A wavelength tuning method for fiber Bragg grating based on bidrectional temperature control

A novel strain and temperature sensor based on the fiber Bragg grating (FBG) cascaded two-tapered four-core fiber (FCF) Mach–Zehnder interference (MZI) is proposed and fabricated. The two optical fiber tapers, acting respectively as a beam splitter and a coupler, are able to produce interference phenomena, so the high interference extinction ratio (above 20 dB) can be obtained. The attenuation peak at 1562 nm and the FBG center wavelength at 1550 nm in the transmission spectra are, respectively, selected to represent MZI and FBG as the monitoring wavelengths. The results indicate that the sensitivities of MZI to strain and temperature are −1.83 pm μϵ−1 and 46.93 pm C−1, respectively, and those of FBG to strain and temperature are 1.26 pm μϵ−1 and 10.58 pm C−1, respectively. Both the FBG and MZI exhibit insensitivity to the refractive index. The cascaded sensor has good linearity and is applied to measure the strain and temperature simultaneously.

A novel fast response and high precision water temperature sensor based on Fiber Bragg Grating

This work presents a fiber Bragg grating (FBG) wide-range tilt sensor based on a cam structure. Two FBGs are fixed on a specially-designed sensor shell. When one FBG is stretched by the rotating cam driven by tilt, the other FBG moves along a standard semicircle with a constant radius, and compensates for temperature variations of the stretched FBG. By detecting the difference of the central wavelength shifts of two FBGs, variations of the tilt angle can be measured. The detailed mechanical structure design and measurement theory of the sensor is presented, and the sensor prototype is discussed. Testing results of comprehensive performance show that there is a good linear relationship between the tilt angle and the central wavelength of the FBG over three intervals from -90° to 90°. The repeatability and creep resistance of the FBG tilt sensor are good, the measuring accuracy is 1.516°, and the measuring resolution is 0.003°. The measurement range is much larger than comparable existing sensors, and it avoids cross-sensitivity between temperature and strain for FBG. The sensitivity of the sensor can be easily adjusted by changing the outline of the cam, or the length of the optical fiber between two fixed points.

A novel Bidirectional output Oscillating-Amplifying Integrated Fiber Laser (B-OAIFL) which combines the advantages of the bidirectional output fiber laser oscillator, and the Oscillating-Amplifying Integrated Fiber Laser (OAIFL) is proposed and studied theoretically. The influences of the reflectivity of Fiber Bragg Grating (FBG), the length ratio, the absorption coefficient and other related parameters on the characteristics of the output laser were studied theoretically. The reflectivity of FBGs and the length of active fiber in the oscillating section show a negative correlation with the output power and efficiency. The 915 nm-pumping and the center wavelength of FBGs in the range from 1070 nm to 1080 nm show a better performance on the suppression of ASE. And the center wavelength of FBGs shows little effect on the output power and efficiency.

A fiber-optic anemometer based on fiber Bragg gratings (FBGs) is presented. A short section of cobalt-doped fiber was utilized to make a fiber-based "hot wire" for wind speed measurement. Fiber Bragg gratings (FBGs) were fabricated in the cobalt-doped fiber using 193 nm laser pulses to serve as localized temperature sensors. A miniature all-optical fiber anemometer is constructed by using two FBGs to determine the dynamic thermal equilibrium between the laser heating and air flow cooling through monitoring the FBGs' central wavelengths. It was demonstrated that the sensitivity of the sensor can be adjusted through the power of pump laser or the coating on the FBG. Experimental results reveal that the proposed FBG-based anemometer exhibits very good performance for wind speed measurement. The resolution of the FBG-based anemometer is about 0.012 m/s for wind speed range between 2.0 m/s and 8.0 m/s.

Fiber Bragg gratings (FBGs) are ubiquitous as sensors for a range of parameters and also as optical components in telecommunications systems. However, their temperature dependence of around +10 pm °C −1 is a limiting factor, making it challenging for sensors to discriminate strain from temperature, while telecommunications components require additional thermal stabilization. The temperature‐dependent properties of optical fiber are micro‐engineered by creating microchannels within the cladding using femtosecond laser‐assisted etching. These channels are filled with low‐loss refractive index liquids which have thermo‐optic coefficients that are around 50 times greater magnitude than silica and the opposite sign. Low‐loss FBGs are microfabricated in standard single‐mode fiber, with wide control over their temperature coefficient between +10 and −55 pm °C −1 . A temperature‐insensitive FBG is also fabricated which is stable to ±12.5 pm over a 17–45 °C range, which is an order of magnitude reduction in sensitivity. It has only ±3.5% reflectivity variation from the mean over this range and only 1.29 dB insertion loss.

The relationship between resistivity and temperature in ordered α2-Ti3Al and γ-TiAl intermetallic compounds single crystals

A temperature measurement system and algorithm method based on Fiber Bragg Grating (FBG) sensors and Fabry-Perot Filter (FPF) is put forward. Three reference FBGs were used to eliminate the change of the FPF induced by the environment temperature and the nonlinearity of the FPF. Two FBG temperature sensors with different temperature sensitivity were used to measure the temperature, without the expensive standard light wave length component that provide absolute stable light wave length. Arithmetic was induced how to using the fixed wavelength difference of the reference FBGs to eliminate the influence of the environment temperature, and how to using the difference sensitivity of the temperature FBGs to get the absolute temperature of the transmission lines. Experiments with a glass of water were made to contrast the measurement results of this system with that of a mercury temperature meter whose precision is 0.1°C. The experiment results shown that this FBG system has precision bigger than 99.5%.

