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two polarization modes, applied coherently, can lead to a large power transfer to the horizontal mode, completely changing the wave's net state of polarization. Since that coupling coefficient was unintended and a result of arbitrary stress or bending applied to fiber, the output state of polarization will itself be random, and will vary as those stresses or bends vary; it will also vary with wavelength.
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in such a fiber, or bending in the fiber, will cause a tiny amount of crosstalk from the vertical to the horizontal polarization mode. And since even a short portion of fiber, over which a tiny coupling coefficient may apply, is many thousands of wavelengths long, even that small coupling between the
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state, with a return to the original polarization state after an integer number of beat lengths. Consequently, if visible laser light is launched into the fiber exciting both polarization modes, scattering of propagating light viewed from the side, is observed with a light and dark pattern periodic
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does. Rather, PM fiber maintains the linear polarization of linearly polarized light provided that it is launched into the fiber aligned with one of the fiber's polarization modes. Launching linearly polarized light into the fiber at a different angle will excite both polarization modes, conducting
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Image of the cross section of a polarization-maintaining optical fiber patch cord, taken with an illuminated microscopic viewer called a fiberscope. The two small, eye-like circles are the stress rods and the tiny circle between them is the core. The larger circle surrounding them is the cladding,
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optical fiber just using an ordinary (circularly symmetric) single-mode fiber and twisting it, thus creating internal torsional stress. That causes the phase velocity of right and left hand circular polarizations to significantly differ. Thus the two circular polarizations propagate with little
193:; this may be accomplished using rods of another material included within the cladding. Several different shapes of rod are used, and the resulting fiber is sold under brand names such as "PANDA" and "Bow-tie". ("PANDA" refers to the resemblance of the fiber's cross-section to the face of a
123:. Now consider that there might be a random coupling between the two polarization states over a significant length of such fiber. At point 0 along the fiber, the wave in polarization mode 1 induces an amplitude into mode 2 at some phase. However at point 1/2 L
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of such a fiber (for a particular wavelength) is the distance (typically a few millimeters) over which the wave in one mode will experience an additional delay of one wavelength compared to the other polarization mode. Thus a length
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Several different designs are used to create birefringence in a fiber. The fiber may be geometrically asymmetric or have a refractive index profile which is asymmetric such as the design using an elliptical
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is thus eliminated. Most of the wave's power remains in the original polarization mode, and exits the fiber in that mode's polarization as it is oriented at the fiber end.
237:, since the modulator requires polarized light as input. They are rarely used for long-distance transmission, because PM fiber is expensive and has higher
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it is again out of phase and so on. The possibility of coherent addition of wave amplitudes through crosstalk over distances much larger than L
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in the fiber, so that there are two well defined polarization modes which propagate along the fiber with very distinct phase velocities. The
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In an ordinary (non-polarization-maintaining) fiber, two polarization modes (say vertical and horizontal polarization) have the same nominal
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along the fiber, the same coupling coefficient between the polarization modes induces an amplitude into mode 2 which is now 180 degrees
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used for PM fibers are specially keyed so that the two polarization modes are aligned and exit in a specific orientation.
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the same wave at slightly different phase velocities. At most points along the fiber the net polarization will be an
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65:, exiting the fiber in a specific linear polarization state; there is little or no cross-coupling of optical
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over each beat length, since scattering is preferentially perpendicular to the polarization direction.
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73:. Such fiber is used in special applications where preserving polarization is essential.
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Carter, Adrian; Samson, Bryce (August 2004). "PANDA-style fibers move beyond telecom".
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Polarization-maintaining optical fibers are used in special applications, such as in
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197:, and is also an acronym for "Polarization-maintaining AND Absorption-reducing".)
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61:, if properly launched into the fiber, maintains a linear polarization during
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256:(PER)—the ratio of correctly to incorrectly polarized light, expressed in
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along the fiber the coupling is again in the original phase, but at 3/2 L
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Note that a polarization-maintaining fiber does not polarize light as a
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due to the fiber's circular symmetry. However tiny amounts of random
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272:. Good PM fibers have extinction ratios in excess of 20 dB.
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The output of a PM fiber is typically characterized by its
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Single-mode optical fiber for linearly polarized light
249:, which are widely used in the aerospace industry.
131:with the wave coupled at point zero, leading to
189:permanently induced in the fiber will produce
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343:Specs for the most common type of PM fiber
176:Cross sections of three types of PM fiber.
185:as shown in the diagram. Alternatively,
98:Polarization-maintaining fibers work by
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40:polarization-maintaining optical fiber
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229:for the connection between a source
119:/2 of such fiber is equivalent to a
245:. Another important application is
347:Polarization Crosstalk in PM Fiber
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225:. They are also commonly used in
306: This article incorporates
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102:introducing a systematic linear
319:General Services Administration
1:
254:polarization extinction ratio
69:between the two polarization
268:can be characterized with a
200:It is possible to create a
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205:crosstalk in between them
223:quantum key distribution
149:Optical fiber connectors
202:circularly birefringent
341:Fujikura's PANDA Fiber
314:Federal Standard 1037C
308:public domain material
247:fiber-optic gyroscopes
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161:elliptically polarized
94:Principle of operation
77:Polarization crosstalk
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175:
24:
325:on January 22, 2022.
260:. The quality of PM
191:stress birefringence
215:fiber optic sensing
50:) is a single-mode
227:telecommunications
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56:linearly polarized
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290:Laser Focus World
243:single-mode fiber
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321:. Archived from
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335:External links
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330:MIL-STD-2196
323:the original
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209:Applications
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135:. At point L
133:cancellation
129:out of phase
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36:fiber optics
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30:in diameter.
26:usually 125
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239:attenuation
108:beat length
63:propagation
276:References
262:patchcords
270:PER meter
235:modulator
156:polarizer
54:in which
356:Category
266:pigtails
258:decibels
183:cladding
48:PM fiber
168:Designs
28:microns
233:and a
187:stress
310:from
241:than
231:laser
195:panda
71:modes
67:power
59:light
264:and
221:and
46:or
44:PMF
34:In
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317:.
217:,
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145:b
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125:b
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115:L
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110:L
42:(
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