Transmission Spectrum Of Fiber Research Articles

Ultrasensitive Fiber SPR Magnetic Field Sensor Using Au/TiO₂ Schottky Junction

This paper presents an ultrasensitive fiber surface plasmon resonance (SPR) magnetic field sensor using an Au/TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Schottky junction coated on a plastic-clad multimode fiber (PMF) and immersed in the magnetic fluid (MF). The MF acts as the magnetic-sensitive material, and the Au/TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> film with a high dielectric constant excites SPR with high sensitivity. When the magnetic field strength applied to the MF changes, the MF’s refractive index alters accordingly, which changes the phase-matching condition of the surface plasmon polaritons, shifting the resonance dip in the fiber transmission spectrum. Therefore, the magnetic field strength can be measured by monitoring the resonance dip shift. The proposed sensor achieved a maximum magnetic sensitivity of -2.791 nm/Oe in the 5 to 35 Oe range, higher than most MF-based fiber magnetic field sensors. Additionally, the temperature response of the sensor was measured to be -0.4861 nm/°C, which has little effect on the magnetic sensing performance. The experimental results indicate that the proposed fiber SPR sensor can measure magnetic field strength variations with high sensitivity and accuracy, making it suitable for practical applications in various scenarios.

Refractive index sensing performance of stepped-mTFBG fabricated by flexibly-regulating wet etching process

In this paper, an interesting method was proposed to flexibly prepare the micron titled fiber Bragg grating (mTFBG) by using a quartz capillary. The etching region of mTFBG can be precisely controlled by inserting in and moving it out from the protection of the quartz capillary. In this way, the mTFBG with stepped diameter has been fabricated and demonstrated with its refractive index sensing performance. Compared with the uniformly-etched mTFBG, the refractive index sensitivity of stepped-mTFBG has been significantly-improved from 5.785 nm/RIU to 17.077 nm/RIU. Although this sensitivity is much lower than other types of refractive index optical fiber sensors, it provides the new method for the flexible design of FBG structures. Furthermore, it reveals that the transmission spectrum of mTFBG can be modulated continuously during the etching process, which suggests a new way to adjust the transmission spectra of optical fibers.

Hollow-Core Fiber-Based Biosensor: A Platform for Lab-in-Fiber Optical Biosensors for DNA Detection.

In this paper, a novel platform for lab-in-fiber-based biosensors is studied. Hollow-core tube lattice fibers (HC-TLFs) are proposed as a label-free biosensor for the detection of DNA molecules. The particular light-guiding mechanism makes them a highly sensitive tool. Their transmission spectrum is featured by alternations of high and low transmittance at wavelength regions whose values depend on the thickness of the microstructured web composing the cladding around the hollow core. In order to achieve DNA detection by using these fibers, an internal chemical functionalization process of the fiber has been performed in five steps in order to link specific peptide nucleic acid (PNA) probes, then the functionalized fiber was used for a three-step assay. When a solution containing a particular DNA sequence is made to flow through the HC of the TLF in an ‘optofluidic’ format, a bio-layer is formed on the cladding surfaces causing a red-shift of the fiber transmission spectrum. By comparing the fiber transmission spectra before and after the flowing it is possible to identify the eventual formation of the layer and, therefore, the presence or not of a particular DNA sequence in the solution.

Infrared fibers manufacture from single crystals of the AgBr – AgI system

The article is devoted to the manufacture of infrared polycrystalline optical fibers based on crystals of the AgBr–AgI system. The synthesis of a charge with a purity of up to 99.9999 wt % was performed. Single crystals of the AgBr0.96I0.04, AgBr0.92I0.08, AgBr0.87I0.13 compositions were grown. By means of computer simulation, the extrusion parameters of unjacketed optical fibers based on crystals were selected, namely, the temperature was 180 °C, the speed of the plunger movement was 0.2–0.3 mm/min. Using the selected parameters, from the crystals by the extrusion method, fibers with a diameter of 525 μm and a length of 0.55–2.2 m were manufactured, and their optical transmission was measured. The fiber transmission spectra have covered the range from 3 to 25 μm. Optical losses were estimated using the cut-off method. They amounted to 0.3 ± 0.1 dB/m in the region from 10 to 14 μm. The fiber resistance to ionizing β-radiation has been investigated. The transmission parameters were retained when the fibers had been irradiated with doses up to 400 kGy.

