Core Cladding Research Articles

Comparison Study of Radiation-Resistant Polarization-Maintaining PANDA Fibers With Undoped- and N-Doped-Silica Core

For the first time, radiation-induced absorption (RIA) of light is compared in two types of polarization-maintaining PANDA fibers having 1) undoped-silica core and F-doped-silica cladding, or 2) N-doped-silica core and undoped-silica cladding. RIA at λ = 1.55 μm is compared under γ-irradiation and post-irradiation recovery at room temperature (RT) and −60 °C. The post-irradiation RIA decay at RT is used to extrapolate RIA to the postulated end of the PANDA space mission (15 years) with the help of the “nth-order kinetic” model. The RIA extrapolation values for both PANDA types are found to be comparable. RIA spectra are measured in the PANDAs in the spectral range ∼0.5–4 eV in the process of both γ-irradiation and recovery; then the spectra are deconvolved into Gaussians components. The RIA spectra of both PANDA types are found to be composed of inherent and strain-assisted self-trapped holes (STHs), some undoped PANDAs demonstrating, in addition, a long-wavelength RIA tail affecting λ = 1.55 μm. No N-related color centers are revealed. Finally, RIA at λ = 1.55 μm is compared upon pulsed-X-ray irradiation. Undoped PANDAs are found to feature much smaller RIA at RT at post-pulse times larger than ∼40–1000 μs, whereas at smaller times, an N-doped PANDA proved to be superior. At −60 °C and at t > 1 ms, both PANDA types demonstrate approximately equal RIAs. Thus, the experiments showed that the two PANDA types are quite comparable, each type having its own advantages and disadvantages.

A Flexi-PEGDA Upconversion Implant for Wireless Brain Photodynamic Therapy.

Near-infrared (NIR) activatable upconversion nanoparticles (UCNPs) enable wireless-based phototherapies by converting deep-tissue-penetrating NIR to visible light. UCNPs are therefore ideal as wireless transducers for photodynamic therapy (PDT) of deep-sited tumors. However, the retention of unsequestered UCNPs in tissue with minimal options for removal limits their clinical translation. To address this shortcoming, biocompatible UCNPs implants are developed to deliver upconversion photonic properties in a flexible, optical guide design. To enhance its translatability, the UCNPs implant is constructed with an FDA-approved poly(ethylene glycol) diacrylate (PEGDA) core clad with fluorinated ethylene propylene (FEP). The emission spectrum of the UCNPs implant can be tuned to overlap with the absorption spectra of the clinically relevant photosensitizer, 5-aminolevulinic acid (5-ALA). The UCNPs implant can wirelessly transmit upconverted visible light till 8 cm in length and in a bendable manner even when implanted underneath the skin or scalp. With this system, it is demonstrated that NIR-based chronic PDT is achievable in an untethered and noninvasive manner in a mouse xenograft glioblastoma multiforme (GBM) model. It is postulated that such encapsulated UCNPs implants represent a translational shift for wireless deep-tissue phototherapy by enabling sequestration of UCNPs without compromising wireless deep-tissue light delivery.

Estimation of cover sensitivity of a planar polymer waveguide through double path broadband difference interferometeric analysis

Broadband difference interferometeric analysis of a double path planar polymer optical waveguide is presented for bio-sensing applications. Mathematical formulation of intensity of output signal is obtained using interferometeric analysis. Further, the dispersion equation is obtained by matching the field at core cladding interface that gives the cutoff film thickness for TE0 and TM0 modes in considered spectral range. The waveguide is analyzed by propagating either same polarized (TETE or TMTM) modes or unlike polarized (TETM) modes in the reference arm and sensing arm. It is observed that difference of propagation constant for same polarized mode increases with increase of wavelength while for unlike polarized modes it first increases up to a maximum value and then decreases in the considered wavelength range. The maxima of output interference signal shifted prominently with the cover refractive index for the wavelength range near the maximum value of propagation constant difference. The obtained sensitivity 9.226 for unlike polarized modes in arms is much larger than the sensitivity 0.071 of same polarized modes in arms.

