【正文】 Overview of Fiber Optic Sensors Abstract: With the development of optical sensor technology, fiber optic sensor has the advantages of resistance to electromagic interference, corrosion, resistance, excellent insulation, wide measuring range, easy for multiplexing, solving problems that other sensors can39。t solve, etc, these sensors as one of the fasterdeveloping technology are widely applied in the field of civil engineering, aerospace, electric power, medical treatment, shipbuilding industry, and so on. In this paper, we study the basic knowledge on optical sensor technology. Keywords: fiber optic。 fiber Bragg grating。 optical fiber sensor 1. Introduction Optical fiber sensor is developed at the end of 70s as a new type of sensor, it has not affected by electromagic field effect, in essence safety explosionproof, small size, corrosion resistance, the advantages of high sensitivity. Used in traditional sensor is difficult to set foot in the extreme environment, so in the military, aviation, biological medicine, building construction field is popular. So to optical fiber sensor research has very important practical significance. Sensing technology is popular in recent years, the application of the technology in the sensitive, accurate sensor, strong adaptability, cabi and wisdom of the direction of development. In this process, optical fiber sensors the sensor to the new members of the family is extremely popular. Optical fiber has many excellent properties, such as: the electromagic interference and atomic radiation performance, diameter is fine, soft and light weight of mechanical properties, insulation, without induction electrical properties, water resistant, high temperature resistant and corrosion resistance of the chemical properties, it can not reach people places (such as high), or harmful to the person of the area (such as nuclear area), plays the role of the refreshing, and still can transcend boundaries, receiving of physiological the senses of not feeling outside information. Optical fiber sensor is a new technology in recent years, can be used to measure physical quantities, such as sound field, electric field, pressure, temperature, angular velocity, acceleration, etc, but also can plete the existing measuring technology difficult to plete measuring task. In the narrow space, in strong electromagic interference and high voltage environment, optical fiber sensors shows the unique charm. Therefore, the optical fiber sensing technology application research has the very good prospects. Optical fiber sensor light sensitive information carrier, as the optical fibre as sensitive information transmission medium. Therefore, it also has the characteristics of optical fiber and optical measurement. (1) the electric insulation performance is good. (2) antielectromagism interference ability. (3) the noninvasive. (4) the high sensitivity. (5) to be easy to implement the measured signal remote monitoring 2. Basic knowledge of transducers A transducer is a device which converts the quantity being measured into an optical, mechanical, ormore monlyelectrical signal. The energyconversion process that takes place is referred to as transduction. Transducers are classified according to the transduction principle involved and the form of the measured. Elements Although there are exception, most transducers consist of a sensing element and a conversion or control element. For example, diaphragms, bellows strain tubes and rings, bourdon tubes, and cantilevers are sensing elements which respond to changes in pressure or force and convert these physical quantities into a displacement. This displacement may then be used to change an electrical parameter such as voltage, resistance, capacitance, or inductance. Such bination of mechanical and electrical elements form electromechanical transducing devices or transducers. Similar bination can be made for other energy input such as thermal. Magic and chemical, giving thermoelectric, electromaaic, and electrochemical transducers respectively. Sensitivity The relationship between the measured and the transducer output signal is usually obtained by calibration tests and is referred to as the transducer sensitivity K1= outputsignal increment / measured increment . In practice, the transducer sensitivity is usually known, and, by measuring the output signal, the input quantity is determined from input outputsignal increment / K1. of an ideal transducer 1) high fidelitythe transducer output waveform shape be a faithful reproduction of the measured。 there should be minimum distortion. 2) There should be minimum interference with the quantity being measured。 the presence of the transducer should not alter the measured in any way. 3) Size. The transducer must be capable of being placed exactly where it is needed. 4) There should be a linear relationship between the measured and the transducer signal. 5) The transducer should have minimum sensitivity to external effects. 6) The natural frequency of the transducer should be well separated from the frequency and harmonics of the measurand. Photoconductive Cells The photoconductive cell, uses a lightsensitive semiconductor material. The resistance between the metal electrodes decrease as the intensity of the light striking the semiconductor increases. Common semiconductor materials used for photoconductive cells are cadmium sulphide, lead sulphide, and copperdoped germanium. The useful range of frequencies is determined by material used. Cadmium sulphide is mainly suitable for visible light, whereas lead sulphide has its peak response in the infrared region and therefore most suitable for flamefailure detection and temperature measurement. 3. Optical fiber system An optical fiber is a flexibl