THORLABS FPC020 User manual

Manual Fiber
Polarization Controllers
User Guide

Manual Fiber Polarization Controllers
Table of Contents
Chapter 1Warning Symbol Definitions.....................................1
Chapter 2General Description...................................................2
2.1.3‐PaddleFiberPolarizationControllers....................3
2.2.Miniature2‐PaddleFiberPolarizationControllers....6
2.3.RecommendedNumberofLoops.............................8
Chapter 3Setup .........................................................................10
3.1.LoadingtheFiber...................................................10
3.1.1.3-Paddle Fiber Polarization Controllers.............................10
3.1.2.Miniature 2-Paddle Fiber Polarization Controllers.............11
3.2.RemovingtheFiber(AllModels)............................11
Chapter 4Specifications...........................................................12
4.1.3‐PaddlePolarizationControllers...........................12
4.2.Miniature2‐PaddlePolarizationControllers..........14
Chapter 5Regulatory ................................................................16
Chapter 6Thorlabs Worldwide Contacts................................17

Manual Fiber Polarization Controllers Chapter 1: Warning Symbol Definitions
Rev H, September 11, 2018 Page 1
Chapter 1 Warning Symbol Definitions
Below is a list of warning symbols you may encounter in this manual or on
your device.
Symbol Description
Direct Current
Alternating Current
Both Direct and Alternating Current
Earth Ground Terminal
Protective Conductor Terminal
Frame or Chassis Terminal
Equipotentiality
On (Supply)
Off (Supply)
In Position of a Bi-Stable Push Control
Out Position of a Bi-Stable Push Control
Caution: Risk of Electric Shock
Caution: Hot Surface
Caution: Risk of Danger
Warning: Laser Radiation
Caution: Spinning Blades May Cause Harm

Manual Fiber Polarization Controllers Chapter 2: General Description
Page 2 1167-D02
Chapter 2 General Description
These manual polarization controllers utilize stress-induced birefringence to
alter the polarization in single mode fiber that is looped around two or three
independent spools to create two or three 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 an 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) is used. The retardance of each paddle may be
estimated from the following equation:
󰇛󰇜2

󰇛󰇜

Here, φis the retardance, ais a constant (0.133 for silica fiber), Nis the
number of loops, dis the fiber cladding diameter, λis 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 Nfor Ø900 µm
jacketed fiber).
The FPC020, FPC030, and FPC560 are empty controllers in which the user
can install a fiber of their choice. The rest of our fiber polarization controllers
have fiber pre-installed to optimize the polarization control at common
wavelengths. These controllers can also be customized using the information
provided in Sections 2.1 through 0.

Manual Fiber Polarization Controllers Chapter 2: General Description
Rev H, September 11, 2018 Page 3
2.1. 3-Paddle Fiber Polarization Controllers
A 3-paddle polarization controller combines a quarter-wave plate, half-wave
plate, and quarter-wave plate in series to transform an arbitrary polarization
state into any other 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.
Therefore, adjusting each of the three paddles (fiber retarders) allows
complete control of the output polarization state over a broad range of
wavelengths from 300 to 2100 nm. The 3-paddle polarization controllers are
available with paddles that support either Ø27 mm loops or Ø56 mm loops.
Using FPC030 as an example for the controllers with a Ø27 mm loop
diameter, a plot of calcuated retardation per paddle versus wavelength is
shown in Figure 1 for a fiber with a cladding diameter of 80 μm. For fiber with
a cladding diameter of 125 μm, the retardation per paddle versus wavelength
is shown in Figure 2.

Manual Fiber Polarization Controllers Chapter 2: General Description
Page 4 1167-D02
Figure 1
Figure 2

Manual Fiber Polarization Controllers Chapter 2: General Description
Rev H, September 11, 2018 Page 5
Figure 3 and Figure 4 show the results for Ø80 µm and Ø125 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.
Figure 3
Figure 4

Manual Fiber Polarization Controllers Chapter 2: General Description
Page 6 1167-D02
2.2. Miniature 2-Paddle Fiber Polarization Controllers
The 2-paddle polarization controllers use two quarter-wave plates to transform
an arbitrary polarization state into any other polarization state. In this
configuration, however, the control of the polarization will be coupled between
the two paddles. These controllers allow complete control of the output
polarization state over a broad range of wavelengths (300 to 2100 nm).
The retardation per paddle is a function of loop number and the cladding
diameter of the fiber if the loop diameter is fixed. The retardation, in radians,
is plotted for 1, 2, 3, and 4 loops per paddle for a fiber with cladding diameters
of 80 µm and 125 μm (Figure 5 and Figure 6). Due to its small size, the
FPC020 cannot accommodate more than 4 loops per paddle.

Manual Fiber Polarization Controllers Chapter 2: General Description
Rev H, September 11, 2018 Page 7
Figure 5
Figure 6

Manual Fiber Polarization Controllers Chapter 2: General Description
Page 8 1167-D02
2.3. Recommended Number of Loops
The retardation of multi-order (including zero order) quarter-wave plate is
given by the following equation:
󰇛2  1󰇜
2
where mis an integer. Similarly, the retardation of multi-order (including zero
order) half-wave plate is given by:
󰇛2  1󰇜
See the table below for several solutions to the equations
Order m
Quarter-Wave
Plate Retardation
Half-Wave Plate
Retardation
Zero 0 
21.57   3.14
1st 1 3
24.71 3  9.42
2nd 2 5
27.85 5  15.71
3rd 3 7
2 11.00 7  21.99
4th 4 9
2 14.14 9  28.27
5th 5 11
2 17.28 11  35.56
The retardation of each paddle should be close to any number above. The
paddle rotation sensitivity should also be taken into consideration when
determining the number of fiber loops. In creasing the number of loops
increases the sensitivity to rotation. One loop is usually too insensitive for most
applications and is rarely used.