Polarization Analyzer SK010PA

Measurement tool for polarization-maintaining fiber cables

SK010PA

Features

The Polarization Analyzers series SK010PA are universal measurement and test systems for coupling laser beam sources into polarization-maintaining fiber cables.

New! Software Upgrade: Modernized design, a customizable user interface, real-time monitoring and long-term logging capabilities as well as DLLs for direct, seamless communication via Python or C++.
Determination of the state of polarization (SOP), with all four Stokes parameters, PER (Polarization extinction ratio), degree of polarization (DOP), ellipticity, etc.
USB 2.0-powered device (control, data transfer and power supply)
Display of the SOP on Poincaré sphere or as polarization ellipse
Special routines for PM-fiber evaluation and polarization alignment
Compatible with microbench system, rail or cage system for free beam applications, FC APC adapter included for fiber applications

Description

SK010PA Polarization Analyzers (sometimes referred to as polarimeters) are universal devices for measuring polarization and adjusting the coupling of coherent laser beam sources to polarization-maintaining fiber cables. They were developed from practical experience with a focus on high usability.

The SK010PA is a plug-and-play device that connects directly to the USB port of a (Windows) computer*, enabling rapid measurement and alignment. Real-time measurements of the Stokes parameters are performed and displayed interactively on a Poincaré sphere to depict the state of polarization. The compact device can be easily integrated into existing systems.

Measurement method
Coherent radiation entering the polarization analyzer is passed through a rotating quarter-wave plate and fixed a polarizer before being recorded by a photodetector.

The SKPolarizationAnalyzer software evaluates the Stokes parameters retrieved from a detailed analysis of the photodiode signal and the time/position information of the quarter-wave plate.

Any change in the state of polarization including the direction of rotation (depicted on the northern or southern hemisphere) is conveniently visualized on the Poincaré sphere.

Polarization Alignment for Coupling into PM fibers
The SK010PA Polarization Analyzer provides procedures for optimizing the alignment of the incoming polarization direction of the coherent source with the polarization axes of the fibers, and for measuring the resulting Polarization Extinction Ratio (PER).
This process begins with recording the exit polarization states while the fiber is gently heated or bent to cause the exit polarization to fluctuate. A circle is then automatically fitted to the data points on the Poincaré sphere and the mean and minimum PER values are displayed.

The radius of this circle indicates the quality of the alignment, as it shows the deviation angle between the fiber polarization axis and the polarization axis of the incoming coherent radiation. For an optimally aligned ideal fiber, the data circle converges on the center of the circle.

A second measurement then reveals the parameters of the optimized polarization alignment of the fiber.

Free Beam Measurements
The Polarization Analyzer can also be used to set a well-defined state of polarization for free-beam applications. For this type of measurement, a correct alignment of the laser beam axis with the Polarization Analyzer is essential. This can be achieved using the microbench or 40 mm cage system and using the connection with 4 rods or the rail system.

Adjustment of Quarter-Wave Plates
Retardation optics can be quantified and aligned using the SK010PA Polarization Analyzer, for example when using fiber collimators with integrated quarter-wave plates 60FC-Q. The outcome polarization of these collimators is adjusted by rotating the built-in quarter-wave plate. Circularly polarized light is set when the poles are reached, with right-handed circular polarization located at the north pole, and left-handed polarization located at the south pole.

Standard delivery

SK010PA of choice
USB cable
Adapter for wide key fiber connectors of type FC APC PA-FC-4-0
Adapter for post-mounting PA-AP-M4
Operating software: SKPolarizationAnalyzer for Windows 11/10 (32/64 Bit)
DLLs

* The Polarization Analyzer can be used on Windows or Linux machines via Python or C++ DLLs. A graphical user interface is provided for Windows machines only.

Technical data

Polarization Analyzer SK010PA

Interface

USB 2.0

Power Supply

via USB

Fiber adapter

FC APC (standard)

Free beam diameter

max. 4 mm

Power range

0.01 - 50 mW

Sampling rate

15 Hz

SOP accuracy

± 0.4°

PER accuracy

PER dependent, 0.5dB @ 25dB

DOP accuracy

Warm-up time

5 min

Housing

40 x 70 x 82 mm (WxLxH)

Temperature range

10 - 36°C

System requirements

x64-processor with min. 1.2 GHz, min. 2 GB RAM, 100 MB free disc space, min. 1920 x 1080 px graphic resolution, (Full-screen mode is not supported for widescreens) Software requirements Windows®10 – 64 bit (supported), Windows®11 – 64 bit (recommended), Linux (DLL use only)

Order options

Order Code	Wavelength Range
SK010PA-UV+	350 - 450 nm
SK010PA-UVIS	400 - 700 nm
SK010PA-VIS	450 - 800 nm
SK010PA-NIR	700 - 1100 nm
SK010PA-IR	1100 - 1660 nm