All-Optical Directional Control of Emission in a Photonic Liquid Crystal Fiber Laser

This study investigates the all-optical directional control of emission in a cholesteric liquid crystal (CLC)-infiltrated photonic crystal fiber (PCF) laser. A laser dye-doped CLC (LD-CLC) and an azobenzene LC-doped CLC (ALC-CLC), which are selectively infiltrated into the hollow core and holey-matrix cladding of the PCF, function as an optically active cavity and an all-optical emission direction-controllable light valve, respectively, in the photonic LC fiber (PLCF) laser. Experimental results show that the PLCF has a low energy threshold (approximately 63 nJ/pulse) and a large circular polarization anisotropy (g ≅ 2) in lasing output. The lasing output from the LD-CLC-filled core of the PLCF can be all-optical controlled to emit omni- or semi-directionally or to off-emit by controlling the isothermal phase transition of the CLC between the scattering focal conic state and the transparent isotropic state by the all-optical-induced reversible photoisomerization of the doped ALCs in the cladding region. The emission direction-controllable PLCF laser has significant potential in various applications, such as bio-image, photo-therapy, wearable devices, displays, sensors, and lighting.

Changes in the mechanical properties of bioactive borophosphate fiber when immersed in aqueous solutions

AbstractBioactive fibers have become increasingly prevalent for applications in optical sensing and as reinforcement in fully biodegradable devices. However, the typical bioactive glass fibers drawn from silicate glasses have poor mechanical properties. Here, we present our latest study on the development of new bioactive single‐core (SC) borophosphate fiber with the composition (in mol%) 47.5P2O5‐20CaO‐20SrO‐10Na2O‐2.5B2O3 and of core‐clad (CC) borophosphate fiber, the composition (in mol%) of the clad and the core being 47.5P2O5‐20CaO‐20SrO‐10Na2O‐2.5B2O3 and 0.025CeO2‐0.975(47.5P2O5‐20CaO‐20SrO‐10Na2O‐2.5B2O3), respectively. We show that the immersion in aqueous solutions such as Tris(hydroxymethyl)aminomethane (TRIS) increases first the mechanical properties of the fibers due to the early congruent glass dissolution and so due to the reduction in the density of surface flaws. However, for long immersion in TRIS or in Simulated Body Fluid (SBF), the mechanical properties decrease due to the precipitation of a reactive calcium‐phosphate layer at the surface of the fibers. Especially when immersed for a long time in SBF, the fibers become too fragile to allow one to measure their mechanical properties. Nonetheless, we clearly show in this study that the newly developed fibers are promising materials for reinforcing composite and/or as biosensors as these fibers still possess sufficiently high mechanical properties after immersion for significant time in SBF and/or TRIS.

Simulation of Mach-Zehnder Interferometer plastic optical fibre for temperature and refractive index measurement

This work presents simulation of light propagation inside tapered structure-plastic optical fibre (POF) subjected to various surrounding temperatures and refractive index (RI). The tapered structure served as Mach-Zehnder interferometer (MZI) which split light into core modes and clad modes that recombined at the end of the taper. Simulation was done by using Beam Propagation Method (BPM) solved using Finite Difference Method (FDM). The light launched in to the MZI was varied from 611nm to 655nm. In order to give temperature effect, the temperature was varied from 30°C to 80°C with increment of 10°C. The results showed that the free spectral range (FSR) of the MZI are shifted as temperature increased. The sensitivity for the peak and dip of the FSR are -0.0158 nm/°C and -0.0153 nm/°C, respectively. For RI sensitivity investigation, the surrounding RI was varied from 1.333 to 1.349. The sensitivity of peak FSR and dip FSR to RI change are -98.638 nm/RIU and 105.4 nm/RIU. Therefore, the MZI can be used to measure RI and temperature simultaneously.

