Patent Publication Number: US-2012033710-A1

Title: Optical temperature sensor

Description:
TECHNICAL FIELD 
     The present invention relates to an optical temperature sensor, and more particularly, to an optical temperature sensor for measuring temperature by detecting received light quantity that is changed in response to an operation of a bimetal device according to a temperature change. 
     BACKGROUND ART 
     Various types of sensors for measuring temperature have been known. Recently, a structure capable of measuring temperature for facilities to be monitored in remote places using an optical fiber has been proposed. 
     An optical temperature sensor relating to the present invention is disclosed in Japanese Laid-Open Publication No. 55-080021. The optical temperature sensor senses a temperature change by allowing the bimetal vertically installed to a light beam emitted from an input stage optical fiber to shield the light beam according to a temperature change and detecting the light beam at an output stage optical fiber. 
     However, the temperature sensor does not accurately sense the temperature change since the input and output stages are configured of a single optical fiber and a detailed mechanism capable of sensing the temperature change is not described. 
     As another invention relating to the present invention, an optical fiber using optical fiber grating is disclosed in Korean Patent Application No. 1993-0006932. The temperature sensor using the optical fiber may be implemented. 
     The optical fiber uses a transmissive optical fiber grating. The transmissive optical fiber grating is created by inputting strong light to the optical fiber so as to generate interference. The optical fiber device is manufactured by a mechanism of breaking a phase matching condition by coupling the optical fiber grating with a polarizer, a mode canceller, or an echogenic coupler. The optical fiber device may be used for a polarizer, a wavelength filter, an optical switch, a logic device, a stress sensor, a temperature sensor, a multi-divider, or the like. 
     However, there are problems in that engraving the grating into the optical fiber increases manufacturing costs and facilities required to calculate temperature are complicated since the temperature is calculated by detecting a change in a peak wavelength. 
     Disclosure 
     Technical Problem 
     An object of the present invention is to provide an optical temperature sensor capable of measuring temperature by allowing a photo detector to detect light quantity shielded by a bimetal device moving according to a temperature change while simplifying a structure of the optical temperature sensor by using an optical fiber as it is. 
     Technical Solution 
     Provided is an optical temperature sensor. The optical temperature sensor includes a housing, an optical transmitter mounted in the housing and emitting the light transmitted through an optical fiber to an inner space of the housing, and a bimetal device flexibly mounted in the housing so as to change transmitted light quantity, whereby the temperature is measured by changing the shielded light quantity of light transmitted through the optical fiber by a warpage of the bimetal device according to a temperature change or the light quantity received by reflecting the transmitted light, thereby providing the optical temperature sensor having less space limitation for the installation while simplifying the structure. 
     The exemplary embodiments of the present invention measure the temperature by changing the light quantity transmitted through the optical fiber by the warpage of the bimetal device according to the temperature change. Three exemplary embodiments are disclosed according to the number of input stage optical fibers and types of the input stage and the output stage. 
     A first exemplary embodiment of the present invention includes a housing, two input stage and output stage optical fibers in a straight line within the housing, and a bimetal device mounted between the input stage and output stage optical fibers so as to detect the light quantity shielded by the bimetal device in the photo detector mounted at the output stage, thereby calculating the temperature. 
     A configuration of the optical temperature sensor according to a first exemplary embodiment of the present invention is as follows. 
     The optical temperature sensor includes: a housing in which a first support part and a second support part are formed so as to be spaced apart from each other, while being protruded with respect to a base part; an input stage optical transmitter supported on the first support part to emit light transmitted through an optical fiber; an output stage optical transmitter spaced apart from each other to face the input stage optical transmitter and supported on the second support part so as to receive and transmit light emitted from the input stage optical transmitter through the optical fiber; and a bimetal device flexibly mounted in the housing so as to change light quantity transmitted to the output stage optical transmitter while going in and out a transmission path of light beam transmitted from the input stage optical transmitter to the output stage optical transmitter according to a temperature change. 
     Preferably, the input stage optical transmitter may include first and second input stage optical fibers that are supported on the first support part so as to separate from each other to emit transmitted light, the output end optical transmitter may include first and second output stage optical fibers, of which ends are supported on the second support part, facing the first and second input stage optical fibers so as to receive and transmit the light emitted from the first and second input stage optical fibers, and the bimetal device may be flexibly mounted in the housing between the first and second output stage optical fibers. 
     In addition, the optical temperature sensor may further include a light source; an optical splitter receiving the light emitted from the light source and separately transmitting the light to the first and second input stage optical fibers; first and second photo detectors detecting the light transmitted through the first and second output stage optical fibers; and a temperature calculator calculating temperature of an environment in which the housing is mounted from signals output in response to the light quantity transmitted from the first and second photo detectors. 
