Fibre Optical Sensor Modified with Metal Organic Frameworks for Biomedical application

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Project outline

Optical fibre due to its tiny size with diameter down to micrometre, high light transmission and away from electromagnetic filed interaction, are widely used in telecommunications and sensor development. When it comes to sensor development, then photon-sensitive single mode optical fibre can be inscribed into periodical grating in fibre core when exposed under UV radiation, and generate the core-cladding co-propagation mode, Long period grating (LPG). By doing this, evanescent field are exposed under external environment and the sensor can be sensitive to the external vibration such as refractive index, temperature changes and the strain applied on the fibre. When deposited with sensing material, the sensor response to the presence of material due to the changes of refractive index. Once the sensing materials capture its specific binding analytes, it essentially changes the optical properties of the material such as refractive index and absorptions, as a result, change the signal of sensor. Based on that principle, the gas sensing material such as Metal Organic Framework, a porous material with high gas adsorption and storage capacity, can be incorporated with fibre optical sensor for gas measurement.


Fabrication of LPGs

File:LPG Writing.avi

Photo-sensitive fiber is exposed under UV radiation to form a periodical 'burned' pattern inside of fiber core and creates varies refractive index grating resulting in certain wavelength of light been diffracted into cladding and lost from the fiber.


Resonance condition

Equation.jpg

The resonance wavelength is determined by the effective refractive index of core and cladding as well as the grating period of LPGs. The perturbation of surrounding refractive index of cladding or the changes of coated film around fiber cladding basically change the effective refractive index of cladding, result in a shift of resonance wavelength.