A knotted shape core cladding optical fiber interferometer for simultaneous measurement of displacement and temperature

A novel composite structured all-fiber sensor was designed and experimentally demonstrated for simultaneous measurement of displacement and temperature. The sensor consists of a knotted shape core cladding optical fiber. The interferometer notch of a knotted shape fiber was found to be highly sensitive to the micro-displacement as well as environmental temperature, while the core-offset fiber was sensitive to temperature only. Thus the different features of these interferometer notchs of two parts can be used to measure the displacement and temperature. The experimental results showed that the sensor exhibited a high displacement sensitivity of −528.57 pm/μm ranges from 0 mm to 0.012 mm. And the temperature sensitivities of the knotted shape core cladding optical fiber were −114.86 pm/℃ and 31.66 pm/℃ ranges from 35 ℃ to 60℃, respectively. Due to the compact size and dual-parameters measurability, the sensor had a great potential in diverse sensing application.

An Integrated Biological Analysis and Flow Rate Sensing for the Real-Time Detection of Carcinogen in Water Based on Co2+-Doped Optical Fibers

The multi-parameter measurement has significant meaning for biosensor to enhance their practical sensing performance. For the biological detection, simultaneous measurement of biological molecule and flow rate could improve the accuracy and sensitivity of sensors significantly. In this paper, an integrated biological analysis and flow rate sensing based on Co <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> doped tilted fiber Bragg gratings has been proposed and experimentally demonstrated for real-time the detection of the Benzo[a]pyrene molecules. A tilted fiber Bragg grating with a tilted angle of 8° was inscribed into a Co <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> doped fiber. The flow rate and Benzo[a]pyrene molecules can be measured simultaneously by interrogating the resonance wavelength of core mode and wavelength interval between the core mode and cladding mode according to the heat exchange and evanescent field of the cladding mode, respectively. Experimental results show that the real-time measurement sensitivities of 12 pm/pM and -0.13 nm(μL/s) for the Benzo[a]pyrene detection and flow rate were achieved, respectively. Thus the technique appears to have potential applications in chemistry, medicine, and biology.

Design and characterization of a circular sectored core cladding structured photonic crystal fiber with ultra-low EML and flattened dispersion in the THz regime

Abstract A circular sectored core cladding structured photonic crystal fiber (PCF) is presented in this article, where core and cladding are sectored by few number of rectangles. The air fragments of core and cladding are constructed with circular manner that can facilitate the fabrication process. To design the porous core PCF and characterize the properties for THz wave propagation, finite element method based Comsol Multiphysics software version 5.3a is employed. It is shown that the presented design yields an ultra-low effective material loss (EML) of 0.0153 cm−1 with very flat dispersion of ±0.010 (ps/THz/cm) at optimum operating frequency of 1 THz, outperforming a number of recently reported designs in the literature. Additionally, it renders comparable low confinement loss, higher core power fraction, large effective area and exhibits single-mode fiber (SMF) characteristics. Further, since only few air fragments are used in core and cladding regions in a circular fashion, the proposed PCF geometry is feasible for fabrication by using stack and draw, extrusion, 3D printing, capillary stacking, sol-gel, or any other existing fabrication technique.

Design of Single Mode Fiber for Optical Communications

In this work, a step-index fiber with core index and cladding index has been designed. Single-mode operation can be obtained by using a fiber with core diameters 4–13 µm operating at a wavelength of 1.31 µm and by 4–15 µm at 1.55 µm. The fundamental fiber mode properties such as phase constant, effective refractive index, mode radius, effective mode area and the power in the core were calculated. Distributions of the intensity and the amplitude were shown.

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.

Reusable polymer optical fiber strain sensor with memory capability based on ABS crazing.

