| Seismic prospecting as a long-history and mature geophysical exploration is one of the most effective method for detecting the underlying the oil and gas resource. With the development of seismic prospecting, the tranditional seismic geophone can not satisfy the demand of it any more. Therefore, a new type seismic geophone with the high-precision, large dynamic range, high fidelity and immunity to electromagnetic interference (EMI) will be developed. Microring resonator has such advantages of high detection limit, mass production capability, low-cost and easy-compatiable with the CMOS, that could integrated with laser, detector and signal processing unit on single chip, and as result it has possibility of realizing a new high-quality seismic geophone.Supported by the National Basic Research Program of China (Grant No.2006CB302805) and the National Natural Science Foundation of China (Grant No.60578048), we have done some theoretical and experimental researches on acceleration seismic geophone based on the microring resonator, and some original results have been demonstrated:(1) Operation principle for accelerometer based on the microring resonator is analyzed. The external accelerations, which lead to the waveguide length increment and elasto-optic effect, modulate the optical phase per round trip in the resonator waveguide and as result make the resonant wavelength shift. By applying the crossbeam vibration unit, the phase change by the elasto-optic effect can be negated.(2) The physical model for the vibration unit is demonstrated using finite element method (FEM). The dynamic response of the vibration unit is simulated, and the performances of mechanical sensitivity, cross desensitization, and frequency response are calculated and analyzed to optimize the vibration part and thus lay the foundation of its fabrication.(3) The optimization for the optical part of the accelerometer is present. By utilizing the effective index method (EIM) the input optical transmission mode is analyzed and single-mode waveguide is designed. Based on the coupled mode theory (CMT), the coupling coefficient between the straight waveguide and the resonator is determined. Under the intensity-variation scheme, the optimal phase shift is analyzed to obtain higher optical sensitivity. The simulation results show:with a 30-dB signal-to-noise ratio (SNR) measurement system, the detection limit is theoretically obtained as high as 4.6×10-4 g under the frequency of acceleration below 200 Hz.(4) The dynamic range of accelerometer is thoroughly analyzed. It shows that the dynamic range is limited by the self-coupling coefficient t, free spectrum range (FSR) and quality factor Q. As for the intensity-variation scheme, when t approaches amplitude attenuation factorσ, which means the critical coupling condition, we can get such dynamic range value as large as the detection SNR. As for wavelength-shift scheme, FSR limits the resonant wavelength shift, and therefore restricts the largest detectable signal. The resonator with high Q can greatly depress the spectrum noise, and then improve the wavelength detection limit.(5) The single resonator structure is improved by cascading microring resonators with different FSR. By adopting vernier effect technique in such structure, the detection limit is decided by the microring with the minimum FSR and while dynamic range is determined by the maximum one. The simulation results show:with a 30-dB SNR measurement system, the dynamic range for the intensity-variation scheme is theoretically improved from 29.1dB to 47.6dB. Simultaneously, the dynamic range for wavelength-shift one is also doubled compared with the single resonator.(6) The microfabrication technology was studied and demonstrated to realize the optical and mechanical part of the accelerometer based on the microring resonator. The optical part can be done by applying Electron Beam Lithography (EBL), Inductively Coupled Plasma (ICP) etching, and Plasma-enhanced Chemical Vapor Deposition (PECVD). The mechanical part can be fabricated by utilizing the backup mask and back-side etching. The racetrack microring resonator was fabricated based on SOI material. The experiment shows the extinction ratio of the characteristic spectrum was 9.772dB and Q factors of the resonator was as high as 27000.
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