Phase Control in Polarization Maintaining Fiber for Quantum Key Distribution

Polarization encodings for quantum key distribution (QKD) in fiber suffer from strain- and temperature-induced polarization instabilities, which can be addressed using a polarization control system. The polarization instability can be reduced to a single phase parameter by using polarization maintaining (PM) fiber. However, phase control in PM fiber is typically applied to phase stabilization on signals coupled into only one bases of the PM fiber, making such methods insufficient for QKD which encodes signals in orthogonal bases. We describe an active system to monitor and control the phase in PM fiber to enable PM fiber based QKD systems.