In recent years, the optical fiber sensing technology has attracted social more and more attention because it has advantages of strong anti-interference ability, corrosion resistance and high sensitivity. So the research of the optical fiber sensing technology has become a hot issue for researchers. Fiber Bragg grating(FBG) sensing is a kind of optical fiber sensing, and the transmission spectrum or reflection spectrum is affected by the change of external environment. The research of this topic is tilted fiber Bragg gratings(TFBG), there are core modes and a large number of cladding modes in the transmission spectrum of TFBG sensor, which will change with the change of the external environment, so it is of great significance to study its transmission spectrum with the external changes.Firstly, the temperature and refractive index sensing performance of TFBG by Optigrating. Then we measures the temperature sensing, refractive index sensing and strain sensing of the TFBG sensor, and the tilt angle is 8°, the period is 530nm, the modulation depth is grater than15dB, and the experimental results are consistent with the simulation results. We obtained that the temperature sensitivity of the TFBG is 10pm/℃ in the measurement range of 20℃-150℃, and the refractive index sensitivity is 3.2pm/% in the range of 0-25%NaCl solution, and the stress sensitivity is 1.593nm/mm in the range of 0-1.2mm tensile length in our experiment. Therefore, the TFBG sensor has important applications in many fields.
As a key research material, graphene has high thermal expansion coefficient and heat conductivity. FBG with cladding by coated graphene can effectively improve temperature sensing characteristics according to the temperature sensing principle of FBG. Firstly, after removing the coating on FBG surface with acetone and stripping pliers, graphene nanosheets were deposited on the cladding material of FBG by a simple evaporative deposition method. The temperature sensing sensitivity 13.05 pm/°C was obtained in experiment after linear fitting of data, which was about 67% higher than that of bare FBG of 7.82pm/°C. Secondly, in order to improve the purity, compactness and controllable thickness of the coatings, we deposit graphene films of FBG cladding with coating process in vacuum by pulsed laser deposition (PLD) technology. Finally, the temperature sensing sensitivity of the FBG sensor coated with graphene thin film by PLD reached 17.31 pm/°C, which was about 120% higher than that before deposition. Moreover, the whole temperature sensing system of FBG with cladding graphene film has simple structure and high practicability
The influence of different film thickness on grating coupling coefficient and transmittance has been analyzed based on a four-layer structure model of grating and matrix transformation, in which the optimum thickness of coating [(In2O3)9(SnO2)1][indium tin oxide (ITO)] is found, and the influence of environmental refractive index and wavelength for the effective refractive index of cladding mode is simulated in theory, respectively. A structure of long-period fiber grating (LPFG) coated with ITO of high-index nanothin film by the pulsed laser deposition technology is reported. The difference of refractive index sensitivity of LPFG with ITO coating or not is analyzed in experiment. The refractive index sensitivity of LPFG with ITO coating or not is −298 and −150 nm / RIU, respectively.
We propose a high-sensitivity temperature sensor with a long-period fiber grating (LPFG) using Mach-Zehnder and Sagnac interference of the optical path. The LPFG sensor achieved a good repeatability and stability of temperature response with a sensitivity of 0.083nm/°C in the range of 40°C-120°C. Comparing to the traditional fiber Bragg grating (FBG) sensor, the LPFG sensor shows 10 times higher temperature sensitivity than that of the FBG, so the problem of low sensitivity of FBG is solved. Otherwise, Mach-Zehnder and Sagnac interference of the optical path have the advantage of simple structure and good practicability which can replace the complex optical path in the special environment.
In this experiment, the optical parameters of optical fiber sensing measurements with the wavelength division multiplexer (WDM) and Fiber Bragg grating have obtained in temperature-controlled cabinet. The wavelength division multiplexer device not only make different wavelength illuminant input at the same time be possible, but also can achieve multi-channel output based on the feature of WDM. We design and put forward a new method which can realize various parameters measured at the same time, such as temperature and the refractive index or stress measurement. In addition, it can measure the same parameters with different wavelengths of laser at the same time. The contrast analysis results of different wavelengths of illuminant on the same parameter sensitivity and reliability of the measurement will use to provide reference to design the same illuminant with different parameter measurements.
Application of high temperature fiber sensing system is very extensive. It can be mainly used in high temperature test aerospace, such as, materials, chemicals, and energy. In recent years, various on-line optical fiber interferometric sensors based on modular interference of single-mode-multimode-single-mode(SMS) fiber have been largely explored in high temperature fiber sensor. In this paper we use the special fiber of a polyimide coating, its sensor head is composed of a section of multimode fiber spliced in the middle of Single-mode fiber. When the light is launched into the multimode fiber(MMF) through the lead-in single-mode fiber(SMF), the core mode and cladding modes are excited and propagate in the MMF respectively. Then, at the MMF-SMF spliced point, the excited cladding modes coupled back into the core of lead-out SMF interfere with SMF core mode. And the wavelength of the interference dip would shift differently with the variation of the temperature. By this mean, we can achieve the measurement of temperature. The experimental results also show that the fiber sensor based on SMS structure has a highly temperature sensitivity. From 30℃ to 300℃, with the temperature increasing, the interference dip slightly shifts toward longer wavelength and the temperature sensitivity coefficient is 0.0115nm/℃. With high sensitivity, simple structure, immunity to electromagnetic interferences and a good linearity of the experimental results, the structure has an excellent application prospect in engineering field.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.