We propose a vibration detection system based on Phase-sensitive Optical Time Domain Reflectometry (φ-OTDR) and 3D printed sensors. The sensor is composed of a cylindrical elastomer wounded by bend insensitive optical fiber. The cylindrical elastomer is made of flexible material by 3D printing machine. We have demonstrated that the 3D printed sensor is highly sensitive to vibration. Experimental results also show that the sensors in our vibration detection system can distinguish different distances from the vibration source, indicating an accurate locating approach of structural damage in health monitoring for large scale civil engineering structure.
Optical fiber is an important transmission medium in optical communication system. We have designed circular stepindex fiber and circular graded-index fiber for Orbital Angular Momentum (OAM) transmission. And we calculate the existing vector modes in fiber through the software COMSOL Multiphysics. The step-index fiber has a high refractive index ring which doped with PbS quantum dots between the core and the cladding. And the refractive index difference between the ring and the cladding reaches 0.035, which weaken the degeneracy of adjacent eigenmodes. Numerical analyses show the step-index ring core fiber can support the long-distance transmission for the OAM mode of |L|=1,5,6,7 in the wavelength range of 1530nm to 1565nm (|L| refers to the mode order of orbital angular momentum, called topological charge). In order to enhance its stability, we adjust the ring to be a graded refractive index profile, which increases the effective refractive index difference between the vector modes from the same mode order. This fiber design not only increases transmission stability, but also has a better manufacturing process than the step -index fiber. From the simulation results, we can find that the graded-index fiber with a gradation rate α =8 provides a relatively large effective refractive difference. The effective refractive difference is 1.68 × 10−4 , 1.42 × 10−4 and 2.44 × 10−4 respectively corresponding to L=1, 5, and 6 at a wavelength of 1550 nm. While the effective refractive index difference is 1.65 × 10−4 , 0.9 × 10−4 and 1.52 × 10−4 for the step-index optical fiber.
Optical properties of tapered optical fiber deposited with PbS are investigated, which is deposited based on atomic layer deposition technique with Pb(tmhd)2 and H2S as Pb and S precursors. After deposition, morphology of PbS thin film is characterized by a scanning electron microscope, and the composition is confirmed by X-ray photoelectron spectroscopy and energy dispersive spectrum. Raman spectrum shows a typical peak at 204 cm − 1, which is assigned to the influence of the PbS structure, and it further reveals that PbS is deposited on the surface of the tapered optical fiber successfully. With a 980-nm pump laser diode, tapered optical fiber deposited with PbS applied to fiber amplifier exhibits a wide band optical gain at 1550 nm with the largest gain of 5.6 dB.
An optical fiber high temperature sensor is demonstrated by using a special sapphire-derived fiber. An air cavity is easily created through splicing the sapphire-derived fiber with standard single mode fiber (SMF). Utilizing the air cavity as one reflecting face, a Fabry-Perot (F-P) interferometer is fabricated in the special fiber. Attributed to the high ratio alumina component, the F-P interferometer exhibits high sensitivity response to temperature variation within the range up to 1000 °C. The sensitivity is 15.7 pm/°C.
We demonstrated experimentally the fabrication of tilted long-period fiber gratings (TLPFGs) with by CO2 laser. The writing efficiency can be dramatically improved by increasing the tilt angle. We fabricated the non-titled long-period fiber gratings with equivalent grating period in the same fiber. The experimental results show that the transmission spectra of non-titled equivalent LPFGs are similar with that of the TLPFGs. The TLPFG is found to have higher refractive index sensitivity than the corresponding equivalent LPFG.
Recently, specialty fibers with various functional material doping have attracted significant attention. In this paper, we
fabricated Nb-doped silica fiber and measured its resonant optical nonlinearity with long-period fiber gratings (LPFG)
interferometer. The Nb-doped fiber was made with a combined MCVD and ALD technology. Then, we fabricated a pair
of LPFGs and cascaded them as a Mach-Zehnder interferometer (MZI).By measuring the wavelength shifts of the
interference fringe with the 532nm laser pump power, the resonant nonlinear refractive index of Nb-doped silica fiber
around 1537 nm was estimated to be 8.12×10-16m2/W.
