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Mahakud R, Kumar J, Kumar S, Prakash O, Dixit SK, Nakhe SV. Fabrication and analysis of enhanced thermal stability and high-sensitivity turnaround point long-period fiber grating. APPLIED OPTICS 2022; 61:1068-1075. [PMID: 35201080 DOI: 10.1364/ao.447566] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/03/2021] [Accepted: 01/07/2022] [Indexed: 06/14/2023]
Abstract
This paper presents a what we believe is a novel method to fabricate turnaround point long-period gratings (TAP-LPGs) possessing enhanced thermal stability and high sensitivity. It is shown by analysis and by experiment that LPG resonance in photosensitive fibers can be controlled partially by UV fluence and thermal annealing. TAP-LPGs with enhanced thermal stability were fabricated by following three steps: (I) finding grating period versus writing UV fluence for TAP operation; (II) writing gratings at a relatively higher period with higher fluence, in which case the resonance is out of phase; (III) controlled annealing so that the postannealed LPG operates at/near TAP. The thermal stability is enhanced. The average temperature sensitivity of dual peak resonance measured for a typical TAP-LPG in the temperature interval of 70°C-240°C is about 2.3 nm/°C. This study will be useful for the development of high temperature TAP-LPG sensors.
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Høvik J, Yadav M, Wook Noh J, Aksnes A. Waveguide asymmetric long-period grating couplers as refractive index sensors. OPTICS EXPRESS 2020; 28:23936-23949. [PMID: 32752382 DOI: 10.1364/oe.397561] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/13/2020] [Accepted: 07/04/2020] [Indexed: 06/11/2023]
Abstract
A highly sensitive integrated photonic transducer is designed by utilizing asymmetric long-period gratings on a silicon waveguide. These gratings are formed by periodic perturbation of the waveguide width, leading to coupling between the fundamental mode and the 1st order asymmetric leaky mode. The coupled modes are studied via finite-element and finite-difference time-domain methods. Only a single fabrication step is required to realize this novel design. The device is utilized as a refractive index sensor in liquid, yielding a sensitivity of 5078 nm/RIU. The design is a unique combination of being highly sensitive, easily fabricated and highly compact.
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Viveiros D, de Almeida JMMM, Coelho L, Vasconcelos H, Maia JM, Amorim VA, Jorge PAS, Marques PVS. Temperature Stability and Spectral Tuning of Long Period Fiber Gratings Fabricated by Femtosecond Laser Direct Writing. SENSORS 2020; 20:s20143898. [PMID: 32668738 PMCID: PMC7412330 DOI: 10.3390/s20143898] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/19/2020] [Revised: 07/08/2020] [Accepted: 07/09/2020] [Indexed: 11/16/2022]
Abstract
Long period fiber gratings (LPFGs) were fabricated in a standard single mode fiber (SMF-28e) through femtosecond (fs) laser direct writing. LPFGs with longer and shorter periods were fabricated, which allows coupling from the fundamental core mode to lower and higher order asymmetric cladding modes (LP1,6 and LP1,12, respectively). For the grating periods of 182.7 and 192.5 µm, it was verified that the LP1,12 mode exhibits a TAP at approximately 1380 and 1448 nm in air and water, respectively. Characterization of the LPFGs subjected to high-temperature thermal treatment was accomplished. Fine-tuning of the resonance band’s position and thermal stability up to 600 °C was shown. The temperature sensitivity was characterized for the gratings with different periods and for different temperature ranges. A maximum sensitivity of −180.73, and 179.29 pm/°C was obtained for the two resonances of the 182.7 µm TAP LPFG, in the range between 250 and 600 °C.
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Affiliation(s)
- Duarte Viveiros
- Center for Applied Photonics, INESC TEC, 4200-465 Porto, Portugal; (J.M.M.M.d.A.); (L.C.); (H.V.); (J.M.M.); (V.A.A.); (P.A.S.J.); (P.V.S.M.)
