The performance bound of a hybrid radio frequency-underwater wireless optical communication (RF-UWOC) system with inverse Mellin transform is investigated. The RF link obeys the Nakagami-m distribution while the UWOC link undergoes the mixture Exponential-Generalized Gamma(EGG) distribution under heterodyne detection and intensity modulation direct detection. In the first place, the inverse Mellin transform technique is applied to derive closed expressions for the upper bound of the probability density function (PDF). By capitalizing on these statistics, the boundaries of the outage probability, the average bit error rate, and the average channel capacity are acquired. The expressions are verifified by the Monte Carlo simulation. The results indicate that the performance of the system is superior when the relay gain is the second case.
In this paper, a FMF sensor with double gourd structure is prepared. The transmission spectrum and mode changes of double gourd structure with different lengths are studied, the temperature sensitivity and linearity of the sensor are analyzed. Five sensors with different FMF lengths are prepared. The waist-enlarged spacing are 0.7cm, 1.0cm, 1.3cm, 1.6cm and 1.9cm, respectively. The FMF length are 4.1cm, 5cm, 5.9cm, 6.8cm and 7.7cm, respectively. The experimental results show that the highest temperature sensitivity of FMF sensor is 86.95pm/℃. There is no one-to-one correspondence between the temperature sensitivity and the length of the sensor.
A high sensitivity strain sensor based on cascaded cladding mode resonant double-clad fiber (DCF) and simple mode fiber is proposed. The basic principle of the sensor is analyzed, and the preparation of the sensor is performed. In different length of double-clad fiber, the strain sensing characteristics are analyzed detailedly. Experimental results show that, as the length of the connected double-clad fiber increases, the trough of the resonant spectrum will gradually increase. That is, the length of the access DCF is inversely proportional to the free spectral range. With the increase of tensile force, the resonance spectrum is blue shift, and the tension sensitivity can be up to -1.87nm/mε.
Combining with the characteristics of disciplines and OBE mode, also aiming at the phenomena of low learning enthusiasm for the major required courses for senior students, the course of optical fiber sensing was chosen as the demonstration for the teaching mode reform. In the light of "theory as the base, focus on the application, highlighting the practice" principle, we emphasis on the introduction of the latest scientific research achievements and current development trends, highlight the practicability and practicality. By observation learning and course project, enables students to carry out innovative project design and implementation means related to the practical problems in science and engineering of this course.
In view of the current poor learning initiative of undergraduates, the idea of creating a good learning environment and motivating active learning enthusiasm is proposed. In practice, the professional tutor is allocated and professional introduction course is opened for college freshman. It can promote communication between the professional teachers and students as early as possible, and guide students to know and devote the professional knowledge by the preconceived form. Practice results show that these solutions can improve the students interest in learning initiative, so that the active learning and self-learning has become a habit in the classroom.
KEYWORDS: Scientific research, Charge-coupled devices, Optoelectronics, Electronics, Video processing, Video, Signal processing, New and emerging technologies
The CCD principle and application course is professional and comprehensive. It involves many subject contents. The course content includes eight aspects. In order to complete the teaching tasks within a limited time, improve the classroom teaching quality and prompt students master the course content faster and better, so the multidimensional interactive classroom teaching is proposed. In the teaching practice, the interactive relationship between the frontier science, scientific research project, living example and classroom content is researched detailedly. Finally, it has been proved practically that the proposed multidimensional interactive classroom teaching can achieved good teaching effect.
A refractive index sensor based on taper Michelson interferometer in multimode fiber is proposed. The Hydrofluoric acid corrosion processing is studied in the preparation of single cone multimode optical fiber sensor. The taper Michelson interferometer is fabricated by changing corrosion time. The relationship between fiber sensor feature and corrosion time is analyzed. The experimental results show that the interference spectrum shift in the direction of short wave with the increase of the refractive index. The refractive index sensitivity can reach 115.8008 nm/RIU. Thereby, it can be used in detecting the refractive index in different areas including the environmental protection, health care and food production.
A tension sensor of Photonic Crystal Fiber(PCF) is presented based on core-offset splicing and waist-enlarged fiber taper. The tension response characteristics of the sensor are studied experimentally. To analyzing the modal interference, many samples with different PCF lengths between the two splicing areas, different core-offset distances and different waist-enlarged fiber taper diameters are fabricated and tested. When the tension range is 0 to 4000με, the results show that the spectrum is blue shift with the increasing of the axial tension. The sensitivity is-2.1 pm/με. The experimental results show that the tension sensitivity can be not influenced by the PCF lengths, the core-offset distances.The waist-enlarged fiber taper diameters and the tension sensor is very sensitive to axial tension and the relationship between the wavelength shift and tension is linearity. To determine the number of the interfering modes, the transmission spectra of these sensor is transformed by the fast fourier transform (FFT) method. There are several peaks in the spatial frequency spectra at these sensors. Only one cladding mode is dominantly excited, while the other cladding modes are weak. The spatial frequency is proportional to the differential mode group index. Compared with the traditional fiber sensor, this sensor has some advantages including the easily fabricated, simple structure and high sensitivity. It can be used in industrial production, building monitoring, aerospace and other fields.
