The Design Of Sensor Based On Tilted Fiber Bragg Grating

Optical fiber grating is a new kind of passive fiber component that has been developing fast in recent years. It has a lot of applications in optical fiber sensing and optical fiber communication because it has a small volume, has high sensitivity and is easy to be used in wavelength division multiplexing. Tilted optical fiber grating is a new member in this family. It can be easily made and maintained and it is also relatively cheap and highly reliable. And it is more sensitive for the surrounding for its special structure.This thesis is arranged as follows. First, there is a review on the concept and classification of optical fiber gratings and summarize some advantages of optical fiber gratings. Based on these advantages, a summary of recent development and application of optical fiber gratings is listed.In the second part, a brief analysis of the principles that are used in fiber grating sensors are introduced. There are two theories that are widely used-the mode-coupling theory and the transmission matrix theory. Based on these theories, the sensing properties of optical fiber gratings are analyzed.In the third part, the sensing theories of tilted optical fiber gratings is presented, as well as the manufacture method of tilted optical fiber gratings, which is the phase mask method. The good linear property of TFBG have been found in experiments when used to measure force, temperature and refraction index. TFBG is very sensitive to the refraction indices of the surroundings, which implies that TFBG may be used as refractometers and concentration meter. Other possible applications are also discussed.In the final part, a design of a sensor for DNA molecules based on TFBG is presented.In our design, graphene is transferred onto TFBG and a single chain of DNA mol ecules is fixed on the graphene, which is made a probe for DNA molecules. When the probe is immersed into the test liquid, the ssDNA on the graphene will be combined with aim DNA in the liquid to form the double-helical structure, so that the density of the liquid will be changed. Then the sensitivity of TFBG to surroundings will be used to detect this change.