Moving Fibers During Measurement
The traditional JME is known to be extremely sensitive against fiber movements during the measurement process. If the SOP changes between adjacent data points, a significant measurement error is induced. The time between each data point is in the order of seconds due to the stepping speed of the lasers.
In the N7788B measurement system, the pure data acquisition time is in the order of 2.5 seconds for modern laser sources (sweep speed:40nm/s, sweep range: 100nm). The N7788B collects more than 50000 data points during this time. Thus, the N7788B measurement system requires the SOP to be stable within only 50 µs. As a consequence, manually moving the fibers does not significantly disturb the measurement.
The Müller Method is an important and established tool for measuring polarization dependent loss (PDL). With small modifications to this method, the data collected during the measurement sweep can also be used to calculate the device's PDL. Even more interesting is the fact that the measured PDL information can be used to improve the results of the JME-based evaluation which usually is disturbed by the presence of PDL.