Forward phase-matched Brillouin optomechanical resonance, excited by a tapered fiber, in a graphene inner-deposited whispering-gallery-mode microfluidic cavity, is demonstrated for the first time. The generated Brillouin optomechanical modes with Q factor ≈ 47000 show extremely high sensitivity (200kHz/ppm) for absolute gas detection based on frequency variation, achieving a detection limit down to 1 ppb and a dynamic range >105 orders of magnitude.
A dual-mode optofluidic flow rate sensor with a large dynamic range of 4 orders of magnitude is developed. The sensing mechanism is based on the force balance on an optically trapped polystyrene microparticle. As the optical force is very small, the flow rate sensor is very sensitive. In the open-loop mode, the manipulation length is used as the sensing signal. The sensor has an inverse sensitivity, that is, the manipulation length decreases as the flow rate increases, so that it has high sensitivity at low flow rate. In the closed-loop mode, the manipulation length is set to be constant and a feedback signal to tune the laser power for force balance is used as the sensing signal. The closed-loop mode is helpful for extending the upper limit of flow rate and also enhancing the sensitivity at high flow rate.
We demonstrate an optofluidic flow rate sensor based on the heat transfer effect in a microfluidic channel for the lab-on-a-chip applications. By employing an optofluidic ring resonator (OFRR), the wavelength shift of the resonant dip of the whispering gallery mode is detected as a function of the flow rate when the flow is heated by a 1480 nm laser. A measurement range of 2 μL/min - 100 μL/min, a minimum detectable change of 30 nL/min for the flow rate detection are achieved. Experimental results indicate that the OFRR flow rate sensor has good repeatability and the inverse sensitivity is beneficial for detecting the low flow rate with high sensitivity.
An all-fiber graphene oxide (GO) based 'FRET on Fiber' concept is proposed and applied in biochemical detections. This method is of both good selectivity and high sensitivity, with detection limits of 1.2 nM, 1.3 μM and 1 pM, for metal ion, dopamine and single-stranded DNA (ssDNA), respectively.
A highly sensitive fiber-optic Fabry-Perot interferometric geophone (FFPG) with graphene coated PMMA membrane is proposed and demonstrated, where the graphene coating is used for enhancement of the mechanical strength of the membrane. It is found that the sensitivity of the FFPG is much higher than that of the conventional electrical geophone. Such a novel all-optical geophone with low cost, high sensitivity, electromagnetic interference immunity, easy fabrication and robust structure would have great potential for use in oil/gas exploration and seismic wave detection.
The enzyme horseradish peroxidase (HRP) has been extensively used in biochemistry for its ability to amplify a weak signal. By using HRP catalyzed substrate as the gain medium, we demonstrate sensitive ion concentration detection based on the optofluidic laser. The enzyme catalyzed reaction occurs in bulk solution inside a Fabry-Perot laser cavity, where the colorless, non-fluorescent 10-Acetyl-3,7-dihydroxyphenoxazine (ADHP) substrate is oxidized to produce highly fluorescent resorufin. Laser emission is achieved when pumped with the second harmonic wave of a Q-switched YAG laser. Further, we use sulfide anion (S2-) as an example to investigate the sensing performance of enzyme catalyzed optofluidic laser. The laser onset time difference between the sample to be tested and the reference is set to be the sensing output. Thanks to the amplification effects of both the enzymatic reaction and laser emission, we achieve a detection limit of 10 nM and a dynamic range of 3 orders of magnitude.
Sensitive flowmeter with a large dynamic range is highly desirable for microfluidic applications. We developed an optofluidic flow rate sensor, with a dynamic range of about 3 orders of magnitude, based on the optical manipulation of a microparticle by a single mode fiber (SMF) with a flat endface. A single polystyrene microsphere was trapped on the optical axis by the 980 nm laser emitting from SMF and the force balance between the optical force and flow force was used for sensing. The manipulation distance was detected as a function of the flow rate. The measurement range of the flow rate can cover 20 - 22000 nL/min with a laser power of 11.4 mW to 146.3 mW. The maximum manipulation length is about 715 μm. The experimental results indicate that the sensor has a good repeatability for the flow rate measurement.
The excitation of surface field and evanescent enhancement in the graphene based optical waveguide have shown sensitive to the refractive index of surrounding media and potential applications in high-sensitivity biochemical sensing. In this paper, we investigate the graphene-coated microfiber Bragg gratings (GMFBGs) with different diameters for ammonia gas sensing. The maximum sensitivity with 6 pm/ppm is achieved experimentally when the microfiber’s diameter is ~10 μm. Moreover, by adjusting the diameter of the GMFBG, the sensing performance of the GMFBGs can be optimized. Experimental results indicate, when the diameter is range of 8~12 μm, the GMFBG shows the characteristics of high sensitivity, relative low attenuation, and large dynamic range.
