DESIGN OF PHOTONIC CRYSTAL FIBER SENSOR

The present work aims to employ the photonic crystal fiber (PCF) for designing temperature and electric field sensors with intended manufacturing characteristics including: high sensitivity, repeatability and low cost by infiltrated with Nematic N-(4`-ethoxybenzylidene)-4-n-butylaniline liquid crystal(EBBA) liquid crystal. The novelty in this work is the use of EBBA that characterized by its ability to align by an external electric field. Aligned EBBA have the optical properties of uniaxial crystal, which makes it candidate to be useful in different applications The proposed temperature and electric field sensor are designed and implemented, the process of the design is requires passing through two work stages: they are, liquid crystal preparation and sensors design. The liquid crystal preparation phase is responsible on preparing the EBBA using its chemical components to be injected in the PCF in the following work stages. EBBA was identified using Fourier transform infrared spectroscopy (FTIR) at transition temperature range between 36-80 ℃. Then, EBBA was used to measure the values of refractive index at temperature range 25-80℃. The result showed that the values of refractive index decreases with increasing the temperature. Later, EBBA was used in the following sensors design phase. Whereas, the sensor design phase is responsible on constructing the sensor components and setting them according to the proposed design.The implementation of the temperature sensor was carried out by splicing short lengths of large mode erea (LMA-10) PCF with conventional single mode fiber (SMF-28) in one side and using free space connector from other side. A diode laser of different wavelengths (1550, 1060, 850 nm) and helium-neon laser of 632.8 nm has been used as a light source, where a high sensitive optical spectrum analyzer (OSA) was used to monitor and record the transmitted spectra.Whereas, the implementation of the electric field sensor was carried out by using short length of hollow core (HC-1550) PCF. A diode laser was used of wavelength equal to 650 nm has been used as a light source for guiding the light to the one side of the fiber, the other side infiltration with EBBA liquid crystal by capillary effect. Then, record the transmission a spectrum is recorded by using the fiber optic spectrometer  The proposed sensors are used in the next testing stage. The test includes infiltrating the air holes of the PCFs by liquid crystal instead of air. For temperature sensing, the EBBA liquid crystal material was prepared to infiltrate the air holes for the solid core (LMA-10) PCF, which leads to change the refractive index of the PCF and affects the transmission of the laser inside the PCF due to the change happen in the value of the refractive index of the liquid crystal.The results showed that the power of transmission spectrum after PCF infiltration will be increased with increasing temperature. The value of sensitivity can be achieved by the slope of the line for the figure of transmission and temperature.The highest sensitivity has been obtained that reached 0.02 dBm/oC  at 1550 nm with less loss and less attenuation. For electric field sensing, the EBBA liquid crystal infiltrate the air holes for the hollow core (HC-1550) PCF. The infiltrated section of photonic crystal fiber was equal to ~1 cm. The results show that the power of transmission spectrum will be remains unchanged until reach the electric field intensity to 97.2 Vrms/mm. Implies the region of the electric field sensor operating is between (97.2 Vrms/mm to 146.8 Vrms/mm).After this region, there is no change may happen in the electric field. The sensitivity can be finding by the slope of transmission and electric field intensity. It was found that the intensity of the proposed electric field sensor was 0.00123 dBm.mm/Vrms at 650 nm.the achieved sensitivity values were acceptable in comparison with that mentioned in latretures,this ensure the correct results and methodology.