     According to the first exemplary embodiment of the present invention, the temperature calculator may include a lookup table in which temperature values corresponding to signals output from the first and second photo detectors are written. 
     A second exemplary embodiment of the present invention includes a housing, a reflecting surface mounted in the housing, an input stage optical transmitter mounted in the housing so as to emit light inclined to the reflecting surface at a position opposite to the reflecting surface, an output stage optical transmitter mounted in the housing so as to receive and transmit light emitted from the input stage optical transmitter and reflected from the reflecting surface at a position opposite to the reflecting surface, and an optical interference unit configured of a bimetal device mounted in the housing, which changes the light quantity transmitted to the output stage optical transmitter, thereby calculating the temperature. 
     A configuration of the optical temperature sensor according to a second exemplary embodiment of the present invention is as follows. 
     The optical temperature sensor includes: a housing; an optical transmitter mounted in the housing to emit light transmitted through an optical fiber to an inner space of the housing and receive light reflected within the housing; and an optical interference unit formed of a bimetal device flexibly mounted in the housing so as to change light quantity reversely transmitted in the optical transmitter direction while going in and out a transmission path of light beam emitted from the optical transmitter to the housing according to a temperature change. 
     According to an exemplary embodiment of the present invention, a surface opposite the optical transmitter of the housing may be provided with a reflecting surface reflecting light, the optical transmitter may include an input stage optical transmitter mounted in the housing to emit the light transmitted through the optical fiber so as to emit light inclined to the reflecting surface at a position opposite to the reflecting surface of the housing and an output stage optical transmitter mounted in the housing so as to receive and transmit through the optical fiber the light reflected from the reflecting surface among the light emitted to be inclined toward the reflecting surface from the input stage optical transmitter at the position opposite to the reflecting surface of the housing, and the optical interference unit may be flexibly mounted in the housing so as to change the light quantity transmitted to the output stage optical transmitter while going in and out a transmission path of light beam transmitted from the input stage optical transmitter to the output stage optical transmitter through the reflecting surface according to the temperature change. 
     In addition, the input stage optical transmitter may include first and second input stage optical fibers inserted so as to separate from each other through first and second input stage connection grooves inclinedly provided to the reflecting surface at the position opposite to the reflecting surface of the housing to emit the transmitted light, the output stage optical transmitter may include the first and second output stage optical fibers inserted so as to separate from each other through the first and second output stage connection grooves provided in the housing according to an angle direction symmetrical with each other with respect to an optical axis of the first and second input stage optical fibers based on the reflecting surface so as to receive and transmit light emitted from the first and second input stage optical fibers and reflected and transmitted from the reflecting surface, and the optical interference unit may be provided with the bimetal device that extends in a direction toward the reflecting surface from between the first input stage optical fiber and the second input stage optical fiber, such that the terminal portion of the bimetal device is flexibly mounted within the housing in a direction crossing the first input stage optical fiber and the second input stage optical fiber. 
     The optical interference unit may be formed in a structure in which one end of the bimetal device configured of first and second plates and having different thermal expansion coefficients so as to be bonded to each other is fixedly coupled to the housing and the other end thereof extending toward the reflecting surface is provided with an interference piece having a width expanding from the bimetal device toward the reflecting surface, and the interference piece may be formed to partially interfere light beam emitted from the first and second input stage optical fibers at temperature in which the first plate and the second plate of the bimetal device are aligned so as to be parallel with each other on a straight line. 
     In addition, the reflective optical temperature sensor may further include: a light source; an optical splitter receiving the light emitted from the light source and separately transmitting the light to the first and second input stage optical fibers; first and second photo detectors detecting the light transmitted through the first and second output stage optical fibers; and a temperature calculator calculating temperature of an environment in which the housing is mounted from signals output in response to the light quantity transmitted from the first and second photo detectors. 
     According to the second exemplary embodiment of the present invention, the optical interference unit may include: a bimetal device having one end fixedly mounted to the housing and the other end flexibly mounted to the housing; a reflector coupled with the other end of the bimetal device to reflect light emitted from the optical transmitter and change light quantity reflected to the optical transmitter according to the movement in response to the temperature change of the bimetal device; a photo detector detecting light reflected from the reflector and reversely transmitted through the optical fiber of the optical transmitter; and a temperature calculator calculating the temperature from signals output from the photo detector. 
     More preferably, the optical temperature sensor may further include: first and second circulators mounted on the first and second optical fibers to transmit the light transmitted from the light source to a first path continued to the housing direction and transmit the light reflected from the housing to a second path; an optical splitter receiving the light emitted from the light source and to separately transmit the received light to the first and second circulators; and first and second photo detectors detecting the light transmitted through the second path and outputs the detected light to the temperature calculator, wherein the optical transmitter may include first and second optical fibers facing the reflector and mounted so as to be spaced apart from each other. 