During last decades, sensor elements based on the fiber Bragg grating (FBG) have been widely studied and developed due to the advantages of immunity to electromagnetic interference, compact size, high precision, and so on. The FBG itself is sensitive to axial strain and temperature variation directly and can indirectly measure these complex physical parameters, such as pressure, displacement, and vibration, by using some specially designed elastic structures to convert them into the axial strain of the FBG. Whether the FBG is fixed on the measured object to measure the strain directly or fixed on an elastic structure body to measure other physical quantities, these types of FBGs could be collectively called as strain sensing FBGs. The packaging of the FBG has important influence on FBG characteristics that directly affect the measurement accuracy, such as strain transfer, temperature characteristic, and spectral shape. This paper summarizes the packaging methods and corresponding temperature compensation methods of the currently reported strain sensing FBGs, focusing especially on fully pasted FBG, pre-stretched FBG with double-end fixed, and metallic packaging. Furthermore, the advantages and drawbacks of different packaging methods have been analyzed, which can provide a reference for future researches.

In this paper, a novel arc-shape FBG (Fiber Bragg Grating) load sensor is developed with a pair of FBGs embedded symmetrically in an elastic bending beam. The FBG pair is produced with peak wavelength separation of about 0.4 nm. The FBG with shorter wavelength is located above the neutral layer and another with longer wavelength below the neutral layer. As a result, the two peak wavelengths of the FBG pair move apart with lateral force applied but move together in the same direction when surrounding temperature varies, both in a linear manner. A very low temperature-dependency of only 0.04 pm/°C across the temperature range from 35°C to 82°C has been achieved, which makes it suitable for dynamic lateral force measurement even when the environmental temperature varies. Due to the fact that the sensor module consists of only the grating fiber with two FBGs and some elastic material, which are purely passive components, hence, the temperature effect of this sensor can be self-compensated without a need of any active temperature controller or other temperature-isolation mechanism, thus in principle, this sensor module is passively temperature-independent.

The intelligent sense of equipment is a key link in cloud manufacturing. Identical fiber Bragg gratings (FBG) have a flexible multiplexing number and are unaffected by the laser’s bandwidth. A distributed identical grating system oriented to cloud manufacturing equipment’s intelligent sense is developed by combining wavelength tunable laser and broadband laser source in this paper. The system collects the reflect spectroscopy to calculate the center wavelength of each FBG by Gaussian fitting. Some optimization is also done to the Gaussian fitting algorithm to increase the demodulation speed in this paper. In the system, 100 reflective FBGs of only 0.1 % reflection with the interval space of 5 m are connected to a long fiber. All the central wavelengths and positions of the FBGs can be measured. The results show that the linearity of the center wavelength with temperature is up to 99.8 % in range of −10 °C to 60 °C.KeywordsFiber optic sensorIntelligent senseCloud manufacturing

We demonstrate a dispersion compensation device based on thermal chirping of a glued fiber Bragg grating. The device can change the group velocity dispersion (GVD) while maintaining a center wavelength or change the center wavelength while preserving a GVD value. The GVD can be tuned from -122.5 to -57 ps/nm with a center wavelength at 1552.9 nm. On the other hand, the center wavelength can be shifted by 2.2 nm with a GVD value around -105 ps/nm.

We demonstrate a wavelength-tunable semiconductor pump diode for Raman amplification. Thediode is stabilized by a fiber Bragg grating (FBG) that can be continuously tuned over more than 20 nm. Tuning of the diode output wavelength is achieved by varying the center wavelength of the FBG, since the diode preferentially lases within the FBG bandwidth. We investigate the effects of wavelength tuning on the diode spectrum on its corresponding Raman gain, and on pump-pump four-wave mixing in fiber having zero-dispersion wavelength coincident with the Raman pumps.

Characterization and patterning of novel high-TCR Ta–Si–N thin films for sensor application

Fiber Bragg gratings (FBGs) embedded in conventional fibers may serve as temperature sensors over a wide temperature range and withstand temperatures around 1200 K. A variety of linearly polarized (LP) modes for the wavelengths between 400 and 700 nm may be sustained in fibers with and without FBGs. The composition of the LP modes and their competition is instrumental for understanding physics of thermo-optics and thermal expansion effects in silica-based fibers. The first objective of this work was to model mathematically the competition between LP modes and modal distribution using the solutions of Bessel equations for the fibers with and without the gratings. Computer generated modes were constructed and the cut-off V-numbers (and Eigen values <i>W</i> and <i>U</i>) were determined. Theoretical results then were compared with experimental observations of LP modes for two separate ranges of temperatures: 77– 300 K and 300-1200 K. To study the formation of LP modes over the first temperature range, liquid nitrogen was used to cool down the fiber and a thermocouple was used to monitor the temperature of the fiber. Real time recording of the modal structure was performed using digital imaging and data acquisition instrumentation. To study LP modes between 300– 1200 K, the fibers were inserted into a tube furnace with temperature control. The wavelength of the infrared radiation was reflected by a FBG and detected by an optical spectrum analyzer. Radiation at the visible wavelength propagated through the fibers, and transmitted visible light was collected, analyzed and recorded with a CCD camera to monitor distribution of the LP modes in the samples with and without the FBGs.