- Department of Physics and Astronomy, Faculty of Science, University of Porto, 4169-007 Porto, Portugal
- Correspondence: ; Tel.: +351-22-040-2301
| | - José M. M. M. de Almeida
- Center for Applied Photonics, INESC TEC, 4200-465 Porto, Portugal; (J.M.M.M.d.A.); (L.C.); (H.V.); (J.M.M.); (V.A.A.); (P.A.S.J.); (P.V.S.M.)
- Department of Physics, University of Trás-os-Montes e Alto Douro, 5001-801 Vila Real, Portugal
| | - Luís Coelho
- Center for Applied Photonics, INESC TEC, 4200-465 Porto, Portugal; (J.M.M.M.d.A.); (L.C.); (H.V.); (J.M.M.); (V.A.A.); (P.A.S.J.); (P.V.S.M.)
| | - Helena Vasconcelos
- Center for Applied Photonics, INESC TEC, 4200-465 Porto, Portugal; (J.M.M.M.d.A.); (L.C.); (H.V.); (J.M.M.); (V.A.A.); (P.A.S.J.); (P.V.S.M.)
- Department of Physics, University of Trás-os-Montes e Alto Douro, 5001-801 Vila Real, Portugal
| | - João M. Maia
- Center for Applied Photonics, INESC TEC, 4200-465 Porto, Portugal; (J.M.M.M.d.A.); (L.C.); (H.V.); (J.M.M.); (V.A.A.); (P.A.S.J.); (P.V.S.M.)
- Department of Physics and Astronomy, Faculty of Science, University of Porto, 4169-007 Porto, Portugal
| | - Vítor A. Amorim
- Center for Applied Photonics, INESC TEC, 4200-465 Porto, Portugal; (J.M.M.M.d.A.); (L.C.); (H.V.); (J.M.M.); (V.A.A.); (P.A.S.J.); (P.V.S.M.)
- Department of Physics and Astronomy, Faculty of Science, University of Porto, 4169-007 Porto, Portugal
| | - Pedro A. S. Jorge
- Center for Applied Photonics, INESC TEC, 4200-465 Porto, Portugal; (J.M.M.M.d.A.); (L.C.); (H.V.); (J.M.M.); (V.A.A.); (P.A.S.J.); (P.V.S.M.)
- Department of Physics and Astronomy, Faculty of Science, University of Porto, 4169-007 Porto, Portugal
| | - Paulo V. S. Marques
- Center for Applied Photonics, INESC TEC, 4200-465 Porto, Portugal; (J.M.M.M.d.A.); (L.C.); (H.V.); (J.M.M.); (V.A.A.); (P.A.S.J.); (P.V.S.M.)
- Department of Physics and Astronomy, Faculty of Science, University of Porto, 4169-007 Porto, Portugal
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Trono C, Valeri F, Baldini F. Discretized superimposed optical fiber long-period gratings. OPTICS LETTERS 2020; 45:807-810. [PMID: 32058475 DOI: 10.1364/ol.382325] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/11/2019] [Accepted: 12/15/2019] [Indexed: 06/10/2023]
Abstract
A novel technique, to the best of our knowledge, for the inscription of superimposed long-period gratings with arbitrary grating pitches is proposed and experimentally validated. The technique is based on the discretization of an ideal continuous sinusoidal refractive index (RI) pattern with a step function. The RI variation is induced by means of the irradiation of a photosensitive fiber with a 248 nm UV laser beam. The nonlinear relation between the induced RI change and the UV fluence was experimentally derived. Two superimposed long-period grating (LPGs) with different grating pitches have been realized with the discretization technique; the transmission spectrum was compared with that of two superimposed LPGs obtained with the traditional square wave RI modulation. The validity of the proposed technique was demonstrated by the better spectral characteristics of the discretized superimposed LPGs.
