introduction the agilent n7781b is a compact high-speed polarization analyzer that provides comprehensive capabilities for analyz- ing polarization properties of optical signals. this includes representation of the state of polarization (sop) on the poincar sphere (stokes parameter). the on-board algorithms together with the on-board calibration data ensure highly accurate operation across a broad wavelength range. the agi- lent N7781BD also contains a windows based computer unit which allows operation independent from external pcs. due to its real time measurement capability (1 msamples/s), the instrument is well suited for analyzing disturbed and ? uc- tuating signals as well as for control applications requiring real time feedback of polarization information. analog data output ports are provided, for example for support of control loops in automated manufacturing test systems. the provided analysis software allows a comprehensive analysis of the obtained measurement data. agilent n7781b/N7781BD polarization analyzer data sheet key features measurement of stokes parameter (sop) measurement of degree of polarization (dop) high-speed operation (> 1 msamples/s) analog output ports for dop/sop data robust, no moving parts ? ? ? ? ? agilent n7781b agilent N7781BD
applications 2 monitoring / measurement of: - state of polarization (sop) - stokes parameter - degree of polarization (dop) high-speed analysis of sop/dop of signals in recirculating loop setups analysis of pm-? ber extinction ratio performance analysis of polarization scramblers intrusion detection ? ? ? ? ? 45 45 0 0 /4 pol. optical signal usb gpib trigger in / out 4 ch. adc dsp & memory ampl ampl ampl ampl figure 1. agilent n7781b/bd polarization analyzer setup n7781b/bd instrument setup and application examples the instrument setup of the n7781b/bd polarization analyzer is shown in figure 1. it consists of a unique polarimeter optics and a high-speed sampling subsystem. the measurement principle is based on splitting the light into four sub beams which are ? ltered through different polarization ? lters. the re- sulting four power levels are evaluated using on-board calibra- tion data to obtain an accurate sop- and dop-measurement. figure 2. recirculating loop experiments n7781b/bd polarization analyzer computer trigger gpib/usb tx unit ampli?er switch rx unit tap coupler fiber loop pol contr figure 3. alignment of polarization maintaining ? bers polarization analyzer computer dut pmf swept laser gpib/usb gpib/usb n7781b/bd alignment of polarization maintaining ? bers accurate alignment of the polarization axis of polarization maintaining ? bers is crucial for the performance of a large range of optical components. the n7781b/bd allows, due to its high-speed capability, real time feedback regarding the currently achieved polarization extinction ratio (per). see also n7783b for automated per measurements. recirculating loop experiments managing the polarization properties of the ? ber loop is mandatory for successfully conducting experiments with such structures. the n7781b/bd high speed polarization analyzer allows an analysis of the sop and the dop of the circulating signal. the high sampling rate and the trigger capabilities of the instrument, allow detailed analysis of the evolution of the sop and the dop along each revolution. agilent n7781b/bd polarization analyzer data sheet
3 event trigger advanced communication systems are sensitive to rapid polarization changes (events) on ? ber links. such events may be caused for example by trains passing by or by vibrations on bridges. the speed of the polarization events are of concern for system integrators and network operators. the event trigger function of the n7781b/bd allows detecting and recording such events. table 1. speci? cations 1) - n7781b/bd polarization analyzer figure 4. recirculating loop experiments tap coupler transmitter receiver n7781b/bd polarization analyzer agilent n7781b/bd polarization analyzer data sheet wavelength speci? cation wavelength range 1270 nm ... 1375 nm (opt 300, o-band) 1270 nm ... 1375 nm, 1460 nm ... 1620 nm (opt 400, o/c/l-band) 1460 nm ... 1620 nm (opt 500, c/l-band) operating wavelength range 2) 1260 nm ... 1640 nm polarization analysis sop uncertainty (typical) 3),4) 1.5 dop uncertainty 3) 2.0 % dop uncertainty after user calibration (typical) 3),5) 0.5 % maximum sampling rate 1 mhz optical power measurement relative power uncertainty 3) c/l-band: 30 mdb ( 20 mdb typ.) o-band: 70 mdb ( 40 mdb typ.) input power range -50 dbm ... +7 dbm maximum safe optical input power 12 dbm 1) ambient temperature change max. 0.5c since normalization. specification valid on day of calibration. 2) sop/dop measurements are possible outside the specification wavelength range if the user performs a manual calibration. 3) input power > -30 dbm 4) dop > 95% 5) user calibration requires a source with dop = 100%.
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