PMMA Cladding Research Articles

Salinity Concentration Sensing Based on a Tapered Dual-Core As2Se3-PMMA Hybrid Fiber

A method to measure salinity concentration in a 10cm-long tapered dual-core As <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Se <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> -Polymethyl methacrylate (As <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Se <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> -PMMA) hybrid fiber with an As <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Se <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> core diameter of 1.5μm and a PMMA cladding diameter of 88.5μm is proposed. When the salinity concentration is changed in a water bath where the dual-core hybrid taper is placed, the strain on As <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Se <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> cores by the volume change of PMMA cladding and the refractive index of PMMA cladding are varied, which induce the change of effective refractive index difference between odd and even modes and the wavelength dip shift of the interference spectra in two polarization axes of the dual-core taper. The maximum salinity sensitivities of -0.883nm/(mol/L) and -0.847nm/(mol/L) are experimentally measured in fast and slow axes, respectively, when the salinity concentration changes from 0 to 5mol/L. The salinity sensitivity of the dual-core taper is higher than that of polymer-coated fiber Bragg grating due to the large hygral-induced strain on As <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Se <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> microwires with small Young's modulus by the volume change of PMMA and the refractive index change of PMMA cladding. The tapered dual-core As2Se3-PMMA hybrid fiber sensor is a good candidate for salinity concentration sensing as high sensitivity, easy to be fabricated and good repeatability.

Wide-range strain sensor based on Brillouin frequency and linewidth in an As2Se3-PMMA hybrid microfiber.

We propose a wide-range strain sensor based on Brillouin frequency and linewidth in a 50 cm-long As2Se3-polymethyl methacrylate (As2Se3-PMMA) hybrid microfiber with a core diameter of 2.5 µm. The distributed information over the hybrid microfiber is measured by a Brillouin optical time-domain analysis (BOTDA) system. The wide dynamic range strain from 0 to 15000 µɛ is enabled by measuring the Brillouin frequency and linewidth due to the low Young's modulus of As2Se3 core and the high mechanical strength of PMMA cladding. The deformation of the As2Se3-PMMA hybrid microfiber is observed when the strain is greater than 1500 µɛ by measuring the distributed Brillouin frequency and Brillouin linewidth over the 50 cm-long hybrid microfiber. The measured errors based on the Brillouin frequency in the range of 0-1500 µɛ and 1500-15000 µɛ are 42 µɛ and 105 µɛ, respectively. The measured error based on the Brillouin linewidth is 65 µɛ at 0-1500 µɛ and the maximum error is 353 µɛ when the tensile strain is 15000 µɛ. No strain memory effect is observed compared with the polymer optical fiber due to Young's modulus in As2Se3 is larger than that in polymer. Numerical simulations are developed to accurately predict the strain dependence of Brillouin frequency in the As2Se3-PMMA hybrid microfiber.

Fabrication of chirped fiber Bragg gratings in a non-uniform single-core As$_{2}$Se$_{3}$-PMMA tapered fiber

A chirped fiber Bragg grating (FBG) is fabricated using a non-uniform single-core As2Se3-PMMA tapered fiber that is pre-stretched by 0.52 mm during the inscription process. The inscription is based on a standing wave formed by two counter-propagating continuous-wave lights in the stretched non-uniform single-core As2Se3-PMMA taper. A periodical refractive index change by the standing wave in the high photosensitivity As2Se3 core is induced, which creates a FBG along the taper. A strain gradient is formed along the grating due to the non-uniform structure when the elongation is changed, which produces a varying shift in the Bragg spacing at different position along the taper leading to a tunable chirped grating. The central wavelength and bandwidth are linearly dependent on the strain change applied to the chirped grating. The wide tuning range is attributed to the low stiffness of the chalcogenide core and PMMA cladding. An exponential dependence of the amplitude of the chirping spectrum on the wave number is derived, which shows the potential for applications such as weak forces detections. Furthermore, long chirped FBGs can be easily inscribed using standing waves in As2Se3-PMMA tapered fibers, which is far beyond the practical length of phase masks and is desirable for chromatic dispersion compensation in high-bit-rate optical fiber transmission systems and distributed sensors. A 50 cm long chirped FBG with chirped wavelength range of ∼15 nm is inscribed and characterized. Fabrication of chirped FBGs in non-uniform single-core As2Se3-PMMA tapers opens the path towards the realization of novel sensors and devices.

