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A Novel Electrically Tunable Long-Period Fiber Grating Using a Liquid Crystal Cladding Layer

100%
Czapla A., Woliński T., Nowinowski-Kruszelnicki E., Bock W.
Acta Physica Polonica A
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2010
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vol. 118
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issue 6
1104-1107
EN
The main aim of the presented work is the integration of a long-period fiber grating and a liquid crystal into a hybrid structure, in order to develop an innovative fiber optic device controlled by an external electric field. The studied long-period fiber grating was fabricated using UV irradiation in a boron co-doped fiber (PS1250/1500, manufactured by Fibercore). As a liquid crystal we used a typical 5CB nematic liquid crystal. The sensing mechanism of the proposed loss filter relies on long-period fiber grating attenuation bands sensitivity to optical properties of the liquid crystal layer. The results obtained show that the long-period fiber grating with a nanosized liquid crystal layer exhibits one order of magnitude higher electrical sensitivity and a lower level of the voltage control than the long-period fiber grating with a micro-sized liquid crystal layer.
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Towards tuning of thermal sensitivity of the long period fiber gratings using a liquid crystal layer

100%
Czapla A., Bock W., Mikulic P., Woliński T.
Bulletin of the Polish Academy of Sciences: Technical Sciences
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2010
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issue 4
3
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Temperature Cross-Sensitivity for Highly Refractive Index Sensitive Nanocoated Long-Period Gratings

88%
Grochowski J., Myśliwiec M., Mikulic P., Bock W., Śmietana M.
Acta Physica Polonica A
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2013
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vol. 124
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issue 3
421-424
EN
There is a demand for highly refractive index sensitive devices simultaneously insensitive to temperature (T) changes. We investigate both T and refractive index sensitivity of long-period gratings coated with 100 nm thin high refractive index (n ≈ 1.9 at λ = 1550 nm) silicon nitride (SiN_{x}) film. The long-period gratings with period of 500 μm were induced in standard Corning SMF28 fibre using electric arc and nanocoated with SiN_{x} by radio frequency plasma enhanced chemical vapour deposition method. As a sensorial effect we investigated resonance shift with temperature variations (from 30 to 70°C) for measurement in deionized water (n_{D} = 1.33) and glycerine (n_{D} = 1.46). In case of measurements in water for resonance observed at λ = 1510 nm, refractive index sensitivity of - 85 nm/RIU and temperature sensitivity of 0.09 nm/C (H_2O) were obtained which gives refractive index-T sensitivity ratio (RI/T) of - 944°C/RIU. Refractive index and T sensitivity of sensor covered with SiN_{x} film increased to - 618 nm/RIU and 0.22 nm/°C, respectively. Thanks to nanocoating deposition, refractive index-T sensitivity ratio was improved by factor of 3. In case of measurements in glycerine significant influence of glycerine's thermo-optic coefficient on obtained results was observed. It is worth noticing that SiN_{x} coating stabilizes sensing behaviour of the sensor.
4
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Spectral Tuning of the Long-Period Fiber Gratings by Using Low Birefringence Liquid Crystals

88%
Czapla A., Bock W., Woliński T., Dąbrowski R., Nowinowski-Kruszelnicki E.
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EN
The work presented in this paper is focused on investigation of the spectral properties of the long-period fiber gratings combined with the liquid crystals, named liquid crystal long-period fiber gratings. The experiments carried out showed that the proposed designs of the liquid crystal long-period fiber gratings can offer very interesting spectral properties and can introduce a new level of sensitivity. In particular, a high-efficiency thermal tuning of the long-period fiber gratings coated with low-birefringence liquid crystal layers could be achieved and gave rise to a fast and wide switching ability of the attenuation bands within their transmission spectrum.
5
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Effect of Wet Etching of Arc-Induced Long-Period Gratings on Their Refractive Index Sensitivity

76%
Myśliwiec M., Grochowski J., Krogulski K., Mikulic P., Bock W., Śmietana M.
Acta Physica Polonica A
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2013
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vol. 124
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issue 3
521-524
EN
The paper presents highly refractive index sensitive operation of long-period gratings enhanced by wet etching of the fiber cladding. Long-period gratings with period of 283 μm were induced in Corning SMF28 optical fibre using electric arc technique. Then etching in hydrofluoric (HF) acid solution has been applied to improve operation of the sensor. Sensitivity improvement effect induced by fiber cladding reduction has been numerically simulated. The developed numerical model enables quick estimation of cladding thickness reduction essential to achieve dispersion turning point. At this point long-period gratings reaches maximum sensitivity to external medium refractive index. Simulation showed that dispersion turning point for this long-period grating is achieved by cladding thickness reduction of 1.7 μm. We obtained good simulation match with experimental results, where approximately the same thickness was etched. The refractive index sensitivity of the long-period grating-based sensor has been improved by factor of 5. Since long-period grating period is limited when using electric arc fabrication method, this physical limitation makes difficult achievement of dispersion turning point and reaching maximum sensitivity of the long-period grating. We show that sensitivity of electric arc induced long-period grating can be significantly improved by post processing techniques such as wet etching.
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