Abstract
We develop and experimentally verify a theory of evolution of polarization in artificially-disordered multi-mode optical fibers. Starting with a microscopic model of photo-induced index change, we obtain the first and second order statistics of the dielectric tensor in a Ge-doped fiber, where a volume disorder is intentionally inscribed via UV radiation transmitted through a diffuser. A hybrid coupled-power & coupled-mode theory is developed to describe the transient process of de-polarization of light launched into such a fiber. After certain characteristic distance, the power is predicted to be equally distributed over all co-propagating modes of the fiber regardless of their polarization. Polarization-resolved experiments, confirm the predicted evolution of the state of polarization. Complete mode mixing in a segment of fiber as short as ∼ 10cm after 3.6dB insertion loss is experimentally observed. Equal excitation of all modes in such a multi-mode fiber creates the conditions to maximize the information capacity of the system under e.g. multiple-input-multiple-output (MIMO) transmission setup.
Highlights
The last decade has witnessed a shift in the general perception of disorder in optical systems from a nuisance [1] to an exploitable feature which may enable some unique functionalities [2,3,4,5,6]
Mutiple-input-multiple-output (MIMO) approach [10,11,12] has become the backbone of the wireless IEEE 802.11n standard for local area networks (LANs)
Beginning with a microscopical model of photo-sensitivity in a germano-silicate glasses, we analytically derived formulae describing the spatial correlations between the components of the dielectric tensor, c.f
Summary
The last decade has witnessed a shift in the general perception of disorder in optical systems from a nuisance [1] to an exploitable feature which may enable some unique functionalities [2,3,4,5,6]. Mutiple-input-multiple-output (MIMO) approach [10,11,12] has become the backbone of the wireless IEEE 802.11n standard for local area networks (LANs) It takes advantage of the differences in propagation from multiple sources to multiple receivers to maximize the bandwidth of the transmitted signal – with the theoretical limit of improvement over single-input-singleoutput (SISO) being proportional to number of sources or receivers, whichever is smallest [11]. We develop a hybrid coupled-power/coupled-mode approach which shows that the limiting modal distribution is uniform – all co-propagating modes (including those with orthogonal polarization) of the MMF are statistically excited. This implies optimum MCD to maximize the information capacity in transmission through MMF. The developed formalism allowed us to describe and interpret a crossover from an initial mode distribution to the limiting one
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