     A third exemplary embodiment of the present invention includes a housing, one input stage and two output stage optical fibers in a straight line within the housing, and a bimetal device mounted between the input stage and the output stage optical fibers so as to detect the light quantity shielded by the bimetal device in the photo detector mounted at the output stage, thereby calculating the temperature. 
     A configuration of the optical temperature sensor according to the third exemplary embodiment of the present invention is as follows. 
     The optical temperature sensor includes: a bimetal device having one end supported on the first support part protruded with respect to a base part and the other end flexibly mounted thereto; an input stage optical transmitter emitting light transmitted through the optical fiber of which the terminal portion is coupled with the bimetal device so as to be warped by interworking with the bimetal device; and an output stage optical transmitter mounted in the housing so as to face the input stage optical transmitter so that light quantity received through the optical fiber is varied in response to a change of a light path of a light beam transmitted to the input stage optical fiber corresponding to a movement of the bimetal device according to the temperature change. 
     In addition, the input stage optical transmitter may include a first input stage optical fiber of which the terminal portion is coupled with the bimetal device so as to interwork with each other, the output terminal optical transmitter may include first and second output stage optical fibers having ends supported on the housing to face the first input stage optical fiber so as to separately receive and transmit light emitted from the first input stage optical fiber when the bimetal device maintains a straight state, and the bimetal device may be flexibly mounted in the housing between the first and second output stage optical fibers. 
     The first input stage optical fiber may be coupled with any one plate of the bimetal device configured of a first plate and a second plate. 
     The optical temperature sensor may further include: a light source transmitting light to the first input stage optical fiber; first and second photo detectors detecting light transmitted through the first and second output stage optical fibers; and a temperature calculator calculating temperature of an environment in which the housing is mounted from signals output in response to the light quantity transmitted from the first and second photo detectors. 
     Advantageous Effects 
     As set forth above, the optical temperature sensor according to the first exemplary embodiment of the present invention can measure the wide range of temperature while simplifying the structure of the optical temperature sensor, by varying the shielded light quantity of light transmitted through the optical fiber by the warpage of the bimetal device according to the temperature change. 
     The optical temperature sensor according to the second exemplary embodiment of the present invention can mitigate the space limitation for installation by aligning the optical fiber transmitting and receiving light at a portion opposite to the reflecting surface while simplifying the structure of the optical temperature sensor by varying the reflected and received light quantity of light transmitted through the optical fiber by the warpage of the bimetal device according to the temperature change. 
     The optical temperature sensor according to the third exemplary embodiment of the present invention can measure the temperature by varying the light emitting direction and varying the received light quantity of the output stage optical fiber receiving light, by the warpage of the input stage optical fiber coupled so as to interwork with the bimetal device transmitting light according to the temperature change, thereby simplifying the structure of the optical temperature sensor. 
    
    
     
       DESCRIPTION OF DRAWINGS 
       The above and other objects, features and advantages of the present invention will become apparent from the following description of preferred embodiments given in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a perspective view of an optical temperature sensor according to a first exemplary embodiment of the present invention. 
         FIG. 2  is a control system circuit diagram of an optical temperature sensor of  FIG. 1 . 
         FIGS. 3 and 4  are diagrams for describing a state in which light quantity transmitted through the first and second output stage optical fibers by the bimetal modification of  FIG. 1  is changed. 
         FIG. 5  is a perspective view of an optical temperature sensor according to a second exemplary embodiment of the present invention. 
         FIG. 6  is a cross-sectional view of an optical temperature sensor of  FIG. 5 . 
         FIG. 7  is a diagram showing an optical trace by extracting some elements of the optical temperature sensor of  FIG. 5 . 
         FIG. 8  is a control system circuit diagram of an optical temperature sensor of  FIG. 5 . 
         FIGS. 9 and 11  are diagrams for describing a state in which light quantity transmitted through the first and second output stage optical fiber by the modifications of the bimetal device of  FIG. 5  is changed. 
         FIG. 12  is a diagram showing an optical temperature sensor according to another exemplary embodiment different from the second exemplary embodiment of the present invention. 
         FIG. 13  is a perspective view of an optical temperature sensor according to a third exemplary embodiment of the present invention. 
         FIG. 14  is a control system circuit diagram of an optical temperature sensor of  FIG. 13 . 
         FIGS. 15 and 17  are diagrams for describing a state in which light quantity transmitted through the first and second output stage optical fibers by the modifications of the bimetal device of  FIG. 13  is changed. 
     
    
    
     BEST MODE 
     Hereinafter, an optical temperature sensor according to exemplary embodiments of the present invention will be described in more detail with reference to the accompanying drawings. 
     First, an optical temperature sensor according to a first exemplary embodiment of the present invention will be described below. 
       FIG. 1  is a perspective view of an optical temperature sensor according to the present invention and  FIG. 2  is a control system circuit diagram of an optical temperature sensor of  FIG. 1 . 
