We experimentally demonstrate the fabrication of silicon optical fibers by using the powder-in-tube technique. The fibers are drawn from a preform utilizing a custom-made fiber drawing system. Silicon optical fibers having cladding diameters in the range of 40 to 240 µm, core diameters in the range of 10 to 100 µm, and an approximate overall length of 7 cm have been fabricated. The powder-in-tube technique is versatile and can be utilized to fabricate fibers with different dimensions and core/cladding materials.
A long period grating-based pH sensor has been designed in order to measure the pH in the ocean. The pH-sensitive
hydrogel, which is made through the thermal crosslink of poly vinyl alcohol and poly acrylic acid, can
swell or contract in response to the pH change in the surrounding environment. The sensor is designed in a single
mode-multimode-single mode (SMS) fiber structure. The long period grating is written into the multimode fiber
of the SMS structure using a focused CO<sub>2</sub> laser at the critical period (1 mm) of this particular multimode fiber.
The hydrogel is glued underneath the SMS structure and will physically stretch or compress the long period
grating hence change the phase matching condition in the SMS structure. Because of the different core sizes
of the single mode fiber and the multimode fiber, only energy coupled in and out of the fundamental mode
in the multimode fiber will be detected directly. The SMS structure has a higher sensitivity than using just
the multimode sensing fiber. This sensor has been utilized in the seawater pH sensing in the range of 6 ~ 8.
Experiments show that the sensor has a pH resolution of 0.0042.
A fiber-optic PH sensor is developed based-on the long period grating (LPG). The LPG is fabricated by using
CO<sub>2</sub> laser with a point-by-point technique. Then the grating portion is coated with PH sensitive hydrogel. The
hydrogel, made of PVA/PAA, swells its volume in response to the PH change in the surrounding environment
and results in a change in the refractive index. As a result, the LPG can response to the refractive index change
in the coating by shifting its wavelength. Therefore, change in refractive index can be measured by tracking the
wavelength shift using an optical spectrum analyzer (OSA).
In this research, the LPG is dip-coated by the hydrogel. A chemostat is designed to simulate the marine
environment. The PH in the chemostat is varied by controlling the CO<sub>2</sub> concentration in the sea water. A PH
resolution 0.046/nm using the OSA has been obtained. This sensor is designed to monitor the sea water PH
change in a long term basis.
Poly Methyl Methacrylate (PMMA) is an advantageous material than glass in oceanographic sensing applications
because of its inhospitality for marine organisms. Waveguide sensors fabricated in PMMA are often used to
measure the parameters in ocean such as PH, CO<sub>2</sub>, O<sub>2</sub> concentrations, etc. A tightly-focused femtosecond laser
is often used to produce such a waveguide or even more complicated structures through the nonlinear effect in
the bulk of PMMA, with pulse energy at μJ or mJ level. And such a laser system requires the amplifier from
chirped-pulse amplification (CPA). The oscillator itself can produce pulse energy only at nJ level which is under
the threshold of nonlinear effect. However, in our experiment, a modification to the oscillator cavity, which
elongates the cavity length approximately 3 times and as a result, decreases the repetition rate from 93mHz to
32 mHz, can increase the pulse energy to 15 nJ. Under a tight focusing lens (100x 1.40 microscope objective),
such an intensity exceeds the nonlinear threshold of PMMA. Thus, waveguide can be fabricated in PMMA using
only a femtosecond oscillator and oceanographic sensors can be also made by this simple technique.
A novel fiber Bragg grating (FBG)-based weigh-in-motion (WIM) system is introduced in order to achieve a better performance compared with the existing WIM systems. This novel WIM system uses the fiber-reinforced composite (FRC) as the load-supporting material in combination with the FBG technology. The sensor is designed as a multiply FRC laminate with the FBG embedded inside it. A theoretical model is developed to analyze the mechanism of this WIM system. Both static and dynamic tests are conducted to verify the system performance. With the extraordinary mechanical properties of the FRC, this novel WIM system has achieved larger dynamic range and higher sensitivity than prior works. The simple design of the system also reduces the engineering difficulties and overall costs.
The modeling of through-wall sensing using ultra-wideband (UWB) signals is considered. The combined method of ray tracing and diffraction (CMRTD) is employed to analyze the interaction between the UWB signal and the target. The result is obtained in frequency
domain, and then transformed into time domain by use of inverse Fourier transform (IFT). Scattering from a two-dimensional (2D) perfectly conducting circular cylinder is calculated and the result is shown in agreement with that obtained from the eigenfunction
expansion method. Furthermore, the attenuating effects of walls are
considered based on the geometrical optics. Numerical results of scattering from a 2D perfectly conducting circular cylinder behind a
homogeneous, single-layered wall are given in both graphical and tabular formats.
In this weigh-in-motion (WIM) research, we introduce a novel design
of WIM system based-on fiber Bragg grating (FBG) technologies. The
novel design comes from the idea using in-service bridge as the
weigh scale. While vehicles traveling over the bridge, the weights
can be recorded by the strain gauges installed on the bridge
abutments. In this system, the bridge beam is replaced by a piece of
steel plate which supports the weight of the traveling vehicle. Four
steel tubes are attached firmly at the corners of the plate serving
as the bridge abutments. All weights will be finally transferred
into the tubes where four FBGs are attached and can record the
weight-induced strains by shifting their Bragg wavelengths.
Compared with other designs of fiber-optic WIM systems, this design
is easy and reliable. Especially it's suitable for heavy vehicles
because of its large capacity, such as military vehicles, trucks and
trailers. Over 40-ton load has been applied on the system and the
experimental results show a good repeatability and linearity under
such a large load. The system resolution has been achieved as low as
This paper introduces a novel design of "bridge style" fiber-optic
weigh-in-motion (WIM) sensor using fiber Bragg grating (FBG)
technology. Compared with other designs of fiber-optic WIM sensors,
the bridge-style design is reliable, sensitive and can bear more
loads. With these advantages, the bridge-style WIM sensor is
specifically suitable for heavy vehicle dynamic weighing, especially
for military vehicles, cargos and equipments. Experiment is
conducted and the results show good repeatability and sensitivity
under large loads. The minimum achieved resolvable weight is 7.1
kilograms. Finally, WIM sensor on-site installation method is
This study investigates the modeling of through-wall sensing using
ultra-wideband (UWB) signals. The combined method of ray tracing and
diffraction (CMRTD) is employed to model and study the interaction
between the UWB signal and the target. The result is obtained in
frequency domain, and then transformed into time domain by use of
inverse Fourier transform. Numerical results of scattering from a
two-dimensional (2D) perfectly conducting circular cylinder are
obtained and compared with those from the eigenfunction expansion
method. Good agreements between the results are achieved. In
addition, the attenuating effects of walls are considered and
numerical result of scattering from a 2D perfectly conducting
circular cylinder behind a homogeneous, single-layered dry wall is
presented. The model can be easily extended to handle the dielectric
target and the multiple-layered walls.
This paper introduces a novel application of fiber microbending
sensor to monitor the highway vehicles, i.e. overtime pull-over
vehicles. Precise locations and durations of the overtime pull-over
vehicles can be detected and alarms can be sent to highway
administrators. Highway administrators can use these data to
maintain the traffic order, secure the passengers and enforce the
law. The sensor is designed based on fiber microbending effect and
optical time-domain reflectometry method is utilized to generate,
collect and process the optical signals. The experiment is designed
to simulate the highway shoulder with vehicle parking on it.
Different vehicle weight-induced fiber microbending losses are
detected and measured. By the optical time domain reflectometry
technique, the precise locations of pull-over vehicles have been