Optical Fiber Tip Research Articles

Optimization of Temperature Sensing with Polymer-Embedded Luminescent Ru(II) Complexes.

Temperature is a key parameter in many fields and luminescence-based temperature sensing is a solution for those applications in which traditional (mechanical, electrical, or IR-based) thermometers struggle. Amongst the indicator dyes for luminescence thermometry, Ru(II) polyazaheteroaromatic complexes are an appealing option to profit from the widespread commercial technologies for oxygen optosensing based on them. Six ruthenium dyes have been studied, engineering their structure for both photostability and highest temperature sensitivity of their luminescence. The most apt Ru(II) complex turned out to be bis(1,10-phenanthroline)(4-chloro-1,10-phenanthroline)ruthenium(II), due to the combination of two strong-field chelating ligands (phen) and a substituent with electron withdrawing effect on a conjugated position of the third ligand (4-Clphen). In order to produce functional sensors, the dye has been best embedded into poly(ethyl cyanoacrylate), due to its low permeability to O2, high temperature sensitivity of the indicator dye incorporated into this polymer, ease of fabrication, and excellent optical quality. Thermosensitive elements have been fabricated thereof as optical fiber tips for macroscopic applications (water courses monitoring) and thin spots for microscopic uses (temperature measurements in cell culture-on-a-chip). With such dye/polymer combination, temperature sensing based on luminescence lifetime measurements allows 0.05 °C resolution with linear response in the range of interest (0–40 °C).

Nanosphere Lithography on Fiber: Towards Engineered Lab-On-Fiber SERS Optrodes.

In this paper we report on the engineering of repeatable surface enhanced Raman scattering (SERS) optical fiber sensor devices (optrodes), as realized through nanosphere lithography. The Lab-on-Fiber SERS optrode consists of polystyrene nanospheres in a close-packed arrays configuration covered by a thin film of gold on the optical fiber tip. The SERS surfaces were fabricated by using a nanosphere lithography approach that is already demonstrated as able to produce highly repeatable patterns on the fiber tip. In order to engineer and optimize the SERS probes, we first evaluated and compared the SERS performances in terms of Enhancement Factor (EF) pertaining to different patterns with different nanosphere diameters and gold thicknesses. To this aim, the EF of SERS surfaces with a pitch of 500, 750 and 1000 nm, and gold films of 20, 30 and 40 nm have been retrieved, adopting the SERS signal of a monolayer of biphenyl-4-thiol (BPT) as a reliable benchmark. The analysis allowed us to identify of the most promising SERS platform: for the samples with nanospheres diameter of 500 nm and gold thickness of 30 nm, we measured values of EF of 4 × 105, which is comparable with state-of-the-art SERS EF achievable with highly performing colloidal gold nanoparticles. The reproducibility of the SERS enhancement was thoroughly evaluated. In particular, the SERS intensity revealed intra-sample (i.e., between different spatial regions of a selected substrate) and inter-sample (i.e., between regions of different substrates) repeatability, with a relative standard deviation lower than 9 and 15%, respectively. Finally, in order to determine the most suitable optical fiber probe, in terms of excitation/collection efficiency and Raman background, we selected several commercially available optical fibers and tested them with a BPT solution used as benchmark. A fiber probe with a pure silica core of 200 µm diameter and high numerical aperture (i.e., 0.5) was found to be the most promising fiber platform, providing the best trade-off between high excitation/collection efficiency and low background. This work, thus, poses the basis for realizing reproducible and engineered Lab-on-Fiber SERS optrodes for in-situ trace detection directed toward highly advanced in vivo sensing.

Reconfiguration of the multiwavelength operation of optical fiber ring lasers by the modifiable intra-cavity induced losses of an in-fiber tip probe modal Michelson interferometer

A straightforward and versatile method for switching from single to different multiwavelength laser emission in ring cavity fiber lasers is proposed and demonstrated experimentally. The method is based on using the changeable interference pattern from an optical fiber modal Michelson interferometer as a wavelength selective filter into the ring cavity laser. The interferometer is constructed using a bi-conical tapered fiber and a single-mode fiber segment, with these being spliced together to form an optical fiber tip probe. When the length of the single-mode fiber piece is modified, the phase difference between the interfering modes of the interferometer causes a change in the interferometer free spectral range. As a consequence, the laser intra-cavity losses lead to gain competition, which allows us to adjust the number of simultaneously generated laser lines. A multiwavelength reconfiguration of the laser from one up to a maximum of eight emission lines was obtained, with a maximum SNR of around 47 dBm.