     Referring to  FIGS. 1 and 2 , an optical temperature sensor  100  includes a housing  110 , a bimetal device  120 , a light source  151 , an optical splitter  160 , first and second input stage optical fibers  131  and  132 , first and second output stage optical fibers  141  and  142 , first and second photo detectors  171  and  172 , and a temperature calculator  180 . 
     The housing  110  has a structure in which a first support part  110   b  and a second support part  110   c  are formed so as to be protruded from each other with respect to the base part  110   a.    
     Although not shown, a cover may be further provided so as to interrupt the input of the external light into the spaced space between the first support part  110   b  and the second support part  110   c  of the housing  110 . 
     As an input stage optical transmitter, the first and second input stage optical fibers  131  and  132  mounted so as to be supported on the first support part  110   b  and emitting the transmitted light are used. 
     Ends of the first and second input stage optical fibers  131  and  132  are each connected to the optical splitter  160  and the other ends, that is, terminals  131   a  and  132   a  thereof are supported on the first support part  110   b  of the housing  110  so as to be separated from each other, thereby emitting the transmitted light toward the first and the second output stage optical fibers  141  and  142  through the spaced space 
     As the output stage optical transmitter, the first and second output stage optical fibers  141  and  142  spaced apart from each other so as to face the first and second input stage optical fibers  131  and  132  and mounted so as to be supported on the second support part  110   c  are used so as to receive and transmit the light emitted from the first and second input stage optical fibers  131  and  132  that are the input stage optical transmitter. 
     The bimetal device  120  has a structure in which first and second plates  121  and  122  made of a material having different thermal expansion coefficients are bonded to each other. 
     The bimetal device  120  may be flexibly mounted within a housing so as to change light quantity transmitted to the first and second output stage optical fibers  141  and  142  while going in and out a transmission path of light beam transmitted to the first and second output stage optical fibers  141  and  142  from the first and second input stage optical fibers  131  and  132  due to the warpage of the bimetal device  120  in a horizontal direction according to the temperature change. 
     That is, one end of the bimetal device  120 , which is flexibly mounted in the housing  110  between the first support part  110   b  and the second support part  110   c , may be fixedly mounted in the housing  110  between first and second output stage optical fibers  141  and  142 . In addition, the bimetal device  120  is mounted in parallel with a direction of the first and second input stage optical fibers  131  and  132 . 
     The bimetal device  120  is warped left and right according to the peripheral temperature change. As a result, the bimetal device  120  goes in and out the path of the light beam from the first and second input stage optical fibers  131  and  132  to the first and second output stage optical fibers  141  and  142  due to the warpage, thereby controlling a cross sectional area of the light beam that may be shielded. 
     In order to increase the temperature measurement precision due to the warpage of the bimetal device  120 , the first and second plates  121  and  122  of the bimetal device  120  are disposed so as to partially cover a light emitting region of the first and second input stage optical fibers  131  and  132  equally to each other, under a temperature condition so that the first and second plates  121  and  122  of the bimetal device are maintained in parallel with each other. In this case, the light quantity received in each of the first and second output stage optical fibers  141  and  142  is fluctuated to each other by a minute warpage of the bimetal device  120 , thereby increasing the temperature measurement precision. As the light source  151 , a light emitting diode may be used. 
     The optical splitter  160  separately transmits light transmitted from a leading end optical fiber  130  receiving light emitted from the light source  151  to the first and second input stage optical fibers  131  and  132 . 
     The first and second photo detectors  171  and  172  detect the light transmitted through the first and second output stage optical fibers  141  and  142  to output electrical signals corresponding to the detected light quantity. 
     The temperature calculator  180  calculates the temperature of the environment in which the housing  110  is mounted from signals output corresponding to the light quantity transmitted from the first and second photo detectors  171  and  172 . 
     The temperature calculator  180  calculates the temperature of the environment in which a lookup table (LUT)  181  written with temperature values output corresponding to the signals output from the first and second photo detectors  171  and  172  is installed. 
     An output unit  190  outputs the temperature values controlled and calculated by the temperature calculator  180 . As the output unit  190 , a display unit displaying the temperature values may be used in the case of a short distance and a transmitter transmitting the temperature value calculated in wireless or wired in the case of a long distance may be used. 
     In the optical temperature sensor, when the second plate  122  of the bimetal device is warped to the first plate  121  of the bimetal device by making the temperature higher than the basic temperature making the first and second plates  121  and  122  of the bimetal device  120  so as to be maintained in parallel with each other, the light quantity received through the second output stage optical fiber  142  of the first and second output stage optical fibers  141  and  142  is further reduced at the time of non-shielding, if some of an end  131   b  of the second input stage optical fiber  132  of ends  131   a  and  131   b  of the first and second input stage optical fiber is covered, as shown in  FIG. 3 . Similarly, when the first plate  121  is warped to the second plate  122  by making the temperature lower than the basic temperature making the first and second plates  121  and  122  of the bimetal device  120  maintained so as to be parallel with each other, the light quantity received through the second output stage optical fiber  142  of the first and second output stage optical fibers  141  and  142  is further reduced than in the case of non-shielding, if some of the end  131   a  of the first input stage optical fiber  131  of the ends  131   a  and  131   b  of the first and second input stage optical fibers  131   a  and  131   b  is covered, as shown in  FIG. 4 . 
     As described above, the light quantity emitted from each of the first and second input stage optical fibers  131  and  132  is selectively shielded according to the temperature change and the light quantity received through each of the first and second output stage optical fibers  141  and  142  is changed by changing the shielded amount according to the temperature change. The temperature values corresponding to the variable value of the received light quantity are previously written in the lookup table  181  by the experiment. 
     Therefore, the temperature calculator  180  confirms the values output to correspond to the light quantity received from each of the first and second photo detectors  171  and  172  from the lookup table  181  to calculate the temperature. 
     Meanwhile, in the shown example, two output stage optical fibers  141  and  142  corresponding to two input stage optical fibers  131  and  132  are used so as to expand the temperature measurement range, but a single output stage optical fiber corresponding to a single input stage optical fiber may be used when the measurement is performed only in the measurement temperature range of the predetermined temperature or higher. 
     Hereinafter, an optical temperature sensor according to a second exemplary embodiment of the present invention will be described below. 
       FIG. 5  is a perspective view of an optical temperature sensor according to a second exemplary embodiment of the present invention,  FIG. 6  is a cross-sectional view of an optical temperature sensor of  FIG. 5 ,  FIG. 7  is a diagram showing an optical trace by extracting some elements of the optical temperature sensor of  FIG. 5 , and  FIG. 8  is a control system circuit diagram of an optical temperature sensor of  FIG. 5 . 
     Referring to  FIGS. 5 and 8 , an optical temperature sensor  200  includes a housing  210 , a bimetal device  220 , a light source  251 , an optical splitter  260 , first and second input stage optical fibers  231  and  232 , first and second output stage optical fibers  241  and  242 , first and second photo detectors  271  and  272 , and a temperature calculator  280 . 
     The housing  210  is formed to have a squared case shape and an inside thereof is provided with an inner space  214  having a reflecting surface  213 . 
     The inner space  214  of the housing  210  is formed to be able to sufficiently move according to the temperature change of the bimetal device  220  and an interference piece  225  as described below. 
     One side  211  of the housing  210  is provided with first and second input stage connection grooves  216  and first and second output stage connection grooves  217  that are each connected to the first and second input stage optical fibers  231  and  232  emitting light toward the reflecting surface  213  and the first and second optical fibers  241  and  242  receiving light reflected from the reflecting surface  213 . 
     The first and second input stage connection groove  216  and the first and second outputs stage connection grooves  217  of the housing  210  are formed so as to extend by a predetermined length toward the reflecting surface  213  so as to have an inclined angle symmetrical with each other with respect to the reflecting surface  213 . 
     The housing  210  is formed to have a first block body  210   a  made of a material having thermal conductivity while providing high reflectivity, for example, aluminum and a second block body  210   b  made of a synthetic resin material bonded to the first block body  210   a  and provided with the first and second input stage connection grooves  216  and the first and second output stage connection grooves  217  connected to the first and second input stage optical fibers  231  and  232  and the first and second output stage optical fibers  241  and  242 . On the other hand, the housing  210  is made of a synthetic resin material but may be formed to have a reflecting layer of which the reflecting surface  213  is coated with a high reflecting material. 
     Reference numeral  218  is a shielding plate  218  bonded to the housing  210  so as to interrupt external light from being input into the inner space  214  in which the top portion of the first block body  210   a  is opened and reference numeral  219  is a ring to suspending the housing  210  within the space to be measured at the time of mounting the housing  210 . 
     The first and second input stage optical fibers  231  and  232  used as the input stage optical transmitter are separately mounted from each other through the first and second input stage connection grooves  216  of the housing  210  so as to emit light inclined to the reflecting surface  213  at a position opposite to the reflecting surface  213  of the housing  210 , thereby emitting light transmitted through the optical fiber. 
     Each end of the first and second input stage optical fibers  231  and  232  is connected to the optical splitter  260  and the other ends, that is, terminals thereof are mounted so as to separate from each other through the first and second input stage connection groove  216  of the housing  210 , thereby emitting the transmitted light toward the reflecting surface  213 . 