Technotes

FAQ

General Questions
- How is the polarization defined? Along or opposite to the direction of propagation?
  The polarization of the beams is defined opposite to the direction of propagation.
- Can I use the Polarization Analyzer for free beam measurements and for PM fiber coupling?
  Yes, the Polarization Analyzer is suitable for both applications. Standard delivery includes an FC APC adapter, so that the PM fiber cable can be directly attached to the device. For free beam applications the Polarization Analyzer is compatible with the microbench system, rail or cage system.
- What is the standard delivery?
  The standard delivery includes:
  - SK010PA of choice
  - USB cable
  - Adapter for wide key fiber connectors of type FC APC PA-FC-4-0
  - Adapter for post-mounting PA-AP-M4
  - Operating software: SKPolarizationAnalyzer for WINDOWS7, WINDOWS 10, WINDOWS Vista/XP (32/64 Bit)
  - DLLs
- Do I need a separate power supply for the SK010PA?
  No, a separate power supply is not necessary. The SK010PA Polarization analyzer is powered by your PC via USB (USB 2.0).
- How do I mount the Polarization Analyzer. What are the possibilities?
  The Polarization Analyzer is compatible with the microbench system, rail or cage system for e.g. free beam applications. An M4 post-mount adapter is supplied within the standard delivery of the Polarization Analyzer, to mount the analyzer on a post-mount with M4 thread. Other adapters with other thread diameters are available as accessory.
- How do I connect the Polarization Analyzer?
  The Polarization Analyzer is a plug&play device and connects directly to the USB port of a Windows computer.
- I have not installed the SKPolarizationAnalyzer software. Can I download it somewhere?
  Yes! Please download it from the Downloads section or from the SKPolarizationAnalyzer webpage (for registered users only).
- Where do I find more information on the SKPolarizationAnalyzer software?
  Please visit the SKPolarizationAnalyzer webpage for more info. You can also find additional information in the Polarization Analyzer manual (available in the Downloads section).
- How precise is the PER measurement?
  Assessing the accuracy of the PER measurement is not trivial. It is itself PER dependent and increases disproportionately with PER value. For a typical PER of 25 dB, the PER measurement accuracy can be given to be ± 0.5 dB.
  PER Measurements with values above 35 dB have a much larger measurement inaccuracy in the order of already a few dB and should not be taken too literally.
- I want to measure a free beam? What do i need to think about?
  If you use the SK010PA Polarization analyzer with a collimated beam, the beam has to be aligned with respect to the system better than 3°. Otherwise you will get implausible results.
- What is the input beam power measurement range?
  The power range of the SK010PA Polarization analyzer is 0.01 - 50 mW. You can reduce the input radiation by using the integrated iris diaphragm in the front part of the Polarization Analyzer.
- Does the Polarization Analyzer need annual calibration?
  There is no need for an annual calibration.
  However S+K offers to service the SK010PA Polarization Analyzers. This service includes an updated service report.
- Does the Polarization Analyzer work with pulsed sources?
  Yes and no.
  The system operates with a measuring frequency of 15 Hz. If the pulse rate of your laser is much faster you can measure the polarization of a pulsed laser.
  
  However, the PER measurement of a PM fiber does work with a CW laser only.
- Does the Polarization Analyzer work with incoherent laser sources, e.g. superluminiscent diodes?
  The Polarization Analyzer can be used with low-coherent laser sources or incoherent laser sources like e.g. superluminiscent laser diodes only to some extent.
  
  Free beam
  The Polarization Analyzer has a single wavelength input that all SOP measurements are based on, i.e. that when using the SK010PA with broadband sources the SOP measurements may not be correct.
  For example, superluminiscent diodes have a spectral bandwidth of about 20nm. This will lead to SOP measurements that have a large error margin.
  
  PM Fiber Alignment
  The SK010PA cannot be used for aligning the polarization axis of the laser source to that of the fiber cable with incoherent laser sources: You can see this on the Poincare sphere. Regardless of the alignment between the axes, the measured SOP remains constant on the horizontal (H) or vertical axis (V).
  In some cases, e.g. with short fiber lengths, and/or small laser bandwidths, the Polarization Analyzer may deliver reliable results nevertheless. The PER measurement routine will then lead to SOP measurement points varying on a circle, as expected.
- What is the measurement frequency of the Polarization Analyzer?
  The system operates with a measuring frequency of 15 Hz. This value is intrinsic to the device and cannot be changed or read-out.
- There are two adapter options - one without integrated optics and one with integrated optics. What is the best option for me?
  For standard applications we recommend to use an adapter without optics since any additional optics may show birefringence and so may falsify the measurement result.
- Can I use two Polarization Analyzers with a single computer at the same time?
  Sometimes it might be necessary to have two Polarization Analyzers working at the same time with the same computer. This is possible.
  Several polarimeters can be addressed simultaneously using the DLLs. Depending on the order of connection, these receive different IDs via which they can be addressed specifically.
Questions about the Fiber PER Measurement Procedure
- What does the value min PER mean?
  The min PER results from the worst possible state of polarization (SOP) possible with the current setup. It is the point farthest from the equator. Thus, this value considers both the radius of the circle AND the distance of its center from the equator. More information can be found here.
- What is the difference between lin. PER and PER?
  The extinction ratio PER is the ratio of the powers in the two (linear) principal states of polarization in logarithmic scale.
  The extinction lin. PER is the ratio of linear polarized light to the total amount of light measured in logarithmic scale. For depolarized sources the lin. PER will be lower than PER.
  You cannot caculate the PER from the lin. PER and vice versa.
  For coherent light sources (like e.g. most lasers) you need to use PER to optimize the polarization adjustment of the fiber.
  So what do you need the lin. PER for?
  
