KEYWORDS: Fiber lasers, Temperature metrology, Sensors, Temperature sensors, Structured optical fibers, Single mode fibers, Sensing systems, Photonics, Water
A single mode fiber-tapered multi-core fiber-single mode fiber (SMFTMCF-SMF) structure for the temperature measurement with fiber ring cavity laser at 2 μm band is proposed and demonstrated. The sensor consists of a tapered MCF spliced between two single-mode fibers. By tapering the MCF, the modal fields of the different multi-cores run out and then couple with each other. Experimental results show that the proposed laser works stably at the resonant wavelength of 1979.2 nm at ambient temperature. A sensitivity of -4 pm/°C was obtained with the temperature changing from 70°C to 35°C.
A non-invasive vital signs monitoring system based on fiber-optic interferometers using single mode fiber (SMF) is presented in this paper. The fiber-optic interferometers was formed by a dual biconical structure without splicing point.The experimental setup was designed to collect the vital signs data of user on bed for processing. With optimized algorithm, human being’s heart beat and respiration signals can be monitored in an contactless and non-invasive way. The experimental results on the measurements of breathing rate and heart rate agree well with the results obtained from medical equipment.
This paper studies a humidity dual biconical fiber sensor coated with agarose gel. The sensor was fabricated by the taper drawing technique of using a LZM-100 fusion splicer from single mode fiber, forming a Mach-Zehnder interferometer. Humidity modifies the refractive index of the coating layer, which in turn alters the high order modes along the dual biconical fiber segment and causes a detectable shift to the interference pattern. Due to the strong light absorption of agarose at 2 μm, the sensitivity of sensor was greatly enhanced. It has been found that the sensor’s sensitivity operated at 2 μm is tens of times higher than that at 1.55 μm region.
We have demonstrated a highly sensitive microbend fiber optic sensor for perioperative pediatric vital signs monitoring that is free from direct contact with skin, cableless, electromagnetic interference free and low cost. The feasibility of our device was studied on infants undergoing surgery and 10 participants ranging from one month to 12 months were enrolled. The sensor was placed under a barrier sheet on the operating table. All patients received standard intraoperative monitoring. The results showed good agreement in heart rate and respiratory rate between our device and the standard physiological monitoring when signals are clean.
In this paper, we report a field test of a microbend fiber sensor for simultaneous measurement of breathing rate, breathing pattern, Ballistocardiogram and heart rate during magnetic resonance imaging (MRI). Comparative experiments conducted between our sensor and commercial physiologic device on a healthy male subject showed an accuracy of +/-2bpm for simultaneous measurement of both breathing rate and heart rate. Our preliminary field test on simultaneous measurement of breathing rate and heart rate in a clinical trial conducted on 11 healthy subjects in the 3.0 Tesla MRI environment showed very good agreement compared with measurements obtained from conventional MRcompatible devices.
We propose and demonstrate the feasibility of using a highly sensitive microbend multimode fiber optic sensor for simultaneous measurement of breathing rate (BR) and heart rate (HR). The sensing system consists of a transceiver, microbend multimode fiber, and a computer. The transceiver is comprised of an optical transmitter, an optical receiver, and circuits for data communication with the computer via Bluetooth. Comparative experiments conducted between the sensor and predicate commercial physiologic devices showed an accuracy of ±2 bpm for both BR and HR measurement. Our preliminary study of simultaneous measurement of BR and HR in a clinical trial conducted on 11 healthy subjects during magnetic resonance imaging (MRI) also showed very good agreement with measurements obtained from conventional MR-compatible devices.
We characterized the dynamic response of a Bragg grating-based fiber laser sensing system. The sensing system comprises of a narrow line width fiber laser based on π -phase-shifted fiber Bragg grating formed in an active fiber, an unbalanced fiber Michelson interferometer (FMI), which performs wavelength-to-phase mapping, and a phase detection algorithm, which acquires the phase change from the interferometric output signal. The novel phase detection algorithm is developed based on the combination of the two traditional phase generated carrier algorithms: differential-cross-multiplying and arctangent algorithms, and possesses the advantages of the two algorithms. The modulation depth fluctuation of the carrier does not affect the performance of the sensing system. A relatively high side mode suppression ratio of above 50 dB has been achieved within a wide range of carrier amplitude from 1.6 to 5.0 V which correspond to the modulation depth from 1.314 to 4.106 rad. The linearity is 99.082% for the relationship between the power spectral density (dBm/Hz ) of the detected signal and the amplitude (mv) of the test signal. The unbalanced FMI is used to eliminate the polarization effect.
