The mode converter 4, wherein {HEAD ~ the core} of the tapered optical fiber has {TAIL ~ a multi step refractive index distribution} or a multi graded refractive index distribution such that the power of the single mode optical signal is coupled to each mode of the multi mode optical signal 
has
The mode converter 4 , wherein { HEAD ~ the core } of the tapered optical fiber has { TAIL ~ a multi step refractive index distribution } or a multi graded refractive index distribution such that the power of the single mode optical signal is coupled to each mode of the multi mode optical signal
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH