Single-mode Silica Fiber Research Articles

Detection of riboflavin concentration by sol-gel silica coated dual-peak long period fiber grating sensor

A dual-peak long period fiber grating (DP-LPFG)-based sensor was designed and fabricated for the sensitive detection of riboflavin concentration. LPFGs with a period of 163 μm and a cladding mode of LP0, 12 were inscribed on a standard single-mode silica fiber using a femtosecond laser direct writing technique. Coatings of silica-based materials doped with β-cyclodextrin (β-CD), prepared via the sol-gel method, were applied to the surface of the LPFGs for the detection of riboflavin. To investigate the impact of coating thickness on the sensing sensitivity, sol-gel coatings of different thicknesses were applied to the surface of the LPFG sensor. Experimental findings revealed that the sensor with a thickness of approximately 540 nm sol-gel coatings exhibited superior sensing performance. The detection limit of the prepared DP-LPFG sensor was tested to be 0.08 nM, and it exhibits a response time of less than 3 minutes, along with high sensitivity, excellent repeatability, and selectivity. Thus, this sensor holds significant promise for applications in disease treatment and diagnosis, as well as in ensuring food quality.

Dual-wavelength lasing at ∼1.2 μm and ∼2.0 μm in a Ho3+-doped fluoroaluminate glass microsphere

This study presents the experimental realization of a microsphere laser resonator designed to operate within the approximate wavelength range of 1.2 μm and 2.0 μm. This resonator, employing a Ho3+-doped fluoroaluminate glass microsphere, was stimulated by a 1150 nm laser, marking the first demonstration of its kind. The observed laser emissions at ∼1.2 μm and ∼2.0 μm were ascribed to the transitions of Ho3+ ions, specifically 5I6 → 5I8 and 5I7 → 5I8, respectively. The fabrication of the microsphere, possessing a characteristic diameter of approximately 50 μm, entailed the controlled melting of a fluoroaluminate glass filament through the application of a focused CO2 laser beam. Concurrently, a tapered fiber with a waist diameter of ∼2 μm was created by subjecting a standard silica single-mode fiber to a process of controlled heating and stretching. The findings of this investigation suggest promising prospects for the development of multi-wavelength lasers utilizing fluoroaluminate glass microspheres, particularly in intricate environmental settings.

Thin-film-based optical fiber interferometric sensor on the fiber tip for endovascular surgical procedures.

Endovascular surgery requires accurate measurement of parameters such as pressure, temperature, and biomarkers within vessels for real-time tissue response monitoring and ensuring targeted therapeutic interventions. However, the availability of small tip-based sensors capable of precise application, for example, navigating an aneurysm's lumen, is limited. With their capabilities for real-time analysis, flexibility, and biocompatibility, optical fiber sensors (OFS) hold promise in addressing this need. This proof-of-concept study investigates the feasibility of OFS in endovascular surgery scenarios. The sensor is based on a single-mode silica fiber with an interferometric forward-facing thin-film tip. The thin-film materials may be tailored for detecting various physical parameters and, when functionalized, also specific analytes. Materials applied in this sensor are thin metal oxides deposited using magnetron sputtering. A full-scale 3D-printed vascular model was employed to simulate endovascular setup. The experiments showed the high mechanical robustness of the approach, i.e., the sensor maintained functionality while being maneuvered through the endovascular model. The forward-facing tip remained intact and worked adequately, ensuring consistent and stable readouts. Moreover, the fiber showed sufficient flexibility, with no significant bending loss observed during simulations. Finally, the performance of the OFS in bovine serum samples was assessed. The sensor performed well in serum, and the results suggest that low-concentration serum may be used to reduce nonspecific surface interactions. Overall, this OFS system offers a promising solution for endovascular surgery and other biomedical applications, allowing for precise and on-the-spot analysis. Our study pioneers the feasibility of thin-film interferometric label-free OFS with a forward-facing sensitive area for sensing during endovascular procedures.