Development and validation of a multilateration test bench for particle accelerator pre-alignment

The development and validation of a portable coordinate measurement solution for fiducialization of compact linear collider (CLIC) components is presented. This new solution addresses two limitations of high-accuracy state-of-the-art coordinate measuring machines, i.e. lack of portability and limited measurement volume. The solution is based on frequency scanning interferometry (FSI) distances and the multilateration coordinate measurement technique. The developments include a reference sphere for localizing the FSI optical fiber tip and a kinematic mount for repositioning the reference sphere with sub-micrometric repeatability. This design enables absolute distance measurements in different directions from the same point, which is essential for multilateration. A multilateration test bench built using these prototypes has been used to fiducialize a CLIC cavity beam position monitor and 420 mm-long main beam quadrupole magnet. The combined fiducialization uncertainty achieved is 3.5 μm (k = 1), which is better than the CLIC 5 μm (k = 1) uncertainty specification.

All-Fiber Raman Biosensor by Combining Reflection and Transmission Mode

A novel all-fiber on-line Raman cell based on metal (silver)-lined capillary is proposed, which could collect reflection and transmission Raman signal simultaneously. In our configuration, two optical fiber tips are inserted into both sides of the hollow-core metal-lined capillary to form a Raman cell. The other ends of fiber tips are closely bound together as a Sagnac loop and coupled with a Raman probe. Each fiber tip not only works in reflection mode, but also acts as the collection lens for the transmission mode of the other side's excitation. The hollow-core all-fiber structure could extend the interaction length between the samples and pump laser. Moreover, the Raman signal collection mechanism was significantly improved. With the combination of both Raman excitation modes, a Raman signal with two times of magnitude enhancement is observed in experiment and it agrees well with the theoretical analysis. We have also detected different concentrations (0.5-8 mg/mL) of antibiotic (Cefotaxime sodium, CTX), which proves that our proposed all-fiber and well-encapsulated Raman cell has tremendous potential for portable on-line rapid Raman biosensor.

Optical fiber tip interferometer gas pressure sensor based on anti-resonant reflecting guidance mechanism

Abstract We propose and demonstrate a gas pressure sensor based on an anti-resonant reflecting guidance (ARRG) mechanism in quartz capillary tube with an open cavity. The device is simple in fabrication by only fusion splicing a segment of capillary tube with single mode fiber. It has compact size, robust structure, convenient mode of operation, and high sensitivity of 4.278 nm/MPa. Moreover, as two Faby-Perot cavities exist in the device, which create the interference spectrum with several distinct resonance dips, a simultaneous gas pressure and temperature detection can be readily achieved by tracing two dip wavelengths. The error in the measurement due to the choice of different resonant dips can be effectively reduced by using the Fourier band pass filtering method.

Large area laser scanning optical resolution photoacoustic microscopy using a fibre optic sensor.

A laser scanning optical resolution photoacoustic microscopy (LS OR-PAM) system based on a stationary fibre optic sensor is described. The sensor comprises an optically resonant interferometric polymer cavity formed on the tip of a rounded single mode optical fibre. It provides low noise equivalent pressure (NEP = 68.7 Pa over a 20 MHz measurement bandwidth), a broad bandwidth that extends to 80 MHz and a near omnidirectional response. The latter is a significant advantage, as it allows large areas (>1cm2) to be imaged without the need for translational mechanical scanning offering the potential for fast image acquisition. The system provides a lateral resolution of 8 µm, an axial resolution of 21 µm, and a field of view up to 10 mm × 10 mm. To demonstrate the system, in vivo 3D structural images of the microvasculature of a mouse ear were obtained, showing single capillaries overlaying larger vessels as well as functional images revealing blood oxygen saturation.

Fibre-optic metadevice for all-optical signal modulation based on coherent absorption

Recently, coherent control of the optical response of thin films in standing waves has attracted considerable attention, ranging from applications in excitation-selective spectroscopy and nonlinear optics to all-optical image processing. Here, we show that integration of metamaterial and optical fibre technologies allows the use of coherently controlled absorption in a fully fiberized and packaged switching metadevice. With this metadevice, which controls light with light in a nanoscale plasmonic metamaterial film on an optical fibre tip, we provide proof-of-principle demonstrations of logical functions XOR, NOT and AND that are performed within a coherent fibre network at wavelengths between 1530 and 1565 nm. The metadevice has been tested at up to 40 gigabits per second and sub-milliwatt power levels. Since coherent absorption can operate at the single-photon level and with 100 THz bandwidth, we argue that the demonstrated all-optical switch concept has potential applications in coherent and quantum information networks.

