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