If you unsure how good your fiber optic cabling is, you could use the following command on a Cisco switch to determine dBm loss of a particular connection. This command does support all the Cisco optics, but most. Give it a try:
rt-sc-cr#sh interfaces transceiver sw 1
Transceiver monitoring is disabled for all interfaces.
If device is externally calibrated, only calibrated values are printed.
++ : high alarm, + : high warning, – : low warning, — : low alarm.
NA or N/A: not applicable, Tx: transmit, Rx: receive.
mA: milliamperes, dBm: decibels (milliwatts).
Optical Optical
Temperature Voltage Current Tx Power Rx Power
Port (Celsius) (Volts) (mA) (dBm) (dBm)
———- ———– ——- ——– ——– ——–
Te1/1/1 37.1 0.00 44.5 — -1.9 -9.6
Te1/1/3 44.3 0.00 44.3 — -1.4 -2.9
Te1/1/4 44.6 0.00 42.6 — -1.4 -6.2
Te1/1/6 44.2 0.00 48.6 — -1.4 -3.9
Te1/1/7 43.6 0.00 38.6 — -1.4 -3.1
Te1/1/8 38.2 0.00 41.1 — -1.4 -2.5
Te1/2/1 36.6 0.00 44.6 — -2.0 -5.2
Te1/2/2 43.0 0.00 42.5 — -1.5 -37.0 —
Te1/2/4 43.3 0.00 38.2 — -1.5 -5.9
Te1/2/5 43.8 0.00 43.5 — -1.4 -2.2
Te1/2/6 43.1 0.00 41.9 — -1.4 -2.9
Te1/4/1 35.4 0.00 44.3 — -1.8 -2.8
Te1/4/4 34.0 0.00 40.8 — -1.3 -6.2
Te1/4/5 34.3 0.00 44.4 — -2.0 -3.4
Te1/4/6 32.3 0.00 41.2 — -2.4 -2.9
Te1/5/4 30.2 0.00 41.6 — -2.0 -3.2