High-Sensitivity Temperature and Strain Measurement in Dual-Core Hybrid Tapers

We demonstrate an approach for high-sensitivity temperature and strain measurement in a dual-core As2Se3-PMMA taper with an As2Se3 core diameter of $2.5~\mu \text{m}$ . To improve the sensitivity of temperature and strain measurement, we designed the dual-core As2Se3-PMMA fiber with inorganic As2Se3 cores and organic PMMA cladding and also the even and odd modes to build an interferometer. The variation of the difference between phases of the two modes with respect to wavelength ( $\partial \phi _{d}(\lambda)/\partial \lambda)$ decreases with the As2Se3 core diameter increasing, and consequently, thermally induced and strain-induced change of the difference between phases of the two modes $\phi _{d}(\lambda)$ leads to a large wavelength shift indicating enhancement of the temperature and strain measurement sensitivity. Furthermore, thermally induced longitudinal and transverse forces on the As2Se3 cores further enhance the temperature measurement sensitivity. High sensitivities of 436 pm/°C, −6.23 pm/ $\mu \boldsymbol {\varepsilon }$ and 572 pm/°C, and −3.63 pm/ $\mu \boldsymbol {\varepsilon }$ from the transmission spectra of axis-1 and axis-2 in the dual-core As2Se3-PMMA taper are obtained.

Simultaneous Measurement of Temperature and Strain in a Dual-Core As2Se3-PMMA Taper

We propose and demonstrate an approach for high-sensitivity simultaneous temperature and strain measurement in a dual-core As2Se3-polymethyl methacrylate (PMMA) taper. High measurement sensitivity is achieved by combining the large thermal-expansion coefficient of the PMMA cladding, the low stiffness of the micrometer diameter As2Se3 core, and the large difference between the refractive indices of As2Se3 and PMMA. High measurement sensitivities of −115 pm/°C and −4.21 pm/ $\mu \varepsilon $ are measured from the transmission spectrum of one principal polarization axis of the dual-core fiber, and −35.5 pm/°C and −3.16 pm/ $\mu \varepsilon $ are obtained from the transmission spectrum of the second polarization axis of the dual-core fiber. Decorrelation between the temperature and strain measurement sensitivities of the principal polarization axes is achieved through thermally induced squeezing of the As2Se3 cores by the PMMA cladding due to an order of magnitude difference between the thermal-expansion coefficients of As2Se3 and PMMA, enabling simultaneous measurement of temperature and strain variations with the temperature and strain uncertainty of 0.15 °C and 1.87 $\mu \varepsilon $ .

Bragg grating-based Fabry–Perot interferometer fabricated in a polymer fiber for sensing with improved resolution

We demonstrate for the first time a Bragg grating-based Fabry–Perot interferometer (FPI) fabricated in the polymer fiber with a core made of PMMA/PS copolymer and pure PMMA cladding. The FPI was formed by two gratings with the same Bragg wavelength, λB = 1312 nm, separated by a small gap. The FP cavity was created directly during the grating inscription process by placing a narrow blocking aperture, in the center of the UV beam. Good long-term stability was achieved by fabricating the gratings of type II with long irradiation time (8 min). By choosing an appropriate width of the blocking aperture, we could control the number and the width of interference fringes visible in the grating’s reflection spectrum. Sharp fringes were obtained, of 3 dB width within the range of 50–100 pm, allowing for a significant increase in measurement resolution compared to direct interrogation of a single grating. The proposed interferometer was tested in measurements of strain and temperature in the range of 0–20 mstrain and 20 °C–70 °C, showing the sensitivity of 1.074 nm mstrain−1 and −25.1 pm °C−1, respectively.

Inscription of long period gratings using an ultraviolet laser beam in the diffusion-doped microstructured polymer optical fiber.