KEYWORDS: Graphene, Fiber Bragg gratings, Sensors, Reflection, Chemical analysis, Gas sensors, Refractive index, Adsorption, Biological and chemical sensing, Signal attenuation
In this paper, a novel graphene-coated microfiber Bragg grating (GMFBG) sensor is proposed and demonstrated for detection of gas concentration, for the first time. Taking advantage of the surface field enhancement and polar molecular adsorption by the graphene film, we find that this structure is very sensitive to local chemical gas concentration, and the obtained sensitivities are 0.2 and 0.5ppm for NH3 and Xylene gas for tiny gas variation, respectively. Such a miniature GMFBG sensor could find applications in biological or chemical sensing, such as for trace analysis.
A high sensitivity NH3 gas sensor based on graphene/microfiber hybrid waveguide (GMHW) is reported for the first time. Enhanced by the graphene, a very high sensitivity of 0.3ppm is achieved for GMHW-based NH3 gas sensing. This work may open a window for development of novel GMHW-based gas sensors with high sensitivity, small footprint, easy fabrication and low cost.
In this paper, we presented a successful field test of a fully distributed fiber-optical intrusion detection system for security monitoring of 220km long national borderline in China. Such a fiber fence shows its outstanding ability to operate at extreme weather conditions, like strong wind, heavy snow and storm, wide temperature range from -55℃ to +50℃, et al, which may be the most difficult and complicated environment for practical applications of fiber fences.
Capacity of the sensor network is always a bottleneck problem for the novel FBG-based quasi-distributed fiberoptical defending system. In this paper, a highly sensitive sensing network with FBG vibration sensors is presented to relieve stress of the capacity and the system cost. However, higher sensitivity may cause higher Nuisance Alarm Rates (NARs) in practical uses. It is necessary to further classify the intrusion pattern or threat level and determine the validity of an unexpected event. Then an intelligent identification method is proposed by extracting the statistical features of the vibration signals in the time domain, and inputting them into a 3-layer Back-Propagation(BP) Artificial Neural Network to classify the events of interest. Experiments of both simulation and field tests are carried out to validate its effectiveness. The results show the recognition rate can be achieved up to 100% for the simulation signals and as high as 96.03% in the real tests.
In this paper, a novel method to sensing the complex refractive index (CRI) of graphene waveguide (GW) is demonstrated. Theoretical analysis and simulated results indicate the spectral properties of evanescent wave guided by microfiber would be modulated by the GW nearby. In experiment, evanescent waves with wavelength from 1510nm to 1590nm transimitting on the surface of the GW for a few centimeters, which are launched and collected by specially designed microfiber knot sensors (MFKSs). Repeated experiments and statistic results verifie that the CRI of the GW varies from 2.59-i2.66 to 2.51-i2.84 for 1510nm-1590nm band. Such an application of MFKS is suitable not only for the GW, but also for other thin films, which would be significant for the design and research of state-of-art optical devices.
Optical fiber tweezers based on a graded-index multimode fiber (GIMMF) tip is proposed. Light propagation characteristics and gradient force distribution near the GIMMF tip are numerically investigated, which are further compared with that of optical fiber tips based on conventional single mode fibers. The simulated results indicated that by selecting optimal GIMMF length, the gradient force of the GIMMF tip tweezers is about 4 times higher than that of the SMF tip tweezers with a same shape. To prove the feasibility of such a new concept, optical trapping of yeast cells with a diameter of ~5 μm using the chemically-etched GIMMF tip is experimentally demonstrated and the trapping force is also calculated.
Phase-sensitive Optical-Time-Domain Reflectometry (OTDR) system is a typical distributed fiber-optic sensing technology to detect and locate multiple dynamic disturbances from the outside, which provides a cost-effective and highly sensitive solution especially for monitoring long or ultra-long perimeters. However, the system is liable to be interfered by laser frequency drifts and environmental noises due to its phase sensitivity. The fluctuant and time-varying backgrounds severely obscure real intrusion signals, which always cause bad detection results or high Nuisance Alarm Rates (NARs). In this paper, an effective signal separation method is proposed to extract true intrusion information from the complicated noisy backgrounds of phase-sensitive OTDR system. The sensing signal in the time-domain at each spatial point is obtained by accumulating the changing trails at different moments. Multi-scale wavelet decomposition is employed on the temporal signal to get the detailed components at different scales. By selectively recombining the scale components, it can easily extract the real intrusion signal, and separate the fluctuant frequency-drift induced phase noises, and the time-varying sound or other interferences caused by the air movements, which are respectively located at different time-frequency components. Moreover, the experimental results show that the event type could be divided and discerned from the time-frequency energy distribution at different scale. Thus nuisance and false alarms in practical applications of phase-sensitive OTDR system can be decreased significantly by this way of signal separation and extraction. This technique provides a useful solution for the intrusion detection and identification of the phase-sensitive OTDR in complicated environments, and paves the way for many important applications such as long perimeter security, oil or gas pipe safety monitoring, large-scale structure health detection and fault diagnosis and so on.
