Swept Wavelength Method
The swept wavelength method uses a tunable laser source which is able to repeatedly change the wavelength around the center wavelength. While the laser wavelength is swept back and forth, the output polarization state of the PMF draws a circle on the Poincaré sphere. If the signal is perfectly aligned to one of the PMF's axis, the circle would degenerate to a single point. Tuning ranges in the order of 5nm are sufficient for 1m PMD pigtails.
