Sensitivity Enhancement of Turn-Around-Point Long Period Gratings By Tuning Initial Coupling Condition
TL;DR: In this paper, a TAP-LPG with similar to 3dB attenuation at resonance was used to attain a sensitivity of similar to 1850 nm/RIU with similar 3 dB attenuation.
Abstract: Long period grating (LPG) at turn-around-point (TAP) has been studied with a view to enumerate the dependence of sensitivity of a particular resonant mode at the TAP to surrounding refractive index on the initial coupling strength. It has been shown theoretically and also validated experimentally that sensitivity can be enhanced significantly by tailoring the coupling strength of the cladding mode at the resonant wavelength near the TAP. Sensitivity characteristics have been studied for surrounding refractive index in the range 1.335-1.360, which is of interest in the field of biosensors, where the sensitivity of conventional LPGs is relatively small. We could attain a sensitivity of similar to 1850 nm/RIU using a TAP-LPG with similar to 3-dB attenuation at resonance.
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TL;DR: The combination of these parameters results in an improved sensitivity of 8734 nm/refractive index unit (RIU) for the LP0,3 mode in the 1400-1650 wavelength range, similar to that obtained with thin-film coated LPFGs, which permits to avoid the coating deposition step.
Abstract: This work presents a refractive index sensor based on a long period fiber grating (LPFG) made in a reduced cladding fiber whose low order cladding modes have the turning point at large wavelengths. The combination of these parameters results in an improved sensitivity of 8734 nm/refractive index unit (RIU) for the LP0,3 mode in the 1400-1650 wavelength range. This value is similar to that obtained with thin-film coated LPFGs, which permits to avoid the coating deposition step. The numerical simulations are in agreement with the experimental results.
62 citations
TL;DR: In this paper, the authors developed gas-sensitive coatings for both single-mode and multi-mode optical fibers through the application of polymer/nanocrystalline metal-organic frameworks (MOFs) composites as methane sensors for monitoring natural gas infrastructure.
Abstract: Functional polymer coating integrated with optical fiber is an intriguing approach to develop low-cost point and distributed fiber sensors for large-scale applications. This paper presents the development of gas-sensitive coatings for both single-mode and multi-mode optical fibers through the application of polymer/nanocrystalline metal-organic frameworks (MOFs) composites as methane sensors for monitoring natural gas infrastructure. Silicone polymers based on PDMS with optimized optical and mechanical properties were developed as host materials for the well-known metal organic framework ZIF-8. Integration of ZIF-8 nanocrystals within the PDMS polymer modified the physical properties of the material and led to an enhancement of the CH4 solubility and permeability of the resulting film. The refractive indices, viscosities, and mechanical properties of the ZIF-8 functionalized polymers were optimized by adjusting the ZIF-8/polymer weight ratio and subsequently used as the fiber coating. Both multi-mode and single-mode optical fibers coated with the MOF-functionalized polymers showed scaled changes in transmitted power upon exposure to various concentration of CH4 in a N2 carrier gas. The variations in transmitted power through the fiber were the result of changes in evanescent wave interactions with the sensor coating due to shifts in the polymer cladding refractive index upon CH4 sorption. A methane detection limit of 1 % in nitrogen was achieved using both multimode fiber and D-shaped single mode fibers. Overall, our paper presents a low-cost approach to perform point and distributed sensing for CH4 through an innovative method of functional polymer material integration on optical fiber sensor platforms.
39 citations
TL;DR: In this paper, an important member of the optical fiber sensor family, long period fiber gratings (LPFGs) have attracted increased attention due to their outstanding characteristics, and the LPFG is a transmission medium.
Abstract: As an important member of the optical fiber sensor family, long period fiber gratings (LPFG) have attracted increased attention due to their outstanding characteristics. The LPFG is a transmission ...
34 citations
Cites background from "Sensitivity Enhancement of Turn-Aro..."
...In addition, Biswas et al.([33]) and Villar et al....
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...In addition, Biswas et al.[33] and Villar et al.[34] etched the fiber cladding to increase the sensitivity of the sensor....
