Study On Modulation Transfer Function Characterization Methods Of HgCdTe Infrared Focal Plane

Modulation transfer function(MTF)of infrared detector is the key parameter to connect device fabrication and whole system application.Its essence is the attenuation degree of the signal frequency component in the cut-off space frequency range after the photoelectric imaging system,which can truly reflect the spatial resolution and imaging quality of the infrared detector.MTF has gradually become an important index to measure the imaging performance of infrared detectors.In this paper,in view of the test requirements of the self-made HgCdTe infrared focal plane detector MTF,The MTF test method for array and line array devices as well as the structure of the device MTF are studied in depth,and the test system for testing the MTF of the array /line HgCdTe infrared focal plane detector by the slant knife edge method is built and implemented.The main research contents are as follows:1.The array HgCdTe infrared detector imaging eliminates stripe noise.Due to the material growth,device fabrication level and readout circuit,there are stripe noise in output array.The blind pixel detection accuracy of the array device and the subsequent array MTF computation cause interference.By using dual-density doubletree complex wavelet transform the array detector imaging of black body uniform radiation from time domain to frequency domain,the high-frequency coefficients are submitting to Gauss distribution after wavelet decomposition,and the high frequency wavelet coefficients are given different weights according to the correlation of stripe noise and single branch reconstruction is carried out.The experiment proved the effectiveness of the method.2.The array HgCdTe infrared detector MTF calculation.Blind pixels detection of blackbody radiated image after striped noise is removed,the global 3*Sigma criterion is applied to blind pixels detection.Due to the large error of the global detection method,to improved this method,using the local 3*Sigma rule with sliding window is used for blind pixels detection.Experiments show that the accuracy of the blind pixels detected by this method is more accurate than that of the global detection.Because of the influence of circuit system,there is random noise in output image when collecting knife edge target.The traditional median filtering algorithm blurs the edge details of the knife while removing the random noise,and uses an adaptive median filter to judge whether each pixel is a noise point or not.The method can remove noise and preserve the details of edge.At last,the Canny operator and Hough transform are used to detect the edge position of the knife edge and the angle of the knife edge,then the edge is projected and the MTF value of the array detector is calculated.3.The linear HgCdTe infrared detector MTF calculation.When using the slanted knife edge method to measurement the linear infrared detector,it is necessary to solve the problem of how to make the edge position of the target image exactly cross the pixel of the linear device,so as to output the ESF function required for the calculation of MTF.The target is transformed into a 'K' type,when to move the detector while observe the output pixel value through the data acquisition platform,then the edge across the pixel until the shape of the line of output pixels is shaped as a step.The output of the linear device values are acquired by ESF curve.When the MTF is calculated by the projection method,the output of all pixels can not be used as an effective pixel to calculate the MTF value of the line.The improved slanted knife edge method is compared with the slit scanning method.4.MTF of different structure detectors are measured.Crosstalk is one of the main factors to reduce the MTF value of the detector.To suppress crosstalk with metal frame structure and ion implantation structure of HgCdTe infrared detector array are designed.The two structures absorb the transverse diffusion carriers effectively to reduce electrical crosstalk.The MTF measurement was carried out on the linear detector without-frame structure,metal-frame structure and ion-injection-frame structure by the improved slanted knife edge method,and the measurement results were analyzed and compared.