Optical Telecom Networks as Weak Quantum Measurements with Postselection

We show that weak measurements with postselection, proposed in the context of the quantum theory of measurement, naturally appear in the everyday physics of fiber optics telecom networks through polarization-mode dispersion (PMD) and polarization-dependent losses (PDL). Specifically, the PMD leads to a time-resolved discrimination of polarization; the postselection is done in the most natural way: one postselects those photons that have not been lost because of the PDL. The quantum formalism is shown to simplify the calculation of optical networks in the telecom limit of weak PMD.

Figure 1

When a polarized pulse passing through a PMD fiber, the $P$ mode $H$ (parallel to the birefringency axis in the Poincaré sphere) and its orthogonal $V$ are separated in time. A measurement of the time of arrival (TOA) is a measurement, strong or weak, of the polarization.