silicon quantum dots is around 3 nm diameter excluding the oxide layer this size exalts the transfer of energy between the quantum dot and the rare earth ion at the same time as minimizing the losses by diffusion of these quantum dots however the size of the quantum dots may advantageously be situated in the range 2 nm 5 nm in the case of silicon quantum dots of 3 nm diameter the pumping wavelength may advantageously be from 400 nm to 500 nm in this embodiment it is preferable for the concentration of erbium ions not to exceed 7 10 18 ions cm 3 so as to limit the effects of cooperation between ions and to maintain good conversion efficiency in this case the typical length of a fiber would be 7 m to obtain a gain of 21 db the quantum dots are chosen as a function of the target application in particular the material used and the size of the quantum dots are chosen as a function of the selected wavelength of the pumping signal for example the semiconductor material of the quantum dots is chosen from at least one of the following materials si ge pbte pbs there is represented in fig4 an amplifying optical fiber according to a second embodiment of the invention elements identical to those in fig3 carry identical reference numbers the fig4 embodiment differs from that of fig3 in that the particles 30 of dopant and the semiconductor material quantum dots 32 are disposed in a ring 34 around the monomode core 24 this embodiment reduces.