N7785B Synchronous Scrambler

Introduction

The Keysight Technologies N7785B is a high-speed synchronous scrambler. It contains a polarization controller plus microcontroller-based driving circuitry. This unit can operate in various modes:

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 N7785B allows switching the internal waveplates to user definable angles with very high speed and repeatability.

As a traditional scrambler, the Keysight N7785B 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 N7785B are supported by Keysight’s PC software package which comes with this instrument.

 Key benefits

• Comprehensive polarization control and  management capabilities.
• Covers S-, C-, and L-band plus 1.3 μm window.
• Compact size.
• Robust, no moving parts.
• PC software package included

The results obtained in re-circulating loop experiments depend heavily on the PMD and PDL properties of the loop. Loop synchronous polarization scrambling schemes have proven to be necessary for generating results comparable to deployed systems.

The synchronized scrambling feature of the N7785B is a unique enhancement to conventional polarization scramblers. The polarization can be scanned according to a pseudo-random but reproducible path. Instead of a continuously changing SOP, the SOP is switched in discrete steps that are synchronized with an input or output trigger signal. After switching, a stable SOP is quickly reached and held until the next step.

The N7785B is ideally suited to provide the synchronous scrambling capability in such experiments.

This is a key capability for providing realistic change of polarization from cycle to cycle around the loop, while providing a stable SOP during passage of the bit train through the scrambler. This avoids the unrealistic effect rapid change of the polarization during the bit train caused by continuous scramblers.

Light emitted by a laser is typically highly polarized. In order to avoid polarization effects it is common in some applications to depolarize light. This can be achieved highly effectively using the N7785B synchronous scrambler unit.