165 research outputs found
Understanding Silent Failures in Medical Image Classification
To ensure the reliable use of classification systems in medical applications,
it is crucial to prevent silent failures. This can be achieved by either
designing classifiers that are robust enough to avoid failures in the first
place, or by detecting remaining failures using confidence scoring functions
(CSFs). A predominant source of failures in image classification is
distribution shifts between training data and deployment data. To understand
the current state of silent failure prevention in medical imaging, we conduct
the first comprehensive analysis comparing various CSFs in four biomedical
tasks and a diverse range of distribution shifts. Based on the result that none
of the benchmarked CSFs can reliably prevent silent failures, we conclude that
a deeper understanding of the root causes of failures in the data is required.
To facilitate this, we introduce SF-Visuals, an interactive analysis tool that
uses latent space clustering to visualize shifts and failures. On the basis of
various examples, we demonstrate how this tool can help researchers gain
insight into the requirements for safe application of classification systems in
the medical domain. The open-source benchmark and tool are at:
https://github.com/IML-DKFZ/sf-visuals.Comment: Accepted at MICCAI 2
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Hollow square core fiber sensor for physical parameters measurement
The measurement of physical parameters is important in many current applications, since they often rely on these measurands to operate with the due quality and the necessary safety. In this work, a simple and robust optical fiber sensor based on an antiresonant hollow square core fiber (HSCF) is proposed to measure simultaneously temperature, strain, and curvature. The proposed sensor was designed in a transmission configuration where a segment of HSCF, with a 10 mm length, was spliced between two single mode fibers. In this sensor, a cladding modal interference (CMI) and a Mach-Zehnder interference (MZI) are enhanced along with the antiresonance (AR) guidance. All the present mechanisms exhibit different responses towards the physical parameters. For the temperature, sensitivities of 32.8 pm/°C, 18.9 pm/°C, and 15.7 pm/°C were respectively attained for the MZI, AR, and CMI. As for the strain, sensitivities of 0.45 pm/μϵ, -0.93 pm/μϵ, and -2.72 pm/μϵ were acquired for the MZI, AR and CMI respectively. Meanwhile, for the curvature measurements, two regions of analysis were considered. In the first region (0 m-1 - 0.7 m-1) sensitivities of 0.033 nm/m-1, -0.27 nm/m-1, and -2.21 nm/m-1 were achieved, whilst for the second region (0.7 m-1 - 1.5 m-1) sensitivities of 0.067 nm/m-1, -0.63 nm/m-1, and -0.49 nm/m-1 were acquired for the MZI, AR and CMI, respectively
Hybrid sensor based on a hollow square core fiber for temperature independent refractive index detection
In this work, a hybrid sensor based on a section of hollow square core fiber (HSCF) spliced between two single mode fibers is proposed for the measurement of refractive index of liquids. The sensor, with a length of a few millimeters, operates in a transmission configuration. Due to the HSCF inner geometry, two different interferometers are generated. The first, a Mach-Zehnder interferometer, is insensitive to the external refractive index, and presents a sensitivity to temperature of (29.2 ± 1.1) pm/°C. The second one, a cladding modal interferometer, is highly sensitive to the external refractive index. An experimental resolution of 1.0 × 10-4 was achieved for this component. Due to the different responses of each interferometer to the parameters under study, a compensation method was developed to attain refractive index measurements that are temperature independent. The proposed sensor can find applications in areas where refractive index measurements are required and the control of room temperature is a challenge, such as in the food and beverage industry, as well as in biochemical or biomedical industries.publishe
Negative curvature hollow core fiber sensor for the measurement of strain and temperature
Three different types of strain and temperature sensors based on negative curvature hollow core fiber (NCHCF) are proposed. Each sensor is produced by splicing a small section of the NCHCF between two sections of single mode fiber. Different types of interferometers are obtained simply by changing the splicing conditions. The first sensor consists on a single Fabry-Perot interferometer (FPI). The remaining two configurations are attained with the same sensing structure, depending on its position in relation to the interrogation setup. Thus, a double FPI or a hybrid sensor, the latter being composed by an FPI and a Michelson interferometer, are formed. The inline sensors are of submillimeter size, thus enabling nearly punctual measurements
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Capillary based hybrid fiber sensor in a balloon-like shape for simultaneous measurement of displacement and temperature
In this work, a hybrid sensor based on a silica capillary in a balloon-like shape for simultaneous measurement of displacement and temperature is proposed for the first time, to the best of our knowledge. The sensor is fabricated by splicing a segment of a hollow core fiber between two single mode fibers (SMF) and by bending the fiber in a balloon shape with the capillary at the top-center position. In a transmission scheme, the SMF-capillary-SMF configuration excites an antiresonant (AR) guidance and the balloon shape enhances a Mach-Zehnder interferometer (MZI). The different responses of the interferometers to external displacement and temperature variations are conducive to a hybrid application of the sensor for simultaneous measurement of these parameters. Experimental results show that, for a capillary length of 1.2 cm and a balloon length of 4 cm, AR is insensitive to displacement and its sensitivity to temperature is 14.3 pm/°C, while the MZI has a sensitivity to displacement of 1.68 nm/mm and twice the sensitivity of AR to temperature, of 28.6 pm/°C. The proposed fiber sensor consists of only one sensing element in one configuration exciting two interferometers at the same time, which makes it of simple fabrication as well as low cost