Dual-purpose optical fiber sensor: relative humidity and ammonia detection

We propose a dual−purpose sensor to detect ammonia besides relative humidity with tapered multimode fiber (TMMF) as the sensor structure and silica gel as the sensing layer. In achieving the desired TMMF, we heated and pulled a few pieces of multimode fibers to obtain 9-mm long tapered regions with different diameters in the range of 4−40 µm. Then synthesized silica gel by sol-gel method and passed the tapered section of the TMMFs through drops of silica gel to form the sensing layers. Using the wavelength shift and output power reduction appearing in the fiber transmission spectrum, we determine the sensor response to the alteration of ammonia concentration and relative humidity in the environment. Our experimental results reveal that a decrease in the tapered waist gives rise to an increase in the sensor sensitivity. The same results show that the highest measured sensitivity is 14.8 pm/ppm (for ammonia) and 0.435 dB/%RH (for relative humidity) when we coat the tapered region of a TMMF of 4−µm waist diameter with silica gel. Moreover, the time responses for relative humidity and ammonia sensors are 10 and 32 s, and their corresponding recovery times are 8 and 19.5 s.

Carboxymethyl Cellulose (CMC) Optical Fibers for Environment Sensing and Short-Range Optical Signal Transmission.

Optical fibers are a key component in modern photonics, where conventionally used polymer materials are derived from fossil-based resources, causing heavy greenhouse emissions and raising sustainability concerns. As a potential alternative, fibers derived from cellulose-based materials offer renewability, biocompatibility, and biodegradability. In the present work, we studied the potential of carboxymethyl cellulose (CMC) to prepare optical fibers with a core-only architecture. Wet-spun CMC hydrogel filaments were cross-linked using aluminum ions to fabricate optical fibers. The transmission spectra of fibers suggest that the light transmission window for cladding-free CMC fibers was in the range of 550–1350 nm, wherein the attenuation coefficient for CMC fibers was measured to be 1.6 dB·cm–1 at 637 nm. CMC optical fibers were successfully applied in touch sensing and respiratory rate monitoring. Finally, as a proof-of-concept, we demonstrate high-speed (150 Mbit/s) short-distance signal transmission using CMC fibers (at 1310 nm) in both air and water media. Our results establish the potential of carboxymethyl cellulose-based biocompatible optical fibers for highly demanding advanced sensor applications, such as in the biomedical domain.

Simulation of the Transmission Spectrum of Long-Period Fiber Gratings Structures with a Propagating Acoustic Shock Front.

In this paper, we investigate modification of transmission spectra of long-period fiber grating structures with an acoustic shock front propagating along the fiber. We simulate transmission through inhomogeneous long-period fiber gratings, π-shift and reflective π-shift gratings deformed by an acoustic shock front. Coupled mode equations describing interaction of co-propagating modes in a long-period fiber grating structures with inhomogeneous deformation are used for the simulation. Two types of apodization are considered for the grating modulation amplitude, such as uniform and raised-cosine. We demonstrate how the transmission spectrum is produced by interference between the core and cladding modes coupled at several parts of the gratings having different periods. For the π-shift long-period fiber grating having split spectral notch, the gap between the two dips becomes several times wider in the grating with the acoustic wave front than the gap in the unstrained grating. The behavior of reflective long-period fiber gratings depends on the magnitude of the phase shift near the reflective surface: an additional dip is formed in the 0-shift grating and the short-wavelength dip disappears in the π-shift grating.