Gold core silver shell nanoparticles with different molar ratios of gold and silver were prepared by chemical reduction
with microwave heating method. Uv-vis absorption spectrometer and transmission electron microscope (TEM) were
used to detect their absorption and surface topography. The results show that core-shell nanoparticles had controllable
size and uniform distribution. With Rhodamine 6G (R6G) as detection molecules, gold core silver shell sol with a molar
ratio of 1:10 had the best surface-enhanced Raman scattering (SERS) effect. And we detected 10-17 mol/l and 10-9mol/l
R6G solution respectively after they were self-assembled on silica substrates and optical fiber endface.
An optical fiber label-free antigen-antibody immunosensor was proposed and demonstrated. It was fabricated by a
special double cladding fiber (DCF) which presents a band-rejection resonant transmission spectrum. With the 3-
aminopropyltriethoxysilane (KH-550) as the crosslink agent, goat anti rabbit IgG was immobilized on the surface of the
DCF sensor. The whole process of immobilization and the antigen-antibody reaction was monitored through the shifts of
the cladding mode resonant spectrum. Experimental results show that the resonant spectrum shifted toward longer
wavelength during antigen-antibody reaction process. And the spectrum shift presented a saturation trend at high
concentration rabbit IgG.
An interrogation scheme for an in-series double cladding fiber (DCF) sensor is proposed and demonstrated, which can be
used for simultaneous refractive index (RI) and temperature measurement. It utilizes two commercial distributed
feedback lasers to match two cascade DCF sensors which have two band-rejected filtering spectra at different
wavelengths. The two lasers were intensity modulated by different frequencies and demodulated by a lock-in amplifier.
Experimental results indicated that a resolution of ±2×10-5 in RI and ±1.2°Cin temperature were achieved. Based on the
simple and low cost interrogation scheme, the dual parameters sensor system will find potential applications in chemical
sensors and biosensors.
In this paper, we report an in vivo experimental study of liver tissue during Laser Induced Interstitial Thermotherapy
(LITT). Single FBG was used in the experiments to measure the temperature distribution profile of the bio tissue in real
time. Ideally, the goal of LITT is to kill pathological tissue thoroughly and minimize its damage to surrounding healthy
tissue, especially vital organs. The extent of treated tissue damage in the therapy is mainly dependent on the irradiation
time and the laser power density at the tissue surface. Therefore, monitoring the dynamic change of the exact
temperature distribution of the tissue is a key point for the safety of this treatment. In our experiments, FBG was
embedded in the laser irradiated bio tissues and used as fully distributed temperature sensor. During the therapy, its
reflection spectra were recorded and transmitted to PC in real time. The temperature profile along the FBG axial was
reconstructed from its reflection spectrum by the spectra inversion program running on the PC. We studied the
dependence of the temperature distribution and the laser output power experimentally and compared the results of in
vivo and in vitro under similar laser irradiating conditions. Experimental results demonstrate the effectiveness of this
method. Due to influence of body temperature, the in vivo measured temperature is higher than the in vitro one with an
almost constant temperature difference value, but the slope and trend of the measured temperature curves in vivo and in
vitro are almost identical.
Nanosized colloidal gold was prepared by the reduction of chloroauric acid with trisodium citrate in aqueous solution
with microwave heating method. The diameters of gold nanoparticles were from 13 to 70 nm with the ratio of the
trisodium citrate and chloroauric acid. With rhodamine 6G (R6G) as the detection molecules, the SERS properties of
gold colloid were studied. Experimental results show that the gold colloids with 50-60nm particle diameters are excellent
SERS substrates and sodium chloride (NaCl) can improve gold colloid's surface-enhancement effect.
We demonstrate the packaging of CO2 laser written long-period fiber gratings (LPFGs) using different polymer materials.
