| Mode coupling theory is widely used in the fiber optic sensors,and it is a very important factor affecting fiber optic sensors.It can be used to improve the performance of the optical fiber sensor,but it can also restrict the performance of the optical fiber sensor.Now,many fiber optic sensors are mostly based on the frequency shift of the sensor,because it can effectively improve the performance of the optical fiber sensor.But it also increases the manufacturing cost of an optical fiber sensor and reduces its practical value.The sensor based on the power has lower precision and accuracy.Therefore,we need further study mode coupling theory,improve the performance and reduce the cost of fiber optic sensors.Meantime,in the optical fiber sensor based on the ring waveguide,mode coupling theory also has a significant impact on the performance of the optical fiber sensor.It is still necessary for us to study.We urgently need to use the mode-coupling theory to put forward a new range of fiber optic sensors,lay a foundation for further improving the practicality of fiber optic sensors.With the improvement of the optical fiber manufacturing capacity,and the development of various optical fibers,it provides a new idea for solving accuracy and cost issues.Starting from research subject of mode coupling theory of fiber sensor,we carry out study on new optical fiber sensor to improve the performance,and reduce the manufacturing cost of an optical fiber sensor.The following main topics are included in this dissertation:(1)Based on the mode coupling theory of multi-core optical fiber,we propose a novel wavelength selective coupler based on the all solid nine-core Ge-doped fiber.Based on the phenomenon of multi-core coupling,we change the index of central core different from the outer core and realize the wavelength division.Meantime,we derived and analyzed the all solid nine-core Ge-doped wavelength selective coupler.(2)Based on the mode coupling theory of bending dual-core optical fiber,we study a structure of a bent dual-core photonic crystal fiber and propose the controllable wavelength-selective coupling photonic crystal fiber.Meantime,we analyzed the mode field intensity effective refractive index of the optical fiber under the bending condition.From the simulation,we can find that the coupling length can be changed by bending the dual-core PCF.Different from the common wavelength-selective coupler,the coupler can realize the separation of multiple wavelengths.(3)We analysis the method that light is injected in the two-core,and introduce the equation of the method.We introduce the characteristics and functions of photonic crystal fiber,and analyze the characteristics and advantages of the three-core photonic crystal fiber.Meantime,we analyze the impact of structure on the three-core photonic crystal fiber.From the simulation,we can find that the coupling characteristics of three-core photonic crystal fiber can significant change by changing the size of the core of fiber.Based on a traditional three-core photonic crystal fiber,we design an incompletely coupled three-core photonic crystal fiber.Meantime,based on the analysis of mode coupling theory above,we proposed the double core beam method,and proposed a microbending sensor.Coupling characteristic and beam propagation analysis of the microbending sensor are performed.From the simulation,we find that this microbending sensor is easy to fabricate,low cost,and possesses simple signal acquisition,since no spectral manipulations are required,which enormously decreases the sensor cost and increases the practical value(4)Based on the incomplete coupling triple-core photonic crystal fiber,in order to decrease the difficulty of fiber connection,we propose a fiber-optic based on the tuning fork structure for bend and refractive index(RI).We analyzed the impact of the structure on the tuning fork type optical fiber.Meantime,we analyzed the refractive index detector performance in detail and compared with the existing sensor on the sensitivity,range and manufacturing cost.It proved that the new bend/RI sensor based on the tuning fork structure is easy of fabrication,and has low cost and simple signal acquisition.(5)We derived and analyzed optical waveguide gyroscope propagation equations in detail,and analyzed the multi-resonator waveguide gyroscope problems in detail.We presents a new coupled resonator optical waveguide(CROW)? Here,we have added a number of bus waveguides between each ring,which can significantly improve gyroscope sensitivity.In this work we have analyzed the sensitivity to the inertial rotations of a MROW gyroscope,and we will demonstrate the effect of resonator losses,coupling coefficients,and the radius of a resonator on the rotational sensitivity of a MROW gyroscope.This work shows that adding a number of bus waveguides can significantly increase the sensitivity of the CROW.Meanwhile,using the appropriate parameters heightens the sensitivity of the MROW compared to single-ring gyroscopes with same radius in a certain range.It provides some ideas for further analysis of the optical waveguide gyroscope. |
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