mW / -20.97 dBm
Check for the output of the Receiver signal average optical power, make sure the value is higher than 0 mW. Value of 0 indicates the receiving end is not receiving any optical signal from the remote end.
4. Make sure the interface is not Admin disabled
5. Make sure the interfaces is not disabled via STP
6. Make sure the speed/duplex and MTU matches between the corresponding segments
7. Make sure if there are any intermediary network devices such as media converters in between the segments. This one can be tricky.
8. Check if there are any incrementing errors on the feed interfaces:
show interfaces ge-0/0/4 extensive |match error
Link-level type: Ethernet, MTU: 1514, MRU: 0, Speed: 1000mbps, BPDU Error: None, MAC-REWRITE Error: None, Loopback: Disabled, Source filtering: Disabled,
Input errors:
Errors: 0, Drops: 0, Framing errors: 0, Runts: 0, Bucket drops: 0, Policed discards: 0, L3 incompletes: 0, L2 channel errors: 0, L2 mismatch timeouts: 0,
FIFO errors: 0, Resource errors: 0
Output errors:
Carrier transitions: 3, Errors: 0, Drops: 10947052, Collisions: 0, Aged packets: 0, FIFO errors: 0, HS link CRC errors: 0, MTU errors: 0,
Resource errors: 0, Bucket drops: 0
CRC/Align errors 0 0
FIFO errors 0 0
Output packet error count 0
9. Try moving the existing fiber pair to a new pair if thats a possibility.
10. Make sure to change optical transceiver to eliminate problems with transceiver (which is a rare issue, but could be possible).
Hope this helps!!