An optical code generating device for a portable optical access-card system was constructed using the plastic optical fibre (POF) waveguide coupler. The newly constructed device provided output light intensities which were used as optical codes in a portable optical access-card system. The construction of a basic 1 × 2 waveguide design combined two major components which were the asymmetric Y-junction splitter and the linear taper. A hollow waveguide structure was utilized as it provided more flexibility in guiding light rays. A basic 1 × 2 waveguide coupler was designed using the CAD tool and then the ray was traced using the non-sequential ray tracing tool. A linear relationship between the tap-off ratio and the waveguide tap-width enabled a higher-level hollow waveguide coupler to be designed using the simple cascading technique. Construction of a 1 × 4 and higher level waveguide coupler was easily realized using the basic 1 × 2 waveguide coupler design together with a simple cascading technique.
This research was focused on the thermoluminescence (TL) response of commercially produced single-mode telecommunication optical fibre manufactured by INOCORP (Canada). The fibres were either in the form of pure silica (SiO2) or as SiO2 doped with Ge or Al at concentrations appropriate for total internal reflection, as required for telecommunication purposes. Each of these INOCORP fibres had a core diameter of 125 ± 0.1 μm. It was noted that dopant concentration was not included among the data provided in the accompanying product data sheet. A particularly important parameter for obtaining the highest TL yield in this study was the dopant concentration of the SiO2 fibre. The dopants tended to diffuse during the production of the optical fibre. To obtain this parameter, proton induced X-ray emission (PIXE) analysis was utilised. PIXE while having limited depth resolution could unambiguously identify elements and analyse trace elements with a detection limit approaching μg g–1. For Al-doped fibres, dopant concentrations in the range of 0.98 – 2.93 mol% had been estimated, the equivalent range for Ge-doped fibres was 0.53 – 0.71 mol%. A linear dose response was observed following 2.5 MeV proton irradiation for Ge- and Al-doped fibres for up to 7 min exposure.
We demonstrate a simple configuration for generating a double Brillouin frequency shift through the circulation of an odd-order Brillouin Stokes signal. It is operated based on cascaded Brillouin scattering in single-mode optical fibers that behave as the Brillouin gain media. A four-port circulator is incorporated into the setup to circulate the odd-order Brillouin Stokes signal in the fiber. It thus initiates a higher order Brillouin Stokes signal, which is double Brillouin frequency downshifted from the input signal. For the 5 km long fiber, the Brillouin pump power at 23 mW gives a clean output spectrum with 30 dB sideband suppression ratio. The output signal is 0.174 nm or approximately 21.7 GHz downshifted from the input signal.
We demonstrate an opto-optical gain-clamped L-band erbium-doped fiber amplifier by manipulating the C-band lasing wavelength as the control signal. The L-band gain-clamped value is achieved by tuning the control laser in the C-band wavelength range that propagates in the opposite direction to the L-band signal. Within the wavelength range of 1538 nm and 1560 nm, the L-band gain decreases linearly with the increment of the C-band lasing wavelength. The L-band gain dynamic range decreases with the increment of the cavity loss. By combining two different levels of cavity loss, the gain dynamic range of 10 dB from 11 dB to 21 dB is achieved with an average noise figure of less than 5.9 dB. The whole gain spectrum of the L-band can be used for multiple-channel amplification because the laser is created outside its signal band.
We demonstrate mode locking of a thulium-bismuth codoped fiber laser (TBFL) operating at 1901.6 nm, using a graphene-based saturable absorber (SA). In this work, a single layer graphene is mechanically exfoliated using the scotch tape method and directly transferred onto the surface of a fiber pigtail to fabricate the SA. The obtained Raman spectrum characteristic indicates that the graphene on the core surface has a single layer. At 1552 nm pump power of 869 mW, the mode-locked TBFL self starts to generate an optical pulse train with a repetition rate of 16.7 MHz and pulse width of 0.37 ps. This is a simple, low-cost, stable, and convenient laser oscillator for applications where eye-safe and low-photon-energy light sources are required, such as sensing and biomedical diagnostics.
