Polarization Mode Dispersion Compensation Towards Improved Polarization Based Quantum Networks*

Polarization Mode Dispersion (PMD) describes the depolarization effects in single-mode fibers. The compensation of PMD within optical fibers is critical for implementing quantum networks, since it limits the transmission distance and usable spectral bandwidth of polarization-entangled qubits. When PMD is present in optical fiber, it leads to temporal delays depending on the input polarization state. This effect can also be understood as a wavelength-dependent transformation of polarization. We define the principal states of polarization (PSP) for 1st order PMD as an axis on the Poincaré sphere around which wavelength dependent polarization transformations occur. We compensate for PMD using polarization-maintaining fiber aligned with the PSP and characterize the PMD in a 55 km segment of real-world fiber connecting the University of Illinois at Urbana-Champaign to the nearby town of Rantoul. We show significantly different and time varying polarization transformations, even for wavelength differences of 1 nm. We then compensate for the PMD over this bandwidth, corresponding to the bandwidth of entanglement sources we wish to use in quantum networks. We present the comparative results of the polarization transform at wavelengths of 1559.5 nm and 1560.5 nm to confirm the impact of our PMD analysis and compensation system.