Innovative optical pH sensors for the aquaculture sector: Comprehensive characterization of a cost-effective solution

Optical fiber sensors show potential for monitoring multiple parameters essential to the growth and health of fish, particularly the pH value of the aquaculture medium. Two types of optical fiber sensors, using tapered silica single mode fibers with a Bragg grating inscribed and D-shaped plastic optical fibers (home-made and reused) were produced. A pH-sensitive layer made of polyaniline (PANI) was deposited on the optical fibers’ surface. The sensors demonstrated reproducibility and repeatability with a sensitivity of −0.22 ± 0.02 dB/pH, −472 ± 9 Counts/pH, and −(26 ± 2) × 102 Counts/pH for tapers, D-shape home-made, and reused, respectively, but only for increasing pH. Stabilization time tests indicated that a minimum of 60 s is required for a stable response, with no significant cross-sensitivities regarding temperature and ionic strength.

Proof-of-concept demonstration of double-slope-assisted Brillouin optical correlation-domain reflectometry

We develop a new configuration of distributed strain and temperature sensing technology called double-slope-assisted Brillouin optical correlation-domain reflectometry. Its loss-independent operation is demonstrated through simplified simulation and proof-of-concept experiments using a standard silica single-mode fiber.

Observation of strong photorefractive-like effect in silica micro-fibers

We observe the strong photorefractive (PR)-like effect in silica micro-fibers, which is different from the previously reported nonlinear behaviors in optical fiber devices. The micro-fiber is fabricated by tapering a standard silica single-mode fiber using the hydrogen flame. Two fiber Bragg gratings are fused at each end of the micro-fiber to form a Fabry–Pérot cavity, enabling us to observe the nonlinear dynamics. By situating the silica micro-fiber in a gas medium (i.e., N2, Ar, He, and air), we observe the remarkable PR-like effect, especially under the low-pressure condition below 80 Torr. In fact, the nonlinear effect increases with the reduced pressure as a power function. Such a nonlinear effect is also affected by the laser wavelength detuning rate, input laser power, and micro-fiber diameter. Finally, a nonlinear cavity dynamics model is adopted to well describe the observed nonlinear effect.

Pilot-scale testing of natural gas pipeline monitoring based on phase-OTDR and enhanced scatter optical fiber cable

In this paper, we present the results of lab and pilot-scale testing of a continuously enhanced backscattering, or Rayleigh enhanced fiber cable that can improve distributed acoustic sensing performance. In addition, the Rayleigh-enhanced fiber is embedded within a tight buffered cable configuration to withstand and be compatible for field applications. The sensing fiber cable exhibits a Rayleigh enhancement of 13 dB compared to standard silica single-mode fiber while maintaining low attenuation of ≤ 0.4 dB/km. We built a phase-sensitive optical time domain reflectometry system to interrogate the enhanced backscattering fiber cable both in lab and pilot-scale tests. In the laboratory experiment, we analyzed the vibration performance of the enhanced backscattering fiber cable and compared it with the standard single-mode telecom fiber. Afterward, we field validated for natural gas pipeline vibration monitoring using a 4-inch diameter steel pipeline operating at a fixed pressure level of 1000 psi, and a flow rate of 5, 10, 15, and 20 ft/s. The feasibility of gas pipeline monitoring with the proposed enhanced backscattering fiber cable shows a substantial increase in vibration sensing performance. The pilot-scale testing results demonstrated in this paper enable pipeline operators to perform accurate flow monitoring, leak detection, third-party intrusion detection, and continuous pipeline ground movement.

Hydrostatic Pressure Sensor Based on Polymer Optical Fiber Multimode Interferometer

In this work, we report for the first time, to the best of our knowledge, a hydrostatic pressure sensor based on a polymer optical fiber (POF) multimode interferometer (MMI). The sensor was constructed using a polymethylmethacrylate (PMMA) multimode POF sandwiched between two silica single-mode fibers (SMFs). The characterization of the sensor revealed a linear positive wavelength shift with a sensitivity of 58 pm/bar. The sensitivity of the POF-MMI was compared to that of a silica-based MMI, revealed to be <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10\times $ </tex-math></inline-formula> higher, allowing it to reach higher resolutions of 0.1 bar, considering a detection system resolution of 5 pm.

