Features

• Convert Between Linear, Circular, and Elliptical Polarization States
• Operates over Full Fiber Bandwidth
• Empty Controllers for Ø900 µm Jacketed FC/PC or FC/APC Patch Cables
• Preloaded Controllers with FC/PC- or FC/APC-Terminated Fibers (2.0 mm Narrow Key)
• Three Loop Diameters Available
  • Three-Paddle Controllers: Ø1.06" or Ø2.2"
  • Two-Paddle Controllers: Ø0.71"

Thorlabs' Fiber Polarization Controllers use stress-induced birefringence produced by wrapping the fiber around two or three spools to create independent wave plates that will alter the polarization of the transmitted light in a single mode fiber. The fast axis of the fiber is in the plane of the spool, allowing an arbitrary input polarization state to be adjusted by rotating the paddles. See Video 1.1 and the Operation tab for more details.

The controllers are available in a 3-paddle configuration with either 1.06" or 2.2" diameter loops as well as a mini 2-paddle configuration with 0.71" diameter loops. Thorlabs offers an empty controller in each style to allow the user to insert single mode fiber with a Ø900 µm jacket, such as a bare fiber, FC/PC patch cable, or FC/APC patch cable. To ensure proper usage of the controllers, fiber cables must be long enough to achieve the recommended number of loops; see the Operation tab for more details. For fibers with higher bend loss, we recommend using the version with the largest spools (FPC560), thereby causing the least amount of bending. Controllers are also available preloaded with one of six fiber types, although the preloaded fiber may be replaced with another fiber should a different wavelength range be required for future applications. See the Specs tab for the available configurations.

We also offer In-Line Polarization Controllers. These controllers create a single continously variable wave plate similar to a Soleil-Babinet compensator, enabling polarization control over the full Poincaré sphere.

Fiber Polarization Control Selection Guide
Polarization Controllers					Linear Polarizers
Motorized Fiber Polarization Controllers	Manual Paddle Fiber Polarization Controllers	In-Line Manual Fiber Polarization Controller	Free-Space FiberBench	Faraday Mirrors	In-Line Fiber Polarizers	Polarizing Fiber

3-Paddle Polarization Controllers, Ø56 mm Loop

• Retardance varies as a function of wavelength. See the Operation tab for details.
• Devices with preloaded fiber, as shipped by Thorlabs, are configured to approximate quarter-wave, half-wave, and quarter-wave plates when used at this wavelength.
• Hytrel^® is a registered trademark of DuPont Polymers, Inc.
• Total fiber length is the total length of pre-loaded fiber inside and outside the controller.
• Fiber lead length refers to the length of fiber protruding from the device on either side of the controller, as shipped by Thorlabs.
• All connectors are 2.0 mm narrow key.
  
  

3-Paddle Polarization Controllers, Ø27 mm Loop

• Retardance varies as a function of wavelength. See the Operation tab for details.
• To order this patch cable, please see our Custom Fiber Patch Cable Configurator or contact Tech Support.
• Devices with preloaded fiber, as shipped by Thorlabs, are configured to approximate quarter-wave, half-wave, and quarter-wave plates when used at this wavelength.
• Hytrel^® is a registered trademark of DuPont Polymers, Inc.
• Total fiber length is the total length of pre-loaded fiber inside and outside the controller.
• Fiber lead length refers to the length of fiber protruding from the device on either side of the controller, as shipped by Thorlabs.
• All connectors are 2.0 mm narrow key.
  
  

2-Paddle Fiber Polarization Controllers, Ø18 mm Loop

• Retardance varies as a function of wavelength. See the Operation tab for details.
• To order this patch cable, please see our Custom Fiber Patch Cable Configurator or contact Tech Support.
• Devices with preloaded fiber, as shipped by Thorlabs, are configured to approximate quarter-wave and half-wave plates when used at this wavelength.
• Hytrel^® is a registered trademark of DuPont Polymers, Inc.
• Total fiber length is the total length of pre-loaded fiber inside and outside controller.
• Fiber lead length refers to the length of fiber protruding from the device on either side of the controller, as shipped by Thorlabs.
• All connectors are 2.0 mm narrow key.

