Optical dB loss, sounds to me like the rate of loss of optical signal in a given medium, as measured in decibels.
Please note that in most cases, this refers to optical fibers, but can refer to air gap transmission.
As to optical fiber earlier technologies had a higher rate of loss, per unit distance.
As for a Faraday Cage it is method of isolating a device for testing. By isolating, one can determine the functionality of said device.
Or protect it Corona Mass Ejections, or Electromagnetic Pulses - either a Nuclear event, or a chemical event.
Several years ago now Popular Mechanics Magazine had an article on how to generate an EMP from High Explosive...
It requires a thermos holding a superconducting coil charged with electricity...imploding the magnet will release the field. Short range only. About 2,000 feet in radius.
In terms of time a a Nuclear EMP lasts micro seconds at most. A chemical EMP milliseconds. Which requires a different design.
I am a bookworm.
You may start running now.