Photoionization-Induced Broadband Dispersive Wave Generated in an Ar-Filled Hollow-Core Photonic Crystal Fiber

The resonance band in hollow-core photonic crystal fiber (HC-PCF), while leading to high-loss region in the fiber transmission spectrum, has been successfully used for generating phase-matched dispersive wave (DW). Here, we report that the spectral width of the resonance-induced DW can be largely broadened due to plasma-driven blueshifting soliton. In the experiment, we observed that in a short length of Ar-filled single-ring HC-PCF the soliton self-compression and photoionization effects caused a strong spectral blueshift of the pump pulse, changing the phase-matching condition of the DW emission process. Therefore, broadening of DW spectrum to the longer-wavelength side was obtained with several spectral peaks, which correspond to the generation of DW at different positions along the fiber. In particular, we numerically used the super-Gauss windows with different central wavelengths to filter out these DW spectral peaks and studied the time-domain characteristics of these peaks respectively using Fourier transform method. We observed that these multiple-peaks on the DW spectrum have different delays in the time domain, which is in good agreement with our theoretical prediction. More interestingly, we found that the broadband DW with several spectral peaks can be compressed to ~29 fs after proper dispersion compensation. The results reported here, on the one hand, provide some useful insights into the resonance-induced DW generation process in gas-filled HC-PCFs. On the other hand, the DW-emission mechanism could be used to generate the ultrashort light sources with a wide spectral range through using the proper design of the resonance bands of the HC-PCFs, which has many applications in the ultrafast related experiments.

Wavelength Tunable Filter Based on Acousto-Optic Modulation of a Double-Core Fiber

A tunable notch filter is acoustically modulated in the transmission spectrum of a double-core optical fiber. Flexural acoustic waves dynamically change the coupling power and the wavelength of the propagating modes, allowing to switch and tune wavelengths between the two cores. A maximum modulation depth of 5.4 dB and a tuning wavelength range of 8.4 nm are achieved with the present configuration. The results indicate new possibilities for application in space division multiplexing systems, dynamic couplers, gain equalizers, and fibers lasers.

Hollow Core Inhibited Coupling Fibers for Biological Optical Sensing

In this paper, we report how tube lattice hollow-core fibers can be successfully used to build sensors for molecule detection. The inner silica surface of the fiber is functionalized and coated with a probe layer, which permits to bond only with a particular molecule (the target). When the fiber is infiltrated with a solution containing the target, an additional layer is created on the silica surface, causing a redshift of the fiber transmission spectrum. The technique does not require any additional transducer component, such as Bragg gratings, amplifying techniques, such as nano-particles, nor coherent sources. It simply consists of the measurement of the transmission spectrum of a piece of fiber some tens of centimeters long. The principle is validated with experimental results showing the detection of the streptavidin protein. A solution containing streptavidin was flowed through the hollow core of the fiber coated with biotin. The measurement of the transmitted spectrum before and after the infiltration showed the presence of a few nanometer thick bio-layer.

Simultaneous Measurement of Strain and Temperature With a Few-Mode Fiber-Based Sensor

This paper proposes a novel detection scheme simultaneously to measure strain and temperature, based on a simple to construct device using a section of a specially designed few-mode fiber (FMF). The parameters and index profile of the FMF used as the key sensor element are such that the fiber supports only the LP01 and LP02 modes. The propagation constant difference between LP01 and LP02 modes Δ β has a maximum corresponding to the critical wavelength (CWL) in the fiber transmission spectrum. Because the two peaks located closest to the CWL from both sides, left peak 1 and right peak 1, shift in opposite directions, with different sensitivities under axial strain and temperature variations, the FMF device is capable of measuring the strain and temperature simultaneously. A theoretical analysis has been carried out as part of the design process and the experimental results obtained are found to agree well with the theoretical predictions. The characteristics of this sensor scheme are discussed in light of other competing approaches to simultaneous temperature and strain monitoring and are found to show advantages that suit several practical applications including compactness, ease of fabrication and implementation, relatively high sensitivities, and low cost.

