| Summary: | 碩士 === 國立成功大學 === 工程科學系碩博士班 === 100 === An adaptive optics system (AOS) consists of three main components: wavefront sensor, wavefront corrector, and reconstruction controller. This thesis has developed a Shack-Hartmann wavefront sensor (SHWS) that can achieve 30 Hz frame rate via a video decoder circuit. Moreover, a 32-channel deformable mirror (DM) is used to compensate the phase distortion from external disturbances. A field programmable gate array (FPGA)-based Shack-Hartmann wavefront sensor has been setup for AOS, and it can compensate the optical aberration from surrounding environment in real time.
The overall system of the wavefront sensor is composed of a lab-made SHWS, a video decoder circuit, and a FPGA-based control model. A FPGA-based control model not a CPU base, the AOS can achieve a real-time compensation. Due to the multitasking operation system of a CPU-based PC Window system, the timer of the control loop will be unstable at a speed higher than 10 Hz. The lab-made wavefront sensing system depends on the hardware clock of the FPGA, so it can maintain a fixed speed easily. The frontend of the wavefront sensing system is based the Shack-Hartmann configuration. The wavefront information is obtained by positioning the focal spots on a charge coupled device camera, and then uses a Zernike model to remodel the wavefront information. The system between the DM and the SHWS is identified by a multichannel-input-multichannel-output (MIMO) state-space system identification algorithm, and then the controller is designed by a linear-quadratic-integral (LQI) controller via the identified system model. Currently, the lab-made AOS can reduce the aberrations caused by external disturbances at control loop of 30 Hz and the Strehl ratio of focusing spot is increased up to 1.75 times.
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