In this paper, a refractive index insensitive PbS fiber temperature sensor based on Sagnac interferometer is proposed. Firstly, the sensing mechanism of refractive index and temperature is analyzed. Then a large amount of sensors with different length are fabricated. Comparing the transmission spectrum of these sensors, the PbS fiber with the length of 4mm and 10mm are chosen for sensing experiments. Finally, the experiment platform is established to measure temperature and refractive index. Under the condition of different temperature and refractive index, the relationship between the interference spectrum, temperature and refractive index is analyzed, respectively. In temperature experiment, the temperature range is 30℃-65℃. The experimental results show that the interference spectrum is red shifted. When the PbS fiber length is 4mm, the temperature sensitivity can be up to 78.23pm/℃. When the PbS fiber length is 10mm, the temperature sensitivity is 59.16pm/℃. The refractive index range is 1.3525-1.4505 corresponding to the glycerite solution concentration of 10%-80%. The experimental results show that there is no wavelength shift in the interference spectrum. So this PbS fiber sensor is almost insensitive to refractive index.
In order to improve the equilibrium between fiber sensor performance and cost, a curvature sensor based on Few Mode Fiber(FMF) is proposed. A length of FMF is spliced with waist enlarge between two Single mode Fibers(SMFs) to form two spherical- shape structure. Fiber core mode interfere with clad mode due to the excite and couple function of spherical-shape structure, respectively. The phase difference between the cladding and core regions of the fiber changes with the external strain increase, and then the interference spectrum changes. Two sensors with different length of FMF are fabricated, and the transmission spectrum are obtained. The result shows the optical power at certain wavelength is increasing with the curvature increasing. When the curvature range is 0~0.42m-1 and the FMF is 5.7cm, the curvature sensitivity can be 11.22dB/m-1. When the FMF is 5.9cm, the curvature sensitivity can be climbed to 14.08dB/m-1.
A refractive index insensitive curvature sensor based on cladding-mode resonance of specialty triple-clad fiber (STCF) is proposed. The corresponding mode properties of STCF are investigated theoretically based on the coupled mode theory. The different mode dispersion curves are calculated and a resonance wavelength is obtained. A straightforward experiment is performed to prove the curvature sensitivity. Experimental results shows that the curvature sensitivity can be achieve -11.03374nm/m-1 in the range of 0~1.17m-1, and it also has good linearity. This curvature sensor has the advantages of simple structure, easy manufacturing, highly sensitivity and has no cross-sensitivity when it compared to the other sensors. Thus it can be used for curvature monitoring in time.
An in-line Mach-Zehnder interferometer temperature sensor is proposed based on cladding-etched quartz specialty fiber. For different etching depth for the outer cladding of quartz specialty fiber, the relationship between transmission spectrum and temperature is analyzed, respectively. Experimental results show that the interference spectrums shift with the temperature changing. The peaks and valleys of spectrum have a red shift as temperature increasing. The temperature sensitivity can be up to 62.89pm/°C in 25-90°C. Thus, this temperature sensor is low-cost, easy to be fabricated and high sensitivity, so it can be used in industrial production, biomedicine, aerospace and power electronics.
A fiber-optic temperature sensor based on specialty triple-clad fiber (STCF) is proposed. Based on coupling mode theory, the STCF can be equivalent to a rod waveguide and two tube waveguides. The different mode dispersion curves are calculated and a resonance wavelength is obtained. A straightforward experiment is performed to prove the temperature sensitivity. Experimental results shows that the temperature sensitivity can be achieve 97.2pm /°C in 20~90°C and there is a good repeatability. The resonance wavelength has a red shift and increase as increasing temperature. Thus, this sensor can be used for temperature monitoring in time.
A specialty optical taper is proposed for receiving optical signal. According to the geometrical optics, the coupling
efficiency for different shape curve is analyzed, such as piecewise function type, parabola type, and linear type. The
relationship between the different large endface radius, small endface radius, taper length, refractive index and coupling
efficiency is analyzed, respectively. By comparing the input and output light energy of specialty optical taper, the
coupling efficiency can be analyzed in experiment. The experimental results are in good accordance with the theoretical
data. For the ±1.5 mm radial displacement, the coupling efficiency can be more than 50% in different directions,
respectively. Finally, the errors are also given.