     As the output stage optical transmitter, the first and second output stage optical fibers  241  and  242  separately connected to each other through the first and second output stage connection grooves  217  provided in the housing  210  according to an angle direction symmetrical with each other with respect to the optical axis of the first and second input stage optical fibers  231  and  232  based on the reflecting surface  213  are used so as to receive and transmit light reflected from the reflecting surface  213  among light emitted to be inclined toward the reflecting surface  213  from the bottom portions of the first and second input stage optical fibers  231  and  232  at the position opposite to the reflecting surface  213  of the housing  210 . 
     The optical interference unit includes the bimetal device  220  and the interference piece  225  that are flexibly mounted in the housing  210  so as to change the light quantity transmitted to the first and second output stage optical fibers  241  and  242  while going in and out a transmission path of light beam emitted from the first and second input stage optical fibers  231  and  232  and to the first and second output stage optical fibers  241  and  242  through the reflecting surface  213  according to the temperature change. 
     One end of the bimetal device  220  may be fixedly coupled to the housing  210  and the other end thereof may be flexibly mounted within the inner space  214 , by bonding a first plate  221  and a second plate  222  having different thermal expansion coefficients to each other and 
     That is, the bimetal device  220  extends in a direction toward the reflecting surface  213  from between the first input stage optical fiber  231  and the second input stage optical fiber  232 , such that the terminal portion thereof may be flexibly mounted within the housing  210  in a direction crossing the first input stage optical fiber  231  and the second input stage optical fiber  232 . 
     The interference piece  225  is mounted at the other end, that is, the terminal portion toward the reflecting surface  213  of the bimetal device  220  and is formed in a triangular shape so as to have a width expanding from the bimetal device  220  toward the reflecting surface  213 . 
     Preferably, as shown in  FIG. 9 , the interference piece  225  is formed to partially interfere the light beams  235  and  236  emitted from each of the first and second input stage optical fibers  231  and  232  under the temperature condition in which the first plate  221  and the second plate  222  of the bimetal device  220  are aligned so as to be parallel with each other on a straight line so that the light quantity received in the first and second output stage optical fibers  241  and  242  may be reduced to correspond to the interfered amount. 
     The optical interference unit controls a cross sectional area of the light beam received in the first and second output stage optical fibers  241  and  242  by going in and out the path of the light beam transmitted to the first and second output stage optical fibers  241  and  242  through the reflecting surface  213  from the first and second input stage optical fibers  231  and  232  due to the warpage of the bimetal device  220  left or right according to the peripheral temperature change. 
     Further, in order to increase the temperature measurement precision due to the warpage of the bimetal device  220 , the first and second plates  220  and  221  of the bimetal device  220  are disposed so as to partially cover a light emitting region of the first and second input stage optical fibers  231  and  232  equally to each other, under a temperature condition so that the first and second plates  221  and  222  of the bimetal device  220  are maintained in parallel with each other. In this case, the light quantity received in each of the first and second output stage optical fibers  241  and  242  is fluctuated to each other even by a minute warpage of the bimetal device  220 , thereby increasing the temperature measurement precision. 
     As the light source  251 , a light emitting diode may be used. 
     The optical splitter  260  separately transmits light transmitted from a leading end optical fiber  230  receiving light emitted from the light source  251  to the first and second input stage optical fibers  231  and  232 . 
     The first and second photo detectors  271  and  272  detect the light transmitted through the first and second output stage optical fibers  241  and  242  to output electrical signals corresponding to the detected light quantity. 
     The temperature calculator  280  calculates the temperature of the environment in which the housing  210  is mounted from signals output corresponding to the light quantity transmitted from the first and second photo detectors  271  and  272 . 
     The temperature calculator  280  calculates the temperature of the environment in which the housing  210  is provided with a lookup table (LUT)  281  in which temperature values output corresponding to the signals output from the first and second photo detectors  271  and  272  are written. 
     An output unit  290  outputs the temperature values controlled and calculated by the temperature calculator  280 . As the output unit  290 , a display unit displaying the temperature values may be used in the case of a short distance and a transmitter transmitting the temperature value calculated in wireless or wired in the case of a long distance may be used. 
     In the optical temperature sensor  200 , when the first plate  221  is warped to the second plate  222  by making the temperature higher than the basic temperature making the first and second plates  221  and  222  of the bimetal device  220  so as to be maintained in parallel with each other, as shown in  FIG. 10 , the shielding region of the light beam  235  emitted from the first input stage optical fibers  231  is reduced and the shielding region of the light beam  236  emitted from the second input stage optical fiber  232  is increased, such that the light quantity received through the second output stage optical fiber  242  of the first and second output stage optical fibers  241  and  242  is further reduced. On the other hand, when the second plate  222  is warped to the first plate  221  by making the temperature lower than the basic temperature making the first and second plates  221  and  222  of the bimetal device  220  so as to be maintained in parallel with each other, as shown in  FIG. 11 , the shielding region of the light beam  235  emitted from the first input stage optical fibers  231  is larger than the shielding region of the light beam  236  emitted from the second input stage optical fiber  232 , such that the light quantity received through the first output stage optical fiber  242  of the first and second output stage optical fibers  241  and  242  is further reduced. 
     As described above, the cross sectional area of the light beam emitted from each of the first and second input stage optical fibers  231  and  232  is selectively shielded according to the temperature change and the light quantity reflected through the reflecting surface  213  and received through each of the first and second output stage optical fibers  241  and  242  is changed by changing the shielded amount according to the temperature change. The temperature values corresponding to the variable value of the received light quantity are previously written in the lookup table  281  by the experiment. 
     Therefore, the temperature calculator  280  confirms the values output to correspond to the light quantity received from each of the first and second photo detectors  271  and  272  from the lookup table  281  to calculate the temperature. 
     Meanwhile, in the shown example, two output stage optical fibers  241  and  242  corresponding to two input stage optical fibers  231  and  232  are used so as to expand the temperature measurement range, but a single output stage optical fiber corresponding to a single input stage optical fiber may be used when the measurement is performed only in the measurement temperature range of the predetermined temperature or higher. 
     Meanwhile, differently from the shown example, so as to reduce the number of optical fibers connected to the housing, the temperature calculator may be build to calculate temperature by emitting light through the optical fiber and again receiving the reflected light from the same optical fiber and the example thereof is shown in  FIG. 12 . Components performing the same function as components shown above are denoted by the same reference numerals. 
     Referring to  FIG. 12 , the optical temperature sensor includes the housing  210 , the bimetal device  220 , first and second optical fibers  321  and  322 , and first and second circulators  341  and  342 . 
     One of the bimetal device  220  used as the optical interference unit is mounted so as to be supported on the housing  210  having the inner space and the flexible other end thereof is provided with a reflector  313  extending in a direction orthogonal to the extending direction. 
     The reflector  313  reflects the light emitted from each of the first and second optical fibers  321  and  322  used as the optical transmitter and changes the light quantity reflected to the optical fibers  321  and  322  according to the left and right movement of the bimetal device  220  according to the temperature change. 
     Reference numerals  320   a  and  320   b  are a collimating lens that converts the beam emitted and diffused from the first and second optical fiber into parallel light. 
     In this case, the size of the reflecting region may be determined so that the reflector  313  may partially reflect the light beam emitted from the first and second optical fibers  321  and  322  in the state in which the bimetal device  220  is maintained in a straight state without being warped as described with reference to  FIG. 9 . 
     The first and second circulators  341  and  342  transmit the light emitted from the light source  251  and separately transmitted from each of the first and second split optical fibers  331  and  332  in the optical splitter  260  to the first and second optical fibers  321  and  322  and transmits the light received in the first and second optical fibers  321  and  322  to the first and second photo detectors  271  and  272 . 
     In this case, the first and second photo detectors  271  and  272  detect the light reflected from a reflector  313  and reversely transmitted through the first and second optical fibers  321  and  322 . 
     The temperature calculator  280  calculates the temperature from the signal output from the first and second photo detectors  271  and  272  as described above. 
     The reflective optical temperature sensor may reduce the number of optical fiber connected to the housing  210 . Hereinafter, an optical temperature sensor according to a third exemplary embodiment of the present invention will be described below. 
       FIG. 13  is a perspective view of an optical temperature sensor according to a third exemplary embodiment of the present invention and  FIG. 14  is a control system circuit diagram of an optical temperature sensor of  FIG. 13 . 
     Referring to  FIGS. 13 and 14 , an optical temperature sensor  400  includes a housing  410 , a bimetal device  420 , a light source  451 , a first input stage optical fiber  431 , first and second output stage optical fibers  441  and  442 , first and second output stage photo detectors  471  and  472 , and a temperature calculator  480 . 
     The housing  410  has a structure in which a first support part  411  and a second support part  412  are formed so as to be spaced apart from each other, while being protruded with respect to the base part. 
     Although not shown, a cover may be further provided so as to interrupt the input of the external light into the spaced space between the first support part  411  and the second support part  412  of the housing  410 . 
     One end of the bimetal device  420  may be mounted to be supported on the first support part  411  and the other thereof may be flexibly mounted to extend in a direction toward the second support part  412 . 
     The bimetal device  420  has a structure in which first and second plates  421  and  422  made of a material having different thermal expansion coefficients are bonded to each other. 
     The bimetal device  420  is mounted to the first support part  411  so as to be disposed at the center of the first and second output stage optical fibers  441  and  442  between the first and second output stage optical fibers  441  and  442 . 
     The first input stage optical fibers  431  used as the input stage optical transmitter emits the transmitted light by coupling a terminal portions  431   a  with the bimetal device  420  so that the first input stage optical fiber  431  may be warped left and right by interworking with the bimetal device  420 . 