Important thermoluminescence (TL) properties of five (5) different core sizes Ge-doped optical fibers have been studied to develop new TL material with better response. These are drawn from same preform applying different speed and tension during drawing phase to produce Ge-doped optical fibers with five (5) different core sizes. The results of the investigations are also compared with most commonly used standard TLD-100 chips (LiF:Mg,Ti) and commercial multimode Ge-doped optical fiber (Yangtze Optical Fiber, China). Scanning Electron Microscope (SEM) and EDX analysis of the fibers are also performed to map Ge distribution across the deposited region. Standard Gamma radiation source in Secondary Standard Dosimetry Lab (SSDL) was used for irradiation covering dose range from 1Gy to 10Gy. The essential dosimetric parameters that have been studied are TL linearity, reproducibility and fading. Prior to irradiation all samples ∼0.5cm length are annealed at temperature of 400°C for 1h period to standardize their sensitivities and background. Standard TLD-100 chips are also annealed for 1h at 400°C and subsequently 2h at 100°C to yield the highest sensitivity. TL responses of these fibers show linearity over a wide gamma radiation dose that is an important property for radiation dosimetry. Among all fibers used in this study, 100μm core diameter fiber provides highest response that is 2.6 times than that of smallest core (20μm core) optical fiber. These fiber-samples demonstrate better response than commercial multi-mode optical fiber and also provide low degree of fading about 20% over a period of fifteen days for gamma radiation. Effective atomic number (Zeff) is found in the range (13.25-13.69) which is higher than soft tissue (7.5) however within the range of human-bone (11.6-13.8). All the fibers can also be re-used several times as a detector after annealing. TL properties of the Ge-doped optical fibers indicate promising applications in ionizing radiation dosimetry.
A method for improving the thermoluminescence (TL) yield of silica-based optical fibres is demonstrated. Using silica obtained from a single manufacturer, three forms of pure (undoped) fibre (capillary-, flat-, and photonic crystal fibre (PCF)) and two forms of Ge-doped fibre (capillary- and flat-fibre) were fabricated. The pure fibre samples were exposed to 6 and 21MeV electrons, the doped fibres to 6MV photons. The consistent observation of large TL yield enhancement is strongly suggestive of surface-strain defects generation. For 6MeV irradiations of flat-fibre and PCF, respective TL yields per unit mass of about 12.0 and 17.5 times that of the undoped capillary-fibre have been observed. Similarly, by making a Ge-doped capillary-fibre into flat-fibre, the TL response is found to increase by some 6.0 times. Thus, in addition to TL from the presence of a dopant, the increase in fused surface areas of flat-fibres and PCF is seen to be a further important source of TL. The glow-curves of the undoped fibres have been analysed by computational deconvolution. Trap centre energies have been estimated and compared for the various fibre samples. Two trap centre types observed in capillary-fibre are also observed in flat-fibre and PCF. An additional trap centre in flat-fibre and one further trap centre in PCF are observed when compared to capillary fibre. These elevated-energy trap centres are linked with strain-generated defects in the collapsed regions of the flat fibre and PCF.
Thermoluminescence (TL) properties (radiation sensitivity, dose response, signal fading) of Nd-doped SiO2 optical fibers irradiated with 1.25MeV photons to 1-50Gy were studied. The peak of the glow curve is around 190°C regardless of the dose. The dose response is linear up to 50Gy. The radiation sensitivity is 219nCmg(-1)Gy(-1). The fiber can be a potential candidate for photon radiotherapy dosimetry due to its high radiation sensitivity, linear dose response in a wide range, slow fading, and high spatial resolution due to the small size of the fiber.
Characteristics of the thermoluminescence (TL) responses of Yb- and Yb-Tb-doped optical fibers irradiated with 6MV photons are reported. The concentration of Yb in the Yb-doped optical fiber was 0.26mol%; the concentrations of Yb and Tb in the Yb-Tb-doped optical fiber were 0.62 and 0.2mol%, respectively. The TL dose responses are linear in the dose range 0.5-4Gy. The radiation sensitivity of the Yb-Tb material is almost two orders of magnitude higher than the sensitivity of the material doped with Yb alone.
Radiation effects of photon irradiation in pure Photonic Crystal Fibres (PCF) and Flat fibres (FF) are still much less investigated in thermoluminescense dosimetry (TLD). We have reported the TL response of PCF and FF subjected to 6 MV photon irradiation. The proposed dosimeter shows good linearity at doses ranging from 1 to 4 Gy. The small size of these detectors points to its use as a dosimeter at megavoltage energies, where better tissue-equivalence and the Bragg-Gray cavity theory prevails.
We have investigated the thermoluminescent response and fading characteristics of germanium- and aluminium-doped SiO(2) optical fibres. These optical fibres were placed in a solid phantom and irradiated using 6 and 10 MV photon beams at doses ranging from 0.02 to 0.24 Gy delivered using a linear accelerator. In fading studies, the TL measurements were continued up to 14 days post-irradation. We have investigated the linearity of TL response as a function of dose for Ge-, Al-doped optical fibre and TLD-100 obtained for 6 and 10 MV photon irradiations. We have concentrated on doses that represent a small fraction of that delivered to the tumour to establish sensitivity of measurement for peripheral exposures in external beam radiotherapy.
