近红外线列探测器传递函数测试系统

Modulation Transfer Function Measurement of Near Infrared Linear Focal Plane Arrays

器件的调制传递函数(MTF)表征了光电成像器件对空间频率的对比度传递特性,可以全面地评价其成像性能。随着器件的发展,用MTF来评价器件越来越受到重视。针对近红外InGaAs焦平面器件MTF的测试需求,搭建了一套用狭缝法测试该波段线列器件MTF的系统。系统采用全反射式Offner光学结构将狭缝高质量地成像在待测器件上。成像光学结构由两块共轴的球面反射镜构成,1∶1成像,F数为4;在芯片工作波长为1.7μm时,在高达8mm×30mm的宽视场内,20lp/mm(对应尺寸25μm×25μm的芯片特征频率)处的实测MTF高于0.8,接近衍射极限。利用该系统对8元InGaAs线列探测器进行MTF测试(标称光敏元尺寸为100μm×100μm),6次重复测试得到的MTF数据的标准偏差与均值之比,在截止频率10lp/mm内小于2%,测量的相对不确定度小于4.7%。

The modulation transfer function （MTF） of an electro-optical device describes the image quality in terms of contrast as a function of spatial frequency, which is a much better way to evaluate a device. With the development of electro-optical devices, MTF becomes a popular technique in device evaluation. A system to measure the MTF of near infrared InGaAs linear focal plane arrays is built and an all-reflective Offner relay is used to image the slit onto the measured device. The Offner relay consists of two coaxial spherical mirrors, operating as a 1 ： 1 imager. At the working wavelength of 1.7 7μm, the Offner relay shows a nearly diffraction limited performance over an 8 mm×30 mm field, and the measured MTF at 20 lp/mm is above 0.8 everywhere in the field. Using this system, the MTF of an 8 × 1 InGaAs linear focal plane array （FPA）, of which the nominal pixel size is 100 μm × 100 μm is successfully measured. The result shows that the ratio of the standard deviation to the average of 6 repeated tests is below 2 % within the cutoff frequency of 10 lp/mm. The relative uncertainty of the MTF measurement of the 8 × 1 linear FPA is below 4.7 %.