Agilent 71451B/11896A swept-wavelength PDL test system
The Agilent 71451B/11896A Swept-Wavelength PDL Test System provides a high-speed method for measuring PDL across a 1250 to 1600 nm wavelength range. Measurement data examples are shown in Figures 10 and 11.
This measurement uses the Agilent 71451B Optical Spectrum Analyzer to monitor changes in DUT insertion loss versus wavelength. Automatically swept wavelength coverage is provided by the built-in, white-light source and monochromator of the Agilent 71451B Option 002 (see Figure 12). The test signal’s polarization state is automatically adjusted using the Agilent 11896A Polarization Controller (included as part of the Agilent 71451B Option 003). PDL calculations are done automatically using the built-in down loadable program provided on a memory card (included as part of the Agilent 71451B Option 003).
Measurement procedure
This 14-step procedure enables PDL measurements to be performed over a specified wavelength span. It is assumed that Agilent 71451B Optical Spectrum Analyzer has already been configured and the PDL down-loadable program card(included with the Agilent 71451B Option 003) has already been installed according to the instructions included with the Option 003 documentation.
Agilent 71451B settings (1/2):
1. Activate the swept polarization-dependent loss measurement personality by pressing USER and then PDL.
2. Press Detectr Internal Ext so that Ext is underlined indicating that an external photodetector is being used.
3. Press Source On Off so that On is underlined indicating an On condition.
4. Set the start and stop wavelengths for the measurement using the Start and Stop keys on the keypad.
5. Press the RES BW AutoMan soft key and set the resolution bandwidth to 10 nm. This resolution bandwidth setting is for the greatest measurement range and signal-to-noise performance. Narrower bandwidths can be used if greater wavelength resolution is required.
6. Wait for at least one sweep of the entire wavelength span to be completed and press AUTO SCALE.
7. If the noise level of the measurement is not acceptable it can be adjusted by using the video bandwidth filter. Note that a reduction in the video bandwidth reduces the noise floor and automatically increases the measurement sweep time. Press VID BW AutoMan and use the up/down arrows to adjust as needed.
8. Begin the PDL measurement by pressing INIT PDL. This activates the maximum and minimum hold function which generates a set of traces from the maximum and minimum power points encountered at each wavelength during the measurement.
Agilent 11896A settings (1/1):
9. Press SCANRATE.
10. Use the far right knob to select SCAN RATE: 1 and press ENTER. Refer to the Uncertainty Analysis for this measurement for further information about scan rate selection.
11. Press AUTOSCAN.
12. When 05:00 (5 minutes) appears in the scan time indicator, press Manual. This stops the polarization scan. Refer to the Uncertainty Analysis for this measurement for further information about a 5 minute scan time recommendation.
Agilent 71451B settings (2/2):
13. PDL across the measured wavelength range is automatically calculated and graphically displayed by pressing CALC+DISPLAY. Press AUTO SCALE and marker functions as needed to optimize the view of the measurement trace.
14. To test additional devices, connect a new test device as shown in Figure 12 and return to step #8.
Uncertainty analysis
PDL measurement uncertainty for the Agilent 71451B/11896A Swept-Wavelength PDL Test System is based upon the inherent uncertainty of the measurement system (values shown in Table 7).
It is assumed that the Agilent 71451B Option 002 white light source is used and the PDL value is between 0 to 5 dB, as shown in Table 2. The Agilent 11896A Polarization Controller scan time should be long enough to allow the maximum and minimum traces (shown in Figure 10) to stabilize. Actual system performance will vary depending upon the individual performance of the specific equipment in the system.
Refer to the Appendix for additional ways to ensure maximum possible PDL measurement accuracy from a given PDL measurement system.
Additional information about swept-wavelength Agilent 71451B settings and polarization scan rate
Typical Agilent 71451B Option 002 (white light source option)/003 (swept PDL measurement kit with Agilent 11896A included) settings are shown below. The PDL down loadable program (included with Option 003) automatically sets values to within these typical ranges.
Under these conditions and an Agilent 11896A Polarization Controller scan rate of 1, the Agilent 71451B is able to make an entire sweep at approximately the same polarization state. Over a five minute period, a sufficiently large sampling of random polarization states can be measured in order to accurately measure PDL over a specified wavelength range.