N7784B High Speed Polarization Controller

Data Sheets


The Keysight Technologies N7784B polarization controller contains a high-speed polarization controller plus microcontroller-based driving circuitry. This unit can operate in various modes. As a polarization stabilizer, it provides a stable output state of polarization (SOP) even with fluctuations and drifts of the input SOP as occurring for example through temperature drift and mechanical settling processes. The stabilized output signal is aligned into a polarization maintaining fiber (PMF). Alternatively, an external electrical feedback signal can be provided for stabilizing the SOP. As a synchronous scrambler, the device switches the SOP of the output signal in a random (pseudo) way. Switching of the SOP occurs within a few microseconds. The SOP is stable for a predefined time until it again switches to a new SOP. An electrical trigger input can be used to synchronize the scrambler with external events. As an SOP switch, the N7784B allows switching the internal waveplates to user definable angles with very high speed and repeatability. As traditional scrambler the N7784B varies the output SOP smoothly in a random/pseudo random way. The unit does not contain any moving parts and therefore is robust and withstands even rough environmental conditions. All above-mentioned applications of the N7784B are supported by a PC software package.

  • PC-based application software comes with this instrument.
  • Other instrument drivers for various software interfaces are available.


  • Interferometry: polarization stabilization to maximize contrast ratio.
  • Recirculating loop experiments: loop-synchronous polarization scrambling.
  • System test: polarization sensitivity analysis on link/ transmission quality.

Keysight N7784B Instrument Setup and Application Examples

The instrument setup is shown in Figure 2. If a scrambling or switching operation is desired, only ports I and II are used. If the SOP of the signal is stabilized and the signal is fed in a PMF, then port II and port III have to be connected by an SMF. In this situation, the output signal is available on port IV. If an external feedback signal is available for stabilization, only ports I and II are occupied.

Application Examples

Fiber optic based interferometers or coherent receiver schemesneed polarization stabilization in order to avoid fading problems of the interference signal. These fading effects are caused by orthogonally polarized fractions of the light. The N7784B allows elimination of such effects by alignment of the signal polarization.


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