【正文】 And the use of optical fiber birefringence sex constitute the temperature, pressure, vibration for the sensor. This kind of sensor can avoid light source of strength changes of ah, so high sensitivity. 3).Frequency modulation fiberoptic sensors It is a use of monochromatic shot to the object to be tested the reflected light changes the frequency of the monitor to the sensor. Use of sports objects reflect light and scattering light doppler effect of the optical fiber speed, vibration, pressure, flow velocity and acce。s effect of the electric field, make voltage sensor。 And the material of the fluorescent light radiation or the road block to form such as pressure, vibration, temperature, displacement, gas, etc. Advantages: simple structure and easy to implement, and the cost is low. Faults: light intensity by fluctuations and connectors loss of changes greatly. 2).Polarization modulation fiberoptic sensors It is a kind of polarization of light changes to deliver the tested object information of the sensor. Favorable light in magic field in the medium of the spread of Faraday effect of current, magic field sensors made。 Vibration film or LCD reflected light intensity change。 Tlight transmission time. Visible, if make light intensity, polarization direction of A(vector), frequency and phase one of the parameters such as with the change of state is measured and change, or is measured by A, then, through the light intensity modulation, polarization modulation frequency modulation, or phase modulation of demodulation, gain needed be measured information. Fiber optic sensors are often loosely grouped into two basic classes referred to as extrinsic or hybrid fiber optic sensors, and intrinsic or all fiber sensors. Figure 1 illustrates the case of an extrinsic or hybrid fiber optic sensor. Figure1. Extrinsic fiber optic sensors consist of optical fibers that lead up to and out of a black box that modulates the light beam passing through it in response to an environmental effect. The classification of the optical fiber sensor The classification of fiber optic sensor has some forms, can according to optical fiber sensor in the role of classification, also can according to light modulation of the tested object by the form of classification to the function of optical fiber sensor in classification Optical fiber sensor into functional, the functional and picked up three types of light type 1).Functional (all fiber type) optical fiber sensor Use has sensitive to outside information ability and the ability of testing (or special optical fiber optical fiber sensor), will pass and feeling integrated sensor. Not only the light on optical fiber effect, and still use of optical fiber in the external factors (bending, phase transformation) function, its optical properties (light intensity, phase, the change of polarization, etc.) to realize pass and sense function. Therefore, the optical fiber sensor is continuous. Due to the continuous fiber, increase its length, can improve the sensitivity. 2).The functional (or says lighttransmission type) optical fiber sensor The only light guide fiber role, the not only sense to outside information, feel function depend on other physical properties of functional ponent finish. Optical fiber discontinuous. This kind of optical fiber sensor to need not special optical fiber and other special technology, much easier to achieve, and the cost is low. But sensitivity is low, the sensitivity requirement is not too high for the occasion. 3).Pick up the light fiberoptic sensor With optical fiber probe, as received from tested object radiation light or be its reflection, scattering of light. Its typical examples such as optical fiber laser doppler velocity gauge, FuSheShi optical fiber temperature sensors, etc. to the form of light modulated by the object being measured 1).Intensity modulation fiberoptic sensors It is a use of tested object of the change sensitive ponents the refractive Signal processing Light accept the signal Light transmitter Optical fiber sensing elements index, absorb or reflection of the parameters such as changes, and lead to the light intensity changes to achieve sensitive sensors measuring. Use of optical fiber bending loss of micro。 ωthe vibration frequency。s equations as reduced to the electromagic wave equation. As an optical waveguide, the fiber supports one or more confined transverse modes by which light can propagate along the fiber. Fiber supporting only one mode is called singlemode or monomode fiber. The behavior of largercore multimode fiber can also be modeled using the wave equation, which shows that such fiber supports more than one mode of propagation. The most mon type of singlemode fiber has a core diameter of 8–10 micrometers and is designed for use in the near infrared. The mode structure depends on the wavelength of the light used, so that this fiber actually supports a small number of additional modes at visible wavelengths. Multimode fiber, by parison, is manufactured with core diameters as small as 50 micrometers and as large as hundreds of micrometers. The normalized frequency V for this fiber should be less than the first zero of the Bessel function J0 (approximately ). Fiber grating Fiber grating is one of the most rapid passive optical fiber ponents in recent years. Since 1978, the year when K. O. Hill and others first used the standing wave writing way in the germaniumdoped fiber and make the world39。 there is no crosstalk between signals in different cables, and no pickup of environmental noise. Nonarmored fiber cables do not conduct electricity, which makes fiber a good solution for protecting munications equipment in high voltage environments, such as power generation facilities, or metal