Check a GBIC Optical Power

Recently I had the opportunity to troubleshoot a fiber link.  I was worried about burning out some very expensive GLC-ZX-SM Gbics.  Due to the length restrictions , these can easily burn out if the thresholds aren't properly calculated and attenuators installed if they are needed. The link in question was a wan link utilizing dark fiber from the local utility provider, and a distance of 5.6 miles. I had planned on using long haul modules as they are rated to handle up to 6 miles, but the degaradation on the  link due to a bend on the fiber also a bad splice had made this impossible - the link wouldn't come up. So to verify that there would even be any connectivity I put some ZX modules on either end and alas  the link came up.

I was quick to check that the transciver power and tempereture on both ends :

 

                   - Output Omitted -
Switch Superstack#sh int g1/0/1 transceiver
ITU Channel not available (Wavelength not available),
Transceiver is externally calibrated.
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  Tx Power  Rx Power
Port       (Celsius)    (Volts)  (dBm)     (dBm)
---------  -----------  -------  --------  --------
Gi1/0/1      49.3       3.30       2.8     -21.4 - 
 
Switch TMC#sh int g1/0/25 transceiver 
ITU Channel not available (Wavelength not available),
Transceiver is externally calibrated.
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  Tx Power  Rx Power
Port       (Celsius)    (Volts)  (dBm)     (dBm)
---------  -----------  -------  --------  --------
Gi1/0/25     30.4       3.30       3.0      -4.5 
 
- Output Omited -
 
 
 
Turns out the link was so degraded that leaving the modules in place wasn't a problem demarced by the (- )low alarm warning on both ends.