Keysight 81618A/9A and Keysight 81620B/3B/4B/6B/8B Optical Heads User’s Guide 65Performance Tests 411 Now connect the open end to the optical head.12 Enter the Power reading [P] on the optical head as [FPDelta] on theReturn Loss Meter. Make sure you en ter the sign of this value correctly.13 Note the Return Loss reading as the Return Loss result into the testrecord.Relative Uncertainty due to Polarization (Optional Test)Refer to Figure 13 on page -66 for a setup to verify the relative uncertaintydue to polarization of the sensor module.Generally, during this measurement procedure the tunable laser source isswept through a predefined wavelength range. After every wavelengthstep, a single PDL-measurement is made, where the polarizationcontroller generates all the different polarization states. The highest PDLvalue is taken as the "relative uncertainty due to polarization". The lowoutput power path of the coupler is used to monitor the power stability ofthe setup.NOTE The performance test "Relative Uncertainty due to Polarization" isoptional, since the polarization is given with the production of the unit bymechanical and optical cavities and is unchanged by normal use of thesensor module.