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...[60,61] Biswas et al.[62] used the strongly over-coupled resonant modes of LPFG to characterize the adulteration of olive oil....
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TL;DR: The diameter of long-period fiber gratings fabricated in optical fibers with a low cutoff wavelength was reduced by hydrofluoric acid etching, enhancing the sensitivity to refractive index by more than a factor of 3, demonstrating the ability of this method to enhance the sensitivity of thin-film-coated LPFG chemical sensors.
Abstract: The diameter of long-period fiber gratings (LPFGs) fabricated in optical fibers with a low cutoff wavelength was be reduced by hydrofluoric acid etching, enhancing the sensitivity to refractive index by more than a factor of 3, to 2611 nm/refractive index unit in the range from 1.333 to 1.4278. The grating period selected for the LPFGs allowed access to the dispersion turning point at wavelengths close to the visible range of the optical spectrum, where optical equipment is less expensive. As an example of an application, a pH sensor based on the deposition of a polymeric coating was analyzed in two situations: with an LPFG without diameter reduction and with an LPFG with diameter reduction. Again, a sensitivity increase of a factor of near 3 was obtained, demonstrating the ability of this method to enhance the sensitivity of thin-film-coated LPFG chemical sensors.
23 citations
Cites background or methods from "Sensitivity Enhancement of Turn-Aro..."
...However, as was stated in the i troduction, some authors defin sensiti ity as the ratio between two parameters: the increase or decrease of the separation between the left and the right band in the DTP region, and the surrounding refractive index variation [16,17]....
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...LPFGs in the telecommunications spectral range without cladding reduction (1309 nm/RIU in [16], 1847 nm/RIU in [17], and 944 nm/RIU in [18]), and is a third of the value of 8374 nm/RIU obtained with DTP-tuned LPFGs in the telecommunications spectral range with cladding reduction [9]....
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...Using this parameterization, the sensitivity is 2667 nm/RIU, which is larger than those obtained in DTP-tuned LPFGs in the telecommunications spectral range without cladding reduction (1309 nm/RIU in [16], 1847 nm/RIU in [17], and 944 nm/RIU in [18]), and is a third of the value of 8374 nm/RIU obtained with DTP-tuned LPFGs in the telecommunications spectral range with cladding reduction [9]....
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...However, as was stated in the introduction, some authors define sensitivity as the ratio between two parameters: the increase or decrease of the separation between the left and the right band in the DTP region, and the surrounding refractive index variation [16,17]....
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TL;DR: In this article, a theoretical study on the design of long period fiber grating (LPFG) sensor where its add-layer sensitivity is enhanced is presented, where two different methodologies: dual overlay layer and tailoring of the intermodal separation between two cladding modes have been used to enhance the add layer sensisstivity.
Abstract: We present our theoretical study on the design of long period fiber grating (LPFG) sensor where its add-layer sensitivity is enhanced. Add-layer sensitivity quantifies the sensitivity of the sensor to the changes taking place within few tens of nanometers around the receptor molecules. Two different methodologies: the use of dual overlay layer and tailoring of the intermodal separation between two cladding modes have been used to enhance the add-layer sensisstivity. Using coupled mode analysis, we compute several examples to carry out a detailed comparative analysis between the results obtained, focusing on the cladding mode near mode transition.
22 citations
Cites background from "Sensitivity Enhancement of Turn-Aro..."
...Moreover, it can be enhanced even further if the initial coupling condition of the cladding mode is tailored suitably [4]....
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References
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TL;DR: In this article, the authors demonstrate that the change in wavelength of a long period fiber grating attenuation band with changes in external index of refraction can be enhanced by proper selection of the grating period.
Abstract: This paper demonstrates that the change in wavelength of a long period fiber grating attenuation band with changes in external index of refraction can be enhanced by proper selection of the grating period. We calculate and experimentally verify that the wavelength shift caused by changing the external index from n=1 to n=1.44 of the attenuation band which appears in the 1400-1600 nm region in a 200-/spl mu/m period grating is four times that in a 350-/spl mu/m period grating. Changes in the spectrum over a wavelength range from 1100 to 1600 nm and 1
747 citations
"Sensitivity Enhancement of Turn-Aro..." refers background in this paper
...The basic working principle of LPG sensors for refractive index measurement is well understood [1], [2]....
