Search

The interaction effect of the fundamental mode in a special photonic crystal fiber (PCF) with a thin-film absorbing coating deposited on a surface of a fiber cladding on the optical transmission of the PCF is theoretically studied. It is shown that the transmission has a multi-peak spectrum that is determined by the resonance capture of the fundamental PCF mode energy by the coating. In some cases, this capture is explained by a resonance coupling between the fundamental core mode and leaky modes of the coating, or between the fundamental PCF mode and cladding modes located between PCF air channels and the coating. Examples are presented of using this effect to develop fiber-optic sensors of refractive index or pressure, and to sense a nanoscale adsorption layer of ammonia molecules deposited on a coating surface contacting air. [ABSTRACT FROM AUTHOR]

A photonic crystal fiber consisting of three rings of air holes was tapered down to 3–5 μm. The voids of the fiber were collapsed so a solid microtaper was formed. In this microtaper two selective higher-order modes propagate and interfere. This makes the transmission of the taper to exhibit a sinusoidal pattern with subnanometric width fringes. It was found that the device was highly sensitive to gas molecules. The latter is attributed to surface refractive index changes, number of molecules enveloping the taper, and high sensitivity of the modes participating in the interference. [ABSTRACT FROM AUTHOR]

Background: Photonic crystal fiber Mach-Zehnder modal interferometers based on no adiabatic tapered fibers are perspective for bio-chemical sensing, since they have very high refractive index sensitivity and it is possible for them to use a very small quantity of investigated samples. To obtain a desirable sensitivity to a needed analyte, it was proposed to coat a sensing surface of the refractive index sensor with ultra-thin films. Methods: In this work, we reported on a no adiabatic tapered special photonic crystal fiber coated with an ultra-thin layer of a Bovine Serum Albumin (BSA) antigen or with an 8 nm palladium film to detect interaction between the BSA antigen and an anti-BSA antibody or for fast detection of hydrogen concentrations, respectively. Results and conclusion: During our experiments, we received a record detection limit of 125 pg/ml of the anti-BSA antibody concentration. Fast detection of hydrogen concentrations up to 5.6 vol% was carried out. By using a proposed electrodynamics model of a hydrogen sensor, an optimal taper sensing length was determined. [ABSTRACT FROM AUTHOR]

The authors report a highly sensitive (∼2.8 pm/μ[variant_greek_epsilon]) wavelength-encoded strain sensor made from a piece of photonic crystal fiber (PCF) spliced to standard fibers. The authors intentionally collapse the PCF air holes over a short region to enlarge the propagating mode of the lead-in fiber which allows the coupling of only two modes in the PCF. The transmission spectrum of the interferometer is stable and sinusoidal over a broad wavelength range. The sensor exhibits linear response to strain over a large measurement range, its temperature sensitivity is very low, and for its interrogation a battery-operated light emitting diode and a miniature spectrometer are sufficient. [ABSTRACT FROM AUTHOR]

• Simple fabrication of a MZI using a capillary hollow core fiber. • Low insertions loss and high signal contrast. • Narrow linewidth (around 0.03 nm). • High SMSR (53 dB) and high SNR (66). • The output of the laser exhibits low power fluctuations (0.1379 dB) and practically no wavelength variations (0.0108 nm). In this paper, a narrow spectral linewidth and wavelength-tunable erbium-doped fiber laser based on a Mach-Zehnder interferometer (MZI) as a filter is proposed and experimentally demonstrated. The filter is fabricated by splicing a short length of capillary hollow-core fiber (CHCF) between two small sections of multimode fibers (MMF). The interference pattern generated by the filter has a free spectral range of 10.5 nm and a maximum extinction ratio of 36 dB at 1560 nm. Then, by incorporating the filter inside a ring cavity laser, a single laser emission centered at 1566.46 nm with a spectral width around 0.03 nm and a high SNR of 66 dB (also has a SMSR of 53 dB) is obtained. By changing the temperature of the filter, the wavelength emission of the laser can be tuned from 1566.46 to 1570.09 nm. Considering that the fabrication process of the filter is relatively simple and can be easily implemented in an EDFL, we strongly believe that it can have a great deal of interest in telecom applications. [ABSTRACT FROM AUTHOR]

