The Agilent 11896A adjusts polarization and not power and is an important part of a PDL test system. Its optical fiber loop design, shown in Figure 2, provides all states of polarization (see Figure 3) with extremely small optical insertion-loss variations (0.004 dB) over a 1250 to 1600 nm spectral range. This performance combination maximizes measurement accuracy for power sensitive PDL measurements (see Figure 4).
The Agilent 11896A adjusts the polarization of a transmitted signal as it passes through the internal four-fiber-loop assembly. Each loop’s dimensions are optimized to approach a quarter-wave retarder response over the controller’s specified wavelength range. Complete and continuous polarization adjustability is achieved by independently rotating each loop over a 180° angular range. This range is divided into 1000 equal steps (front panel reading 000 to 999), providing adjustment resolution of 0.18°. Adjustments are made manually, using front panel knobs, or automatically, using remote GPIB commands or built-in auto scanning control and Save/Recall registers.