Fiber amplifiers such as Erbium-doped fiber amplifier (EDFA) played a key role in developing long-haul transmission
system and have been an important element for enabling the development of optical communication system. EDFA
amplifies the optical signal directly, without the optical-electric-optical switch and has the advantages such as high gain,
broad band, low noise figure. It is widely used in repeaterless submarine system, smart grid and community antenna
television system. This article describe the application of optical-fiber amplifiers in distributed optical fiber sensing
system, focusing on erbium-doped fiber preamplifiers in modern transmission optical systems. To enhance the
measurement range of a spontaneous Brillouin intensity based distributed fiber optical sensor and improve the receiver
sensitivity, a two cascaded EDFAs C-band preamplifier with an optical bridge structure is proposed in this paper. The
first cascaded EDFA is consisted of a length of 4.3m erbium-doped fiber and pumped in a forward pump light using a
laser operating at 975nm. The second one made by using a length of 16m erbium-doped fiber is pumped in a forward
pump light which is the remnant pump light of the first cascaded EDFA. At the preamplifier output, DWDM, centered at
the signal wavelength, is used to suppress unwanted amplified spontaneous emission. The experimental results show that
the two cascade preamplifier with a bridge structure can be used to amplify for input Brillouin backscattering light
greater than about -43dBm. The optical gain is characterized and more than 26dB is obtained at 1549.50nm with 300mW
pump power.
A humidity sensor is proposed for detecting air moisture content based on tapered optical fiber. According to optical
energy transmission theory, geometrical optics, the sensing mechanism of humidity sensor is described by analyzing the
evanescent field around the sensing fiber. The relationships between the dimensions and spectral characteristics of the
taper have been analyzed, respectively. The results show that the taper shape is important for designing a humidity
sensor. The experimental curves can be obtained by comparing the transimission loss and humidity, and the errors are
also given. The humidity is analyzed in different air moisture content. The humidity measurement resolution is 1% as the
measuring range varies within 50~95%. The transmision loss decreases as increasing humidity. Thus, the high dynamic
performance can allows this sensor to be used for humidity monitoring in time.
For rectilinear mobile/free-space optical (RM-FSO) links, laser beam divergence and deflection angles are key factors to get highly accurate receiving power. The effective receiving area of the receiving-lens (R-lens) is presented and used to investigate receiving power under different circumstances. By comparing the optical spot size on the receiving plane with the R-lens diameter, the effects of laser beam divergence and deflection angles on receiving power are analyzed. The results show that the theoretical simulation is basically consistent with the experimental data, and the errors are given. Thus, given different moving situations of RM-FSO links, the solution can be used to analyze the receiving power more effectively by considering the effect of laser beam divergence and deflection angles.
A specialty solid coupled (SSC) optical taper was introduced into the receiving termination for the rectilinear mobile
wireless optical communication. Based on the curvature-shape matching relationship, the profile curve equation for SSC
optical taper has been deduced. According to ray-tracing method, the optical coupling efficiency can be analyzed by the
comparing the input and output light energy based on Fresnel reflection loss principle. The variation relationships among
the taper length, shape factor, large end radius, small end radius, radial displacement, incidence depth, and coupling loss
are analyzed. The results show that the theoretical simulation is in good accordance with the experimental data. The
errors were also given. The coupling loss was less than 10dB as the radial displacements vary within 1.5 mm in x and y
directions, respectively. For this experimental system, the receiving performance of SSC optical taper can satisfy the
communication.
For a special solid coupled optical taper, a differential equation of its shape curve is deduced using the curvature-shape matching relationship, and the closed-form solution of the equation can be acquired by its concrete initial curvature and shape boundary condition. Since the physical formation process in different tapering conditions can be described conveniently by the solution, the variation relationships among the taper length, shape factor, large-end radius, small-end radius, and shape function are analyzed. The results show that the theoretical simulation is basically in accordance with the experimental data and the errors are also given. Thus, given the shape factor parameters of the special solid coupled optical taper, the solution can be properly used to predict the taper shape curve for any taper length, large-end radius, and small-end radius.
A novel optical receiver in wireless optical communication system is presented. The receiving method is demonstrated
based on an optical taper. The taper is mounted near the focus spot of the receiving lens along the principal axis. The
larger-area end of the taper receives the converging beam and the smaller-area end transmits optical power to detector or
optical fiber. In this way, the immunity to light beam deviation in wireless optical communication system can be
enhanced evidently. The theoretical and experimental results show that the system has a perfect performance and realizes
a low loss of 4dB for the range of field of view within 1mrad.
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