(a) it is found that approximately 200 ow is coupled into a multimode step index fiber from a surface-emitting led when the current is 75 ma and the voltage across the led is about 1.5 v. what is the overall efficiency of operation? (b) experiments are carried out on coupling light from a 1310 nm eled (edge-emitting led) into multimode and single-mode fibers. (i) at room temperature, when the eled current is 120 ma, the voltage is 1.3 v and light power coupled into a 50 om multimode fiber with na (numerical aperture) of 0.2 is 48 ow. what is the overall efficiency? (ii) at room temperature, when the eled current is 120 ma, the voltage is 1.3 v and light power coupled into a 9 om single mode fiber is 7 ow. what is the overall efficiency?