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.
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.
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.
The RP Photonics Buyer's Guide contains 5 suppliers for single-polarization fibers. Among them:
|||V. Ramaswamy et al., “Single polarization optical fibers: exposed cladding technique”, Appl. Phys. Lett. 33, 814 (1978), doi:10.1063/1.90538|
|||T. Hosaka et al., “Low-loss single polarization fibers with asymmetrical strain birefringence”, Electron. Lett. 17, 530 (1981), doi:10.1049/el:19810371|
|||K. Okamoto et al., “Polarization properties of single-polarization fibers”, Opt. Lett. 7 (11), 569 (1982), doi:10.1364/OL.7.000569|
|||T. Katsuyama et al., “Propagation characteristics of single polarization fibers”, Appl. Opt. 22 (11), 1748 (1983), doi:10.1364/AO.22.001748|
|||D. A. Nolan, “Single-polarization fiber with a high extinction ratio”, Opt. Lett. 29 (16), 1855 (2004), doi:10.1364/OL.29.001855|
|||D. T. Walton et al., “Challenges in single-polarization fibers”, Proc. SPIE 5709, 316 (2005), doi:10.1049/el:19810371|
|||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|
|||M.-J. Li et al., “High bandwidth single polarization fiber with elliptical central air hole”, J. Lightwave Technol. 23 (11), 3454 (2005)|
|||J. R. Folkenberg et al., “Broadband single-polarization photonic crystal fiber”, Opt. Lett. 30 (12), 1446 (2005), doi:10.1364/OL.30.001446|
|||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|
|||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|
|||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|