Ion beams are used in radiotherapy to deliver a more precise dose to the target volume while minimizing dose to the surrounding healthy tissue. For optimum dose monitoring in ion-beam therapy, it is essential to be able to measure the delivered dose with a sensitivity, spatial resolution and dynamic range that is sufficient to meet the demands of the various therapy situations. Optical fibres have been demonstrated by this group to show promising thermoluminescence properties with respect to photon, electron and proton irradiation. In particular, and also given the flexibility and small size of optical fibre cores, for example 125.0+/-0.1 microm for the Al- and Ge-doped fibres used in this study, these fibres have the potential to fulfill the above requirements. This study investigates the thermoluminescence dosimetric characteristics of variously doped SiO(2) optical fibres irradiated with alpha particles from (241)Am. Following subtraction of the gamma contribution from the above source, the thermoluminescence characteristics of variously doped SiO(2) optical fibres have been compared with that of TLD-100 rods. The irradiations were performed in a bell jar. Of related potential significance is the effective atomic number, Z(eff) of the fibre, modifying measured dose from that deposited in tissues; in the present work, a scanning electron microscope and associated energy dispersive X-ray spectroscopy facility have been used to provide evaluation of Z(eff). For Ge-doped fibres, the effective atomic numbers value was 11.4, the equivalent value for Al-doped fibres was 12.3. This paper further presents results on dose response and the glow curves obtained. The results obtained indicate there to be good potential for use of variously doped SiO(2) optical fibres in measuring ion-beam doses in radiotherapeutic applications.
Modern linear accelerators, the predominant teletherapy machine in major radiotherapy centres worldwide, provide multiple electron and photon beam energies. To obtain reasonable treatment times, intense electron beam currents are achievable. In association with this capability, there is considerable demand to validate patient dose using systems of dosimetry offering characteristics that include good spatial resolution, high precision and accuracy. Present interest is in the thermoluminescence response and dosimetric utility of commercially available doped optical fibres. The important parameter for obtaining the highest TL yield during this study is to know the dopant concentration of the SiO2 fibre because during the production of the optical fibres, the dopants tend to diffuse. To achieve this aim, proton-induced X-ray emission (PIXE), which has no depth resolution but can unambiguously identify elements and analyse for trace elements with detection limits approaching microg/g, was used. For Al-doped fibres, the dopant concentration in the range 0.98-2.93 mol% have been estimated, with equivalent range for Ge-doped fibres being 0.53-0.71 mol%. In making central-axis irradiation measurements a solid water phantom was used. For 6-MV photons and electron energies in the range 6, 9 and 12 MeV, a source to surface distance of 100 cm was used, with a dose rate of 400 cGy/min for photons and electrons. The TL measurements show a linear dose-response over the delivered range of absorbed dose from 1 to 4 Gy. Fading was found to be minimal, less than 10% over five days subsequent to irradiation. The minimum detectable dose for 6-MV photons was found to be 4, 30 and 900 microGy for TLD-100 chips, Ge- and Al-doped fibres, respectively. For 6-, 9- and 12-MeV electron energies, the minimum detectable dose were in the range 3-5, 30-50 and 800-1400 microGy for TLD-100 chip, Ge-doped and Al-doped fibres, respectively.
Over the past decade and more, considerable interest has been shown in the thermoluminescence (TL) properties of silica-based single-mode optical fibres, in particular investigating potential ionising radiation dosimetry applications. Herein, study has been made of TL glow curve, dose response, reproducibility and fading of 6mol% Ge-doped silica, fabricated in-house and produced in the form of cylindrical fibres. Three different pairings of doped-core and silica cladding diameters were produced: (40, 241)µm, (80, 483)µm and (100, 604)µm. The TL results were compared against that of TLD-100, one of the most sensitive commercially available LiF-based TL media. For all three pairings of diameters, closely similar TL glow curve were obtained, formed of a single peaked structure with a maximum TL yield located between the temperatures 250 and 310°C. The TL yield of the fibres were linear over the range of doses investigated, from 1Gy up to 10Gy, their dose response exceeding that of TLD-100, the samples also being found to be reusable, without evidence of degradation.