Measurement of the birefringence variation induced by dihydrogen diffusion into a polarization-maintaining fiber.

We report continuous measurements of the transmission spectrum of a fiber loop mirror interferometer composed of a Panda-type polarization-maintaining (PM) optical fiber during the diffusion of dihydrogen (H2) gas into the fiber. Birefringence variation is measured through the wavelength shift of the interferometer spectrum when the PM fiber is inserted into a gas chamber with H2 concentration from 1.5 to 3.5 vol.% at 75 bar and 70°C. The measurements correlated with simulation results of H2 diffusion into the fiber lead to a birefringence variation of -4.25 × 10-8 per mol m-3 of H2 concentration in the fiber, with a birefringence variation as low as -9.9×10-8 induced by 0.031 μmol m-1 of H2 dissolved in the single-mode silica fiber (for 1.5 vol.%). These results highlight a modification of the strain distribution in the PM fiber, induced by H2 diffusion, leading to a variation of the birefringence that could deteriorate the performances of fiber devices or improve H2 gas sensors.

Effect of dipping number of polyvinyl alcohol (PVA) -coated on optical Fiber for Humidity Sensor

Optical Fiber Humidity Sensors (OFHSs) have attracted significant research interest due to their several advantages including small size, high durability and can withstand the extreme environment regardless of high temperature, high pressure and high electromagnetic radiation. In this study, the proposed sensors were built from standard single-mode silica fibers working at telecommunication wavelengths and exhibited very good humidity sensing characteristics. Single-mode optical fibers were coated with different dipping numbers (2, 4, 6 8, and 10 times) of polyvinyl alcohol (PVA) solution using a dip coating method. The sensing performance of uncoated and PVA-coated optical fiber sensors in terms of its sensitivity for various relative humidity (RH) percentages ranging from 40 to 90 % RH was monitored using Ocean Optics spectrometer. The intensity peaks of PVA-coated optical fibers were increased linearly with dipping numbers. The optimum sensing performance was observed for 10 times dipping number of PVA solution with the highest intensity of 4100 counts at 60 % RH and exhibits good repeatability with precision error values in the range of 0 to 2 %. Furthermore, the gap difference between intensity counts due to % RH changes could be clearly observed for 10 times dipping numbers. These reported results are important to enhance the performance of humidity sensor for sensing and monitoring purposes.

High-Temperature Sensing Based on GAWBS In Silica Single-Mode Fiber.

High temperature detection is a constant challenge for condition monitoring under harsh environments in optical fiber sensors research. In this study, the temperature response characteristics of guided acoustic wave Brillouin scattering (GAWBS) spectra in silica single-mode fiber (SMF) up to 800 °C are experimentally investigated, demonstrating the feasibility of the method for high-temperature monitoring. With increasing temperature, the resonance frequency of GAWBS spectra increases in a nearly linear manner, with linearly fitted temperature-dependent frequency shift coefficients of 8.19 kHz/°C for TR2,7 mode and 16.74 kHz/°C for R0,4 mode. More importantly, the linewidth of the GAWBS spectra is observed to narrow down with increasing temperature with a linearly fitted rate of -6.91 × 10-4/°C for TR2,7 modes and -8.56 × 10-4/°C for R0,4 modes. The signal-to-noise ratio of the GAWBS spectra induced by both modes increase by more than 3 dB when the temperature rises from 22 °C to 800 °C, which indicates that the proposed sensing scheme has better performance in high-temperature environments, and are particularly suitable for sensing applications in extreme environments. This study confirms the potential of high-temperature sensing using only GAWBS in silica fibers without any complex micromachining process, which has the advantages of strong mechanical strength, simple structure, easy operation, and low cost.