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Li Z, Liu S, Bai Z, Fu C, Zhang Y, Sun Z, Liu X, Wang Y. Residual-stress-induced helical long period fiber gratings for sensing applications. OPTICS EXPRESS 2018; 26:24114-24123. [PMID: 30184903 DOI: 10.1364/oe.26.024114] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/12/2018] [Accepted: 08/27/2018] [Indexed: 06/08/2023]
Abstract
We demonstrate a high-efficiency grating fabrication system, which can be used to inscribe a high-quality helical long period fiber grating (HLPFG) on single-mode fiber by means of hydrogen-oxygen flame. Such the HLPFG can be produced in enormous quantities with a uniform grating parameters and good reproducibility of grating inscription. Possible mechanisms for refractive index modulation in the HLPFG can be attributed to residual stress concentration by solidifying the periodic twisting stress under a fused status of optical fiber. Moreover, the HLPFG exhibits an excellence performance of high temperature sensing with a high sensitivity of ~132.8 pm/°C and a measuring range from room temperature to 900 °C. Comparing to the traditional LPFG fabricated by CO2 laser or arc discharge technique, the HLPFG has a low the bending and tensile strain sensitivity of 1.94 nm/(1/m) and 1.41 pm/με, respectively. So the proposed HLPFG could have a great potential in special applications as optical high-temperature sensors.
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Manufacturing and Spectral Features of Different Types of Long Period Fiber Gratings: Phase-Shifted, Turn-Around Point, Internally Tilted, and Pseudo-Random. FIBERS 2017. [DOI: 10.3390/fib5030029] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The manufacturing and spectral features of different types of long period fiber gratings (LPFGs), ranging from phase-shifted, turn-around point, and internally tilted gratings, to pseudo-random gratings, are described and discussed in detail. LPFGs were manufactured on boron-germanium co-doped photosensitive optical fibers with the point-by-point technique using an excimer KrF laser operating at 248 nm. The developed experimental setup to manufacture high-quality LPFGs was designed to totally customize any type of gratings with the possibility of setting different parameters, such as the grating period (or pitch), the number of grating planes, the number of laser shots for each plane, etc. Some important spectral features of the LPFGs’ spectra were taken into account. This allows realizing homemade devices useful in several fiber-based applications, such as optical filtering, coupling systems, random lasers, physical and chemical sensing, and biosensing.
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Shen F, Zhou K, Gordon N, Zhang L, Shu X. Compact eccentric long period grating with improved sensitivity in low refractive index region. OPTICS EXPRESS 2017; 25:15729-15736. [PMID: 28789085 DOI: 10.1364/oe.25.015729] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/18/2017] [Accepted: 06/19/2017] [Indexed: 06/07/2023]
Abstract
We demonstrate a compact eccentric long period grating with enhanced sensitivity in low refractive index region. With a period designed at 15 µm for coupling light to high order cladding modes, the grating is more sensitive to surrounding refractive index in low refractive index region. The intrinsically low coupling coefficients for those high order cladding modes are significantly improved with the eccentric localized inscription induced by the femtosecond laser. The fabricated grating is compact with a length of 4.05 mm, and exhibits an average sensitivity of ~505 nm/RIU in low refractive index region (1.3328-1.3544). The proposed principle can also work in other refractive index region with a proper choice of the resonant cladding modes.
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Partridge M, James SW, Barrington J, Tatam RP. Overwrite fabrication and tuning of long period gratings. OPTICS EXPRESS 2016; 24:22345-22356. [PMID: 27828306 DOI: 10.1364/oe.24.022345] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
The central wavelengths of the resonance bands are critical aspect of the performance of long period gratings (LPGs) as sensors, particularly for devices designed to operate near the phase matching turning point (PMTP), where the sensitivity to measurements can vary rapidly. Generally, LPGs are characterized by their period, but the amplitude of the amplitude of the index modulation is also an important factor in determining the wavelengths of the resonance bands. Variations in fabrication between LPG sensors can increase or decrease the sensitivity of the LPG to strain, temperature or surrounding refractive index. Here, the technique of overwritten UV laser fabrication is demonstrated. It is shown that, on repeated overwriting, the resonance bands of an LPG exhibit significant wavelength shift, which can be monitored and which can be used to tune the resonance bands to the desired wavelengths. This technique is applied to periods in the range 100 to 200 µm, showing the cycle-to-cycle evolution of the resonance bands near the PMTPs of a number of cladding modes. The use of online monitoring is shown to reduce the resonance band sensor-to-sensor central wavelength variation from 10 nm to 3 nm.
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