A fiber Bragg grating (FBG) sensor packaged with a thin-wall alloy tube for simultaneous measurement of temperature and pressure is proposed. The influence of the structural parameters on the pressure sensitivity is investigated both numerically and experimentally. Experimental results agree well with the simulations. The pressure sensitivities of 7.8 pm/MPa and temperature sensitivity of 20.1 pm/°C are obtained in the measurement range of 0-60 MPa and 0-150°C, respectively. High repeatability and high linearity of the pressure measurement are confirmed by the experiment. By changing the materials with different elastic modulus, the inner diameter and thickness of the alloy tube, the measuring range and sensitivity of the sensor can be further optimized. The sensing performance of the sensor is also compared with a FBG sensor with another packaging structure. Preliminary results indicates that the sensor has good sensing performance and is promising to be used for long-term pressure sensing in harsh environments.
Graphene's featureless optical absorption, ultrahigh carrier mobility and optical modulation capacity would enable a new
breed of optical devices with novel photonics characteristics. The complex refractive index (CRI) of graphene can be
modulated by its local boundary conditions when molecules are attaching on the surface of the graphene layer, leading to
change in the CRI of graphene, which would induce altered properties of the evanescent wave propagating between the
graphene film and optical waveguide. In this paper, a novel fiber-optic sensor concept that integrates the graphene film
onto a microfiber is proposed to detect the molecular concentration based on TE intensity measurement. The theoretical
investigation shows that such a sensor could offer a solution for realization of a variety of high sensitivity and fast
response molecular sensing in biological, medical and chemical fields.
Novel fiber Bragg gratings (FBG) based settlement sensors are developed and the sensing performance is evaluated in
both the lab and field environments. The settlement is determined by precisely measuring the pressure of the water level
difference. The experimental results indicated that the sensor has good linearity, good repeatability and high accuracy in
the settlement measurements. The influence of temperature fluctuations on the sensor's performance is eliminated and
long-term test results proved the good stability of better than ±0.1% of the sensor. Such a FBG sensing system has been
applied to monitor the settlement of high-speed railways in practice.
In this paper, a novel graphene-based microfiber sensor is proposed and demonstrated for detection of gas concentration for the first time. As the complex refractive index (CRI) of graphene can be modulated by gas molecules in the surrounding environment, the propagating light along the graphene layer coupled by the microfiber would be altered to induce the attenuation of polarization mode intensity. Based on such a unique TE-polarization mode attenuation feature of graphene, experimental results showed that the acetone concentration can be measured accurately and quickly. Such an approach could open a window for realization of a variety of highly sensitive and fast gas or liquid sensors based on graphene, for wide applications in biological, medical and chemical fields.
Activity identification is very important in a Perimeter Intrusion Detection System (PIDS). In this paper, an intelligent
FBG-based fiber-optic PIDS is presented, which can distinguish effects of different intrusion activities. The intrusion
identification method is proposed based on the Principal Component Analysis (PCA) to tell the essential dissimilarity of
the statistical characteristics of intrusion signal's modalities in the time domain. The experimental results show the
recognition rate can be as high as 96.52% for eight types of common intrusion events.
In this paper, a carbon nanotubes (CNTs) films around microfiber gas sensor is reported. The
CNTs films are deposited uniformly on the surface of microfiber with Langmuir-Blodgett(LB) coating
technology. The CNTs which are rank tightly perform as cladding of microfiber and show the well
absorption characteristic when they are used for gas sensing. The experimental results have shown the
variations of intensity of transmitting light while the concentration of acetone and xylene around CNTs
films based microfiber are different, The changes of light intensity are 3.1dB and 9.5dB respectively,
when acetone and xylene concentrations reached 1200ppm. As the gas vaporizing freely, the results
also show the fine characteristic with real-time response. The results demonstrate that this type of
CNTs films around microfiber structure has great potential applied in trace gases detecting in
micro-scale.