We use three different silicone rubber polymers to package the LPFGs by simply coating it outside the grating. After the
polymer coating, the resonance wavelength of LPFG was found to shift towards shorter wavelength by about 6 nm, and the
temperature sensitivity of the packaged gratings was studied experimentally. Experiments showed that the gratings
packaged by different polymers have different temperature characteristics and all of them have good thermal stability.
A kind of fiber drawing machine based on gas furnace is introduced in this paper. Furnace vents were designed with a
special eccentric angle and elevation angle to form a specific size focus ring. The high temperature area of the furnace is
focused on gas ring. Different heating furnace structure for different preform dimension can be obtained by changing the
eccentric angle and elevation angle. Gas heating source was selected through analysis and comparison of hydrocarbons
and acetylene gas temperature characteristics. In the experiments, we draw out a hollow fiber at about 1280°C and got a
minimum optical fiber drawing speed of 1m / min. The furnace temperature can also be set below this temperature by gas
selection and flow control to draw out various low temperature optical fiber.
We demonstrated experimentally the fabrication of tilted long-period fiber gratings (LPFGs) with different tilt angles by
CO2 laser. The experiment results reveal that the LPFGs written with different tilt angles have quite different
transmission spectra, the polarization sensitive LPFGs can be written with large tilt angles by the CO2 laser.
In this paper, we fabricated fiber-optic extrinsic Fabry-Perot interferometric (EFPI) sensors with photolithography . The
sensor has double-layer SU-8 diaphragm: one is the pressure transduction layer; the other is cavity control layer. Since
SU-8 material has a low Young's modulus, high pressure sensitivity can be achieved with SU-8 diaphragm. The EFPI
were formed by a single mode fiber and a double-layer SU-8 diaphragm. To improve the fringe contrast, gold mirrors
with a reflectivity of 50% were evaporated onto the end face of the single mode fiber and the inner face of the SU-8
diaphragm respectively. Experiments were done to estimate the performance of the sensor for static pressure
measurement. The results show that an expected cavity length of the sensor was obtained and the EFPI sensor has a good
linearity from 100 to 2500 Pa with 100 Pa resolution and a sensitivity of 154.8 nm/kPa.
In this paper, tomato epidermis' surface-enhanced Raman scattering spectra were measured on gold and silver active substrates and analyzed. Preparing and using gold sol and silver sol in similar particle diameters (about 50-60nm), three comparable Raman spectra were obtained. Silver sol and gold sol can both increase Raman scattering signal of tomato epidermis. Through the Raman spectra, silver sol has greater enhancement ability than gold sol to tomato epidermis.
In this paper, Raman spectra of hepatocellular carcinoma cells were analyzed using gold and silver nanoparticles as SERS active substrates. The size of gold and silver nanoparticles is about 50-60 nm, and these nanoparticles have enhancement role to the Raman spectrum of hepatocellular carcinoma cells. The results show that the Raman enhancement effects of gold colloid are more sensitive than silver colloid to cells.
A fiber-optic intrinsic Fabry-Perot interferometric (IFPI) sensor was fabricated in single-mode fiber using femtosecond
(fs) laser. The fs laser was directly focused into the fiber core to form a local mirror by inducing the refractive index (RI)
changes, and the F-P sensor was composed of two local mirrors and the fiber cavity between them. The measured
spectrum has a high fringe visibility up to 10 dB. The temperature sensing characteristics of the F-P sensor were studied.
Experiment results show that the reflection spectrum linearly shifts against the temperature with the sensitivity of
10.6pm/°C.