We show that diffusion of azobenzene from the solution in methanol into a cladding of a polymer fiber facilitates fabrication of long period gratings by the use of a He-Cd focused laser beam. We have measured a diffusion rate into PMMA cladding of the microstructured fibers annealed in advance at different temperatures and showed that the diffusion rate is strongly affected by temperature treatment of the fiber. We have also investigated an impact of the azobenzene diffusion on fiber spectral loss and cladding surface quality. Furthermore, we have examined a temporal stability of the fabricated long period gratings and their response to temperature and tensile strain.

Highly birefringent polymer side-hole fiber for hydrostatic pressure sensing.

We report on the fabrication of a birefringent side-hole polymer optical fiber with an elliptical core made of polymethyl metacrylate-polystyrene (PMMA/PS) copolymer and pure PMMA cladding. The fiber core is located in a narrow PMMA bridge separating the holes. Two fibers with different bridge thickness were fabricated and characterized. We demonstrate, experimentally and numerically, that, by narrowing the bridge between the holes, one can increase simultaneously the fiber birefringence and the polarimetric sensitivity to hydrostatic pressure. In the fiber with the bridge as narrow as 5 μm, we achieved a record-high polarimetric sensitivity to hydrostatic pressure ranging between 175 and 140 rad/MPa/m in the spectral range of 600-830 nm. The phase modal birefringence in this fiber is also high and exceeds 3×10(-5) at 600 nm, which results in small polarization cross talk.

WE-E-18A-08: Towards a Next-Generation Electronic Portal Device for Simultaneous Imaging and Dose Verification in Radiotherapy

Purpose: This work forms part of an ongoing study to develop a next-generation electronic portal imaging device (EPID) for simultaneous imaging and dose verification in radiotherapy. Monte Carlo (MC) simulations were used to characterize the imaging performance of a novel EPID that has previously been demonstrated to exhibit a water-equivalent response. The EPID ' s response was quantified in several configurations and model parameters were empirically validated against experimental measurements. Methods: A MC model of a novel a-Si EPID incorporating an array of plastic scintillating fibers was developed. Square BCF-99-06A scintillator fibers with PMMA cladding (Saint-Gobain Crystals) were modelled in a matrix with total area measuring 150×150 mm{sup 2}. The standard electromagnetic and optical physics Geant4 classes were used to simulate radiation transport from an angled slit source (6 MV energy spectrum) through the EPID and optical photons reaching the photodiodes were scored. The prototype's modulation transfer function (MTF) was simulated and validated against experimental measurements. Several optical transport parameters, fiber lengths and thicknesses of an air gap between the scintillator and photodiodes were investigated to quantify their effects on the prototype's detection efficiency, sensitivity and MTF. Results: Simulated EPID response was more sensitive to variations in geometry than inmore » the optical parameters studied. The MTF was particularly sensitive to the introduction of a 0.5–1.0 mm air gap between the scintillator and photodiodes, which lowered the MTF relative to that simulated without the gap. As expected, increasing the fiber length increased the detector efficiency and sensitivity while decreasing the MTF. Conclusion: A model of a novel water-equivalent EPID has been developed and benchmarked against measurements using a physical prototype. We have demonstrated the feasibility of this new device and are continuing to optimize the design to achieve an imaging response that warrants the development of a next-generation prototype.« less

Birefringence Engineering and High Nonlinearity in Eccentric-Core As$_{2}$Se$_{3}$-PMMA Microtapers

A hybrid fiber with an eccentric As <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Se <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> core and a PMMA cladding is tapered to a submicron diameter to achieve ultra high birefringence and a high nonlinearity. The high birefringence is induced by having the As <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Se <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> core eccentric with respect to the circular PMMA cladding symmetry and the high nonlinearity is induced from a tightly confining As <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Se <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> core. Microwires with high group birefringence up to <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">b</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> =0.018 and a high waveguide nonlinearity γ = 180 W <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> are demonstrated.

