KEYWORDS: Networks, X-rays, Anatomy, Education and training, Diseases and disorders, Optical engineering, Medical imaging, Lithium, Integrated circuits, Head
Dental oral disease is one of the most prevalent diseases worldwide, as of a medical analysis in The Lancet 2022[1]. The most common oral diseases worldwide are dental caries (cavities), periodontal disease, tooth loss, and overdevelopment of the jaw caused by excessive unilateral chewing. Dental radiography plays a very important role in clinical diagnosis, treatment and surgery. Automatic segmentation of medical lesions is a prerequisite for efficient clinical analysis. Therefore, accurate positioning of anatomical landmarks is a crucial technique for clinical diagnosis and treatment planning. In this paper, we propose a novel deep network to detect anatomical landmarks. Our proposed network consists of a multi-scale feature aggregation module for channel attention and a deep network for feature refinement. To demonstrate the superiority of our network, training comparisons with several popular networks are performed on the same dataset. The end result is that our network outperforms several popular networks today in both mean radial error (MRE) and successful detection rate (SDR).
Compared with the classical object detection algorithms with horizontal bounding box, such as Yolo and Faster-R-CNN, the oriented object detector in remote sensing images can be more robust. Considering that the challenge of oriented object detection in remote sensing images, we propose a cross-layer feature fusion improvement strategy. Specifically, to obtain multiple layer feature maps for subsequent object detection, the shallow feature map with texture information merged with the deep feature map with semantic features. The spatial attention mechanism is introduced to enhance our algorithm's attention to the non-local information in these feature maps. Extensive experiments on a public dataset, DOTA, demonstrate the effectiveness of our proposed method. Under the large difference of object scale, arbitrary orientation of object, objects with dense arrangement and complex background, the experimental results show that our method has better performance.
In this paper, we propose and demonstrate a high-integration intracavity displacement-sensor through inserting U-shape single-mode fiber interferometer (U-SMFI) into an Er-doped fiber ring laser. Considering that the U-SMFI can be realized only through bending a SMF, its characteristic of easy fabrication can reduce the cost of manufacturing process in contrast with those wavelength-modulated displacement sensors based on fiber Bragg grating, long-period grating and surface plasmon resonance. When the U-SMFI is inserted into the laser cavity, the variation of the bending radii can modulate the cavity loss so as to have an effect on the spectrum of the output laser. The proposed sensor has a higher signal to noise ratio and a narrower full width at half maximum. Through measuring the change of the spectrum, a high-resolution displacement sensor can be realized. The experimental results indicate that the sensitivities are 39 pm/μm when the bending radius is 6.5 mm.
A chloride ion sensor based on a multitaper modulated fiber fabricated via arc discharge is proposed and studied experimentally and theoretically. The sensing unit consists of four periodic tapers with a diameter of 28.24 μm, a period of 676 μm, and a total length of 2.7 mm. The results show that the concentration sensitivity values are 170 pm/(g/L) at a wavelength of 1303.60 nm and 220 pm/(g/L) at a wavelength of 1389.84 nm when the chloride ion concentration is increased from 0 to 40 g/L. The proposed sensor is characterized by a simple manufacturing process, a compact structure, and a low cost, and this sensing unit has great potential for application in marine chloride detection and environmental safety monitoring, especially for monitoring building corrosion and water pollution.
A compact fiber-optic magnetic-field sensor based on tapered all-solid waveguide-array fiber (WAF) and magnetic fluid (MF) has been proposed and experimentally demonstrated. The transmission spectra of the fiber-optic magnetic field sensor have been measured and analyzed under different magnetic field intensities. Experimental results show that the acquired magnetic field sensitivity is 44.57 pm/Oe for a linear magnetic field intensity range from 50 Oe to 200 Oe. It also indicates that the magnetic field sensor based on tapered all-solid WAF and MF is helpful to reduce temperature cross-sensitivity for the measurement of magnetic field.
In this paper, we have demonstrated a magnetic field sensor based on the fiber taper coupler coated with Magnetic fluid. The proposed sensor is fabricated by immersing a fiber taper coupler into the Magnetic fluid and then sealing it with the paraffin. The sensor exhibits high response as a function of the magnetic field with sensitivities of 0.154 nm/Oe with measurement range from 50 Oe to 200 Oe and -0.06301 dB/ Oe from 75 Oe to 200 Oe. Owing to the advantages of high sensitivity, small footprint, and ease of fabrication, the proposed sensor would find potential applications in magnetic field sensing field.
An ultrasensitive optical fiber twist sensor is proposed by employing a Sagnac interferometer based on polarization-maintaining elliptical core fibers (PM-ECFs). The twist effects are theoretically analyzed and experimentally demonstrated. Based on the photoelastic effect, the wavelength shift in response to twist rate turns out linear tendency and is torsion-direction-dependent. The maximum torsion sensitivity reaches 18.59593nm/(rad/m) (or 0.67582nm/°) for clockwise (CW) torsion direction and 15.83073nm/(rad/m) for anticlockwise (ACW) torsion direction, respectively. Furthermore, it is further improved up to 1.675 nm/° by rotating two ends of PM-ECF simultaneously. The prominent advantage of ultrasensitivity keep it meritorious in the applications of spaceflight and constructional engineering.
