subject: Fiber Grating Sensor Technology And Its Applications - Sensor Technology - Hc Net Electrical [print this page] Overview Fiber Bragg Grating Sensor The basic principles and practical application of the optical fiber grating sensors in geodynamics, space vehicles and shipping, civil engineering structures, power industry, medicine, and chemical sensing application.
I. Introduction 1978 Communications Research Centre in Ottawa, Canada K? O? Hill, who for the first time in Ge-doped silica optical fiber found in the photosensitizing effects, and VSWR is written into the legal system by the world's first fiber grating. In 1989, United Technologies Research Center, G? Meltz, who achieved the fiber Bragg grating (FBG) of the UV laser side of the writing technique, so that fiber grating Make Technology to achieve a breakthrough. With the fiber grating manufacturing technology continues to improve, increasing the results of its application, from the optical fiber communication, optical fiber transmission are optical computing and optical information processing of the entire area will be practical because of the FBG revolutionary change, fiber grating technology is the erbium-doped fiber optical technology Relay Amplifiers (EDFA) technology is another major technological breakthrough after.
Fiber grating is used in the photosensitive optical fiber made of. The so-called optical fiber photosensitivity is when the laser beam through optical fiber, optical fiber's refractive index will vary with the spatial distribution of light intensity changes in the characteristics of the corresponding place. Formed in the fiber core within the space phase grating, its real function is core is formed within a narrow band of the (transmission or reflection) filter or mirror. This feature can be used to create many unique optical properties of the device. These devices have a reflection bandwidth, range, excess loss, small size, easy and fiber coupling, can be compatible with other optical components into one, without environmental impact of a series of excellent properties of dust. Many different types of fiber gratings, primarily divided into two categories: one Bragg grating (also known as reflection or short-period grating); second transmission grating (also called long-period gratings). Grating from the structure can be divided into periodic and aperiodic structure, the structure function can be divided into the filter from the grating and the dispersion compensation grating, dispersion compensation grating non-period grating, also known as chirped grating (chirp grating ). At present the application of fiber gratings in optical fiber communications, the main focus and optical fiber sensors in the field.
In the light The field of fiber sensors, fiber Bragg grating sensors is very broad application prospects. As the fiber grating sensor with anti-electromagnetic interference, small size (standard bare fiber is 125um), light weight, good heat resistance (operating temperature limit up to 400 -600 ), multiplexing capability, transmission distance (sensor to demodulation side up to several kilometers), corrosion resistance, high sensitivity, passive components, more deformable, etc, back in 1988, succeeded in aviation and aerospace fields, as an effective non-destructive testing technology, and fiber Bragg grating sensors can be applied chemistry Medicine , Materials, water conservancy, electric power, shipbuilding, coal and other fields, also civil engineering fields (such as Building Objects, bridges, dams, pipelines, tunnels, containers, Highway , Airport runways, etc.) of the concrete components and structures to determine their structural integrity and internal strain state, so as to establish smart structure, and further implementation of intelligent building.
II The working principle of fiber Bragg grating sensors
We Know that the Bragg grating wavelength B decided by the following equation:
B = 2n (1) Type of , N for the core mode effective index, the grating period. When the fiber grating temperature of their environment, stress, strain or other physical changes, the grating period or the fiber core refractive index will change, so that the wavelength of reflected light changes, by measuring the wavelength of reflected light before and after physical changes Changes , get tested on the physical changes. Such as the use of magnetic field induced spin polarization of waves about the refractive index changes in different, enabling direct measurement of the magnetic field. In addition, specific technology, can realize the stress and temperature were measured, we can also measure. Through the grating coated with a specific functional materials (such as the piezoelectric material), can realize the indirect measurement of physical quantities such as electric field.
1 Chirped fiber grating sensor works
Grating sensor system described above, grating geometric structure is uniform, fixed-point measurement of single parameters is very effective, but requires simultaneous measurement of strain and temperature, or measuring strain or temperature distribution along the grating length, the becomes powerless. A better approach is to use chirped fiber grating sensors.
Chirped fiber grating dispersion compensation due to its excellent ability to apply high-bit-distance communication systems. And fiber Bragg grating sensor works basically the same, in the outside world under the influence of physical addition B chirped fiber grating changes, it will also lead to spectral broadening. That both strain and temperature sensors in the presence of the occasion is very useful, chirped fiber grating as strain caused by the reflected signal broadening and peak wavelength shift and the temperature change due to the temperature dependence of the refractive index (dn / dT), affects only the center of gravity. Through the simultaneous measurement of spectral shift and broadening, we can simultaneously measure strain and temperature.
2, long period fiber grating ( LPG ) Sensor works
Long period fiber grating (LPG) of the cycle is generally believed that there are hundreds of microns, LPG specific wavelengths of light coupled into the fiber core Package Layer: i = (n0-niclad)? . The formula, n0 is the refractive index of fiber core, niclad axial symmetry for the i-order cladding mode effective refractive index. As the light will be clad cladding / air interface and rapid attenuation loss, leaving with a string of losses. LPG may be an independent in a wide range of wavelengths, there are a lot of resonance, LPG resonance wavelength depends primarily on the central core and cladding refractive index difference, the strain, temperature or external refractive index changes resulting from any change resonance produced in a large wavelength shift, by detecting i, physical changes can be obtained outside information. LPG at a given wavelength on resonance with the response rate is usually different, so LPG for multi-parameter sensor.
Third, the application of fiber grating sensor
1, in Geodynamics of
In Land Shock Geodynamics detection area, surface phenomena such as sudden change in principle and risk assessed and the prediction is very complex, and volcanic areas of stress and temperature changes are present