Raman scattering enhancement characteristic of a new kind of Nb-doped silica fiber has been studied in this paper. This
Nb-doped special silica optical fiber is fabricated on Modified Chemical Vapor Deposition (MCVD) (which is the
traditional fiber preform fabrication technologies) combined with Atomic Layer Deposition (ALD). Meanwhile, Raman
spectrum of different length Nb-doped special silica optical fiber samples has been measured with the 785nm exciting
light. Then, it develops the measurement comparison between Nb-doped special silica optical fiber and conventional
single-mode optical fiber in the wavelength range from 820nm to 920nm. The measuring results indicate that the new
Nb-doped special silica optical fiber shows higher Raman scattering intensity compared with conventional single-mode
optical fiber. On the other hand, the inferred spectrum of the new Nb-doped special silica optical fiber is also measured,
and its measurement wavenumber range is from 400 cm-1 to 4000 cm-1. Finally, the loss spectrum of the Nb-doped
special silica optical fiber is measured and its loss at 1550nm is 0.01dB/m.
A fiber-optic intrinsic Fabry-Perot (F-P) interferometric sensor was inscribed in a standard single mode fiber by inducing
refractive index change in the core. It was written directly by using a femtosecond laser. The reflection spectrum of the
fiber-optic F-P interferometric sensor was measured and was investigated as a temperature sensor. The sensitivity of the
sensor is 9.2 pm/°C in the temperature range of -20~80°C.
A surface-enhanced Raman scattering (SERS) optical fiber sensor using biconical taper multi-mode fiber (MMF) is
proposed. It is fabricated by fused elongating a multi-mode fiber and then coated the silver colloid on its waist. The main
advantage of this sensor is that it can increase the SERS active substrate region to make more molecules be excited to
produce Raman signal. Silver colloid is selected as the active substrate of SERS. A modified immobilizing process is
introduced to increase the thickness of the immobilized layer and reduce the preparation time. Various concentration of
R6G is used to detect the performance of the sensor. Strong Raman signal is detected from the waist of the tapered fiber.
The detection sensitivity is up to 10-9M.
In this paper, a new method was proposed to fabricate tapered optical fiber which has strong evanescent field in the
tapered region. Our system relies on a scanned high-frequency pulsed carbon dioxide laser (CO2 laser) beam across the
taper region. The optimal heating and stretching parameters were determined through a series experiments. An effective
laser scanning pattern was designed to obtain a relatively uniform temperature field. Symmetrical fiber tapers with taper
waist diameters of ~10-20μm, overall lengths of ~10-17mm and transmission losses of ~0.8-3dB at 1550nm were
obtained. The taper profile was measured which presents a good fit with the "decaying-exponential" model. The "selfregulating"
law is demonstrated, which shows the desired taper waist diameter as a function of the laser power. A refractive index sensing experiment using the tapered optical fiber is also studied to show the potential application in refractive index sensor.
In this paper, fiber Bragg grating (FBG) is used as a fully distributed sensor to monitor tissue dynamic temperature
changes during laser-induced interstitial thermotherapy (LITT). This work is mainly realized by the correlative single
particle (CSP) algorithm, which is a rapid algorithm for spectrum reconstruction. Experimental LITT treatment was set
up by using 532nm laser applicator on a piece of fresh liver tissue. In the experiments, the dynamic temperature profile
was successfully demodulated with a refreshing speed of 11 seconds. With the aid of dynamic feedback, the
thermotherapy boundary temperature was well controlled around 35°C during the treatment by adjusting the laser output
power in real-time. Therefore, with this method, it is promising to precisely control the tissue temperature in vivo and
improve the safety of the LITT remarkably.
In this paper a novel Surface-enhanced Raman Scattering (SERS) sensor combining with fused taper optical fiber (FBTF)
and the film coating with silver sols is proposed. This structure is designed to obviously increase the SERS active surface
when the radius is reduced and the length of the taper is increased, because the penetration depth is proportional to the
taper length and inversely proportional to the taper radius according to the fiber-optic evanescent-wave theory. Based on
the SERS sensing principle, the feasibility of FBTF sensor is analyzed in this paper. Actually, the Raman spectrum of
R6G is obtained from the taper surface coating with the silver sols in our experiments. The detecting concentration is up
to 10-7M. Moreover, this SERS sensing structure is simple and reproducible.