In this paper, we propose a highly sensitive temperature sensor based on two cascaded Mach–Zehnder interferometers (MZIs) that work using the Vernier effect. The all-fiber MZIs were assembled by splicing a segment of capillary hollow-core fiber (CHCF) between two sections of multimode fibers (MMFs). This cascaded configuration exhibits a temperature sensitivity of 1.964 nm/°C in a range from 10 to 70 °C, which is ~67.03 times higher than the sensitivity of the single MZI. Moreover, this device exhibits a high-temperature resolution of 0.0153 °C. A numerical analysis was carried out to estimate the devices' temperature sensitivity and calculate the magnification of the sensitivity produced by the Vernier effect. The numerical results have an excellent agreement with the experimental results and provide a better insight into the working principle of the MZI devices. The sensor's performance, small size, and easy fabrication make us believe that it is an attractive candidate for temperature measurement in biological applications. [ABSTRACT FROM AUTHOR]

• A sensor to measure temperature and refractive index without ambiguity is proposed. • A fiber Bragg grating and a hybrid Fabry-Perot interferometer are used in series. • The resulting enhanced refractive index measurement ranges from 1.00028 to 1.6068. • Reflectance is analyzed in Fourier domain via a novel signal processing method. • The sensing response is independent of the optical source power fluctuations. We demonstrate the unambiguous measurement of the refractive index (RI) in a wide measurement range (from 1.0003 to 1.6068 RIU at 1550 nm), using a fiber Bragg grating (FBG) and a hybrid fiber Fabry-Perot interferometer (HFFPI) arranged in series. The spectrum of the reflectivity (R HFFPI ) is composed by the interference pattern and the narrowband grating peak. In optical domain the wavelength of the grating peak is used to monitor the temperature, while the RI changes are monitored by the fringe contrast of the interference pattern. Nevertheless, the fringe contrast exhibited an ambiguous behavior that limits the RI measurement range to substances with a RI smaller than that of the core of the optical fiber used. In Fourier domain the spectrum of the R HFFPI showed the three characteristic interference peaks of an HFFPI but superimposed on a broad pedestal, due to the FBG. The amplitude of the three peaks was maximum when the fiber tip is surrounded by air, but two of them diminished when the RI of the external medium (n ext) increased. The amplitude of the second and third peaks decreased below the level of the pedestal, that is, peaks turned into dips, when n ext was larger than the single-mode fiber refractive index (n SMF). Importantly, to the best of our knowledge, a one to one relationship between the amplitude of the Fourier peaks and n ext was established even for values larger than n SMF , for the first time. Additionally, this device allows the simultaneous measurement of refractive index and temperature with good sensitivity and stability since both devices (HFFPI and FBG) are intrinsically immune to the power fluctuations of the optical signal, which is crucial for strict real-world applications such as biosensing. [ABSTRACT FROM AUTHOR]

In this paper, we propose and experimentally demonstrate a simple technique to enhance the curvature sensitivity of a bending fiber optic sensor based on anti-resonant reflecting optical waveguide (ARROW) guidance. The sensing structure is assembled by splicing a segment of capillary hollow-core fiber (CHCF) between two single-mode fibers (SMF), and the device is set on a steel sheet for measuring different curvatures. Without any surface treatment, the ARROW sensor exhibits a curvature sensitivity of 1.6 dB/m−1 in a curvature range from 0 to 2.14 m−1. By carefully coating half of the CHCF length with polydimethylsiloxane (PDMS), the curvature sensitivity of the ARROW sensor is enhanced to −5.62 dB/m−1, as well as an increment in the curvature range (from 0 to 2.68 m−1). Moreover, the covered device exhibits a low-temperature sensitivity (0.038 dB/°C), meaning that temperature fluctuations do not compromise the bending fiber optic sensor operation. The ARROW sensor fabricated with this technique has high sensitivity and a wide range for curvature measurements, with the advantage that the technique is cost-effective and easy to implement. All these features make this technique appealing for real sensing applications, such as structural health monitoring. [ABSTRACT FROM AUTHOR]