Cladding Modified Fiber Bragg Grating for Copper Ions Detection

This paper reports a fiber Bragg grating(FBG)as a biosensor.The FBGs were etched using a chemical agent,namely,hydrofluoric acid(HF).This implies the removal of some part of the cladding layer.Consequently,the evanescent field propagating out of the core will be closer to the environ­ment and become more sensitive to the change in the surrounding.The proposed FBG sensor was utilized to detect toxic heavy metal ions aqueous medium namely,copper ions(Cu^(2+)).Two FBG sensors were etched with 20 and 40μm diameters and fabricated.The sensors were studied towards Cu^(2+)with different concentrations using wavelength shift as a result of the interaction between the evanescent field and copper ions.The FBG sensors showed a good response in terms of significant wavelength shift in corresponding to varying Cu2+concentrations when immersed in aqueous mediums.The sensors exhibited excellent repeatability towards Cu ions.The results demonstrate that the smaller FBG etching diameter,the better optical response in terms of wavelength and linearity.

Etched Optical Fiber Vibration Sensor to Monitor Health Condition of Beam Like Structures

Using a center etched single mode optical fiber, a simple vibration senor is designed to monitor the vibrations of a simply supported beam. The sensor has high linear response to the axial displacement of about 0.8mm with a sensitivity of 32mV/10p, m strain. The sensor is tested for periodic and suddenly released forces, and the results are found to coincide with the theoretical values. This simple design, small in size and low cost sensor may find applications in industry and civil engineering to monitor the vibrations of the beam structures and bridges.

High-Precision Magnetic Field Sensor Based on Fiber Bragg Grating and Dual-Loop Optoelectronic Oscillator

A novel fiber-optic magnetic field sensor with high interrogation speed and resolution by using an etched fiber Bragg grating(FBG)in conjunction with a dual-loop optoelectronic oscillator(OEO)is proposed and experimentally demonstrated.A commercial FBG is firstly dipped into mixed hydrofluoric acid solution to remove the cladding layer and then is embedded with the magnetic fluid(MF)as a sensing element.The central wavelength reflected from the FBG is related to the overall time delay of the dual-loop OEO,which determines the oscillating frequency of the OEO.Therefore,the magnetic field can be estimated by measuring the oscillating frequency shift of OEO.The experimental results show that the oscillating frequency linearly increases with the increment of the magnetic field,achieving the sensitivity of 16.3 Hz/Oe with a R-square of 0.991 in the range of 5 mT-10 mT.In addition,the maximum error is within±0.05 mT in the range of 7 mT-8 mT,which offers potentials in many fields where the high-precision magnetic field measurement is required.