Negative curvature hollow core fiber sensor for the measurement of strain and temperature
Three different types of strain and temperature sensors based on negative curvature hollow core fiber (NCHCF) are proposed. Each sensor is produced by splicing a small section of the NCHCF between two sections of single mode fiber. Different types of interferometers are obtained simply by changing the splicing conditions. The first sensor consists on a single Fabry-Perot interferometer (FPI). The remaining two configurations are attained with the same sensing structure, depending on its position in relation to the interrogation setup. Thus, a double FPI or a hybrid sensor, the latter being composed by an FPI and a Michelson interferometer, are formed. The inline sensors are of submillimeter size, thus enabling nearly punctual measurements.publishe
Simultaneous measurement of refractive index and temperature using a double antiresonant hollow core fiber
In this work, an inline sensor based on a double antiresonant hollow core fiber is proposed for the simultaneous
measurement of refractive index and temperature. The fiber, consisting of four silica capillaries with wall thickness of
~1.5 um and a cladding with a thickness of ~36.5 um, is spliced between two sections of single mode fiber. The spectral
behavior, measured in transmission, results from the combination of different frequencies which enable the
discrimination between the two parameters. The sensing head is subjected to refractive index measurements using
aqueous solutions with different concentrations of ethanol. For a sensor with a length of ~10 mm, and considering the
lower frequency signal, the sensitivity to refractive index is 389.6 nm/RIU, whereas for the higher frequency, the
sensitivity attained is 2.8 nm/RIU. On the other hand, the sensing head presented a sensitivity to temperature of
25.5 pm/K and -27.6 pm/K for the higher and lower frequencies, respectively.publishe
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Nanoscopic tip sensors fabricated by gas phase etching of optical glass fibers
Silica-based fiber tips are used in a variety of spectroscopic, micro- or nano-scopic optical sensor applications and photonic micro-devices. The miniaturization of optical sensor systems and the technical implementation using optical fibers can provide new sensor designs with improved properties and functionality for new applications. The selective-etching of specifically doped silica fibers is a promising method in order to form complex photonic micro structures at the end or within fibers such as tips and cavities in various shapes useful for the all-fiber sensor and imaging applications. In the present study, we investigated the preparation of geometrically predefined, nanoscaled fiber tips by taking advantage of the dopant concentration profiles of highly doped step-index fibers. For this purpose, a gas phase etching process using hydrofluoric acid (HF) vapor was applied. The shaping of the fiber tips was based on very different etching rates as a result of the doping characteristics of specific optical fibers. Technological studies on the influence of the etching gas atmosphere on the temporal tip shaping and the final geometry were performed using undoped and doped silica fibers. The influence of the doping characteristics was investigated in phosphorus-, germanium-, fluorine- and boron-doped glass fibers. Narrow exposed as well as protected internal fiber tips in various shapes and tip radiuses down to less than 15 nm were achieved and characterized geometrically and topologically. For investigations into surface plasmon resonance effects, the fiber tips were coated with nanometer-sized silver layers by means of vapour deposition and finally subjected to an annealing treatment
Three-Dimensional Light Bullets in Arrays of Waveguides
We report the first experimental observation of 3D-LBs, excited by
femtosecond pulses in a system featuring quasi-instantaneous cubic nonlinearity
and a periodic, transversally-modulated refractive index. Stringent evidence of
the excitation of LBs is based on time-gated images and spectra which perfectly
match our numerical simulations. Furthermore, we reveal a novel evolution
mechanism forcing the LBs to follow varying dispersion/diffraction conditions,
until they leave their existence range and decay.Comment: 4 pages, 5 figures - Published by the American Physical Societ
High-power fiber laser based on a non filamented-core fully-aperiodic large pitch fiber
International audienceSince the double-clad fiber architectures development, fiber-based laser have witnessed an impressive power scaling [1]. The extracted power rising has been accompanied by the development of Very Large Mode Area (VLMA) fiber designs allowing overcome some key hurdles like the non-linear process or photo-darkening [2]. However, due to the very large core size of fiber architectures, a new phenomenon, referring to modal instabilities, has been evidenced recently like the current limitation which hampers any further power increase in the field of fiber laser sources without a dramatic degradation of the emitted beam quality [3]. In order to push away the appearance power threshold of this limitation, new aperiodic cladding microstructurations have been proposed to improve the higher-order modes (HOM) rejection out of the gain region and then to optimize the amplification of the sole fundamental mode [4]. These aperiodic microstructures have proved recently their potential to enhance an efficient HOM delocalization enabling singlemode confinement in the core region with passive VLMA fibers [5].In this communication we report on the first high power emission demonstration obtained using a solid non-filamented core fully-aperiodic large pitch fiber manufactured by the REPUSIL method based on the sintering and vitrification of micrometric doped silica powders. Using a simple laser cavity, an average output power of 233 W was achieved with an available pump power of 400 W for the first time in such a fiber. The preliminary M2 measurements have shown an excellent beam quality with values less than 1.4
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