A reusable memory capable polymer optical fiber (POF) strain sensor is reported. The fiber consists of an acrylonitrile butadiene styrene (ABS) core and polymethylmethacrylate cladding. The memory capability is derived from stress whitening due to crazing of the ABS core, which can be reversed by heating the fiber close to the ABS glass transition temperature. The probe was characterized under transverse compressive load, macrobending, and tensile loading. Testing shows that the optical properties of the fiber can be reversed to near pristine ABS conditions after thermal recovery and that the POF can be used on the accurate assessment of indentation, flexural and tensile loading, static or cyclical, even after removal of the load. The reusability of the proposed sensor combined with a deeper understanding of the memory mechanisms in POFs are of great interest for the development of new large-strain sensors for modern applications.

Optical loss characterization of SEO100C electro-optic polymer within single mode rib waveguides

Designing high-performance electro-optic polymer modulators requires insight into device-specific waveguide losses. Losses for rib waveguiding structures fabricated using SE0100C core and NOA73 cladding layers are reported. The waveguide loss was measured at 4.2 dB/cm, which is high compared to losses for different electro-optic rib waveguides reported at 1.2-2.9 dB/cm. The refractive index of unpoled SEO100C was measured at 1.655, expanding on the manufacturer’s reported optical constants of 1.65 (TE) and 1.7 (TM) for poled SEO100C. Utilizing the reported specific structure loss in device design for minimal loss will facilitate high performance electro-optic polymer modulator applications.

Fluoride fiber plasmonic sensor with multilayer variants of tungsten disulfide (WS2): Seeking enhanced figure-of-merit via thermo-optic tuning of radiation damping

Abstract A multilayered fiber SPR sensor is studied with as many as five design variants governed by different number (N varied from 1 to 5) of WS2 monolayer for ethanol detection. The sensor design variants are simulated and analyzed at 785 nm wavelength. The dynamic radiation damping in terms of variable temperature and Ag layer thickness is enforced on the sensor variants to lead to possible sensing performance enhancement. Further, an attempt is made to more comprehensively evaluate the sensor’s performance by including the power loss curve characteristics. At an optimum radiation damping (ORD) condition (23 °C temperature and 55.5 nm thick Ag layer at 785 nm wavelength), the figure of merit (FOM) of the fiber (ZBLAN core and NaF clad) SPR sensor with WS2 bilayer has the potential to reach to an ultrahigh magnitude of 27563.575 RIU−1 while the overall figure of merit (FOM*) reaches to 62293.68 RIU−1. The next best combination (i.e., with 4 monolayers of WS2, 29.1 °C temperature, and 54.6 nm thick Ag layer at 785 nm wavelength) provides FOM of 27028.217 RIU−1 and FOM* of 61813.53 RIU−1). The results are explained in terms of physical concepts such as light absorption, Rayleigh scattering and thermo-optic effects in sensor constituents (Ag and WS2, in particular) converging at dynamic nature of radiation damping in plasmonic structures. The proposed sensor can be an important milestone in developing highly sensitive and accurate fiber optic chemical sensors.

Gain characteristics of fibers with a heavily erbium-doped phosphate-based core and silica cladding

The gain properties of multicomponent fibers with a heavily Er3+-doped phosphate-based core in a silica cladding were investigated in an all-fiber amplifier configuration that included spliced joints of the investigated fibers with silica ones. The maximum value of small-signal gain reached about 38 dB. The maximum small-signal gain per unit length of 3.1 dB/cm was demonstrated in 10 cm long 3 wt.% Er3+-doped fiber.

Heat mitigation of a core/cladding Yb-doped fiber amplifier using anti-Stokes fluorescence cooling

A Core/Cladding Yb-doped fiber amplifier configuration is presented that relies on anti-Stokes fluorescence cooling for effective heat mitigation in high-power operation. In the proposed design, the inner cladding of the double clad fiber is doped with the same ion as in the core; therefore, the excess heat generated from the background absorption is removed by the anti-Stokes fluorescence in both core and inner cladding. We consider both silica and ZBLAN glasses for the host material in the Core/Cladding Yb-doped fiber amplifier. The model incorporates the spatial profiles of the signal and pump intensities, as well as the amplified spontaneous emission. The total linear heat density and temperature distribution in the fiber amplifier are calculated. The results show that the anti-Stokes fluorescence cooling in the Core/Cladding Yb-doped configuration can mitigate the generated heat effectively in high-power operation, which obviates the need for an external cooling system.