Identification of Dielectric, Plasmonic, and Hybrid Modes in Metal-Coated Whispering-Gallery-Mode Resonators

Making available and accessing in a controlled manner optical modes with largely disparate properties in a given system constitutes a prime challenge for different applications. Here, we propose, realize, and optically characterize a high-Q polymeric wedge-like whispering-gallery-mode resonator coated with a thin silver layer that supports pure surface plasmon polariton modes, pure dielectric modes, and hybrid photonic–plasmonic modes with Q-factors larger than 1000 and modal volumes as small as only a few cubic micrometers. We demonstrate both theoretically and experimentally that all three distinct kinds of cavity eigenmodes can be efficiently excited in the infrared via evanescent coupling to a tapered fiber. Performing finite-element simulations and coupled-mode theory, we develop an experimental procedure based on mode filtering to unambiguously identify the resonances observed in fiber transmission spectra. By controlling both the position of the tapered fiber with respect to the resonator and the i...

Role of symmetry in mode coupling in twisted microstructured optical fibers.

We have studied the effect of symmetry on coupling between core and cladding modes in helical microstructured fibers, which gives rise to resonant loss peaks observed in the fiber transmission spectra. We demonstrate that the selection rules for orbital and spin angular momenta of coupled modes, proposed first for twisted conventional fibers, are universal characteristics and correctly identify the coupled cladding modes in helical microstructured optical fibers (MOFs). Moreover, we show for the first time (to our knowledge) the effect of coupling between modes of opposite polarization handedness in twisted MOFs.

Characterization of light transmissions in various optical fibers with proton beam

As a feasibility study on the development of a fiber-optic radiation sensor for proton therapy dosimetry, we characterized light transmissions of various commercial optical fibers such as silica and plastic based optical fibers by the irradiation of proton beams. In this study, we measured light transmission spectra of optical fibers as a function of absorbed doses of proton beams using a deuterium & tungsten halogen lamps and a spectrometer. To be used as a fiber-optic radiation sensor, the optical fibers should have the radiation resistant characteristics and provide stable output signals during the proton beam irradiation. In this study, we could select suitable optical fibers to be used in the fiber-optic radiation sensor without quenching effects for proton therapy dosimetry. As a result, the light transmittance of the optical fibers had decreasing trends with increasing absorbed dose as expected.

The red shift of the semiconductor quantum dots luminescence maximum in the hollow core photonic crystal fibers

Hollow core microstructural optical waveguides (photonic crystal fibers) can affect intensity and spectrum position of luminophores emission located in the hollow core. Most strongly this effects could be in case of luminescence semiconductor nanoparticles – quantum dots (QDs) due to the narrow and symmetrical photoluminescence spectra. Study of the spectral effects arising from the superposition of QDs luminescence band on the photonic band gaps in the fiber transmission spectrum is both of fundamental and applied interest. This paper demonstrates the red shift of photoluminescence maximum of CdSe/ZnS QDs with core-shell structures. Luminescence maximum shift can be more than 10 nm, depending on the position of the photonic band gaps in the fiber transmission spectrum.

Simultaneous measurement of refractive index and temperature using a SPR-based fiber optic sensor

A surface plasmon resonance-based fiber-optic sensor for simultaneous measurement of refractive index and temperature of liquid samples is proposed and experimentally demonstrated. The sensor consists of a gold-coated MM-SM-MM optical fiber structure, whose sensitive section was partially covered with polydimethylsiloxane (PDMS) to generate two independent SPR resonance dips in the fiber transmission spectrum. One of the dips is generated by the bare gold-coated fiber section whose wavelength resonance is tuned by the refractive index and temperature of the surrounding medium. The other dip that is exclusively used to monitor the temperature variations of the liquid sample, whose central wavelength at 900nm corresponds to PDMS refractive index at 20°C, is produced by the polymerized gold-coated fiber section. The high refractive index and temperature sensitivity achieved, 2323.4nm/RIU and −2.850nm/°C respectively, the small size, the ease fabrication process, and the bio-compatibility of the proposed device are appealing characteristics that makes it ideal for practical bio-sensing applications.

On the Identification of Rayon/Viscose as a Major Fraction of Microplastics in the Marine Environment: Discrimination between Natural and Manmade Cellulosic Fibers Using Fourier Transform Infrared Spectroscopy.

