The Design And Demonstration Of Optical Fiber Multiplexing Sensing System Based On Low-Coherence Interferometer

Fiber optic sensors are new type of sensing equipment which utilizes optical fiber as the transmission medium.The researching of the fiber optical sensor has been rolling over the world's laboratory since 1970 s.With the development of the science and technology,the applications of the fiber optical sensor has been involved in industry,military,biochemical and etc.fields.Furthermore,as a high-tech industry,the level of fiber technology is something a symbol of national comprehensive strength.When compared with the traditional electric sensor,optical fiber is inherently corrosion resistance,its density is less than the metal cables so that largely simplified the installation and repair.The optical signals that propagating in the fiber is electromagnetic resistance besides.Based on these theories,the traditional sensors which applied in all around of the human being activity areas were almost replaced by optical fiber sensor.The high sensitivity and resolution make the fiber sensors a way in temperature,strain,vibration and accelerated speed etc.detection,what's more,the development of the optical fiber sensors were promoted with the researching of the special fiber such as fiber grating and photonic crystal fiber,combining with the special structures such as interferometers.But the lower cost and better performance are also the key points which affecting the development of the fiber sensor industry.The optical fiber sensor based on the interferometry is intrinsic high sensitivity since the interferometer fringes matching the magnitude with the optical length,which is normally the micrometers.The under test parameters such as temperature,strain and vibration and so on could cause the phase delay of the light propagating in the optical fiber,hence,the interference could change corresponding,the parameters could be accurately measured by detecting the fringes shift.The fiber optical sensor based on the low coherence interferometer is a low cost fiber sensor which possess the high sensitivity and multiplexed possibility.It utilize a low cost bandwidth source(white light source)as a light source of the system,and the low-coherence structure allows the multi-fiber sensors to connect in parallel in the one system to achieve the quasi distributed parameters detecting.Based on the fast development and the mature theory of technology of the optical fiber sensors,a low-coherence interferometry multiplexed fiber sensing system is proposed,and the temperature and strain sensing experiment of the system are carried out,and the data proves a stable and high sensitivity sensor.The system is composed by two Mach-zehnder interferometers: one for sensing,and the other is utilized to demodulate the sensing signals,the multiplexed structure is induce by three optical fibers connected in parallel in the sensing interferometers,the three arms represented the reference arm,temperature sensing arm and the strain sensing arm,respectively.The optical paths between them can be compensated by the optical tunable delay line which is insert in the demodulation interferometer.So that we can discern the interference shift caused by the under test parameters.In the experiment,a certain length of fiber in the temperature sensing arm is heated by a temperature tunable oven,and a certain length of bare fiber is stretched by a three dimensional platform.Meanwhile,the positions of the interference fringes are recorded by a computer.As a result,the temperature sensitivity and strain sensitivity of this system are 12?m/? and 0.16?m/??,respectively.One should note that the result of the low coherence multiplexed system is heavily rely on the optical tunable delay line,include the scanning range and its stability when it is working.In addition,the experimental result is well matched the theoretic analysis,which is also introduced in the contents.