Development of a Lens‐less Mid‐Infrared Laser Head for the Optical Fiber Tip Oscillation to Apply to Therapeutic Treatment

SUMMARYMid‐infrared lasers having the wavelength of the vicinity of 3 μm are considered as effective for the treatment of biomedical tissue because of the strong absorption to water. The drawback of 3 μm laser is the difficulty to propagate the silica optical fiber. We have reported the optical fiber tip oscillation laser that has a Er,Cr:YAGG laser crystal and coupling lenses on the tip of a silica fiber outputs 2.8 μm laser pumped by laser diode. In this paper, we demonstrated a lens‐less laser head for the optical fiber tip oscillation. By using the silica optical fiber having a core diameter of 105 μm and a numerical aperture of 0.12, the average output power of 1.0 W was achieved from the lens‐less laser head during a squire wave modulation for suppressing heat generation.

Subradiant Dipolar Interactions in Plasmonic Nanoring Resonator Array for Integrated Label-Free Biosensing.

With the development of advanced nanofabrication technologies over the past decade, plasmonic nanostructures have attracted wide attention for their potential in label-free biosensing applications. However, the sensing performance of nanostructured plasmonic sensors is primarily limited by the broad-line-width features with low peak-to-dip signal ratio in the extinction spectra that result from strong radiative damping. Here, we propose and systematically investigate the in-plane and out-of-plane dipolar interactions in an array of plasmonic nanoring resonators that are from the spatial combination of classic nanohole and nanodisk structures. Originating from the strong coupling of the dipolar modes from parent nanohole and nanodisk structures, the subradiant lattice plasmon resonance in the nanoring resonator array exhibits narrow-line width spectral features with high peak-to-dip signal ratio and strong near-field electromagnetic enhancement, making it an ideal platform for high-sensitivity chemical and biomedical sensing. We experimentally demonstrate that the plasmonic nanoring resonator array can be used for high-sensitivity refractive index sensing and real-time monitoring of biomolecular specific binding interactions at nanomolar concentration. Moreover, due to its simple normal incident illumination scheme and polarization independent optical response, we further transfer the plasmonic nanoring resonator array onto the optical fiber tip to demonstrate an integrated and miniaturized platform for label-free remote biosensing, which implies that the plasmonic nanoring resonator array may be a potential candidate for developing high performance and highly integrated photonic biosensing systems.

Nanopatterned Optical Fiber Tip for Guided Mode Resonance and Application to Gas Sensing

This paper reports on an efficient and convenient method of patterning nanostructures on the cleaved facet of an optical fiber to realize a high-performance fiber-optic gas sensor. The fabrication method utilizes an ultraviolet assisted nanoimprint lithography to transfer nanoscale patterns from a pre-formed stamp to the fiber tip. The novelty of this paper lies in utilizing simpler fabrication steps with better control over angle of contact at the fiber tip, which leads to rapid and precise formation of nanostructures with well-defined features. A periodic array of polymer nanoposts are formed at the fiber tip and coated with titanium dioxide to serve as a guided mode resonant (GMR) device. A gas sensor is realized by coating the GMR structure with a thin layer of graphene oxide (GO) nanosheets. We have utilized the resonance sensitivity of the nanopatterned fiber-tip gas sensor to surrounding refractive index. The abundant functional groups available at GO provides an effective adsorption surface for gas molecules. Microscopic imaging and spectroscopic studies are conducted to illustrate the structural and optical properties, and gas-sensing performance of the sensor. Volatile organic compounds, such as ethylene and methanol, associated with crop plant health, are detected by the sensor. The sensor provides sensitivities of 0.92 and 1.37 pm/ppm for ethylene and methanol vapors, respectively, with a three-fold enhancement in sensitivity and 50% reduction in response time compared with the non-GO coated counterpart. In addition, the sensor demonstrates good stability and reproducibility, thus having a great potential in fiber-optic remote sensing applications.

