Selection of refractive index profiles for couple combination of optical crypto-fibers

This work is concerned with some aspects of selection of graded refractive index profiles for couple combination of optical crypto-fibers “encryptor”–“decryptor”. We present some results of experimental approbation of method for differential mode delay (DMD) management by selection and recombination of two corresponding refractive index profiles, differing by technological defects in the core center. Here it is supposed, that combined fiber optic link, containing the sequence of two graded-index multimode optical fibers with strong DMD, occurring due to great technological defect of refractive index profile in the core center with a peak (or dip) in the first and, on the contrary, with a dip (or peak) in the second, provide inverting DMD diagram of selected mode components in the second optical fiber in relation to the first. Therefore, according to earlier on proposed alternative method for implementation of secure data transmission channel protected over physical layer for the "first/last mile" segment of intra-corporate network, the first optical fiber with strong unique distortions is considered as “encryptor”, while the second with inverted DMD diagram implements function of “decryptor” in the optical interface.