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...A change in surrounding refractive index alters the effective indices of the cladding modes which in turn induces a change in the resonant wavelengths and forms the basis of refractive index sensing using LPG [1]....
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TL;DR: In this paper, the sensitivity of long-period fiber gratings (LPFGs) is investigated as a function of temperature, strain, and surrounding refractive index, with particular attention to the higher order cladding modes and the possibilities for ultrasensitive sensors.
Abstract: We present a detailed investigation into the sensitivity of long-period fiber gratings (LPFGs) as a function of temperature, strain, and surrounding refractive index, with particular attention to the higher order cladding modes and the possibilities for ultrasensitive sensors. From a general theoretical analysis, we identify a general sensitivity factor which offers new physical insight into LPFG behavior and represents a useful design aid in conjunction with a set of measurand-specific sensitivity factors. Our analysis reveals the existence of turning points in the mode dispersion characteristics at which ultrasensitive operation may be obtained. In an extensive set of coordinated experiments, we verify the theoretical predictions with close agreement and provide demonstrations of the device behavior close to the turning points. Alternative sensor schemes for temperature, strain, and refractive index based, respectively, on measurement of the dual resonance characteristic of the modes and on the transmission characteristics close to the turning points, utilizing higher order modes of the LPFG, are presented. For two variables at least, we record the highest LPFG sensitivities yet reported.
744 citations
TL;DR: An original design approach based on the modal dispersion curves for the development of long period gratings in transition mode near the dispersion turning point exhibiting ultrahigh refractive index sensitivity places thin film coated LPGs as an alternative to other fiber-based technologies for high-performance chemical and biological sensing applications.
Abstract: We report an original design approach based on the modal dispersion curves for the development of long period gratings in transition mode near the dispersion turning point exhibiting ultrahigh refractive index sensitivity. The theoretical model predicting a giant sensitivity of 9900 nm per refractive index unit in a watery environment was experimentally validated with a result of approximately 9100 nm per refractive index unit around an ambient index of 1.3469. This result places thin film coated LPGs as an alternative to other fiber-based technologies for high-performance chemical and biological sensing applications.
129 citations
"Sensitivity Enhancement of Turn-Aro..." refers result in this paper
...We could demonstrate practically that the enhancement in the RI sensitivity can be achieved by slightly thinning the cladding diameter, which in our opinion is simpler than other methodologies [8], [11], [15] suggested to achieve the equivalent results....
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TL;DR: In this article, a numerical method is presented for determining the transmittance of long-period (LP) fibergratings having arbitrary azimuthal/radial refractive index variations.
Abstract: A numerical method is presented for determining the transmittance of long-period (LP) fiber-gratings having arbitrary azimuthal/radial refractive index variations. The method uses coupled-mode theory and includes both the sine and cosine character of the LP modes. The model treats interactions between the fundamental LP/sub 01/ mode and high-azimuthal-order cladding modes. The method utilizes the transfer matrix method to model cylindrical layers both in the core and the cladding regions.
127 citations
"Sensitivity Enhancement of Turn-Aro..." refers methods in this paper
...Our numerical simulation, by solving coupled mode equations following [13], could make out that the initial coupling strength of a particular mode at TAP, which is primarily set by the detuning factor for a fixed grating length, has a major role on setting the split resonant bands with respect to the TAP i....
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TL;DR: Using an optical biosensor based on a dual-peak long-period fiber grating, the detection of interactions between biomolecules in real time is demonstrated, demonstrating a function of multiple usability.
Abstract: Using an optical biosensor based on a dual-peak long-period fiber grating, we have demonstrated the detection of interactions between biomolecules in real time. Silanization of the grating surface was successfully realized for the covalent immobilization of probe DNA, which was subsequently hybridized with the complementary target DNA sequence. It is interesting to note that the DNA biosensor was reusable after being stripped off the hybridized target DNA from the grating surface, demonstrating a function of multiple usability.
126 citations