Fabrication of Si-based waveguide splitters using photosensitive sol–gel method

In this paper, a photosensitive sol–gel method for 1 × 8 Y-branch optical splitter is reported. The poly (methyl methacrylate) (PMMA) cladding films with different thicknesses (above 10 μm) on Si substrates are prepared on Si substrates by dip-coating, the root-mean-square roughness (Rrms) of which is less than 0.7 nm. The UV photosensitive organic–inorganic composite SiO 2/ZrO 2/H core films are then coated on these PMMA cladding films using photosensitive sol–gel method. The refractive indexes of PMMA cladding films examined by spectroscopic ellipsometer are 1.4854, 1.4815 and 1.4806 at 0.85, 1.31 and 1.55 μm, while that of the SiO 2/ZrO 2/H gel films are 1.5569, 1.5489 and 1.5472 μm, respectively, which is larger than that of PMMA cladding films. Therefore, the composite structure of SiO 2/ZrO 2/H gel films on PMMA-on-Si substrates could be used to fabricate waveguide splitter. Based on the inherent photosensitivity of the SiO 2/ZrO 2/H gel film, 1 × 8 Y-branch optical power splitters with a thickness of 5 μm are fabricated by irradiating the gel film with UV light through a mask followed by dissolving the non-irradiated area in a suitable solvent. The line-width and output spacing of this splitter are 25 and 110 μm, respectively. The observed near-field pattern indicates that the light with a wavelength of 1.53–1.56 μm can be transmitted and split into eight branches in the optical splitter, which is fabricated by using the above technique.

Fabrication process and optical properties of perdeuterated graded-index polymer optical fiber

We proposed a graded-index polymer optical fiber (GI-POF) enabling greater-than-gigabit data transmission in a short reach network by applying a two-step interfacial-gel polymerization process to a perdeuterated polymer material. Using this process, it is possible to fabricate a nearly optimum refractive-index profile with good reproducibility. In this paper, the preparation of a perdeuterated polymethyl methacrylate (PMMA-d8)-based GI-POF utilizing a PMMA cladding is described. This means that the low-loss PMMA-d8 material is used only for the core. Because the cladding transmits only a small fraction of the optical power, a low-loss material is not necessarily required for the cladding. It was verified that the low attenuation of the PMMA-d8 was maintained even if the cladding was composed of hydrogenated PMMA. As a result, a gigabit data transmission over 300 m was achieved by the PMMA-d8-core and PMMA-cladding GI-POF, which was impossible by the conventional PMMA-based GI-POF.

High-Q ring resonators in thin silicon-on-insulator

We have fabricated high-Q microrings from thin silicon-on-insulater SOI layers and measured Q values of 45 000 in these rings, which were then improved to 57 000 by adding a PMMA cladding. The optimal waveguide designs were calculated, and the waveguide losses were analyzed. These high-Q resonators are expected to lead to interesting devices for telecommunication filters and sources as well as optical refractive index sensing.

Studies on scintillating fiber response

Abstract Scintillating fibers of type Bicron BCF-12 with 2 × 2 mm2 cross section, up to 600 mm length, and PMMA cladding have been tested, in conjunction with the multi-channel photomultiplier Hamamatsu R 4760, with minimum ionizing electrons. The impact of cladding, extramural absorbers and/or wrapping on the light attenuation and photoelectron yield is studied in detail. Fibers have been circularly bent with radii of 171 mm and arranged in two layers to bundles forming granulated scintillator rings. Their performance in the EDDA experiment at COSY for detection of high energy protons revealed typically more than 9 (6) photoelectrons per fiber from bundles with (without) mirror on the rear side, guaranteeing detection efficiencies >99% and full compatibility with corresponding solid scintillator rings. The time resolution of 3.4 ns FWHM per fiber read out is essentially due to the R 4760.

Measurement of the reflection coefficient at the core-cladding interface in plastic scintillating fibers

We have measured the reflection coefficient, that is the loss of light, at the boundary between the cladding and the core of a plastic scintillating fiber. The coefficient was measured as a function of the wavelength of light, produced by a krypton laser, between 400 and 620 nm, and as a function of the angle of incidence of the light. The optical scintillating fibers, with a polystyrene core and a PMMA cladding, are those widely used for the detection of high-energy particles. We observed losses of the order of 10 −4 per reflection, which increase when going to shorter wavelengths and which have roughly a linear dependence on the angle of incidence.