A quasi-distributed FBG-based fiber-optic fence is investigated in this paper. A novel intrusion detection method is
proposed based on the autocorrelation characteristics of the signal with and without disturbances, which is very effective
to detect extremely weak signals even from nonequivalent sensor nodes in a large sensor network. When analyzing the
intrusion signal's characteristics and excluding the false alarm sources, such as environmental interferences and others,
Nuisance Alarm Rate (NAR) is well controlled while extremely high Probability of Detection (PD) is assured. The
experimental results show that the PD of the fiber fence using these methods for detecting the single and multiple events
can be both higher than 99.5%, while the NAR can be controlled well below 0.5%.
In this paper, three fiber-optic interferometric humidity sensors based on silica/polymer microfiber knot resonators
(SMKR/PMKR) are reported. These tiny humidity sensors are directly fabricated by using silica/polymer microfibers
without any humidity-sensitive coating. The silica MKR has a humidity sensitivity of ~12pm/10% RH over a range from
14% RH to 60% RH, while the PMMA (poly-methyl methacrylate) MKR has a humidity sensitivity of ~88pm/10% RH,
over a range from 17% RH to 95% RH, and the PAM (Polyacrylamide) MKR with the highest sensitivity of ~270pm/%
RH over the range of 10% to 62%.
Numerical simulations based on the ray-transfer-matrix (RTM) method is realized for explaining the principle of a
graded-index multimode fiber (GI-MMF) based hybrid fiber Fabry-Perot (GI-FFP) sensor. It is verified by the
numerical simulations and experimental results that the high fringe contrast of the reflective spectrum of the
sensor is due to the periodic focusing effect of the GI-MMF. Experimental results are in good agreement with the
theory. A typical GI-FFP sensor is fabricated and its response to the external refractive index is measured with a
maximum sensitivity of ~160 dB/RIU.
A novel fiber-optic sensor structure fabricated by cascading two optical microfiber knot resonators (MKRs) is
proposed and demonstrated in this paper. A theoretical analysis for describing the principle of such a microfiber
double-knot resonators (MDKRs) based sensing structure is given while an experiment is carried out to verify the
design. Experimental results show that high-precision and simultaneous multi-point temperature sensing in
micro-scale can be achieved by using this structure. Such a MDKRs based sensor also shows the potential for
achieving dual-parameter measurement to eliminate the cross-talk in small scale.
An optical accelerometer with a bulk-micromachined silicon proof mass and a microfiber loop resonator (MLR) sensor was developed. The MLR was fixed on the surface of the cantilever beam. The proof mass and cantilever beam were fabricated with a two-mask process. An accelerometer with a range of ±20 g and output sensitivity 624.7 mV/g was fabricated. The design, simulation, fabrication, and preliminary results are presented.
A MOEMS (Micro-Optical Electronic Mechanical System) accelerometer based on a microfiber knot resonator is
proposed and demonstrated in this paper, and the microfiber knot resonator acts as the sensing device for vibration
measurement of the MOEMS structure. The diameters of the microfiber and microfiber knot are 1.1um and 386um,
respectively. The experimental results show that such an accelerometer has a sensitivity of 654.7 mV/g, and a dynamic
range over ±25g. This sensitivity can be increased significantly by increasing the Q factor of the microfiber knot resonators,
which can be achieved by improving fabrication of the microfiber.
In this paper, we report two novel fiber-optic temperature sensors based on silica/polymer microfiber knot resonators
(SMKR/PMKR). These microfiber knots form the resonators by evanescent self-coupling in the overlap region. The
connections between the microfibers and the launching fiber as well as collecting fiber were also realized by evanescent
coupling. Experimental results show that the temperature sensitivity of SMKR is ~52pm/°C within 30°C~700°C, which
can be used as a high temperature sensor, while the sensitivity of PMKR is ~266pm/°C within 20°C~80°C. The actual
temperature resolutions of as small as 0.05°C and 0.009°C for the SMKR and PMKR sensors were obtained, respectively.
Higher resolution can be anticipated due to further improvement of the Q factor of the microfiber knot resonators.
Micro extrinsic fiber-optic Fabry-Perot interferometers (MEFPI) are fabricated by chemically etching Er-doped
fiber and then splicing the etched fiber to a single-mode fiber, for the first time to our knowledge. By using the
mixture of Hydrochloric (HCl) acid and Hydrofluoric (HF) acid as etching solution, a cavity length of up to ~27 μm
and a maximum fringe contrast of ~24dB are obtained. Experimental results show that the MEFPI is insensitive to
temperature change but highly sensitive to strain, with temperature and strain sensitivities of ~0.65 pm/°C and 3.15
pm/ με, respectively. Such type of MEFPI sensors based on the etched Er-doped fiber is compact, cost-effective and
especially suitable for mass production, offering great potential for a wide range of applications.
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