Attenuation & Transmission

The attenuation in an optical fiber is usually expressed in decibels per kilometer (dB/km) in the visible and IR spectrums and in dB/m in the UV. The attenuation is calculated as:

Where P_in is the input power injected into the fiber core and P_out is the output optical collected from the distal end. The NA of the input and output optical test system must be matched and effects of lens focal lengths at the test wavelength must be considered so that the acceptance cone of the fiber under test is not erroneously over-filled. This can cause excessive attenuation values since input energy present in the test standardization or calibration may not enter the input fiber under test. Since both the core and the cladding have transmission characteristics that vary with wavelength, attenuation is normally plotted with respect to optical input wavelength.