Specialty Optical Fibers Handbook

cable right of way, then the damaged section is removed and a short section

of cable is spliced in place to bridge the gap. If the fiber in the short restoration

cable is not effectively single moded at the system operating wavelength, then

there is the potential for the paired splices to generate excess additive noise,

which is referred to as modal noise. Much of the energy lost by the incoming LP

01

mode at the first splice will be coupled into the LP

11

mode of the restoration

fiber. If the transmission loss of the LP

11

mode in the restoration fiber is low

enough, then energy in both the LP

01

and LP

11

mode will reach the second splice

and will add coherently if the optical path length difference for the two modes is

less than the coherence length of