In this paper, we propose and demonstrate a new type of fiber optic sensor system for remote continuous monitoring and
detection of partial discharge (PD) from power equipment. The sensing system uses an antenna which is connected to a
vertical-cavity surface-emitting laser (VCSEL). The modulated light by the PD signal is transmitted through an optical
fiber and measured remotely by an optical receiver. Laboratory experiments have shown that EMOptic sensor has high
sensitivity and signal to noise ratio by comparing Electromagnetic (EM) sensor and other sensors. It provides a feasible
remote PD monitoring technique for power equipments. A completed prototype sensing system based on this technique has
been installed in a commercial building for field trial. The system can be accessed via internet anytime and anywhere.
A novel phase generated carrier (PGC) demodulation algorithm based on differential-cross-multiplying (DCM) and
arctangent function (ATAN) is proposed in this paper. We investigate the stability with light intensity disturbance (LID)
and the harmonic distortion due to nonlinearity both theoretically and experimentally. The nonlinearity of the proposed
PGC demodulation algorithm has been analyzed. Compared with the traditional PGC-arctan and PGC-DCM algorithm,
this PGC algorithm inherently has much lower total harmonic distortion (THD) as well as high stability with LID.
In this paper, we propose and demonstrate a highly sensitive Microbend Fiber Sensor (MFS) for Ballistocardiogram
(BCG) recording. The MFS based BCG sensor is built into a cushion. It is a portable, small, light and low cost device.
High quality and repeatable BCG signals can be obtained by using this device which allows patients at home to monitor
their cardiovascular health. The measured BCG waveforms closely resemble those in the existing literatures. The BCG
heart beat detection agrees well with one from photo-plethysmography (PPG) signal.
A 100-km long distance fiber Bragg Grating (FBG) vibration sensor system is demonstrated by using a Raman pump
laser source at 1395 nm and two segments of erbium doped fiber (EDF). The reflected spectrum of FBG has 30dB signal
noise ratio. By using a wavelength matched FBG to achieve wavelength demodulation, vibration frequencies from 1Hz to
1000Hz has been effectively detected in this 100km long distance vibration sensor system.
We describe a new sensor for patient's breathing measurement by using fiber loop ringdown spectroscopy. The sensing
system consists of a typical single mode fiber-loop ring-down spectroscopy and a sensor mat which is used to introduce
breathing related optical loss. The sensor mat could be put in the chair or embedded in the bed. It is non invasive
measurement. The breathing rate sensor is demonstrated with an accuracy of +/-2 breaths per minute and stable sensor
output.
We describe a new ultra long distance DFB fiber laser hydrophone system by using only one Raman pump laser
source with 1W output power at 1395nm and one section of erbium doped fiber. An all fiber backscattering suppression
module and 1550nm bandpass filter are used to reduce external reflection to DFB laser and remove unwanted the
remaining pump light in 1480nm band. A 50km DFB fiber laser hydrophone system has been successfully demonstrated
to detect acoustic signals.
In this paper, we propose and demonstrate a new method to monitor heart rate using fiber optic microbending based
sensor for in-bed non-intrusive monitoring. The sensing system consists of transmitter, receiver, sensor mat, National
Instrument (NI) data acquisition (DAQ) card and a computer for signal processing. The sensor mat is embedded inside a
commercial pillow. The heart rate measurement system shows an accuracy of +/-2 beats, which has been successfully
demonstrated in a field trial. The key technological advantage of our system is its ability to measure heart rate with no
preparation and minimal compliance by the patient.
A novel simple long distance FBG sensor system is proposed and demonstrated. It can easily achieve 45dB signal-tonoise
ratio (SNR) after transmitting along a 50km single mode fiber (SMF) by using only one 1W Raman pump laser
source at 1395nm and a segment of 5m Erbium doped fiber (EDF) inserted before the FBG.