Temperature sensing based on multimode interference in polymer optical fibers: sensitivity enhancement by PC-APC connections

A simple, stable, and high-sensitivity temperature sensor based on multimode interference in a polymer optical fiber (POF) with higher-order mode excitation has been developed. In a single-mode–multimode–single-mode (SMS) structure, one end of the multimode POF with physical-contact (PC) connectors is connected to a silica single-mode fiber with an angled-PC (APC) connector. We compare the temperature sensing characteristics of the three configurations (no PC-APC, PC-APC at input, and PC-APC at output) and obtain the highest temperature sensitivity of 219.2 pm °C−1, which is more than double the value of the standard (no PC-APC) SMS structure.

Low-cost fabrication and characterization process for development of a sensitive optical fiber structure.

The structure of silica single-mode fiber (SMF) must be modified in order to develop optical fiber-based biosensors. To reduce the diameter of the optical fiber, a low-cost chemical etching method is very popular. The proposed chemical etching method is a simple, rapid, and cost-effective technique for removing the silica cladding up to a desired diameter. In the laboratory, hydrofluoric acid (HF acid, 40% concentration) is used for etching. A variation on etching is also proposed and tested with 40% HF as well as with magnetic stirring at the different speeds. The etching experiments are also carried out at different temperatures. The etching results of silica fiber are presented through a step-by-step procedure using a rapid and resource-efficient method for the fabrication of optical fiber-based biosensors. The etched diameter characterization is done using a calibrated compound microscope. The sensing experiment with unetched and etched optical fiber is also performed for the detection of different concentrations of glucose biomolecules.

Rapid and sensitive detection of ammonia in water by a long period fiber grating sensor coated with sol-gel silica.

A sensitive ammonia sensor based on long-period fiber grating (LPFG) is designed and manufactured for the detection of ammonia concentration in water. Femtosecond laser direct writing technology is used to write LPFGs on standard single-mode silica fiber. A thin layer doped with basic dyes is coated on the optical fiber for sensing by using the sol-gel method. The thicknesses of sol-gel layers, which play a key role in the sensitivity of the LPFG sensor, were carefully studied. Experimental results show that LPFG with a functional layer of ∼340 nm has the best sensing performance, and the detection limit is 0.08 ppm. The response time of the sensor is less than one minute, and the sensor has good repeatability with a short recovery time. Compared with other organic molecules and ions in water, the proposed LPFG sensor has not only good reusability, but also selectivity for the detection of ammonia.

Influence of surface roughness on the sensitivity of a D-shaped optical fiber-based refractive index sensor

This paper presents the evaluation of the influence of surface roughness on the performance of a refractive index sensor based on a D-shaped optical fiber. In addition, the manufacturing process of D-shaped sections on standard silica single-mode optical fibers with different rms roughness values is described. The surface roughness morphology generated by the abrasive process is measured by processing microscopic images using the Gwyddion software. A model for the surface roughness, using the third order Weierstrass fractal function, is proposed and simulated with COMSOL Multiphysics. Experimental and simulation results are presented. The results show that the surface roughness increases the device insertion loss, as expected, but contributes positively to the sensitivity of the refractive index sensor, reaching sensitivity levels of 148.87 dB/RIU with a resolution of 10−4 RIU. The good agreement between the computational and experimental results is highlighted. Due to the good figures of merit obtained, the optical sensor has potential of application in biochemical sensing.

Angle sensor for humidity-insensitive angle measurement based on multimode interference

A multimode interference (MMI) fiber optics angle sensor based on a cyclic transparent amorphous fluoropolymer (CYTOP) multimode fiber is reported Two silica single-mode fibers (SMFs) are glued to a segment of CYTOP fiber to form a single-mode-multimode-single-mode structure that produces an MMI spectrum. The centers of the SMF and the CYTOP fiber are aligned using the translation stage of the fiber fusion splicer in manual mode. The angle sensing mechanism based on MMI theory is investigated and experimentally verified. A large measurement range of 110° and a linear sensitivity of 36.2 pm/deg is demonstrated. The angle measurement is humidity-insensitive due to the weak moisture absorption of the CYTOP fiber and the design of sensor packaging.

