Fiber-Optic Point-Based Sensor Using Specklegram Measurement

Fiber sensors have been widely investigated in many fields.Typically,there have been progressive reports on the excellent performance of fiber Bragg gratings,long-period fiber gratings,Fabry-Perot interferometers and so on.The analysis of these kinds of sensors mostly relies on monitoring the shift of wavelength captured by the optical spectrum analyzer(OSA).Compared with technologically advanced sensors,there exist newly developed sensors relying on speckle analysis techniques.Fiber-optic specklegram sensors are lower in cost,and use a lightweight camera,without the assistance of OSA.Fiber specklegram sensor is a kind of sensor relying on the analysis of the speckle produced by multimode,it can recover the state of waveform through the analysis of the speckle.Fiber specklegram sensor can be used to detect different physical variables,such as micro vibration,displacement and temperature measurement,etc.In this paper,we introduce a certain kind of point-based fiber-optic specklegram sensor,as an alternative to the aforementioned apparatuses.The new-developed fiber-optic point-based sensor can realize the measurement of changes of different temperature or pressure.It has the compact structure,and is light weight,low cost.The sensor has a good response to environmental changes,and this sensor is also suitable for determining the remote situation where a compact and accurate integrated sensor is required.1.A kind of point-based fiber specklegram sensor is proposed to measure the environment variables like temperature and pressure.It is calibrated by speckle pattern generated by spatial multimode interference.Compared with some fiber specklegram sensors proposed before,the point-based sensor is composed of single-mode fiber and multimode fiber,and their connection point is the sensing point.On the one hand,it avoids the environmental perturbation along the multimode fiber,which can reduce the instability of multimode fiber itself.This makes our point-based sensor to be more practical.On the other hand,compared with some other work using spatial speckle analysis,fiber-based model can be more convenient to be integrated.2.Furthermore,except for the sensor for temperature and pressure measurement mentioned above,we also explore the application of environmental refractive index measurement.If we align the fibers directly with a gap between the multimode fiber and the single-mode fiber,expose the coupling region to the environment and immerse it into a solution with an adjustable refractive index,we can use the setup to detect refractive index changes of the environment.3.On the basis of experiments,we also optimize the sensor mentioned above.By adjusting the hardware parameters and optimizing the algorithm,we improve the sensitivity and the response of the sensor.