We demonstrate electrically and mechanically induced long period gratings (LPGs) in a photonic crystal fiber (PCF) filled with a high-index liquid crystal. The presence of the liquid crystal changes the guiding properties of the fiber from an index guiding fiber to a photonic bandgap guiding fiber - a so called liquid crystal photonic bandgap (LCPBG) fiber. Both the strength and resonance wavelength of the gratings are highly tunable. By adjusting the amplitude of the applied electric field, the grating strength can be tuned and by changing the temperature, the resonance wavelength can be tuned as well. Numerical calculations of the higher order modes of the fiber cladding are presented, allowing the resonance wavelengths to be calculated. A high polarization dependent loss of the induced gratings is also observed.
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"LPFGs have found a variety of applications in optical communications as gain-flattening filters for erbium-doped fiber amplifiers (EDFAs), as wavelength division multiplexing (WDM) systems or as wavelength-selective optical fiber polarizer components  . Tuning of the LPFGs is very attractive since it can offer a form of dynamic spectral control . For these reasons filters based on LPFGs have generated a huge interest for applications in optical fiber sys- tems. "
[Show abstract][Hide abstract] ABSTRACT: A high-efficiency thermal tuning filter based on a long-period fiber grating (LPFG) combined with a low-birefringence liquid crystal (LB LC) cladding layer is presented. Two types of LPFGs were studied and compared: the LPFGs based on a standard telecommunication fiber produced by an electric arc technique, and the LPFGs based on a boron co-doped fiber written by a UV technique. Both types of LPFGs when enhanced with an external LB LC layer exhibit two different temperature sensitivities, which depend on the temperature range of operation. For the LPFGs based on standard telecommunication fiber we can conclude that the presence of the LB LC cladding increases the thermal tuning efficiency by more than one order of magnitude over the value for the LPFGs in air. In the case of the LPFGs based on the boron co-doped fiber we discovered it is possible to obtain either a temperature-independent attenuation band or the attenuation bands with high temperature sensitivities, just by careful choice of the order of the cladding mode and the operating wavelength.
Full-text · Article · Dec 2010 · Bulletin of the Polish Academy of Sciences, Technical Sciences
"The coupling is wavelength dependent, so one can obtain a spectrally selective loss. A relatively long period of the modulation gives the possibility of LPG fabrication not only by ultraviolet (UV) irradiation, as commonly used to write fiber Bragg gratings (FBGs), but also by a variety of other methods such as those based on infrared irradiation , electrical arc discharges   or even mechanical pressure . However, modifications of the refractive index of the LPGs are most often realized by UV exposure or arc discharges. "
[Show abstract][Hide abstract] ABSTRACT: The paper presents for the first time a comparative study of long-period gratings (LPGs) written by point-by-point UV irradiation and by electrical arc discharges. These gratings were inscribed in a highly photosensitive boron co-doped fiber that can be considered as a suitable platform for LPG writing using either technology. The experimental transmission data for the manufactured LPG devices fit well when compared to the simulations we carried out in parallel. As a result of each of these writing processes, we were able to obtain a remarkably good quality of grating. Two reasons could explain the observed small differences between the spectra: a slight mismatch of the period of the gratings and an unintentional tapering of the fiber during the arc-based processes. We also found that the UV irradiation at λ = 248 nm can cause clearly visible damage to the fiber's surface. As a result of the UV writing, a coupling to the asymmetrical cladding modes can take place. Moreover, the gratings written using the two technologies show a very similar refractive index and temperature-sensing properties. The only differences between them can come from a physical deformation of the fiber induced by the electric arc discharges.
Full-text · Article · Jan 2010 · Measurement Science and Technology
"Liquid Crystal (LC) infiltrated Photonic Crystal Fibers (PCFs) have attracted significant interest in the past decade due to their unique optical properties and high sensitivity to thermal and electric field       . Since LCs normally have larger electro-optic effect than other high-index liquids, electrically driven Liquid Crystal filled Photonic BandGap (LCPBG) fiber devices for switching , or as long-period grating  with millisecond response time have been developed. Also, a continuously tunable birefringence controller with phase shift of 60° by using a dualfrequency LCPBG fiber has been proposed . "
[Show abstract][Hide abstract] ABSTRACT: A compact tunable waveplate based on negative dielectric liquid crystal photonic bandgap fibers is presented. The birefringence can be tuned electrically to work as a quarter-wave or a half-wave plate in the wavelength range 1520 nm-1580 nm.