Comparative Study of γ- and e-Radiation-Induced Effects on FBGs Using Different Femtosecond Laser Inscription Methods.

This work presents an extensive, comparative study of the gamma and electron radiation effects on the behaviour of femtosecond laser-inscribed fibre Bragg gratings (FBGs) using the point-by-point and plane-by-plane inscription methods. The FBGs were inscribed in standard telecommunication single mode silica fibre (SMF28) and exposed to a total accumulated radiation dose of 15 kGy for both gamma and electron radiation. The gratings’ spectra were measured and analysed before and after the exposure to radiation, with complementary material characterisation using Fourier transform infrared (FTIR) spectroscopy. Changes in the response of the FBGs’ temperature coefficients were analysed on exposure to the different types of radiation, and we consider which of the two inscription methods result in gratings that are more robust in such harsh environments. Moreover, we used the FTIR spectroscopy to locate which chemical bonds are responsible for the changes on temperature coefficients and which are related with the optical characteristics of the FBGs.

2.6-GHz fundamental repetition rate, Q-switched mode-locking Nd[formula omitted]-doped single-mode silica fiber laser, fabricated by zeolite method

We successfully constructed a pulse laser whose fundamental repetition rate is 2.6-GHz in Q-switched mode-lock oscillation. To the best of our knowledge, this is the highest repetition rate among silica glass fiber lasers. The laser cavity was constructed by a 40-mm-long Nd3+-doped single-mode silica glass fiber (Nd-SMF) and a SESAM as a saturable absorber. The core glass of the Nd-SMF was fabricated by a zeolite method and its concentration of Nd2O3 was 1.25 wt%. The maximum laser power reached 27.2 mW, and its slope efficiency and lasing thresholds were 19.6% and 7.3 mW. The peak wavelength of the oscillation was 1062.7 nm. The RF spectrum and the time-dependent waveform from a 20-GHz-bandwidth oscilloscope show a 2.6-GHz repetition rate of an Nd-SMF laser. We also discuss the conditions for achieving a CW-mode-lock (CML) oscillation, which is critical laser output Pout of 180 mW. Such a simple multi-GHz repetition rate laser will be available to make a compact frequency comb or a laser oscillator that will achieve ablation-cooled material removal in laser processing.

Nanostructured active and photosensitive silica glass for fiber lasers with built-in Bragg gratings.

A nanostructured core silica fiber with active and photosensitive areas implemented within the fiber core is demonstrated. The photosensitivity, active and passive properties of the fiber can be independently shaped with this new approach. We show that discrete local doping with active ions in form of nanorods allow to obtain effective laser action as in case of continuous distribution of the ions in the core. Co-existing discrete photosensitive nanostructure of germanium doped silica determine single-mode performance and allow inscription of highly efficient Bragg grating over the entire core area. Each nanostructure do not degrade performance of other one since physical interaction between active and photosensitive areas are removed. As a proof of concept, we have designed and fabricated the nanostructured, ytterbium single-mode silica fiber laser with the Bragg grating inscribed in the entire core area. We demonstrated fiber laser with good quality of generated laser beam (M2=1.1) with lasing efficiency of 44% and inscribed Bragg grating with 98.5% efficiency and -18 dB contrast.

Gold Nanoparticles Coated FBG Sensor Based on Localized SPR for Adulterated Honey Classification

Two types of fiber optics, namely macro etched silica single mode fiber (SMF) and Fiber Bragg Grating (FBG) (Bragg wavelength of 1550 nm and 1554 nm) had been used to detect various types of honey samples, such as Apis Dorsata Honey, Trigona Honey and Capilano Australian Honey. To study the effect of exposure period in open environment at room temperature, all honey samples were exposed in open environment at room temperature from 2 to 10 days. In comparison with macro etched SMF and FBG (λB=1554 nm), the FBG (λB=1550 nm) portrays an excellent sensing properties with sensitivity and selectivity of 33.56 dB/RIU and 24.07 dB/RIU respectively. The output of this work concludes that the quality of honey based on optical output power reduces up to 0.35% as period of exposure to the open environment increased.