Research On Key Techniques Of Short-wave Infrared Imaging Based On Domestic InGaAs Focal Plane Array

Short-wave infrared(SWIR)radiation is an electromagnetic radiation between visible light radiation and medium-long wave infrared radiation,and its wavelength ranges from 0.76 ?m to 3 ?m.The detection of this band can obtain information that is not available in visible light band and medium-long wave infrared band.The principle of SWIR imaging is the same as that of visible light,as the light reflected from the surface of the target is generally used.Compared with the contour images obtained by the medium-long wave infrared imaging,images obtained by SWIR imaging have shadows,rich target details,and high distinguishability.While compared with visible light,the SWIR has better atmospheric transmission characteristic,as well as better imaging results in the harsh environments such as smoke,fog,haze,etc.SWIR imaging,with its unique characteristics,can be used as a beneficial supplement to visible light imaging and medium-long wave infrared imaging,and it becomes an international research hotspot in recent years.At present,SWIR imaging technique has an urgent application demand in military,industrial,medical,agriculture,aerospace,and commercial fields,and has important research significance and application value.Based on the domestic InGaAs focal plane array(FPA)detector,this paper realizes the staring SWIR camera through the development of the key driving and acquisition hardware circuit,the embedded control and processing software,and the host computer processing and display software.In view of the main factors that affect the imaging results of the SWIR camera,the SWIR image processing technique is studied.The SWIR high dynamic range imaging and display technique is studied for imaging in high dynamic range scenes,and the SWIR laser range gated imaging technique is studied for imaging of long-distance targets in poor lighting environments.The main research contents of this paper are as follows:1.A staring SWIR camera based on the domestic InGaAs FPA detector was developed,and the InGaAs FPA detector is the laser gated InGaAs FPA detector designed by Shanghai Institute of Technical Physics of the Chinese Academy of Sciences.Taking FPGA as the core,the driving and acquisition hardware circuit was developed.A high-speed,double sampling,and fully differential signal acquisition circuit was designed,the acquisition speed is up to 40 MSPS,the double sampling technique retains the original data of the reference output and the signal output,and the fully differential technique has the characteristics of large dynamic range,low distortion,and low common mode interference.The processing and display software composed of embedded control and processing software and host computer processing and display software was designed.The embedded control and processing software designed based on FPGA,adopting pipeline architecture,can realize real-time data acquisition and framing,meanwhile,it provides timing for FPA detector.The host computer processing and display software is designed using C#language based on the.NET framework,which has good compatibility with the host computer system and is easy to use.The developed staring SWIR camera has a response wavelength of 0.9 ?m to 1.7 ?m,and a resolution of 640 × 512.The size of the camera without the lens is 76 mm × 68 mm ×62 mm,and the weight is about 300 g.The power consumption of the camera is 2.5 W,and the maximum frame rate of it can reach 122 fps.2.The factors such as non-uniformity and blind pixel affecting the imaging results of the staring SWIR camera were studied,and the image processing methods aimed at these factors were studied.By using the response method mentioned in the national standard of infrared FPA parameter test method,the non-uniformity and blind pixel of the staring SWIR camera were studied.The non-uniformity and blind pixel ratio of the staring SWIR camera were calculated,and its non-uniformity curve and blind pixel distribution map were obtained.According to the characteristics of blind pixels,the blind pixels of the staring SWIR camera can be divided into paired blind pixels,single overhot pixels,single dead pixels,and crossing dead pixels.Here,the laser beam induced current(LBIC)method was used to further explore the causes of these types of blind pixels,and the causes are a wrong connection between the PN junction and readout integrated circuit,defects and impurities,disconnection of the readout circuit,and unformed PN junctions.According to the above research results,for different types of blind pixels,a SWIR image processing method with selective median filtering as the core is proposed,which can effectively eliminate the blind pixels in the image and improve the non-uniformity of the image.Aiming at the situation that blind pixels increase with the working time of the staring SWIR camera,a real-time blind pixel recognition and calibration method based on the response method is proposed.The method