These manual polarization controllers utilize stress-induced birefringence to create two or three independent fractional wave plates to alter the polarization in single mode fiber that is looped around two or three independent spools to create the independent fractional wave plates (fiber retarders). The amount of birefringence induced in the fiber is a function of the fiber cladding diameter, the spool diameter (fixed), the number of fiber loops per spool, and the wavelength of the light. (NOTE: The desired birefringence is induced by the loop in the fiber, not by the twisting of the fiber paddles). The fast axis of the fiber, which is in the plane of the spool, is adjusted with respect to the transmitted polarization vector by manually rotating the paddles to twist the fiber. To transform an arbitrary input polarization state into another arbitrary output polarization state, a combination of three paddles (a quarter-wave plate, a half-wave plate, and a quarter-wave plate) or two paddles (quarter-wave plate and a half-wave plate) can be used. Because a three-paddle configuration decouples the two quarter-wave plates, more polarization states can be achieved compared to a two-paddle configuration. The retardance of each paddle may be estimated from the following equation:

Here, φ is the retardance, a is a constant (0.133 for silica fiber), N is the number of loops, d is the fiber cladding diameter, λ is the wavelength, and D is the loop diameter. While this equation is for bare fiber, the solution for Ø900 µm jacketed fiber will be similar enough that the results for this equation can still be used (i.e., the solution will not vary by a complete loop N for Ø900 µm jacketed fiber).

Recommended Number of Loops
The recommended number of loops, fiber, and patch cables for several wavelengths is given in the following tables. These combinations come close to the desired quarter-wave retardation:

These combinations come close to the desired half-wave retardation:

Three-Paddle Polarization Controllers
A three-paddle polarization controller combines a quarter-wave plate, half-wave plate, and quarter-wave plate in series to transform an arbitrary polarization state into another polarization state. The first quarter-wave plate would transform the input polarization state into a linear polarization state. The half-wave plate would rotate the linear polarization state, and the last quarter-wave plate would transform the linear state into an arbitrary polarization state. This is illustrated in Video 1.1 on the Overview tab. Therefore, adjusting each of the three paddles (fiber retarders) allows complete control of the output polarization state over a broad range of wavelengths from 500 to 1600 nm). Using FPC030 as an example, a plot of calculated retardation per paddle versus wavelength is shown in Figure 3.1 for a fiber with a cladding diameter of 125 μm. For fiber with a cladding diameter of 80 μm, the retardation per paddle versus wavelength is shown in Figure 3.2. The FPC030 has a loop diameter of 27 mm.

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Figure 3.1  Plot of the retardance per paddle for silica fiber with Ø125 µm cladding on the FPC030, which has a loop diameter of 27 mm.

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Figure 3.2  Plot of the retardance per paddle for silica fiber with Ø80 µm cladding on the FPC030, which has a loop diameter of 27 mm.

Figures 3.3 and 3.4 show the results for Ø125 µm and Ø80 µm clad fiber, respectively, for the FPC560 controller, which has three paddles with a loop diameter of 56 mm. The larger loop diameter is ideal for fibers with higher bend loss.

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Figure 3.3  Plot of the retardance per paddle for silica fiber with Ø125 µm cladding on the FPC560, which has a loop diameter of 56 mm.

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Figure 3.4  Plot of the retardance per paddle for silica fiber with Ø80 µm cladding on the FPC560, which has a loop diameter of 56 mm.

Miniature Two-Paddle Polarization Controller
The miniature two-paddle polarization controllers use a quarter-wave plate and a half-wave plate to transform an arbitrary polarization state into another polarization state. In the two-paddle configuration, however, the control of the polarization will be coupled between the two paddles and therefore it may be difficult to achieve a specific polarization state. The design of the FPC020 allows complete control of the output polarization state over a broad range of wavelengths. Figures 3.5 and 3.6 show the calculated retardation per paddle for Ø125 µm and Ø80 µm clad bare fiber, respectively, for the FPC020, which has a loop diameter of 18 mm.

Click to Enlarge
Figure 3.5  Plot of the retardance per paddle for bare silica fiber with Ø125 µm cladding on the FPC020, which has a loop diameter of 18 mm.

