N7747A and N7748A High-Sensitivity Optical Power Meter

To support multichannel applications requiring low-noise measurement and monitoring of optical signals and widest dynamic range, the 2-port N7747A and 4-port N7748A bring a new level of specified performance to the Keysight Technologies, Inc. optical power meter family, in the compact N77 platform offering extended functionality of 100X more memory, faster data transfer rates, and continuous logging.

• Sensitivity to –110 dBm with < 0.1 pW peak-peak noise and drift
• Polarization dependence and spectral ripple < ± 0.005 dB
• In-range linearity: < ± 0.005 dB
• Continuous range of averaging time settings: 25 μs to 10 s

With the N7747A and N7748A, the highest optical performance is now offered in the N77 platform for compact automated instrumentation. The high optical performance encompasses the highest sensi­tivity available with –110 dBm and correspondingly low noise and high stability to accurately measure and monitor weak signals and small signal changes. This is supported by high relative power accuracy with low polarization dependence and low spectral ripple. The high sensitivity together with 9 power ranges at 10 dB spacing provides highest dynamic range with excellent linearity. A new specification that guarantees the highest linearity when the power range is not changed increases confidence in IL measurement accuracy.

Twice the ports in half the rack space. These instruments enhance the proven optical performance of the 81634B sensor modules with the large memory, fast data transfer and small footprint of the N77 series platform. Eight high-sensitivity optical power meters now fit in a single rack unit. Optical connections are made with the interchangeable 81000xI connector interface system so the instrument can be easily adapted to different fiber connector types.

Each optical port has 2 buffers of memory, each able to log up to 1M samples. With the ability to upload one buffer while the other is recording measurements, this permits continuous monitoring over extended times with sensitivity to small transients. Details for programming this logging are given in the application note 5990-3710. The functionality is the same used in the N7744A and N7745A except that the high-sensitivity models use lower bandwidth to match the low-noise performance. This includes flexible choice of averaging times to optimize sampling at any rate.

The N7747A and N7748A also include an analog output for each optical channel. This provides a 0 to 2 V signal proportional to the optical power, scaled by the selected power range and allows analog monitoring of signals with up to 5 kHz bandwidth.

The instruments have USB, LAN and GPIB interfaces for control with the SCPI command set also used for the 816x, N7744A and N7745A optical power meters. The updated versions of the N77xx Viewer user interface program and the 816x VXI Plug&Play driver can be used, also with the N7700A IL engine to measure the high dynamic range in optical filters.