In this work, graphene oxide (GO) is coated on excessively tilted fiber grating (ExTFG) surface through hydrogen bond by using sodium hydroxide (NaOH) solution. The coating effect of GO is inspected by scanning electron microscopy (SEM) and energy spectrum technique. The tuning effects of GO film on the spectrum, the wavelength refractive index (RI) sensitivity and intensity change of TM and TE modes of ExTFG are investigated and analyzed in detail. Experimental results show that the GO film has similar but much less tuning effects on the polarization dependence spectra of ExTFG than that of graphene coated one, and both the wavelength RI sensitivities of TM and TE mode are enhanced by ~5% by GO film. For the TE mode of the GO-coated ExTFG, the reduction of the resonance peak is obviously greater than that of TM mode, which indicates that the surrounding RI change will induce a relatively larger change in imaginary part of TE mode, thus leading more adsorptions for the TE polarization. The coupling intensity change (~9dB) of the TE mode is ~3 times larger than that (~3dB) of the TM mode when the surrounding RI changes from ~1.333 to ~1.37 for the GO-coated ExTFG. In addition, further GO film coating has only a little improvement in the spectrum and sensing performance for the sensor.
A diode-cladding-pumped mid-infrared passively Q-switched Ho3+-doped fluoride fiber laser using a reverse designed
broad band semiconductor saturable mirror (SESAM) was demonstrated. Nonlinear reflectivity of the SESAM was
measured using an in-house Yb3+-doped mode-locked fiber laser at 1062 nm. Stable pulse train was produced at a slope efficient of 12.1% with respect to the launched pump power. Maximum pulse energy of 6.65 μJ with a pulse width of
1.68 μs and signal to noise ratio (SNR) of ~50 dB was achieved at a repetition rate of 47.6 kHz and center wavelength of
2.971 μm. To the best of our knowledge, this is the first 3 μm region SESAM based Q-switched fiber laser with the
highest average power and pulse energy, as well as the longest wavelength from mid-infrared passively Q-switched
fluoride fiber lasers.
We present the mechanism of refractive index (RI) distribution measurement based on an etched fiber Bragg grating
(FBG) with a residual diameter of about 5.73 μm. The etched FBG is installed in a micro-tube where the RI of the liquid
medium decreases linearly alone its axis. Experimental results show that the sensitivity of RI gradient and the average
sensitivity of RI of this sensor is 336.2 nm·mm/RIU and 49.44 nm/RIU, respectively, when the RI ranging from 1.330 to
1.3586. The RI distribution of the inhomogeneous liquid medium can be obtained by the RI gradient sensitivity and the
average RI sensitivity.
We demonstrate a structured fiber Bragg grating (FBG) sensor for the measurement of the refractive-index (RI) gradient
of the inhomogeneous liquid medium. The double-layer fiber waveguide models and the transfer matrix method are
utilized to calculate the reflection spectrum of structured FBG under inhomogeneous liquid medium, the refractive-index
(RI) distribution of which is linear and range from 1.330 to 1.360, showing that the reflection spectrum of the structured
FBG would split into several tiny resonant peaks, and the D-value of the wavelengths of the tow resonant peaks at the
tow sides of reflection spectrum was approximately proportional to the RI gradient. In the experiment, a FBG was etched
to a diameter of about 5.73μm for the RI gradient measurement of the diffusion process of the sucrose solution in the
micro channel, the experimental results conformed the rationality of the simulated results, indicating the possibility of
the RI gradient measurement by using the structured FBG sensors.
Based on the fiber waveguide models, a modified transfer matrix method was utilized to calculate the reflection spectrum
of the thinned fiber Bragg grating (ThFBG) under the uneven surrounding refractive index (SRI) environment. Tow SRI
ranges, including the high SRI region (from 1.42 to the fiber cladding index) and the low ones (from 1.33 to about 1.36),
were considered. Numerical results showed that the responsive characteristics of the reflectance spectrum of the ThFBG
were closely related to the properties of the SRI distribution, first, the original reflection spectrum of the ThFBG would
split into many tinny resonant peaks and the reflectance spectrums are asymmetric since the uneven SRI distributions,
second, the number of the resonant peaks, the decline of the amplitude, and the degree of the asymmetric of the
reflectance spectrums would increase as the increase in the SRI gradient and the D-value of the SRI between the tow
ends of the ThFBG. The same numerical approach could be used to analyze the responsive characteristics of the ThFBG
under the uneven medium environment where the SRI distribution was any other functions.
The applications of Fiber Bragg grating (FBG) sensors have been concerned considerably for many years. However, it is
usually difficult to obtain an accurate result by single FBG in practical applications, since the phenomenon of cross
sensitivity caused by the multi-external fields always exists. In the past, most of researchers presented their studies only
on the cross sensitivity of two parameters including temperature and axial strain, temperature and transverse pressure,
and so on. Actually, FBG sensors might be affected by temperature field, axial strain field and transverse pressure field
simultaneously in some applications, but no previous analysis has been presented on the cross sensitivity caused by these
three parameters. This work extends the previous works on the cross sensitivity of two parameters to that of three
parameters in a FBG sensor. The sensing model of FBG in three external fields is deduced and analyzed theoretically
from the perspective of its physical mechanism, through which the expression of the cross sensitivity function is
obtained. Meanwhile, examples of different external physical factors and fiber parameters are considered for illustration
purposes, and the cross sensitivity term is discussed by the numerical simulation. The simulated results show that the
properties of cross sensitivity would change in a certain regulation with the changes of external effects and fiber
parameters. Compared to the two-parameter analyzing method, this work makes a more comprehensive analysis to the
research object. Some valuable suggestions about how to reduce the systematic error and improve the measurement
accuracy are put forward as well.
Refractive index measurement by optical fiber sensors has proved to be effective in the research of biochemical and biomedical applications. The theoretical principles and technology underlying several microstructured fiber Bragg grating refractive index sensors developed over the past decade are classified and briefly summarized, and their future developments are considered.
KEYWORDS: Adaptive control, Liquids, Control systems, Process control, Microorganisms, Visualization, Resistance, Systems modeling, Biological research, Control systems design
Based on visualization test of biotrickling bed, we analyze the dynamicmodel of the purification process, and get the
dynamic model on liquid flux and purification efficiency. The adaptive control strategy is applied in the purification
process. The simulation test proves that under the same disturbance the adaptive control strategy is more effective than
PID.
KEYWORDS: Digital signal processing, Phase modulation, Robotic systems, Wireless communications, Control systems, Sensors, Picosecond phenomena, Telecommunications, Fuzzy logic, Video processing
This article analyses nowadays in common use of football robots in China, intended to improve the football robots'
hardware platform system's capability, and designed a football robot which based on DSP core controller, and combined
Fuzzy-PID control algorithm. The experiment showed, because of the advantages of DSP, such as quickly operation,
various of interfaces, low power dissipation etc. It has great improvement on the football robot's performance of
movement, controlling precision, real-time performance.
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