Closed-loop control method of optical fiber positioning of center-opening four-quadrant detector

Optical fiber positioning technology is a key technology in multi-target optical fiber spectroscopes. The accuracy of optical fiber positioning is an important factor affecting the observation efficiency of telescopes. With the development of the spectral survey project, the requirements for the optical fiber positioning unit to be miniaturized, high density, integrated and high precision positioning have become a general trend, which poses higher technical requirements and challenges for optical fiber positioning systems. Optical fiber positioning technology was also expected to achieve a high-precision real-time monitoring and feedback system, forming an effective closed-loop control. Based on the requirements, a center-opening four-quadrant（4-Q） detector fiber positioning technology was proposed, and a two-dimensional Gaussian model was used to design the center-opening four-quadrant detector positioning algorithm. The algorithm performs a single calibration of the unit beam spot waist, can achieve high precision multiple real-time spot position determination and fiber position adjustment. The performance of the device and algorithm was simulated with the experiment set up based on the principle of the optical fiber spectroscope telescope. With this closed-loop control method, the absolute positioning error was obtained when the four-quadrant detector had a zero offset diameter of 40 mm and a fiber cross-sectional area of 1 000 μm². It can be controlled within 6 μm, and the relative error can be controlled within 0.15% ,which meets the requirements of the optical fiber spectroscope telescope fiber positioning technology. This device can be applied as an optical fiber positioning system.