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Electrically tunable long-period fiber gratings with low-birefringence liquid crystal near the turn-around point

Czapla A., Bock W. J., Woliński T. R., Mikulic P., Dąbrowski R., Nowinowski-Kruszelnicki E.

Opto-Electronics Review

2017

Vol. 25, No. 4

290--295

In this work, an electrically tunable long-period fiber grating (LPFG) coated with liquid crystal layer (LC) is presented. As a LC layer, a prototype low-birefringence 1550A LC mixture was chosen. As a LPFG host, two types of gratings were studied: the LPFGs based on a standard telecommunication fiber, produced by an electric arc technique with a period of 222 µm, and the LPFGs based on a boron co-doped fiber written by a UV technique with a period of 226.8 µm. The relatively short period of these gratings allowed exploiting unique sensing properties of the attenuation bands associated with modes close to the turn-around point. Experiments carried out showed that for the UV-induced LPFG with a LC layer, on the powered state the attenuation band could be offset from the attenuation band measured in the unpowered state by almost130 nm. When the arc-induced LPFG was coated with the LC, the depth of the attenuation band could be efficiently controlled by applying an external E-field. Additionally, all experimental results obtained in this work were supported by the theoretical analysis based on a model developed with Optigrating v.4.2 software.

Towards tuning of thermal sensitivity of the long period fiber gratings using a liquid crystal layer

Czapla A., Bock W., Mikulic P., Woliński T.

Bulletin of the Polish Academy of Sciences. Technical Sciences

2010

Vol. 58, nr 4

503-508

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.

Transmission analysis of long-period fiber grating with trapezoid index modulation

Wang G. D., Liu C. X., Sun D. M., Guo W. B., Chen W. Y.

Optica Applicata

2006

Vol. 36, nr 1

69-78

The long-period fiber grating (LPG) with trapezoid index modulation is presented as a novel grating. The influence of the difference between the top width and the bottom width (simplified to d in the following text) of the trapezoid index modulation on the transmission characteristics is analyzed. Calculated results show that the resonance location displaces to the long wavelength when the d increases. Compared with the long-period fiber grating with rectangle index modulation, the advantage of this novel grating is that it needs a smaller refractive index change. When d is zero, this model can be used to simulate the LPG with a rectangular index modulation, and the theoretical results are in good agreement with the experimental ones.