     In the shown example, the first input stage optical fiber  431  is coupled with the second plate  422  of the bimetal device  420  by a coupling band  428 . 
     Unlike the shown example, the first input stage optical stage  431  may be coupled with the second plate  422  through the first plate  421  of the bimetal device  420  or may be coupled with both of the first and second plates  421  and  422 . 
     In this structure, the first input stage optical fiber  431  has an outer diameter larger than the first input stage optical fiber  431  on the first support part  411  and is mounted so as to be flexibly supported through a flexible support groove  414  formed so as to penetrate through the first support  411 . 
     The first and second output stage optical fibers  441  and  442  used as the output stage optical transmitter are mounted so as to face the first input stage optical fiber  431  so that the received light quantity may be varied in response to the change of the light path of the light beam emitted from the first input stage optical fiber  431  corresponding to the movement of the bimetal device  420  according to the temperature change. 
     Reference numeral  415  is a first light receiving groove receiving in which the first output stage optical fiber  441  is inserted to receive light and reference numeral  416  is a second light receiving groove in which the second output stage optical fiber  441  is inserted to receive light. 
     Preferably, in order to increase the temperature measurement precision by the warpage of the bimetal device  420 , the first and second output stage optical fibers  441  and  442  are supported on the second support  412  so as to face each other at the position at which they are symmetrical with each other based on the first input stage optical fiber  431  as shown in  FIG. 15  so that each of the first and second output stage optical fibers  441  and  442  may separately receive and transmit the light emitted from the first input stage optical fiber  431  when the bimetal device  420  maintains a straight state. In this case, the light quantity received in each of the first and second output stage optical fibers  441  and  442  is fluctuated to each other even by a minute warpage of the bimetal device  420 , thereby increasing the temperature measurement precision. 
     Therefore, the trace of the light beam emitted from the terminal portion  431   a  of the first input stage optical fiber  431  is fluctuated by the warpage of the bimetal device  420  in the left and right directions according to the temperature change and thus, the light quantity transmitted to the first and second output stage optical fibers  441  and  442  is changed, thereby measuring the temperature. 
     As the light source  451 , a light emitting diode may be used. 
     The first and second photo detectors  471  and  472  detect the light transmitted through the first and second output stage optical fibers  441  and  442  to output electrical signals corresponding to the detected light quantity. 
     The temperature calculator  480  calculates the temperature of the environment in which the housing  410  is mounted from signals output corresponding to the light quantity transmitted from the first and second photo detectors  471  and  472 . 
     The temperature calculator  480  calculates the temperature of the environment in which the housing  481  is provided with a lookup table (LUT)  180  in which temperature values output corresponding to the signals output from the first and second photo detectors  471  and  472  are written. 
     An output unit  490  outputs the temperature values controlled and calculated by the temperature calculator  480 . As the output unit  490 , a display unit displaying the temperature values may be used in the case of a short distance and a transmitter transmitting the temperature value calculated in wireless or wired in the case of a long distance may be used. 
     In the optical temperature sensor, when the second plate  422  of the bimetal device is warped to the first plate  421  of the bimetal device by making the temperature higher than the basic temperature making the first and second plates  421  and  422  of the bimetal device  420  so as to be maintained in parallel with each other, as shown in  FIG. 16 , the light beam  435  emitted through the terminal of the first input stage optical fiber  431  is also warped to the first plate  421  to increase the light quantity received through the first output stage optical fiber  441  of the first and second output stage optical fibers  441  and  442  and reduce the light quantity received through the second output stage optical fiber  442 . Similarly, when the first plate  421  of the bimetal device is warped to the second plate  422  of the bimetal device by making the temperature lower than the basic temperature making the first and second plates  421  and  422  of the bimetal device  420  so as to be maintained in parallel with each other, as shown in  FIG. 17 , the light beam  435  emitted through the terminal of the first input stage optical fiber  431  is also warped to the right to increase the light quantity received through the second output stage optical fiber  442  of the first and second output stage optical fibers  441  and  442  and reduce the light quantity received through the first output stage optical fiber  441 . 
     The light quantity received in each of the first and second output stage optical fibers  441  and  442  is changed by the trace change of the light beam emitted from the first input stage optical fiber  431  mounted so that the terminal portion  431   a  of the first input stage optical fiber  431  is warped by interworking with the bimetal device  420  and the temperature value corresponding to the variable value of the received light quantity is previously written in the lookup table  481  by the experiment. 
     Therefore, the temperature calculator  480  confirms the values output to correspond to the light quantity received from each of the first and second photo detectors  471  and  472  from the lookup table  481  to calculate the temperature. 
     Meanwhile, in the shown example, two output stage optical fibers  441  and  442  corresponding to one input stage optical fiber  431  are used so as to expand the temperature measurement range, but the single output stage optical fiber may be used when the measurement is performed only in the measurement temperature range of the predetermined temperature or higher.