The orientation of talents cultivation for local colleges is to train engineering application-oriented talents, so the exploration and practice on teaching reform of theory curriculum was carried out. We restructured the knowledge units basing on numerical solution problems, and chose the software to build algorithm models for improving the analytical and designed ability. Relying on micro video lessons platform, the teacher-student interaction was expanded from class to outside. Also, we programmed new experimental homework, which was suited for process evaluation. The new teaching mode has achieved good effect, and the students' application ability was significantly improved.
We have carried out a detailed simulative study of the tapered fiber Bragg grating (TFBG) evanescent wave sensor sensitivity by using 3-D Coupled-Mode Theory method. The method is based on the spectral interrogation mode of operation. We also make numerical simulations to figure out how the uniform waist diameter and the difference of the relative refractive indexes between fiber core and external medium affect the sensitivity of this proposed sensor. The simulation results show that the sensitivity of the tapered fiber Bragg grating will be improved when the diameter of the uniform waist decrease as well as the difference of the relative refractive indexes between fiber core and external medium. And with the fixed uniform waist diameter and tapered length, when the difference of the relative refractive index of fiber core and external medium varies is 0.015RIU, the values of wavelength shift is 5.08nm, the sensitivity of the tapered fiber Bragg grating is 317.5nm/RIU. The sensitivity is higher than that of the common FBG. The results are consistent with theoretical models. The simulation results can supply the guidance for the further experimental study and refractive index sensor design, optimization and application.
We have carried out a detailed simulative study of the photonic band-gap crystal fiber sensor sensitivity by using the finite difference beam propagate method. The effect of the incident wavelength and the fill factor on the relative sensitivity of the sensors has been simulated. The simulative results show that with the incident wavelength and the fill factor increased, the relative sensitivity will be improved, the sensitivity of photonic band-gap crystal fiber sensor will be higher. The simulation results can provide the guidance for the further experimental study.
Recently, many programs have been developed for simulation or analysis of the different parameters of light propagation in tapered optical fibers, either for sensing or for communication purposes. In this paper, it is shown the RSOFT BeamPROP as a fairly robust and simple program, due to the existence of a graphical environment, to perform simulations with good accuracy. Results are compared with other simulation analysis, focusing on multimode interference phenomena for refractive index sensing in a tapered optical fiber, where the wavelength of the incident light, in terms of waist diameter and tapered region length are optimized.
Proc. SPIE. 8418, 6th International Symposium on Advanced Optical Manufacturing and Testing Technologies: Design, Manufacturing, and Testing of Smart Structures, Micro- and Nano-Optical Devices, and Systems
High temperature pressure pipes were widely used in the chemical, oil companies and power plants, but the pipe burst incidents occurred from time to time, which had caused some damages on people’s lives and property. Thus, in this paper, with the aim to solve this problem, a FBG (FBG: Fiber Bragg Grating) strain gauge structure which consists of three FBGs is designed and fabricated based on the theoretical strain and stress analysis. The strain gauge can be used for the real-time surface strain monitoring of high temperature pressure pipes. In the strain gauge, the elastic hightemperature alloy(10MoWVNb) is chosen as the substrate. The three FBGs with a similar performance are fabricated on the substrate with the high-temperature glue. Among the three FBGs, FBG1 is used for the horizontal strain sensing of high temperature pressure pipes., FBG2 is used for the longitudinal strain of high temperature pressure pipes, and FGB3 is used for temperature compensation. The strain gauge has a feature of high temperature resistance, temperature compensation and two-dimensional strain measurement. The experiment result shows that : the sensing ranges of temperature is 0~300°C, the transverse strain sensitivity is 1.110nm/με, the temperature sensitivity is 0.0213nm/°C; The longitudinal strain sensitivity is 1.104nm/με, the temperature sensitivity is 0.0212nm/°C; the temperature sensitivity is 0.0103nm/°C. Therefore, the strain gauge can meet the needs of the high temperature and pressure pipes.
In this paper, a general scalar model to analyze the diffraction spectrum of holographic variable line space (VLS) plane
grating at oblique incidence is proposed. The analytic expression for the diffraction spectrum of a VLS plane grating at
oblique incidence with a parallel and uniform beam was obtained on the basis of Fraunhofer diffraction theory. And the
applied scope of the analytic expression is that the grating period is much larger than the incident wavelength. Then
some computing examples are given in the condition of single wavelength incident. This oblique incidence model can
provide a theoretical reference for the real distribution of diffraction spectrum of holographic VLS plane grating. In
future work, the diffraction efficiency and polarization state will be considered.
In recent years, a new fiber position sensor based on wavelength encoding plane variable-line-space gratings is
developed and has attracted more and more interest. In this paper the theoretical background to the fiber position sensor
concept is briefly described. The large slope groove density distribution variable-line-space grating with holographic
recording is used in fiber position sensor. The preliminary results obtained were quite noteworthy. Due to the unevenness
of the incident light intensity in different wavelength, the diffractive intensity of different position change quickly. The
diffraction wavelength curve of the system is given. The resolution of the position sensor is also discussed in this paper.
Variable Line-Space gratings play an important role in focusing and aberration-reduced. They are widely used in spatial spectrum and synchrotron radiation facilities. However the design and fabrication methods of them are difficult. The problem is to be able to record holographically the expected grooves distribution. The geometric theory of aspheric wave-front recording optics is briefly described. We introduce the genetic algorithm to the parameters optimization of holographic variable line-space gratings. In order to obtain a steady set of recording parameters, we propose that the objective function of the genetic algorithm should consider the effect of the recording parameters errors. The integral expression of the objective function is also derived to improve the efficiency of calculation. Design example of holographic variable line-space plane gratings for a position sensor is given to demonstrate the capability of this method. The line-profiles of variable line-space plane gratings with different recording parameters are also compared in this paper.
Ronchi gratings are widely used as beam splitters in interferometry. The phase Ronchi gratings are fabricated in K9 (or BK7) substrates using a photolithographic process and ion beam etching process. The geometry of the gratings was determined within the approximations of the scalar diffraction theory to minimize their diffraction intensities in 0 and 2 orders at 514.5nm. Their diffractive characteristics are measured using Ar+ laser at 514.5 and 496.5nm. The phase Ronchi gratings exhibit the diffraction intensity in 0 or 2 order to be three orders of magnitude less than that in 1 order.
Soft x-ray condenser zone plates are one of the most essential condensing and dispersing elements in the field of soft x-ray microscopy. The zone-plates are used at 3.2nm, whose diameters are 2.8mm. The widths of their outermost zone are 647nm. The zone plate is made of Au. Self-supporting zone plates are fabricated by holography-ion beam etching process to obtain x-ray lithography mask, the x-ray lithography, photolithography and micro electroplating process were used to obtain their self-supporting structure. The self-supporting zone plates are free of membrane absorption and degradation.