I assume this is on ONS15454 MSPP (SDH), I've not seen this particular alarm before but it would indicate that the RX Optical Power is below the minimum threshold, this may be due to a failing laser in the TX Device or fibre plant degredation.
I am not aware that the MSPP variant has any remote monitoring facility to check the opical power levels like you can with the MSTP variant so I think you may have to disconnect the fibre and check with a light meter, I would start at the TX device and then follow it through to the RX device, as I said it may be that the laser is failing in which case it may be a good idea to have a spare card handy to replace the card while you have the service outage.
If you need to know the Optical Specs for the particular STM64 (OC-192) card you are using then while in card view click the Maintenance Tab then the Info Tab at the side, its not available for all cards but it does for the cards we have in one of our networks, failing that specifications for all cards can be found in Appendix A of the Reference Manual, this is a link to the Reference Manual page, just select right one for the software you are running:
http://www.cisco.com/en/US/partner/products/hw/optical/ps2006/prod_technical_reference_list.html
Hope this helps, if not post up again and someone may be able to help further.