Hydrogen Sulfide Gas Sensor Based on Copper/Graphene Oxide Composite Film-Coated Tapered Single-Mode Fibre Interferometer

Abstract A hydrogen sulfide (H2S) gas sensor based on copper (Cu) nanoparticle deposited graphene oxide (GO) composite membrane with two waist-enlarged tapers is proposed. Three segments of the single-mode fibres (SMFs) are sequentially fused to obtain two waist-enlarged bitapers of Mach–Zehnder interferometer (MZI). When the light of a broadband light source transmits through the first bitaper, some light enters the fiber cladding; the lights of core mode and cladding mode are coupled at the second taper and an MZI is successfully fabricated. The copper/graphene oxide (Cu/GO) composite sensing film is coated on the surface of the second SMF, and the effective refractive index of the coating is changed when the sensitive film adsorbs the target gas. The correlation between the gas concentration and the wavelength shift is achieved and the H2S can be measured effectively. The results show that a uniform Cu/GO film is successfully coated on the surface of the fiber, and when the thickness of the sensitive film is about 1.2 μm, the sensor has a sensitivity of 4.42 pm/ppm and a good linearity and selectivity for H2S in the range of 0–60 ppm, and the limit of detection is 2.79 ppm. The response time and recovery time are approximately 31 and 48 s, respectively. The sensor has the advantages of small volume, low cost, simple structure, and easy manufacture and so on, which is suitable for on-line monitoring of H2S.

Optical properties of GaN/Er:GaN/GaN core–cladding planar waveguides

Erbium-doped GaN (Er:GaN) possesses superior optical, mechanical and thermal properties and is a very promising material as a gain medium for solid-state high-energy lasers. We report here the optical properties of GaN/Er:GaN/GaN core–cladding planar waveguides (PWGs). Optical confinement in the core layer has been investigated. The measured optical loss coefficients of Er:GaN PWGs at 1.54 μm are 1.0 cm−1 for the TE polarization mode and 1.2 cm−1 for the TM polarization mode. Approaches to further reduce optical loss and the optimal configuration for resonantly pumped GaN/Er:GaN/GaN PWGs for achieving amplification near 1.5 μm have been identified.

Silicon nitride/titanium oxide hybrid waveguide design enabling broadband athermal operation

This paper presents a special design of a new kind of silicon nitride/titanium oxide hybrid waveguide with multi-layer materials laminate structure aiming at broadband athermal operation. By incorporating three layers of titanium oxide whose thermo-optic coefficient (TOC) is negative in the waveguide core and upper cladding regions, the thermal drift of the conventional strip waveguide induced by the positive TOC of silicon nitride is fully compensated, with the effective TOC of the hybrid waveguide achieving zero at 1550nm and only varying extremely slightly within ±6×10-7/K in the wavelength band from 1350 to 1850nm. In addition, due to the inherent alternate growth manner of titanium dioxide and silicon nitride thin layers, this new kind of multi-layer material laminate structure waveguide holds the potential of avoiding the challenging growth of low-stress crack-free single-layer silicon nitride film thick enough for realizing an anomalous dispersion waveguide. Furthermore, we numerically demonstrate the different influences of the temperature change on optical frequency comb generation between the traditional waveguide and the hybrid waveguide, and we find that the athermal hybrid waveguide is much more temperature insensitive than the strip waveguide.

Femtosecond laser based on a multicomponent fiber with a 3 wt.% Er-doped phosphate core and silica cladding

To the best of our knowledge, we present the first demonstration of a passively mode-locked ring laser based on a multicomponent fiber with silica cladding and a 3 wt.% Er-doped phosphate core. The active fiber length was about 19 cm. The laser emitted 570 fs pulses at a repetition rate of 23.9 MHz with an average output power of 1.4 mW. The pulse energy was about 60 pJ.