The three-wavelength demodulation method plays a significant role in high-speed fiber Fabry-Perot sensing signal processing. It has been applied to demodulate extrinsic Fabry-Perot interferometric interference signals with low-fineness. However, there will be significant errors when it applied to high-finesse Fabry-Perot signals formed by high reflectivity. To address this issue, this paper proposes a three-wavelength arctangent phase demodulation method specifically for high-finesse Fabry-Perot interference signals. By transforming the multi-beam interference signal, the method satisfies the cosine model, enabling high-precision demodulation of optical path variation. Further experiments were conducted on thin-film Fabry-Perot signals at different temperatures, and the results demonstrate that the proposed improved three-wavelength demodulation method achieves a measurement error of less than 6 nm
In the aerospace, military industry and energy sectors, there is a growing demand for dynamic pressure measurement in high-temperature environments. At present, common electrical pressure sensors are difficult to meet the requirements of high temperature and high frequency response at the same time. Combining the characteristics of high temperature cofired ceramics (HTCC) and the structure of fiber optic Fabry-Perot sensor, this paper proposes a realization method of fiber optic Fabry-Perot pressure sensors based on HTCC and high-temperature sintering technology. Based on the theoretical analysis of HTCC materials, a high-temperature resistant pressure sensing film based on HTCC was designed and fabricated. The ceramic sintering process is further used to package and integrate HTCC sensor. The specific experimental results are as follows. Static pressure sensitivity is 1.80 nm/MPa. The goodness of fit linearity reached 0.9998. The resonant frequency of the sensor reaches 495.8 kHz. The survival time at high temperature of 800 °C is more than 80 h. The sensitivity to temperature is 0.0046 nm/℃. The sensor studied is suitable for dynamic pressure measurement in high temperature environment.
Frequency-swept interferometry (FSI) is a well-established technique for static ranging or clearance measurement. However, when measuring the dynamic clearance in turbines, both the FSI-Doppler effect induced by target drift and the sweeping nonlinearity of the light source restricts the measurement accuracy significantly. These are two inevitable problems and must be solved. Therefore, an improved FSI-based system is proposed to realize the dynamic clearance measurement. The system consists of two sensing arms and one reference arm. Two sensing arms refer to an FSI and a frequency-fixed interferometer (FFI) with an acoustic optical modulator (AOM), while the reference arm contains a determined Machzender interferometry. The Machzender interferometry is adopted to correct the nonlinear error of the FSI signal, and the FFI with the AOM is used to suppress the Doppler error. An optimized fusion algorithm will be used combining the information of three arms. And the dynamic clearance can be reconstructed at each sampling point with the algorithm suppressing the Doppler effect and the sweeping nonlinearity problems. The system with its algorithm was verified theoretically by measurement simulations for targets in multiple forms of motion. Further experiments will be carried out in the near future.
Graphene is a candidate material for next-generation high performance transparent conducting film (TCF) to replace indium tin oxide (ITO) materials. However, the sheet resistance of large area graphene obtained by the chemical vapor deposition (CVD) method is higher than other kinds of TCFs. The main strategies for improving the electrical conductivity of graphene films have been based on various doping treatments. AuCl3 is one of the most effective dopants. In this paper, we investigate the influence of AuCl3 doping on the conductive stability of CVD-grown graphene. Large area graphene film synthesized by CVD and transferred to glass substrates is taken as experimental sample. AuCl3 in nitromethane is used to dope the graphene films to improve the electrical conductivity. Another sample without doping is prepared for comparison. The resistances of graphene under periodic visible light irradiation with and without AuCl3 doping are measured. Results show that the resistances for all samples increase exponentially under lighting, while decrease slowly in an exponential form as well after the light is switched off. The relative resistance changes for undoped and doped samples are compared under 445nm light irradiation with 40mW/cm2, 60mW/cm2, 80mW/cm2, 100mW/cm2 in atmosphere and vacuum. The change rate and degree for doped graphene are greater than that of undoped graphene. It is evident from the experimental data that AuCl3 doping may induce conductive unstability for CVD-grown graphene on glass substrate.
The purpose of this study is to investigate the electrical properties of graphene transparent conductive film under visible light irradiation. Sample in the study is chemical vapor deposition (CVD) growth graphene on the surface of copper foils and then transferred to the SiO2 substrate. Three monochromatic visible lights with wavelength of 635nm, 520nm and 450nm representing red (R), green (G) and blue (B) lights are used as irradiation sources. Results show that the graphene resistances increase slowly under light irradiation with all the three different wavelengths, while decrease slowly after the light is switched off. Light irradiation with higher power density will induce larger relative resistance change. When graphene is irradiated at the same density, blue light irradiation may result in the largest resistance change.
This research examines the influence of lighting on the electrical properties of graphene on different substrates, including PET, glass and SiO2, which are the most widely used substrate materials representing the flexible and rigid applications. The graphene sheets were prepared by CVD and subsequently transferred to three substrates. The resistances of graphene under periodic visible light irradiation were measured inside a vacuum chamber. Results show that the resistances for graphene samples on all substrates increased slowly under lighting, while decreased slowly as well after the light was switched off. The change degree and speed were different for graphene on different substrates, which were influenced as well by the illumination time, environment atmosphere and irradiation power. Graphene on flexible PET substrate is more stable than that on other substrates.
Steel cable plays an important role in modern infrastructure due to its special characteristics. Because
most of structure load is transformed to the cable tension in cable stayed structures, it is very important to monitor cable tension. Being a slender element, Fiber Grating Strain Sensor is sensitive to axial strain and is regarded as a most prospective way to monitor the cable tension. The paper reviews a
series of problems of FBG when embedded into the cable, and introduced five different embedded FBG strain sensors. Principle, characteristics, and application states of these five sensor has been discussed in details. The prospective of embedded FBG Strain Sensor for cable tension has been forecast.
Rare earth ions doped luminescence glasses are promising phosphor candidates in the fabrication of LEDs in the future due to their specific advantages such as higher thermal stability, higher transparency, compared to current commercial LEDs. While radiation patterns of luminescent glasses are different from current commercial LEDs fabricated by phosphors, luminescent glasses play roles both in emitting light and adjusting light distribution. In order to investigate radiation pattern of luminescent glasses, luminescence physical model of flat glasses doped with single rare earth ion was presented. Process of photons acting on rare earth ions and transporting in the luminescent glasses, and output light distribution from luminescent glasses were analyzed based on violet LED. At last, the simulating of radiation pattern for luminescent glasses based on Monte Carlo ray-tracing method was proved by experiment.
If a surface light source is in far-field working condition, the error from using the inverse-square law about intensity and distance should be less than 1%. However, the results of where the far-field begin may be quite different with different error definition. In this paper, by comparing several formulas commonly used for error analysis, the root mean square (RMS) weighted by the sum of intensity at infinity is proposed as the preferred error formula for far-field distances calculation. The relative far-field distances (RFFDs) for LED arrays with different radiation pattern are calculated based on this error definition.
Organic light emitting diode (OLED) is a typical surface source with continuous luminous area. It is important to know its far-field condition since most of lighting designs are based on the far-field characteristics. In this paper, the relative far-field distances (RFFD) for OLEDs with round, rectangular, annular, hemispherical and semi-cylindrical shapes are calculated. The RFFDs for LED arrays with the same shapes are also given for comparison. Results show that the RFFDs for OLEDs are smaller than that of LED arrays with the same shapes and sizes for most situations.
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