Performance Analysis of Localized Surface Plasmon Resonance Sensor with and Without Bragg Grating

Abstract The performance of localized surface plasmon resonance-based sensor with and without Bragg grating by using finite difference time domain method is evaluated with nanoparticles used at the tip of optical fiber. The proposed sensor has been analyzed in terms of refractive index (RI) sensitivity and signal-to-noise ratio (SNR). It is observed that the RI sensitivity of surface plasmon resonance sensor is 240 nm/RIU with and without grating as RI of surrounding varies from 1.4 to 1.5. It is found that the value of SNR is 0.875 RIU→1 without grating and 2.75 RIU→1 with grating. So there is an improvement in the SNR when the Bragg grating is inscribed within the core of the fiber.

Effects of low-level laser irradiation on the rate of orthodontic tooth movement and associated pain with self-ligating brackets.

The aim of this study was to evaluate the effect of low-level laser irradiation applied at 3-week intervals on orthodontic tooth movement and pain associated with orthodontic tooth movement using self-ligating brackets. Twenty-two patients (11 male, 11 female; mean age, 19.8±3.1years) with Angle Class II Division 1 malocclusion were recruited for this split-mouth clinical trial; they required extraction of maxillary first premolars bilaterally. After leveling and alignment with self-ligating brackets (SmartClip SL3; 3M Unitek, St Paul, Minn), a 150-g force was applied to retract the canines bilaterally using 6-mm nickel-titanium closed-coil springs on 0.019 x 0.025-in stainless steel archwires. A gallium-aluminum-arsenic diode laser (iLas; Biolase, Irvine, Calif) with a wavelength of 940nm in a continuous mode (energy density, 7.5J/cm2/point; diameter of optical fiber tip, 0.04cm2) was applied at 5 points buccally and palatally around the canine roots on the experimental side; the other side was designated as the placebo. Laser irradiation was applied at baseline and then repeated after 3weeks for 2 more consecutive follow-up visits. Questionnaires based on the numeric rating scale were given to the patients to record their pain intensity for 1week. Impressions were made at each visit before the application of irradiation at baseline and the 3 visits. Models were scanned with a CAD/CAM scanner (Planmeca, Helsinki, Finland). Canine retraction was significantly greater (1.60±0.38mm) on the experimental side compared with the placebo side (0.79±0.35mm)(P<0.05). Pain was significantlyless on the experimental side only on the first day after application of LLLI and at the second visit (1.4±0.82 and 1.4±0.64) compared with the placebo sides (2.2±0.41 and 2.4±1.53). Low-level laser irradiation applied at 3-week intervals can accelerate orthodontic tooth movement and reduce the pain associated with it.

Dispersion of near-infrared laser energy through radicular dentine when using plain or conical tips.

The aim of this study was to investigate the influence of tip design on patterns of laser energy dispersion through the dentine of tooth roots when using near-infrared diode lasers. Diode laser emissions of 810 or 940nm were used in combination with optical fiber tips with either conventional plain ends or conical ends, to irradiate tooth roots of oval or round cross-sectional shapes. The lasers were operated in continuous wave mode at 0.5W for 5s with the distal end of the fiber tip placed in the apical or coronal third of the root canal at preset positions. Laser light exiting through the roots and apical foramen was imaged, and the extent of lateral spread calculated. There was a significant difference in infrared light exiting the root canal apex between plain and conical fiber tips for both laser wavelengths, with more forward transmission of laser energy through the apex for plain tips. For both laser wavelengths, there were no significant differences in emission patterns when the variable of canal shape was used and all other variables were kept the same (plain vs conical tip, tip position). To ensure optimal treatment effect and to prevent the risks of inadvertent laser effects on the adjacent periapical tissues, it is important to have a good understanding of laser transmission characteristics of the root canal and root dentine. Importantly, it is also essential to understand transmission characteristics of plain and conical fibers tips.

Localized surface plasmon resonance sensing structure based on gold nanohole array on beveled fiber edge

This paper proposes a simple, stable, sensitive, and angle-dependent localized surface plasmon resonance (LSPR) sensing structure based on multi-mode optical fiber. We adopted the template transfer method to integrate a nanohole array onto a fiber tip with beveled angle. Experimental results indicated that beveled angle structured probe sensor outperform the flat optical fiber tip structured LSPR sensor in our experiment. We tested the sensitivity and the figure of merit (FOM) of the probe beveled angle from 5°–22°, with refractive index ranging from 1.333–1.385, to find that sensitivity and FOM were optimal at fiber tip bevel angle of 7°, reaching 487 nm/RIU and 29 respectively.

