Definition: optical fibers which transmit only light with a certain polarization
Single-polarization fibers are specialty optical fibers which can transmit light with a certain linear polarization direction, whereas light with the other polarization direction is either not guided or at least experiences strong optical losses. Such fibers should not be confused with polarization-maintaining fibers, which guide light with any polarization state, but can preserve a linear polarization state when the polarization direction is properly aligned with the birefringence axis.
In many cases, single-polarization guidance occurs in only a limited wavelength range. Outside that range, both polarization directions or no light at all may be guided. Also, some fibers exhibit a limited extinction ratio.
Operation Principles
Different principles of operation can be utilized for single-polarization fibers. A common approach is the use an elliptical core, which introduces strong birefringence and also a polarization dependence of a cut-off wavelength, so that only light with one polarization direction is guided, whereas the fiber is a leaky waveguide for the other polarization. Alternatively or in addition, the rotational symmetry may be broken by structures around the fiber core, such as air holes on two sides (side-hole fibers, hole-assisted fibers). Another class of methods uses built-in mechanical stress. In any case, the birefringence serves to reduce the coupling of the two polarization directions.
There are also various types of single-polarization photonic crystal fibers. Here, a suitable arrangement of microscopic air holes again breaks the rotational symmetry and introduces polarization-dependent guiding properties.
Applications
Used in fiber lasers, single-polarization fibers guarantee polarized laser emission. There are also various uses in the field of fiber-optic sensors, where polarization effects in standard fibers can lead to unwanted effects.
Bibliography
[1]
V. Ramaswamy et al., “Single polarization optical fibers: exposed cladding technique”, Appl. Phys. Lett. 33, 814 (1978), doi:10.1063/1.90538
[2]
T. Hosaka et al., “Low-loss single polarization fibers with asymmetrical strain birefringence”, Electron. Lett. 17, 530 (1981), doi:10.1049/el:19810371
[3]
K. Okamoto et al., “Polarization properties of single-polarization fibers”, Opt. Lett. 7 (11), 569 (1982), doi:10.1364/OL.7.000569
[4]
T. Katsuyama et al., “Propagation characteristics of single polarization fibers”, Appl. Opt. 22 (11), 1748 (1983), doi:10.1364/AO.22.001748
[5]
D. A. Nolan, “Single-polarization fiber with a high extinction ratio”, Opt. Lett. 29 (16), 1855 (2004), doi:10.1364/OL.29.001855
[6]
D. T. Walton et al., “Challenges in single-polarization fibers”, Proc. SPIE 5709, 316 (2005), doi:10.1049/el:19810371
[7]
T. Schreiber et al., “Stress-induced single-polarization single-transverse mode photonic crystal fiber with low nonlinearity”, Opt. Express 13 (19), 7621 (2005), doi:10.1364/OPEX.13.007621
[8]
M.-J. Li et al., “High bandwidth single polarization fiber with elliptical central air hole”, J. Lightwave Technol. 23 (11), 3454 (2005), doi:10.1109/JLT.2005.855856
[9]
J. R. Folkenberg et al., “Broadband single-polarization photonic crystal fiber”, Opt. Lett. 30 (12), 1446 (2005), doi:10.1364/OL.30.001446
[10]
X. Chen et al., “Wide band single polarization and polarization maintaining fibers using stress rods and air holes”, Opt. Express 16 (16), 12060 (2008), doi:10.1364/OE.16.012060
[11]
K. K. Y. Lee et al., “Design strategies and rigorous conditions for single-polarization single-mode waveguides”, Opt. Express 16 (19), 15170 (2008), doi:10.1364/OE.16.015170
[12]
M. Chen and Y. Zhang, “Improved design of polarization-maintaining photonic crystal fibers”, Opt. Lett. 33 (21), 2542 (2008), doi:10.1364/OL.33.002542
