Principle of Operation
The N7788B Component Analyzer uses a LiNbO3 polarization controller combined with a high-speed polarimeter to do the measurements needed for the JME.
The polarization controller is capable to quickly switch the input polarization state (SOP) of the Device-Under-Test (DUT) while the polarimeter is monitoring the polarization state at the output of the DUT. The information about the device's PMD is given by the wavelength dependence of the output SOPs. Thus, the PMD can be measured by changing the wavelength of the light source (a tunable laser source) and switching the input SOP while simultaneously measuring the corresponding output SOP.
The main drawbacks of the traditional JME are mainly caused by the operation mode of the tunable laser source (TLS). Due to mode-hopping of older TLS models, the laser could only be operated in stepping mode, i.e. the TLS had to be set step-wise to different wavelengths. Thus, covering the whole C-band with an appropriate resolution resulted in measurement times of 10 to 15 minutes. Modern TLS models are capable of continuously sweeping over the whole wavelength range without mode-hops. Using the continuous sweep of the TLS reduces measurement time to several seconds.