In this paper, a new method is proposed to fabricate an optical fiber extrinsic Fabry-Perot
interferometer (EFPI) as an ultrasonic sensor. An acoustic emission detecting system is constructed
based on multiple EFPI sensors and demodulation circuit. Ultrasound detection experiments were done
from both traditional piezoelectric transducer (PZT) and high voltage discharge. In the experiments,
strong ultrasound signals were detected in both cases. The signal attenuation related to the distance and
the angle between the acoustic emission source and the FP sensor are obtained. The results indicate that
the receiving angle of the FP sensor is nearly 90° and the maximum detection distance in the air is more
than 200cm. Furthermore, four sensors are used to locate the position of the ultrasound source
produced by high voltage discharge.
In the laser induced interstitial thermotherapy (LITT), real-timely detecting the temperature distribution of the cured
tissue is a bottleneck. In this paper, a fully distributed chirped Fiber Bragg grating (FBG) sensor, which is of small size,
immune from electromagnetic interference (EMI) and high sensitivity, is proposed to solve this problem. An experiment
simulation of LITT is set up, and only one chirped FBG is used to detect the dynamic spectral variation with different
laser power. Meanwhile, a high-efficiency spectra inversion algorithm named MSAE of FBG is utilized to demodulate
the system and obtain the temperature distribution. The spatial resolution is 0.25mm and the running time of
demodulation is tens of seconds, which can help doctors control the laser parameters such as the laser power and the
treatment time to guarantee the security of the therapy.
An in-fiber Michelson interferometer is proposed based on a double-cladding (DC) special fiber. With the DC special
fiber, light wave can be partially coupled into outer cladding. The in-fiber Michelson interferometer can be constructed
by splicing a length of DC fiber into standard single mode fiber (SMF). The interferometer is very sensitive to ambient
refractive index change because fiber cladding is as one of interference arms. A sensitivity of 36nm/RIU has been
achieved in the range of 1.33~1.40 in this work. The proposed technique has the dominant advantage of simple
fabrication process, which can be expected to have wide applications in biosensors and chemical sensors.
A fiber-optic refractive index (RI) sensor is proposed based on a double-cladding special fiber. The double-cladding fiber
(DCF) consists of core, inner cladding and outer cladding. And refractive index of core and outer cladding is higher than
that of inner cladding. Through evanescent wave coupling, cladding mode can be excited resonantly at phase-matched
wavelength. Because the cladding mode transmission is sensitive to ambient refractive index variation, the DCF can be
used to solution refractive index sensor. By splicing a section DCF into standard single mode fiber (SMF), SMF-DCFSMF
sensor was constructed and studied for refractive index sensing. A resonant wavelength shift of 65nm was
achieved by changing ambient refractive index within the range of 1~1.4525.
A Fiber-optic liquid-level sensor based on etched fiber Bragg grating (FBG) cladding mode resonance is proposed and
demonstrated both theoretically and experimentally. The theoretical model of the FBG cladding mode liquid-level sensor
is built under a three-layer step-index fiber geometry. Response of cladding mode resonance spectra to the variation of
ambient liquid level are studied and simulated numerically with couple mode theory and transmission matrix method. In
the experiments, a chemical etching method is adopted to diminish the fiber cladding diameter and increase the
sensitivity of cladding mode resonances to the ambient refractive index change. Dependences of FBG cladding mode
resonance spectra on the liquid-level variation are measured and the experiments data match the model well.
A highly sensitive liquid-level sensor based on etched fiber Bragg grating is proposed and demonstrated. The fiber Bragg
grating is etched to enhance the sensitivity to the refractive index of liquid, when a portion of etched fiber Bragg grating
is immersed in the liquid, the original single transmission dip splits into two transmission dips because of the fiber Bragg
grating spectrum is affected by the fraction of the length of the etched fiber Bragg grating that is surrounded by the liquid.
By measuring the transmission dips variations, the liquid level can be measured. The experiments show that for a liquid
level variation of 24mm, the transmission dip difference changes about 32dB. Also in the linear region, a high liquid
level sensitivity of 2.56dB/mm is achieved.
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