A fiber-optic sensor system based on fiber Bragg gratings (FBGs) is proposed and demonstrated to realize water flow
measurement with temperature compensation capability. For the FBG cantilever sensor as the key component of the
sensor system, a change in the water flow rate gives rise to a monotonic shift in the Bragg wavelength of the grating
while the flow direction results in either a redshift or blueshift in the Bragg wavelength due to a stretched or shrunk state
of the grating. The resolutions of the sensor system for the forward and backward flow measurement are 58.1 and 166.7
Three different types of microstructured asymmetrical fiber Mach-Zehnder interferometers (aFMZIs) consisting of a
fiber taper, a lateral-shifted junction, or a femtosecond laser irradiated spot are demonstrated to realize simultaneous
measurement of axial strain and temperature. These aFMZIs of different device architectures exhibit different
environmental sensitivities. For the taper/junction type aFMZI, the experimental results indicate temperature sensitivities
of 60.6 and 64.0 pm/°C (redshifts) and strain sensitivities of -1.48 and -2.72 pm/με (blueshifts) at higher and lower
interference orders m1 (49) and m2 (48), respectively. The other taper/spot and junction/spot type aFMZIs show similar
performance and demonstrate the effectiveness of the approach.
We report an approach to achieve simultaneous measurement of refractive index and temperature by using a Mach-
Zehnder interferometer realized on a tapered single-mode optical fiber with the advantages of low-cost simple
fabrication technique. Electrical arc method has been adopted to fabricate the abrupt tapers. The attenuation peak
wavelength of the interference with specific order in the transmission spectrum shifts with the changes in the
environmental refractive index and temperature. Experiments indicated the corresponding sensitivities of -23.188
nm/RIU (refractive index unit) (blue-shift) and 0.071 nm/°C (red-shift) for the interference orders of 169, respectively.
We report simultaneous salinity/saccharinity and temperature measurement with a fiber Bragg grating (FBG)-based
sensor system. By adopting multiplexing technique, the sensor system consists of two FBG sensing elements in which
one FBG is sensitive to salinity/saccharinity while the other one sensitive to temperature only. Experiments indicated
that the salinity, saccharinity, and temperature sensitivities of the polyimide-coated grating were 0.0165 nm/M
(blueshift), 0.0012 nm/°Bx (blueshift), and 0.0094 nm/°C (redshift), respectively. The temperature sensitivity of the
acrylate-coated FBG was 0.0102 nm/°C (redshift).
A new fiber-optic sensor system consisting of a fiber Bragg grating (FBG) cantilever as a transducer is proposed and
demonstrated to realize simultaneous measurement of magnitude and direction of deflection. For the FBG mounted on a
stainless steel cantilever, a change in the bending deflection gives rise to a monotonous shift in the Bragg resonance
wavelength of the grating while the deflection direction results in either a red- or blue-shift in the Bragg wavelength due
to a stretched or shrunk state of the grating. As an application of this deflection sensor, the water flow rate was
measured, which showed good agreement with the theoretical analysis.
High-resolution optical low-coherence reflectometry is applied to monitor biological samples. It has been found that the
reflectivity of aged cow's milk is significantly lower than that of the fresh milk with a difference of 5.35dB. During the
process of heating the fresh milk at a constant temperature of 80°C, the reflectivity of the milk gradually decreases with
the increase of the heating duration. The technique is proved to be effective in monitoring the change in the refractive
index of the sample.
Bulk-heterojunction photovoltaic devices consisting of poly (3-hexylthiophene) (P3HT) as a donor and [6,6]-phenyl-
C61-butyric acid methyl ester (PCBM) as an acceptor are investigated in this paper. To achieve an efficient photo-induced
charge transfer, the following aspects have been studied: (1) Selection of suitable solvent to obtain good
morphology of the films and optimal absorption spectrum; (2) Determination of the donor/acceptor composition ratio
that yields good film interface and high photon absorption; (3) Thermal annealing process to enhance the photon
absorption, improve the short circuit current and the filling factor, and therefore the efficiency of the devices.
In this article, thermo-reversible compounds have been applied as a transducer in a fiber-optic temperature sensor and the dependence of the reflected optical power on the temperature has been investigated. The reflected optical power indicated a monotonous change in the temperature range of observation, corresponding to an 1.4 dB increase in the optical power when the temperature increased from 20 to 125°C. The temperature dependence of the optical properties was found to be reversible, which indicates that the temperature transducer is reversible as well.
In this paper, the wavelength dependent Polarization Dependent Loss (PDL) characteristics of fiber Bragg gratings (FBG) are discussed. The PDL in FBG is measured by applying the polarization scanning method and the Mueller matrix method. The experiment results indicate that the wavelength dependent PDL in uniform FBG has the potential to realize temperature sensing measurement.
Thermoreversible compounds have been investigated for applications as a transducer in a fiber-optic temperature sensor
utilizing a 2×2 fiber optic coupler. The dependence of the reflected optical power on the temperature has been studied.
The reflected optical power at 632.8 nm indicated a monotonous change in the temperature range of observation,
corresponding to 2.05dB increase in the optical power when the temperature increased from 20°C to 134°C. The
temperature dependence of the optical properties was found to be reversible, which indicates that the temperature
transducer is reversible as well.
A new temperature sensing technique based on high-resolution reflection measurement in a fiber optic system is
demonstrated. The technique adopts thermoreversible compounds as a transducer in a fiber-optic temperature sensor
system. The dependence of the light reflection on the temperature has been studied. The reflected optical power
indicated a change in the temperature range of observation, corresponding to a change of 15.3dB in the reflection signal
when the temperature increased from 20°C to 140°C. The temperature dependence of the optical properties was found
to be reversible, which indicates that the temperature transducer is reversible as well.
A novel fiber optic sensor for simultaneous measurement of temperature and salinity with multiplexed polymer-coated fiber Bragg gratings is demonstrated. It has been found that the polyimide-coated fibre Bragg grating respond to variations of both temperature and salinity while the acrylate-coated fiber Bragg grating is only sensitive to the environmental temperature. The experimental results showed that the temperature and salinity sensitivities of the multiplexed fiber Bragg grating sensor are 0.0102 nm/°C and 0.0038 nm/%S, respectively.
A new fiber optic sensor for simultaneous measurement of temperature and saccharinity with multiplexed polymer-coated fiber Bragg gratings is proposed and demonstrated. It has been found that the polyimide-coated fibre Bragg gratings respond to variations of both temperature and saccharinity while the acrylate-coated fiber Bragg grating is only sensitive to the environmental temperature. The experimental results showed that temperature and saccharinity sensitivities of the multiplexed FBG sensor are 0.0102 nm/°C and 0.0012 nm/°Bx, respectively.
In this article, photosensitivity of optical fibers is discussed. The comparison on the influence of pulse width and
wavelength of different trimming lasers on the fiber Bragg gratings shows significant effects on the performance of the
gratings. The characteristics of the fiber Bragg gratings have been investigated under different environmental conditions
and their dependences can serve as the basis for applications as sensors.
In this article, optical switching effect of a thermochromic thin film is reported. The transmittance of the film increased
from 0.64 at 120°C to 0.96 at 200°C indicating strong temperature dependence for its optical properties. The
temperature dependence of the optical properties was found to be reversible during the heating and cooling processes.
The possibility to reduce the size of the laser beam with the nonlinear optical switching effect of the thermochromic
film is discussed.