This work was sparked by the reported identification of man-made cellulosic fibers (rayon/viscose) in the marine environment as a major fraction of plastic litter by Fourier transform infrared (FT-IR) transmission spectroscopy and library search. To assess the plausibility of such findings, both natural and man-made fibers were examined using FT-IR spectroscopy. Spectra acquired by transmission microscopy, attenuated total reflection (ATR) microscopy, and ATR spectroscopy were compared. Library search was employed and results show significant differences in the identification rate depending on the acquisition method of the spectra. Careful selection of search parameters and the choice of spectra acquisition method were found to be essential for optimization of the library search results. When using transmission spectra of fibers and ATR libraries it was not possible to differentiate between man-made and natural fibers. Successful differentiation of natural and man-made cellulosic fibers has been achieved for FT-IR spectra acquired by ATR microscopy and ATR spectroscopy, and application of ATR libraries. As an alternative, chemometric methods such as unsupervised hierarchical cluster analysis, principal component analysis, and partial least squares-discriminant analysis were employed to facilitate identification based on intrinsic relationships of sample spectra and successful discrimination of the fiber type could be achieved. Differences in the ATR spectra depending on the internal reflection element (Ge versus diamond) were observed as expected; however, these did not impair correct classification by chemometric analysis. Moreover, the effects of different levels of humidity on the IR spectra of natural and man-made fibers were investigated, too. It has been found that drying and re-humidification leads to intensity changes of absorption bands of the carbohydrate backbone, but does not impair the identification of the fiber type by library search or cluster analysis.

Intensity detection scheme of sensors based on the modal interference effect of few mode fiber

The transmission spectrum and power of the few mode fiber (FMF) under different strain/temperature are studied theoretically and experimentally. Significant shift of the critical wavelength of FMF can be produced when the measurement range is large. An intensity detection scheme with broadband source is proposed to overcome the problem encountered by the traditional measurement methods such as peaks shifts detection and transmission detection at a fixed single wavelength. And the scheme show larger dynamic range and larger linear operating range when the length of FMF is shorter, which can make the sensor more compact. The experimental result agrees well with the theoretical calculation.

Humidity sensor based on power leakage at resonance wavelengths of a hollow core fiber coated with reduced graphene oxide

A novel humidity sensor based on power leakage at resonance wavelength in a reduced graphene oxide coated hollow core fiber is demonstrated. The reduced graphene oxide is deposited on the outer surface of the hollow core fiber, and a Fabry–Perot resonator is formed in the cladding region. The leaky mode of the guided light can be achieved at resonant wavelength of the Fabry–Perot resonator, which results in lossy dip in the transmission spectrum of the hollow core fiber. Due to the tunable refractive index of the reduced graphene oxide, the humidity can be measured by interrogating the transmission intensity of the lossy dip. The experimental results show that the sensitivity of up to 0.22dB/% RH is achieved. The humidity sensor possesses good repeatability, fast response time, and low temperature cross-sensitivity. The reduced graphene oxide based humidity sensor appears to have potential applications in researches of chemistry, medicine, and biology.

Integrated terahertz multiparameter sensors using fiber/frequency selective surface couplers

We propose using THz frequency selective surfaces interrogated with THz subwavelength optical fibers as integrated sensors for monitoring of the optical properties of thick optically non-transparent films that are brought into contact with such sensors. Changes in the test film thickness and absorption losses can be measured simultaneously by interpreting variations in the spectral resonant features in the fiber transmission and reflection spectra. In particular, changes in the film thickness induce strong shifts in the fiber transmission peaks, while changes in the film absorption induce notable amplitude variations in the fiber reflection peaks. When applied to the problem of monitoring the thickness and humidity content of paper sheets, the proposed system shows a sensitivity of 1.5 GHz/10 μm to changes in the paper’s thickness and a sensitivity of 0.6/(% of water by volume) to changes in the paper’s humidity. We estimate the detection limit of our device to be 10 μm for the paper thickness variation and 0.02% (of water by volume) for the paper humidity variation. The proposed sensor is implemented in the spirit of integrated optics, where a point device based on the frequency selective surface is interrogated with a THz fiber that is used for remote delivery of THz radiation.