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.
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 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.
In this paper, we present a report about the impact of the distributed second order Raman amplification on Brillouin
Scattering in a long haul 100km fiber system experimentally. The second order lasers at 1486nm created by the primary
pump at 1395nm amplify the signal centered at 1550nm and extend the Brillouin scattering distance. Experimental
results show that, both the Brillouin scattering efficiency at high powers and the Brillouin threshold are reduced.
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).
The temporal characteristics of a fiber ring laser are reported. The laser has a simple configuration, which contains
an Erbium-doped fiber amplifier (EDFA), a polarization controller (PC) and a coupler. The EDFA has a high saturation
power of 27dBm to provide the gain in the cavity. The PC is used to control the polarization state of light. A 99/1
coupler is used to extract the laser output. There is no filter in the cavity to confine the spectrum of the laser. The simple
laser configuration can operate in different temporal modes with different pump power. In the self mode locking state,
the repetition rate is equal to the inverse of the round trip time of the cavity. The repetition rate of the laser can be
increased by increasing the pump power of the EDFA. This self mode locking phenomena is due to the homogeneous
gain medium in the cavity, rather than the nonlinear effect in the cavity. The nonlinear effect can suppress the self mode
locking phenomena by inserting a short length highly nonlinear fiber in the laser cavity.
The onset of supercontinuum generation in a photonic crystal fiber (PCF) is investigated experimentally and numerically as a function of pump optical power with a femtosecond pulse. The pump pulse wavelength is positioned in the normal-dispersion regime close to the zero-dispersion wavelength (ZDW) of the PCF. When the pump power is low, the self phase modulation (SPM) is the dominant nonlinear process. With the increasing pump power, the primary mechanism of spectral broadening is identified as the combined action of stimulated Raman scattering (SRS) and parametric four-wave mixing (FWM). In the experiment, we have also observed the anti-Stokes Raman component, which reveals the importance of the fact that the pump pulses are positioned near the ZDW. Third-order dispersion (TOD) and Raman self frequency shift (RSS) also contribute to the supercontinuum generation. Good agreement between experiment and simulation is obtained.
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.
The onset of supercontinuum generation in a photonics crystal fiber is investigated experimentally and numerically as
a function of pump optical power with a femtosecond pulse. The effects of optical wave breaking of higher-order solitons,
Stimulated Raman scattering (SRS), and coupling between the SRS and parametric four-wave mixing on supercontinuum
generation are investigated. Good agreement between experiment and simulation is obtained.
In this paper, we propose and demonstrate a novel room temperature multiwavelength erbium-doped fiber laser (EDFL) scheme with the wavelength spacing less than homogeneous broadening linewidth based on the inter-channel four-wave mixing (FWM). A stable CW MW-EDFL is firstly implemented based on a length of high nonlinear photonic crystal fiber (HNL-PCF) and sampled-fiber Bragg grating (SFBG). We further extend the idea of FWM induced self-stable operation of MW-EDFL to the multiwavelength mode-locking fiber ring laser to generate ultra-short, ultra-fast, multiwavelength and synchronized pulse sources. 2 and 4 wavelengths anchored on ITU-T standards with 100 GHz channel spacing are successfully mode-locked at 10-GHz simultaneously, without gain competition.
We propose and demonstrate a novel four-wavelength erbium-doped fiber laser using four-wave mixing (FWM). By inserting a length of highly nonlinear photonic crystal fiber (HNPCF) in the laser cavity and using two fiber Bragg gratings as the wavelength-selecting components, four stable wavelengths with equal spacing have been realized at room temperature. The energy-conversion-induced loss caused by the FWM, which happens in the HNPCF among the two oscillating laser lines and the FWM products, is believed to contribute to the stable multiwavelength operation by suppressing the wavelength competition between the two laser lines.
A bandwidth-tunable optical fiber Bragg grating filter with a large tuning range of 36 nm (1.8 - 37.8 nm) has been demonstrated, which represents, to the best of our knowledge, the broadest tuning range in reflection bandwidth of any optical fiber Bragg gratings that has been reported. The unique cantilever beam based chirp-rate tuning method used here may produce a changeable and uniform chirp rate along the length of the grating, with simultaneously keeping the center wavelength of the grating fixed. Based on this study, a spacing-tunable comb filter by using a sampled-chirped fiber Bragg grating has also been demonstrated. The change in spacing, with a tuning range up to 2.1 nm (1.2-3.3 nm), is also obtained by using the unique fiber grating chirp-rate tuning technique.
Picosecond soliton pulse train has been obtained from a passively mode locked erbium-doped ring fiber laser. The passive mode-locking mechanism that is at play in this laser relies on the modulational instability (MI) theory. By accurately adjusting the polarization setting of the circulating cavity light, the repetition rate can be tuned from 58 to 114GHz. Theoretical explanation is also given.
We report the temperature-independent measurement of displacement based on the chirp tuning of a fiber grating and a specially designed cantilever. The 3-dB bandwidth of the chirped grating changes linearly with displacement and is independent of the temperature. The displacement can be monitored directly by measuring the reflected light from the chirp grating. A linear displacement response of 37.063 mV/mm was obtained. The fluctuation of the output signal is less than 5% for a temperature range from 20 to 60°C without any temperature compensation technique. The sensor has potentially low cost due to its simple structure.
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.
A temperature-independent displacement sensor is demonstrated using a chirped fiber grating and a specially designed cantilever. The 3-dB bandwidth of the chirped grating changes linearly with displacement and is independent to the temperature. Linear displacement response of 37.063mV/mm was obtained. By measuring the reflected light from the chirp grating, the displacement can be monitored directly. The sensor has potentially low cost due to its simple structure.
The response of a transmission spectrum to applied axial strain for an in-fiber Mach-Zehnder interferometer that based on two tcascaded long-period fiber gratings is studied theoretically and experimentally. Linear strain-induced wavelength shift with a tuning rate of -0.6 pm per microstrain has been achieved, which suggests that such an optical fiber device can be used as a cost effective, tunable wavelength-division multiplexing (WDM) filter.
A novel structure for multiple wavelength operation and narrow line-width ring Er-doped fiber laser, in which the multiple fiber gratings are in series connection, is proposed. The feasibility of this new structure is confirmed in experiment and the stable operation of dual wavelength is obtained.
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