An acousto-optic fiber interferometer has been proposed and experimentally demonstrated by employing two MgF2 sandwiches to implement concatenated flexural acoustic wave modulation onto single-mode optical fibers. The transmission spectrum of the acoustic grating pair has been experimentally investigated. Experimental results indicate that interferometric spectral fringes possess a frequency sensitivity as large as −499.0 nm/MHz due to the Mach–Zehnder interference. Moreover, the applied radio frequency signal voltage for flexural wave generation has a great impact on the transmission spectral properties. The work presented would be of importance for the understanding of the acousto-optic interaction mechanism in concatenated acoustic fiber gratings and is helpful for the design of related acousto-optic fiber devices.
A magnetic-field-tuned photonics device based on magnetic fluid (MF) and a square tapered no-core fiber (NCF) sandwiched between two single-mode fibers (SMFs) has been proposed. The enhanced evanescent field effect in the NCF is achieved by tapering the square NCF utilizing a fusion splicer. The spectral dependence of the proposed device on the applied magnetic-field intensity has been investigated. The results indicate that a maximal sensitivity of -18.7pm/Oe is obtained for a magnetic field strength ranging from 25Oe to 450Oe. The proposed tunable device has several advantages, including low cost, ease of fabrication, compact structure, and high sensitivity.
An acoustic birefringence suppression scheme for acoustic fiber gratings has been proposed and experimentally demonstrated. Experimental observation of the transmission characteristics of the single-mode-fiber-based (SMF-based) acoustic grating confirms that introduction of one segment of solid-core photonic crystal fiber (PCF) with air-hole array in the cladding region helps to eradicate resonance peak splitting induced by acoustic birefringence, which has been explained by our theoretical analysis from the acoustic wave modulation method and fiber cross-section structure. Moreover, experimental results indicate that the introduction of the solid-core PCF does not have a considerable impact on the frequency dependence of resonance wavelength for the SMF-based acoustic fiber grating, which ensures the performances of the PCF-assisted SMF-based acousto-optic tunable filter for practical applications.
A polarimetric DBR fiber laser sensor array for simultaneous measurement of liquid level and temperature has been
proposed and experimentally demonstrated. Operation principle of the proposed DBR fiber laser sensor has been
theoretically analyzed. Based on beat frequency/wavelength hybrid interrogation, discrimination between liquid level
and temperature has been achieved. Furthermore, three fiber laser sensors were cascaded to build up a serially
multiplexed sensor array, showing a good multiplexing capability for potential network applications.
Weakly tilted fiber Bragg gratings (W-TFBGs) with a certain tilted angle are inscribed in the Ge-doped cladding rods of
all-solid photonic band-gap fibers (AS-PBGF) by UV illumination. There are couplings not only forward-propagating
LP01 mode to counter-propagating LP01 mode but also the couplings to counter-propagating high order supermodes based
on tilted refractive index modulation. The responses of the W-TFBGs to temperature and bend are investigated. The
results indicate that the resonance peaks will shift red-side with increasing temperatures, and the sensitivities of different
resonance peaks are very close in the same grating. When the bend is applied, the grids of W-TFBG will be compressed
or stretched. Two resonance peaks will shift with increasing curvatures, which is related to the orientation of curvature.
Therefore, it is potential to work as a directional bend sensor. For the fiber grating with high-order supermodes coupling,
it could form fiber grating array by different levels. If every grating has individual response to surrounding, such a single
W-TFBG could be used for one point and multi-parameter measurement. In addition, this work provides some insights
into the mechanisms that contribute to the measured properties of TFBG in the photonic crystal fiber. It is also an
effective method to investigate supermode properties of photonic crystal fiber.
In this paper, an active temperature sensor based on beat frequency interrogation of a multilongitudinal-mode fiber laser
has been proposed and demonstrated. Temperature measurement has been achieved through beat frequency interrogation
of the proposed multilongitudinal mode laser. Experimental results show that the temperature sensing curve has good
linearity with a coefficient of determination of 0.996004 for a temperature range of 30°C to 105.3°C. Furthermore, its
application in the measurement of temperature dependence of fiber birefringence has been also investigated. And
calculation results according to experimental observation of the beat frequency spectrum indicate that as temperature
increases intrinsic fiber birefringence also linearly increases with a temperature coefficient of about 4.4x10-10/°C. The
proposed multilongitudinal-mode fiber laser sensor based on beat frequency interrogation has several advantages
including compactness, high signal to noise ratio, etc, which is expected to be employed in future sensing applications.
