Agilent N7784B
High Speed
Polarization Controller
Data Sheet
Figure 1. N7784B-001 bench-top mainframe
Introduction
The Agilent 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 guided in a polarization main-
taining 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 there-
fore 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.
Application examples
Interferogram
Key Benefits
● Comprehensive polarization control and
management capabilities
● Covers S-, C- and L-band plus 1.3 µm
window (O-band)
● Compact size
● Standalone operation
● Robust, no moving parts
● PC software package included
Laser
Sensor
N7784B
high-speed
polarization
controller
Figure 3. Interferometry/coherent detection
Fiber optic based interferometers or coherent receiver
schemes need 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.
N7784B
High Speed
Polarization
Controller
Amplifier
Applications
●
●
●
Interferometry: polarization stabilization to maximize
contrast ratio
Recirculating loop experiments: loop-synchronous
polarization scrambling
Trigger
Fiber loop
Pol contr
Switch
System test: polarization sensitivity analysis on
link/transmission quality
Tx unit
Rx unit
Agilent N7784B Instrument Setup and
Application Examples
The instrument setup is shown in Figure 1. 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.
Optical input
Port I
PC input
Port II
PC output
Port III
PBS
input
Port IV
PBS
output
Analog in
Computer
Figure 4. Recirculating loop
SMF
Polarization
controller
SMF
PMF
Pol splitter
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 N7784B is ideally suited to provide
the synchronous scrambling capability in such experiments.
In addition, the N7781B polarization analyzer provides the
capability of monitoring the SOP evolution on each round trip.
Trigger in
Power In
DSP based control electronics
Trigger out
GPIB
USB
Figure 2. N7784B instrument setup
2
Agilent N7784B High Speed Polarization Controller Data Sheet
Table 1: Specifications
1)
N7784B Polarization Controller
Wavelength
Operating wavelength range
Wavelength range in stabilizer mode
2)
Polarization Control and Stabilization
SOP switching time (open-loop)
PER at PMF output
Stabilizer response time
3)
(typical)
Optical Power
Insertion loss port I - port II
4)
Insertion loss port III - port IV
5)
PDL port I - port II (typical)
Maximum safe input power
Input power range in stabilizer mode
< 3.5 dB (< 3.0 dB, typ.)
< 1.8 dB (< 1.4 dB, typ.)
< 0.2 dB
Port I:
Port III:
Port III:
20 dBm
3 dBm
-30 dBm ... 0 dBm
< 10 µs
> 23 dB
2 ms
1260 nm ... 1640 nm
1520 nm ... 1580 nm
1) Ambient temperature change max. ± 0.5°C since normalization. Specification valid on day of calibration.
2) Outside the stabilizer wavelength range, the PER at PMF output may be degraded.
3) Input power > -20 dBm.
4) For SOP scrambling/switching, only ports I/II are used.
5) Valid for optimum input polarization at PBS input (Port III). Add insertion loss of port I/II and obtain total insertion loss for SOP
stabilizing mode.
Agilent N7784B High Speed Polarization Controller Data Sheet
3
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Product specifications and descriptions in this
document subject to change without notice.
© Agilent Technologies, Inc. 2008
Printed in USA, April 29, 2008
5989-8113EN
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