Capacitive Feedback Tunable F-P Filter And Its Spectral Application

Portable spectrometer has the advantages of compact structure and low cost.It can realize real-time spectral measurement on many occasions.However,the spectral resolution of miniature spectrometer has been restricted due to the limitation of the dispersive elements,the aberration,the size of the optical path and the detector pixel.Fabry-Perot(F-P)interferometer based on multi-beam interference principle has a great advantage in the study of fine spectral structure,and the F-P device generally has high resolution.In order to improve the resolution of the miniature spectrometer,a capacitive feedback controlled tunable F-P filter is designed and fabricated based on theoretical analysis of the basic F-P principle.It includes three parts: the cavity with parallel mirrors,the tuning components with piezoelectric ceramic(PZT),the capacitive sensor and the feedback circuit.The spectral experiments show that the fineness of the tunable F-P filter can reach 15,and the free spectrum range of the filter can reach 3nm.The spectral range of the whole spectrum can be scanned by piezoelectric ceramics,and the spectral resolution of 0.2nm can be obtained in the wide spectrum range with the dispersive spectrometer system.In addition,the capacitive sensors are added on the basis of the parallel plane cavity.The capacitive sensing and feedback control circuit is made and the corresponding software is developed.Through the detection and feedback control of the capacitance on the cavity,the length of the FP filter can be obtained in real time,the parallelism of the cavity can be kept in appropriate state,thus to achieve good filtering characteristics.The capacitive feedback controlled tunable F-P filter developed in this paper has the characteristics of simple structure,small size,wide range of applicable wavelengths,large free spectrum range,strong disturbance resistance and low cost,which can be used to enhance the spectral resolution of miniature spectrometer.