We propose a photonic crystal fiber (PCF) temperature sensor that is based on intensity modulation by
magnetic fluid (MF) filling of air holes with index-guiding PCF. Temperature characteristic of MF-filled PCF is
investigated without magnetic field and with weak magnetic field. The results show that light is still guided by
total internal reflection (TIR) in this device because MF has a smaller refractive index than the material in the
fiber core; the transmission power of the MF-filled PCF is used as the sensor signal to investigate its
temperature properties. The temperature sensitivity of transmission power was experimentally determined to
be 0.06dBm/oC for a 10cm-long PCF without applying magnetic field.
The transmission spectral characteristics of TFBG were reported under a range of curvatures with
different axial rotational orientations. The coupling modes as a result of bending were investigated by examining the
appearance of new modes, the variation in coupling strength and the chirped resonance due to the variance of the
effective tilted angle, coupling coefficient between cladding modes and core mode and the principal strain gradient.
Tilted fibre Bragg grating (TFBG) belongs to short-period gratings family; there is core mode and a lot of
cladding modes in the transmission spectrum. According to the special structure and coupling characteristic of the
TFBG, we propose a novel method of edge filter linear demodulation using tilted fiber Bragg gratings in a fiber
sensor system. The results show that the widely linear range of katabatic edge (1505nm~1535nm) and an
assurgent edge (1545nm~1565nm) can be used in edge filtering; the thermal characteristic of the core mode and
cladding modes is similar to FBG's. Therefore, it can compensate dynamically the temperature shift of the FBG
and the effect of temperature noise on the strain or other sensing signals is eliminated. The advantages of this
simple system are an all-fiber design, quasi static and dynamic operation, high stability and lower cost.
In this letter, a novel optical sensor based on high birefringence fiber loop mirror with a
single Fiber Bragg Grating, available for temperature insensitive measurement for strain, was
proposed and demonstrated. Considering that the HBFLM (high birefringence fiber loop mirror)
and the conditional Fiber Bragg Grating have different response to strain and temperature,
respectively, we can detect both the peak wavelength shift of these two devices. So we can build a
lineal matrix equation between the perturbation of the surrounding and the shift of the
transmission spectrum. Compared with conditional sensors for simultaneous measurement, this
kind of sensor has several advantages, including simple configuration, low cost and easy to be
fabricated.
Simultaneous independent measurement of surrounding refractive index (SRI) and temperature using
the tilted fiber Bragg grating is proposed and experimentally demonstrated. Core mode is sensitive only to the
temperature while cladding modes are sensitive to the temperature and SRI, theirs temperature sensitivities are
equal. The wavelength shifts of two kinds of modes with a change of temperature and SRI allow for simultaneous
discrimination temperature and SRI effect. In addition, the sensitivity of TFBG to SRI is significantly enhanced by
hydrofluoric etching clad; it can satisfy the custom-built sensitivity that the clad of TFBG was etched in different
degrees as well. This sensor is potential for chemical-biochemical sensing application and measuring the
concentration of the chemical solutions accurately.
A novel electric current sensor based on a high-birefringence fiber loop mirror(HBFLM) and a kind of magnetostrictive material rod(MMR) is demonstrated theoretically and experimentally. Part of the high-birefringence fiber(HBF) is pasted onto the MMR which is placed in the central part of a solenoid. The HBFLM is used as the sensor head and the linear filter simultaneously. Part of the high-birefringence fiber(HBF) is pasted onto the MMR which is placed in the central part of a solenoid. The rod will have elastic lengthening along the direction of the magnetic field when the uniform magnetic field changes, which will lead to a change of transmission intensity of the HBFLM filter, thus the variation of the electric current can be determined via the laser wavelength within the quasi-linear transmission range of the HBFLM filter. The sensitivity reaches 0.0153/100mA, the resolution reaches 10mA. Comparing with the previous fiber-optic electric current sensor, it has nothing with the linear birefringence based on Faraday effects in the previous fiber-optic electric current sensor. Comparing with the expensive and complex FBG electric current, the sensing signal can be directly detected by a photodiode(PD) and complicated demodulation devices are avoidable. The advantages of the electric current include optical power detection, simple and smart structure, high sensitivity, low cost, and good repeatability, etc.
A novel high-birefringence fiber loop mirror(HBFLM) force sensor based on a freely supported beam(FSB) is
demonstrated theoretically and experimentally. Part of the high-birefringence fiber(HBF) is pasted onto the central
surface of the FSB. The force is applied to the center of the FSB, which leads to the pre-demarcated wavelength shift of
the transmission spectrum of the HBFLM. The sensitivity reaches 8.9N/nm, the resolution is 0.049N, and the linear
measurement range is 0.049N~0.392N.There is a good linear relationship between the force and the wavelength shift.
The advantages of the sensor include simple structure, high sensitivity, low cost, and good repeatability, etc.
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