agilent N7785B synchronous scrambler data sheet introduction the agilent 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 agilent 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 agilents pc software package which comes with this instrument. figure 1. N7785B-001 bench-top mainframe
2 agilent N7785B synchronous scrambler data sheet figure 3. recirculating loop applications recirculating loop experiments: - loop-synchronous polarization scrambling system test: polarization sensitivity analysis on link / transmission quality characterization of optical components agilent N7785B instrument setup and application examples key bene? ts comprehensive polarization control and management capabilities covers s-, c-, and l-band plus 1.3 m window compact size robust, no moving parts pc software package included the instrument setup is shown in figure 2. the linbo3 polarization controller is controlled by a signal processor which supplies user-de? nable sequences to the polarization controller. in this way, the sop can be controlled in steps but also continuously. the trigger system provides synchro- nization capabilities to external digital signals. 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. in addition, the n7781b polarization analyzer provides the capability of monitoring the sop evolution on each round trip. 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. smf smf usb gpib trigger in trigger out linbo 3 polarization controller power in microcontroller board N7785B synchronous scrambler computer trigger tx unit ampli?er switch rx unit fiber loop pol contr N7785B synchronous scrambler polarized source dop < 5% figure 2. N7785B instrument setup figure 4. scrambling/depolarization
3 agilent N7785B synchronous scrambler data sheet table 1: speci? cations 1) N7785B synchronous scrambler wavelength operating wavelength range 1260 nm ... 1640 nm polarization control sop switching time < 10 s optical power insertion loss < 3 db maximum safe input power 20 dbm 1) ambient temperature change max. 0.5c since normalization. specification valid on day of calibration.
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