A Study On Multimode-Interference-Based Optical Integrated Accelerometer

As an important measuring instrument, accelerometer has wide applications in current scientific research field. So far, researchers have realized various kinds of accelerometers using conversion principle, roughly classified into two main types, i.e., traditional electronic accelerometer and optical accelerometer. In this thesis, an integrated optical accelerometer by using the multimode interference (MMI) principle is proposed and characterized.The characteristics for four types of accelerometer is first reviewed. The structure of the interferometer optical accelerometer is relatively complicated, Bragg grating optical accelerometer is easily influenced by surrounding temperature, while the resonator optical accelerometer has a complicated manufacture process. Furthermore, the optical accelerometers above-mentioned are often discrete components, thus cannot be easily integrated with other elements. Then multimode interference optical integrated accelerometer under the present study is not only simple in structure, convenient to manufacture, but also ease of integration.Next, the present thesis expounds the multimode interference principle, the principle of optical fiber transmission and beam propagation method. Based on these, a new scheme for the multimode interference optical integrated accelerometer is constructed and designed in detail. The multimode interference sensing element is attached to the cantilever beam, whose size can be changed along with the external acceleration forced on the cantilever. According to the elastic-optic effect, the wavelength of the light propagating in the sensing element has the corresponding shift, from which we can obtain the values of the desired acceleration.Finally, the MATLAB subroutines are applied to simulate and analyze the modal characteristics, both the fundamental and higher-order modes, for the multimode optical fiber, and the coupling efficiency between them is computed. The results show that constructive interference can be obtained after the signal propagating nearly 5 cm in multimode fiber, so the length of multimode fiber is determined (say,5 cm). Moreover, the strain of multimode fiber as a function of the imposed acceleration is investigated in detail by using the ANS YS software packages, which indicates that shift the signal wavelength is consistent with analytical results at 1.55 μm under the condition that multimode interference sensing element is affected by external acceleration.Multimode-interference-based optical integrated accelerometer with the characteristics of simple in structure, convenient to manufacture and easy for integration has wide potential applications in vibration sensor field.