In regard to thermoluminescence (TL) applied to dosimetry, in recent times a number of researchers have explored the role of optical fibers for radiation detection and measurement. Many of the studies have focused on the specific dopant concentration, the type of dopant and the fiber core diameter, all key dependencies in producing significant increase in the sensitivity of such fibers. At doses of less than 1 Gy none of these investigations have addressed the relationship between dose response and TL glow peak behavior of erbium (Er)-doped silica cylindrical fibers (CF). For x-rays obtained at accelerating potentials from 70 to 130 kVp, delivering doses of between 0.1 and 0.7 Gy, present study explores the issue of dose response, special attention being paid to determination of the kinetic parameters and dosimetric peak properties of Er-doped CF. The effect of dose response on the kinetic parameters of the glow peak has been compared against other fiber types, revealing previously misunderstood connections between kinetic parameters and radiation dose. Within the investigated dose range there was an absence of supralinearity of response of the Er-doped silica CF, instead sub-linear response being observed. Detailed examination of glow peak response and kinetic parameters has thus been shown to shed new light of the rarely acknowledged issue of the limitation of TL kinetic model and sub-linear dose response of Er-doped silica CF.
In previous work we investigated the real-time radioluminescence (RL) yield of Ge-doped silica fibres and Al2O3 nanodot media, sensing electron- and x-ray energies and intensities at values familiarly obtained in external beam radiotherapy. The observation of an appreciable low-dose sensitivity has given rise to the realisation that there is strong potential for use of RL dosimetry in diagnostic radiology. Herein use has been made of P-doped silica optical fibre, 2 mm diameter, also including a 271 µm cylindrical doped core. With developing needs for versatile x-ray imaging dosimetry, preliminary investigations have been made covering the range of diagnostic x-ray tube potentials 30 kVp to 120 kVp, demonstrating linearity of RL with kVp as well as in terms of the current-time (mAs) product. RL yields also accord with the inverse-square law. Given typical radiographic-examination exposure durations from tens- to a few hundred milliseconds, particular value is found in the ability to record the influence of x-ray generator performance on the growth and decay of beam intensity, from initiation to termination.
Investigation has been made of the radioluminescence dose response of Ge-doped silica flat and cylindrical fibers subjected to 6 and 10 MV photon beams. The fibers have been custom fabricated, obtaining Ge dopant concentrations of 6 and 10 mol%, subsequently cut into 20 mm lengths. Each sample has been exposed under a set of similar conditions, with use made of a fixed field size and source to surface distance (SSD). Investigation of dosimetric performance has involved radioluminescence linearity, dose-rate dependence, energy dependence, and reproducibility. Mass for mass, the 6 mol% Ge-doped samples provided the greater radioluminescence yield, with both flat and cylindrical fibers responding linearly to the absorbed dose. Further found has been that the cylindrical fibers provided a yield some 38% greater than that of the flat fibers. At 6 MV, the cylindrical fibers were also found to exhibit repeatability variation of <1%, superior to that of the flat fibers, offering strong potential for use in real-time dosimetry applications.
Understanding environmental information is necessary for functions correlated with human activities to improve healthcare quality and reduce ecological risk. Tapered optical fibers reduce some limitations of such devices and can be considerably more responsive to fluorescence and absorption properties changes. Data have been collected from reliable sources such as Science Direct, IEEE Xplore, Scopus, Web of Science, PubMed, and Google Scholar. In this narrative review, we have summarized and analyzed eight classes of tapered-fiber forms: fiber Bragg grating (FBG), long-period fiber grating (LPFG), Mach-Zehnder interferometer (MZI), photonic crystals fiber (PCF), surface plasmonic resonance (SPR), multi-taper devices, fiber loop ring-down technology, and optical tweezers. We evaluated many issues to make an informed judgement about the viability of employing the best of these methods in optical sensors. The analysis of performance for tapered optical fibers depends on four mean parameters: taper length, sensitivity, wavelength scale, and waist diameter. Finally, we assess the most potent strategy that has the potential for medical and environmental applications.
This paper describes a system using lensed optical fiber sensors that are arranged in the form of two orthogonal projections. The sensors are placed around a process vessel for upstream and downstream measurements. The purpose of the system is for on-line monitoring of particles and droplets being conveyed by a fluid. The lenses were constructed using a custom heating fixture. The fixture enables the lenses to be constructed with similar radii resulting in identical characteristics with minimum differences in transmitted intensity and emission angle. By collimating radiation from two halogen bulbs, radiation can be obtained by the sensors with radiation intensity related to the nature of the media. Each sensor interrogates a finite section of the measurement section. Each sensor provides a view. Parallel sensors provide a projection. Signal processing is carried out on the measured data in the time and frequency domains to investigate the latent information present in the flow signals.
An investigation of bending loss characteristics of a Polymer Optical Fiber is presented experimentally. Loss of optical power in an optical fiber due to bending has been investigated for a wavelength of 650 nm. Variations of bending loss with different lengths have been measured, with a number of radii of curvature. Bending Loss equations for short length POF is proposed, which shows the dependence of bending loss on the curvature radii. The equations can be an initial reference or aid in predicting the loss contributes by the polymer optical fiber.