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Manual Fiber Polarization Controllers
Empty Controller with Ø1.06" Loops
Preloaded with ClearCurve Fiber, FC/PC Connectors
Empty Controller with Ø2.2" Loops
Empty Controller with Ø0.71" Loops
Full Polarization Control with Paddles
The animation above shows an ideal case. The fractional retardance of each paddle depends upon many factors, including the wavelength, the number of fiber loops, and the fiber type. For more details, please see the Operation tab.
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 the animation to the right 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 any single mode fiber or fiber patch cable with a Ø900 µm jacket. They 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. For fibers with higher bend loss, we recommend using the FPC560, which features the largest spools and therefore the least bending.
Thorlabs also offers a compact CPC900 In-Line Polarization Controller. This controller creates a single continously variable wave plate similar to a Soleil-Babinet compensator, which allows polarization control over the full Poincaré sphere.
3-Paddle Fiber Polarization Controllers
Miniature 2-Paddle Fiber Polarization Controllers
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 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 quarter-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).
Three-Paddle Polarization Controllers
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Figure 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 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 and 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: 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 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
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Figure 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 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.
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Figure 2: Poincaré sphere showing the polarization rotation from a three paddle polarization controller.
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Figure 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 , as shown in Figure 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 S1FC1310 Fabry-Perot Benchtop Laser (1310 nm) as the light source and couple it into a 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 fiber collimator. From here the beam was measured, either directly by a polarimeter or through an analyzer assembly consisting of a λ/4 wave plate, a linear polarizer, and a power meter.
Figure 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 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 2, we used the FPC030 FPC in a 2-3-2 loop configuration. As shown in Figure 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.
 R. Ulrich, A. Simon, “Polarization optics of twisted single-mode fibers” Appl. Opt. 18, 2241-2251 (1979).
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A 3-paddle controller mounted on an optical table utilizing the 1/4"-20 (M6) screw slots.
Thorlabs' 3-Paddle Fiber Polarization Controllers use stress-induced birefringence to create independent wave plates to alter the polarization of the transmitted light in single mode fiber. The three fractional wave plates are created by looping the fiber around three independent spools (see the Operation tab for details). For the polarization controllers preloaded with fiber, the paddles are configured to approximate a quarter-wave, half-wave, and quarter-wave plate when used at the design wavelength (see the table to the right).
Four of the fiber polarization controllers (FPC031, FPC032, FPC561, and FPC562) come preloaded with fiber, while the other two (FPC030 and FPC560) are sold empty to allow customers to insert any single mode fiber or fiber patch cable with a Ø900 µm jacket. The fibers in the preloaded controllers can also be removed and replaced by the user in the event that the controllers are needed for a new application in the future. For fibers with higher bend loss, we recommend using the version with the largest spools (FPC560), thereby causing the least amount of bending.
Knobs on the spool covers allow them to be easily loosened in order to load or unload a fiber. The side clamps can be opened by loosening the Phillips head screws, and the top of the clamp can be completely removed if needed to load connectorized fibers. Two clearance slots in the base accept 1/4"-20 or M6 cap screws for mounting the controller on an optical table. These slots are placed 8.00" (203.2 mm) apart on the small paddle controllers and 12" (304.8 mm) apart on the large paddle controllers. For more mounting options, all 3-paddle controllers have three slots along their base. Two slots at either end of the base accept 1/4"-20 or M6 cap screws. A centered slot accepts 4-40 or M3 cap screws (see the image to right). These slots allow for mounting options to both metric and imperial optical tables.
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2-Paddle Controller Mounted on an Optical Table
Thorlabs' Miniature 2-Paddle Fiber Polarization Controllers use stress-induced birefringence to create two independent wave plates to alter the polarization of the transmitted light in single mode fiber. The two fractional wave plates are created by looping the fiber around two independent spools (see the Operation tab for details). For the polarization controllers preloaded with fiber, the paddles are configured to approximate two quarter-wave plates when used at the design wavelength (see the table to the right).
Five of the fiber polarization controllers (FPC021, FPC022, FPC023, FPC024, and FPC025) come preloaded with fiber, while the FPC020 polarization controller is sold empty to allow customers to insert any single mode fiber or fiber patch cable with a Ø900 µm jacket. The fibers in the preloaded controllers can also be removed and replaced by the user in the event that the controllers are needed for a new application in the future.
The fiber is secured around two removable spools with a lip and two clamps at the ends of the controller. The clamps and spools are held in place by 4-40 cap screws, compatible with an 3/32" hex key or balldriver. Two clearance slots for 1/4"-20 or M6 cap screws are positioned 1" (25.4 mm) apart on the base for mounting the controller to an optical table.