We present an understanding of the effect of external optical feedback due to Rayleigh backscattering on distributed
feedback (DFB) fibre laser. Based on this understanding, a new method is proposed to suppress self-pulsation of DFB
fibre laser hydrophone to extend the sensing distance which is constrained by Rayleigh backscattering. A 2.1km DFB
fibre laser hydrophone system has been successfully demonstrated to detect acoustic signals.
We present a new fibre optic breathing/movement sensor for in-bed non-intrusive monitoring. The light is modulated
through microbending effect during breathing/body movement. The sensing system consists of optical transmitter,
optical receiver, a sensor sheet, and a computer. An algorithm was developed to extract body movement signals and
report breathing rate and information on body movement of bedded person. The breathing rate measurement system
shows an accuracy of +/-1 breath, which has been successfully demonstrated in field trial (FusionWorld).
We propose and demonstrate a novel method to suppress the polarization induced signal fluctuation in Brillouin Optical
Time Domain Analysis (BOTDA) fiber distributed sensing system. The polarization diversity scheme contains two
polarization beam splitters (PBSs) and a piece of single mode fiber (SMF). The pulsed pump wave is split into two
beams with orthogonal polarization states and one of the beams is delayed by a time related to the pulse width. Then, the
two beams are recombined. Theoretically, the Degree-of-Polarization (DOP) of the recombined wave is zero and the
distributed sensing system is insensitive to the polarization state of the probe. Stable distributed temperature
measurement is demonstrated along a 1.2 km SMF.
A self-referenced multimode fiber (MMF) micro bend displacement sensor is presented in this paper. In this
sensor, two single mode fiber Bragg gratings (FBGs) with different wavelengths are employed for the self-reference of
the micro bend displacement measurement. A short piece of MMF with a mechanical micro bender, inserted between the
two FBGs, acts as the sensing part. The sensor output is very stable (variation in the intensity difference was ~ 0.07dB)
within the 8dB dynamic range of the transmission loss. And the maximum variation of the intensity difference with
temperature is about 0.55dB from 20°C to 75°C. The sensor system offers many advantages, including higher stability,
single end access, and high sensitivity.
An optical system for measurement of the intracellular pH (pHi) in a single living cell by using the fluorescent probe, 5(6)-carboxyfluorescein diacetate (CFDA) and fiber optic nanoprobe was demonstrated in this work. The CFDA probe is used to determine pHi in the yeast, Saccharomyces cerevisiae 97 while fiber optic nanoprobe is used to guide excitation light and receive emission light within a single cell. Experimental results showed that our system had higher detection sensitivity than other standard spectrometer, which is important to single-cell analysis, especially for the microanalysis in a single-cell.
Dual-channel fiber ring down force sensor based on the principle of time division multiplexing is descried. The system
has the capability to interrogate more than two micro bend sensors by using more than one fiber delay line to control the
time of flight of the pulse. The dual-channel fiber ring down force sensor with one fiber delay coil is demonstrated with
high force sensitivities of 183.4ns/N and 163.6ns/N, respectively. Our system has also good linear responses.
We present a fiber mode converter incorporated fiber-loop ring-down system for strain measurement. The sensing system
consists of a fiber mode converter and a typical fiber-loop ring-down system including a pulsed VCSEL laser diode at
850 nm, multimode fiber couplers, multimode fiber loop, photo-receiver and high-speed data acquisition and signal
processing. The bending multimode fiber-loop ring-down strain sensor is demonstrated with a resolution of 0.28 &mgr;&Vegr; over a
range of 767 &mgr;&Vegr;.
We report on a narrow band optical fiber filter utilizing a multimode fiber Bragg grating and fiber mode scrambler in order to tune its reflectivity that is useful as variable optical reflector and strain sensor. A change of reflectivity from 81% to 2% is achieved. We develop a novel fiber Bragg grating strain sensor that allows strain to be applied in the portion of the multimode fiber without grating. Particular advantages of this strain sensor are simple design, low system cost and high sensitivity. A strain sensitivity of 0.0013%/microstrain in change of reflectivity and large dynamic range (0-7,000 microstrain) are demonstrated. The strain sensitivity can be improved greatly by using efficient mode conversion structure in the device.
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