Utilization of ZnO nanorods growth on a tip of plastic optical fiber toward the realization of low-cost CO and CO2 gas sensor

This study experimentally demonstrates the feasibility of utilizing zinc oxide nanorods for CO and CO2 gas detection via optical scattering. ZnO nanorods are grown on a plastic optical fiber to measure the effect of gas flow on the optical scattering at room temperature. The presence of nanorods minimizes the coupling of the Fresnel reflection. Placing the optical setup in a home-built gas chamber, an obvious distinguished change of the total reflection was observed when different gas concentrations were present. Reduction of reflection due to the presence of gas indicated that forward scattering leak has a dominant effect on the process. In addition, the results demonstrated that detection of CO gas at a concentration as low as 200 ppm had a higher response in comparison with CO2 gas.

Effect of optical fiber type and absorption medium on the endovenous laser ablation mechanism

Our experimental investigation was aimed at revealing the mechanism behind the action of laser radiation on venous wall under endovenous laser ablation conditions. We determined the critical laser power Pcr at which the objective effect of complete denaturation of the vascular tissue collagen was attained for two types of optical fiber in the presence and absence of blood cells. We demonstrated that for the radial optical fiber the presence of blood cells had no effect on the magnitude of Pcr, which came to 4.3 ± 0.1 and 5.6 ± 01 W for 1.56 and 1.47 µm lasers, respectively. For the bare fiber and 1.56 µm laser, Pcr increased up to 5.2 ± 0.2 W in a blood-filled vessel and up to 7.1 ± 0.2 W when the blood was replaced by a sodium chloride solution. Our data show that the heating and degradation of insufficient veins go on more effectively when the tissue is heated by laser radiation directly absorbed therein, rather than the red-hot carbonized optical fiber tip.

Volume relaxation of quenched silica at room temperature monitored by whispering gallery mode resonance wavelength

We used a resonance wavelength shift of a whispering gallery mode to monitor volume relaxation at room temperature in cylindrical and spherical resonators fabricated by quenching the molten tip of a pure silica optical fiber. The high sensitivity of the method allowed measurement of the linear dimension at sub-ppm resolution. All the resonators registered a volume increase in the first few hours, in agreement with the volume-temperature equilibrium curve of type IV silica below the glass transition temperature. When heating of the fiber was insufficient, the volume increase was greater, ascribed to a larger volume of strained silica. We also formulated thermodynamics to estimate the temperature coefficients of polarizability at constant pressure and at constant density from resonance shift data obtained in experiments performed on relaxed silica resonators.

DNA-based fiber optic sensor for direct in-vivo measurement of oxidative stress

Oxygen is one of the most significant elements for life because almost all living organisms utilize oxygen for respiration and energy generation. However, some derivatives of oxygen including free radicals called reactive oxygen species (ROS) are detrimental and cause several diseases such as neurodegeneration, diabetes, cancer and atherosclerosis. Oxidative stress is essentially an inability of our body to counteract or detoxify the harmful effects of ROS through neutralization by antioxidants. Till date direct in-vivo measurements of oxidative stress are challenging. In this work, we have developed a novel 2,7-dichlorodihydrofluorescein (DCFH) impregnated genomic DNA-based biomaterial, which is completely insoluble in water and forms excellent thin film layers on optical fiber tips. The biomaterial-sensitized fiber tip fluoresces brightly in the proximity of ROS as the entrapped DCFH is oxidized to highly fluorescent DCF. We have demonstrated that an indigenously developed biomaterial-sensitized optical fiber tip can work as an efficient ROS/oxidative stress sensor in an aqueous medium as well as in the blood phantom (hemoglobin solution). A preclinical study on the minimally invasive direct in-vivo oxidative stress detection in mice model has also been successfully demonstrated.

레이저를 이용한 광섬유 곡률 형상 제어 및 초정밀 클리빙 기술

In this study, beam divergence through an optical fiber has been controlled through shaping of the optical fiber tip using a CO₂ laser, which make the beam divergence smaller than the conventional diamond wheel cleaving method. Precise length cleaving of an optical fiber inserted in a ferrule using a femtosecond laser has also been investigated with respect to changes of the laser pulse energy. A ribbon fiber composed of 12 optical fibers could be cut precisely at different lengths in a micrometer scale.