Magnetic Fluid Filled Hollow-core Photonic Crystal Fiber F-P Sensor

Fiber F-P sensor is one kind of optical fiber sensors, which is developed rapidly in recent years. Because of it’s strong anti-interference, potential of measuring various physical quantities, large measurement range, high precision, easiness to combine with optical sensor system, optical fiber F-P sensor have became one of the most mature technologies, and one of the most widely used optical fiber sensors. As a new optical transmission medium, photonic crystal fiber (PCF) has many unique features because of its micro-structure, which provides a chance to solve many difficult problems and has become a research focus in communicating and sensing technologies. Since magnetic fluid appeared, it has been applied in various fields, and has become a novel functional material. Especially its controllable refractive index feature makes it become a new optical material. In this paper, based on the magnetiic fluid controllable refractive index feature, magnetic fluid is used as the sensitive medium, resulting in a new type of fiber F-P sensor.In this paper, we firstly introduce the theories, characteristics and research progresses of optical fiber F-P sensors and photonic crystal fibers. Hereafter we describe the working principle of fiber F-P sensors,the latest structures developed by the researchers, and the signal demodulation methods of the optical fiber F-P sensors.Then, we introduce the optical properties of magnetic fluid, especially those of its light transmission property and the controllable refractive index feature. And we have designed the magnetic fluid filled hollow core PCF(HC-PCF) fiber F-P sensor, in which the core of HC-PCF will be filled with magnetic fluid, working as the cavity of the fiber F-P sensor. By applying a variable external magnetic field, the refractive index of magnetic fluid will be changed, so does the output spectrum of the sensor. Through the demodulation method, the applied magnetic field can be derived from the sensor output spectrum. Method to improve the contrast of interference fringes is also studied. Theoretical simulations of the mode distribution of HC-PCF after filling the magnetic fluid has been carried out, and the sensor production process is introduced.Finally, we proposed the sensor system, and all the components of the sensor system are described in detail. Given the parameters of the magnetic fluid, relationship between the applied magnetic field and sensor output spectral resonance peak is simulated. The effects on the sensor output spectrum with different F-P cavity length are also studied, and the sensor multiplexing capability is discussed as well.