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Figure 3.6  Plot of the retardance per paddle for bare silica fiber with Ø80 µm cladding on the FPC020, which has a loop diameter of 18 mm.

Click for Details
Figure 4.2  Poincaré sphere showing the polarization rotation from a three paddle polarization controller.

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Figure 4.1  Forces produced by the fiber controller paddle

Thorlabs Lab Facts: Using Fiber Paddles to Manipulate Polarization

We present laboratory measurements of the influence on the output polarization state from a fiber due to rotation and twist forces from the fiber polarization controller (FPC). This controller utilizes the effects of stress-induced birefringence to create changes in the polarization of light traveling through a fiber under stress. The stress can be caused either through twisting or rotating [1], as shown in Figure 4.1. It was found that by using the appropriate number of loops on each paddle that the stress-induced birefringence can be adjusted continuously. This then allows for any arbitrary input polarization state to be rotated into any desired output polarization state. We detail the procedures necessary to achieve a desired output polarization, and plot the change in the polarization on a Poincaré sphere to illustrate the steps necessary in reaching a desired polarization state.

For our experiment, we used the previous-generation S1FC1310 Fabry-Perot Benchtop Laser (1310 nm) as the light source and coupled it into a SMF-28-J9 Ø900 µm tight-buffer fiber. The fiber was mounted through a FPC030 Fiber Polarization Controller, and the output was collimated into a free-space beam with a F220FC-C fiber collimator. From here the beam was measured, either directly by a polarimeter or through an analyzer assembly consisting of a WPQ05M-1310 λ/4 wave plate, a LPNIR100 linear polarizer, and a PM100D power meter.

Figure 4.2 summarizes the measured results for manipulating the polarization of light in a fiber as a function of rotation and twist forces and is shown on the Poincaré sphere. The colored lines represent one of the three paddles of the FPC030 and correspond to the colored numbers of Figure 4.1. To produce quarter-wave plate behavior, the fiber needed to be looped around a paddle two times, and for half-wave plate behavior it was 3 times. For the results presented in Figure 4.2, we used the FPC030 FPC in a 2-3-2 loop configuration. As shown in Figure 4.2, starting at any arbitrary polarization state, it is possible to achieve any desired polarization state through rotating each paddle through a number of iterations. This manipulation of the polarization by the FPC does not produce intrinsic loss nor back reflections; instead stress-induced birefringence is utilized as a mechanism for rotating the polarization of light in fiber. Data is presented for each of the paddles of the FPC and the polarization changes due to these are mapped out on Poincaré spheres. For details on the experimental setup employed and the results obtained, please click here.

[1] R. Ulrich, A. Simon, “Polarization optics of twisted single-mode fibers” Appl. Opt. 18, 2241-2251 (1979).

Insights into Polarization Conventions

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• Labels Used to Identify Perpendicular and Parallel Components

Click here for more insights into lab practices and equipment.

Labels Used to Identify Perpendicular and Parallel Components

When polarized light is incident on a surface, it is often described in terms of perpendicular and parallel components. These are orthogonal to each other and the direction in which the light is propagating (Figure 190A).

Labels and symbols applied to the perpendicular and parallel components can make it difficult to determine which is which. Table 190B identifies, for a variety of different sets, which label refers to the perpendicular component and which to the parallel.

The perpendicular and parallel directions are referenced to the plane of incidence, which is illustrated in Figure 190A for a beam reflecting from a surface. Together, the incident ray and the surface normal define the plane of incidence, and the incident and reflected rays are both contained in this plane. The perpendicular direction is normal to the plane of incidence, and the parallel direction is in the plane of incidence.

The electric fields of the perpendicular and parallel components oscillate in planes that are orthogonal to one another. The electric field of the perpendicular component oscillates in a plane perpendicular to the plane of incidence, while the electric field of the parallel component oscillated in the plane of incidence. The polarization of the light beam is the vector sum of the perpendicular and parallel components.

Normally Incident Light
Since a plane of incidence cannot be defined for normally incident light, this approach cannot be used to unambiguously define perpendicular and parallel components of light. There is limited need to make the distinction, since under conditions of normal incidence the reflectivity is the same for all components of light.

Date of Last Edit: Mar. 5, 2020