is simple and easy to use,it can accurately identify this type of blind pixels,and has a good calibration result on these blind pixels.3.In the fields of security monitoring,machine vision,and medical imaging,there are many scenes with high requirements for the dynamic range of imaging.In order to enable the staring SWIR camera to clearly show the brightness details of the scene,a research on SWIR high dynamic range(HDR)imaging and display technique was carried out.Based on the correlated double sampling technique of domestic InGaAs FPA detector,a HDR imaging method was proposed.The pixels in the image acquired by the staring SWIR camera are divided into HDR pixels and regular pixels,they are separately processed and finally synthesized into an image.This method can achieve the expansion of the dynamic range of the image.In addition,for the current problem that regular display devices cannot display HDR images,logarithmic mapping in the global mapping method combined with histogram equalization was used to perform real-time dynamic range compression(DRC)and display on HDR images.Applying HDR imaging and display technique to the staring SWIR camera,the camera still has a good real-time performance of a frame rate of more than 100 fps,and the details of its image is significantly better than the details of image obtained by the regular imaging and display.4.In a poor illumination environment,it is difficult to obtain a good imaging result of long-distance target through passive imaging method or regular active illumination imaging.To address this problem,SWIR laser range gated imaging technique was explored.The SWIR laser range gated imaging system was built by the staring SWIR camera,an active illumination source,and a synchronous control module.Through the adjustment of the delay between the gate opening time of the system and the light emission time of the active illumination source,as well as the adjustment of the width of the gate,the imaging distance and the imaging depth of field of the system can be adjusted to achieve the basic function of selective imaging of targets in different distances.The minimum gate width of the SWIR laser range gated imaging system is 2.6 ?s,and the corresponding imaging depth of field is 390 m.The adjustment of the delay between the gate opening time of the system and the light emission time of the active illumination source can achieve the accuracy of ns level,and the corresponding adjustment accuracy of the imaging distance can be achieved in a magnitude of meter The exploration in this field will provide important reference and technical support for the optimization of the domestic laser range gated imaging FPA detector and the development of highly integrated SWIR laser range gated imaging systemThe main innovations and contributions in this paper are summarized as follows1.A high-speed,double sampling,and fully differential signal acquisition circuit was designed.The circuit can realize the signal acquisition when the FPA detector is operating at the highest frequency,and the double sampling technique adopted retains the original data of the reference output and the signal output at the same time.The fully differential technique can provide a dynamic range twice as high as the method without fully differential technique,and the signal is not easily distorted.The developed staring SWIR camera based on the domestic InGaAs FPA detector can be flexibly adjusted with parameters such as integration time and frequency,and the maximum imaging frame rate can reach 122 fps2.For the domestic InGaAs FPA detector,a more detailed blind pixel classification method was proposed,and the causes of various blind pixels were explored through experiment.According to the results of the exploration,a SWIR image processing method with selective median filtering as the core was proposed.Meanwhile,for the situation that blind pixels increase with the working time of the staring SWIR camera,a real-time blind pixel recognition and calibration method based on the response method was proposed.These two methods can effectively solve the problem of non-uniformity and blind pixels in the staring SWIR camera.3.A SWIR real-time HDR imaging technique based on the correlated double sampling technique of domestic InGaAs FPA detector was proposed,and the related real-time HDR display technique was studied.Applying this technique to the staring SWIR camera,it can realize real-time imaging and display,and enrich the hierarchy and detail information of the image at the same time,which lead to better imaging results in HDR scenes.4.A SWIR laser range gated imaging technique based on the staring SWIR camera was explored.Based on this camera,a SWIR laser range gated imaging system was built,and it can realize the basic function of elective imaging of targets in different distances.The exploration of this technique is conductive to promoting the development of the application of SWIR imaging to long-distance target imaging in poor illumination environments.