  The lin. PER is used to align the polarization axes to a source that has low coherence. In this case, the coherence is less than the difference in time it takes to pass through the fiber in the two principal axes of the fiber. In such a case, the value lin. PER serves as a measure of the polarization alignment. The larger the value lin. PER, the better the alignment.
- When do I use the value lin. PER?
  The lin. PER is used to align the polarization axes to a source that has low coherence. In this case, the coherence is less than the difference in time it takes to pass through the fiber in the two principal axes of the fiber. In such a case, the value lin. PER serves as a measure of the polarization alignment. The larger the value lin. PER, the better the alignment.
Trouble Shooting
- The signal power is too low. What can I do?
  - Have you checked if the aperture is open?
    Please check if the mechanical aperture on the front of the device is opened completely. Open the aperture to increase the signal intensity.
  - Is your laser power too low?
    Please check your laser power and make sure it is above the minimum power level required for using the Polarization Analyzer. Adjust the laser power if possible.
  - Are you using the Polarization Analyzer for a free beam measurement?
    If yes, please make sure that the input beam is centric to the entrance aperture.
- The signal intensity is too high. What can I do?
  - Have you closed the entrance aperture yet?
    Try closing the iris diaphragm at the Polarization Analyzer's entrance to reduce the signal intensity.
  - Is it possible to reduce the laser power?
    Please check if is possible to reduce the laser power. Keep in mind that laser properties may change if the laser power is reduced in such a way that the laser operates near the laser threshold. In case of laser diodes, this can e.g. cause polarization fluctuations.
- I want to mount the Polarization Analyzer to an optical table. How do I do that?
  - Please check the standard delivery for the Post-mount adapter.
    Use the post-mount adapter supplied within the standard delivery of the Polarization Analyzer to mount the analyzer on a post-mount with M4 thread. Other thread diameters are available as accessory.
- The measurement of the azimuth angle phi does not seem correct. What can I do?
  - Have you checked if the displayed angle is the relative angle?
    There are two setting for the angle of polarization Phi: absolute and relative. If the measured angle of linear polarization seems to be off, e.g. vertically polarized light is measured with an arbitrary angle to the vertical alignment of the device, then the setting might be set to "relative".
    Please check, if the angle of polarization Phi is displayed with the suffix “rel.”. Then change the setting from a relative angle to default setting via “Edit” -> “Set Azimuth (default)”.
- The state of polarization for a free beam measurement seems to give implausible results. What can I do?
  - Have you checked the alignment of the Polarization Analyzer to the incoming laser beam?
    An incidence-angle of the incoming laser beam relative to the analyzer can lead to implausible results. Try to align the beam (or the Polarization Analyzer) to minimize the incidence angle. It should be ≤ ±3°.
- The red LED on top of the Polarization Analyzer is flashing.
  - What does that mean?
    Unfortunately that means a failure of electro-mechanical components inside the device. Please contact Schäfter+Kirchhoff immediately and request an RMA.
- My Polarization Analyzer is not recognized by software, even though there is a Polarization Analyzer listed in the Windows Device Manager. What can I do?
  - This sounds like an FTDI driver problem.
    Due to the widespread usage of USB-Communication chips of the same type in different measurement devices it is possible that a driver of another device changed the so called virtual COM-port setting of the Polarization Analyzer. This can be undone quickly. Please contact Schäfter+Kirchhoff to receive the corresponding technical instructions.
Polarization Analyzer accessories
- There are two adapter options - one without integrated optics and one with integrated optics. What is the best option for me?
  For standard applications we recommend to use an adapter without optics since any additional optics may show birefringence and so may falsify the measurement result.

Downloads

090721300125.stp (STEP model)

090721300125.stp (STEP model, for registered users only)

090721300125.pdf (Dimensional drawing)

SKPolarimeter_4_6_4.zip (Software file)

SKPolarimeter_4_6_4.zip (Software file, for registered users only)

SKPolarimeter_x64.zip (Software file)

SKPolarimeter_x64.zip (Software file, for registered users only)

Manual_Polarimeter_464e.pdf (Manual)

Manual_Polarimeter_464e.pdf (Manual, for registered users only)

Article_PolarizationAnalyzer.pdf (Technote)

Benefits of user registration include

Extended information for download including stepfiles, software or manuals
Direct download of user-specific downloads (e.g. user-specific software)
Access to previous online requests and the possibility to add complete previous lists to the "Request for quote" list
Stored item list

Click here to register.