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