高信噪比红外信号采集电路研究

基于某制冷型红外焦平面探测器,介绍了一种高信噪比的模拟信号采集电路。使用了噪声分析法对电路噪声来源进行分析,建立了低噪声的信号变换路径;采用信噪比(SNR)和噪声等效温差(NETD)测试相结合的方法,对电路和成像组件指标进行评价;测试结果表明,组件SNR可达76 dB,NETD可达17.5 mK(环境温度300 K),信号采集过程中噪声引入量少,组件能够实现对远距离微弱小目标的探测。     

通用红外测试系统的精度分析

采用美国PI、Santa Barbara红外和Lumitron的红外测试设备,进行系统集成,构建成了通用的红外测试系统.它既能完成1 024×1 024元以下任意像元数的中波红外和长波红外焦平面阵列性能参数的测试,又能完成中波红外和长波红外热像仪系统级性能参数的测试,具有很好的适用性及技术的先进性.中波红外热像仪的测试结果NETD=15.8 mK,与CEDIP的结果15.13 mK相差0.67 mK.测试精度为±1.49 mK.长波制冷红外焦平面阵列探测器的测试结果NETD为26.47 mK,与Sofradir的结果24.43 mK相差2.04 mK,测试精度为±1.63 mK.     

多次采样平均在长波红外高光谱成像系统中的应用

长波红外高光谱成像系统由于光谱细分导致探测器所接收的目标信号的能量较一般成像系统弱,因此系统噪声对成像效果影响较大。针对这一现象,本文在分析系统噪声成分的基础上,提出采用ADC多次采样平均的方法来降低其噪声,并从理论上推导了该方法的有效性。然后搭建了实验系统,分析计算不同积分时间下,利用多次采样平均技术得到的信号和噪声大小,并计算系统的信噪比和NETD。结果表明,多次(m次)采样平均对系统的信号值几乎无影响,但可以将系统噪声降低至原来的m~(-1/2)倍。因此,该方法可将系统的信噪比提高至原来的m~(1/2)倍,并能有效降低系统的NETD,提高系统灵敏度。该方法为改善长波红外高光谱成像系统成像效果提供了一种方案。     

长波红外高灵敏度信息采集系统设计

本文针对特定长波红外焦平面(288×384像元)探测器,选用低噪直流电源和低压差线性稳压器组合,实现了该红外焦平面模拟和数字驱动电路。分析提升长波红外探测灵敏度的关键要点,设计了高灵敏度信息采集电路。该红外成像系统具有高帧频、高灵敏度的优点。实验室测试得到该长波红外探测系统噪声等效温差(NETD)在300 K下优于30 m K。     

典型背景和目标的长波红外偏振成像实验研究

红外成像可以获得目标的强度信息,偏振成像可以获得目标的偏振信息,二者结合更有利于目标的探测识别。实验选用天空中飞机、海面上船只、草地上车辆三种典型自然背景下的典型目标作为研究对象,并利用自行研制的四通道同时长波红外偏振成像系统实现图像采集。实验结果表明,相对于传统的长波红外成像,长波红外偏振成像具有以下优势:长波红外偏振度图像在一定情况下具有更高的图像对比度,有利于目标的探测识别;长波红外偏振角图像可以突出目标细节,有利于观察者对场景内容的理解;长波红外偏振度和偏振角图像在一定情况下可以抑制杂波干扰,有利于杂波情形下的目标成像研究。     

中/长波切换工作模式的双色量子阱红外焦平面研制

报道了中/长波切换工作模式的双色量子阱红外焦平面研制。通过特殊设计的器件和读出电路结构,获得了可对中波波段和长波波段选择的切换架构。突破了双色量子阱材料、器件以及读出电路等关键技术,研制出384288规模、25 m中心距双色量子阱红外焦平面探测器。在70 K条件下器件性能优良,噪声等效温差为28 mK(中波)和30 mK(长波),响应峰值波长分别为5.1 m(中波)和8.5 m(长波)。室温目标红外成像演示了探测器的双色探测功能。     

高灵敏度II类超晶格长波红外探测系统研究

以Ⅱ类超晶格320×256长波红外探测器为核心部件,开发了一套高灵敏度长波红外探测系统.介绍了Ⅱ类超晶格红外探测器的技术指标及系统的主要结构和工作方式.为充分发挥该红外探测器的灵敏度,设计了高灵敏度信息获取系统,并介绍了该信息获取系统的软硬件设计.该信息获取系统采用了自适应信号调理技术,以降低信息获取噪声,提升探测系统的灵敏度和动态范围.最后对整套长波红外探测系统开展了信息获取噪声测试、系统性能测试及外场成像实验.实验结果表明:长波红外探测系统的信息获取噪声低至0. 065 m V,系统的噪声等效温差(NETD)达到19. 6 m K,黑体探测率为7. 72×10~(10),外场成像质量良好,图像细节清晰,对比度高.该长波红外探测系统有利于推动Ⅱ类超晶格红外探测器在高灵敏度长波红外遥感探测中的应用.     

点源目标的红外搜索与跟踪系统的作用距离估算

红外目标的探测在告警、制导等领域具有重要意义.在中远距离探测中,红外搜索与跟踪系统的作用距离受到大气传输、红外探测器的性能以及目标的辐射功率等因素的影响.传统红外系统的作用距离方程具有一定的局限性.考虑到目标成像弥散斑和背景辐射的影响,对红外搜索与跟踪系统(IRST)的作用距离方程进行修正,得到IRST系统的作用距离与系统的噪声等效温差(NETD)之间的关系,推导出探测器噪声限下对点源目标的作用距离方程.为IRST系统的综合评估和设计提供了一个重要的依据.     

制冷型热红外焦平面成像系统数据处理的关键技术

长波红外(8~12.5μm)焦平面的性能在很多方面弱于中短波红外器件,其非均匀性及盲元状况较严重。本课题首次在国内引进了法国Sofradir公司的320×256像元HgCdTe长波红外焦平面探测器MARS VLW RM4,其波长响应范围为7.7~12μm。基于一套高帧频低噪声信息获取系统,经过动态范围标定,实现了一套动态范围为250~330K、噪声等效温差(Noise Equivalent Temperature Difference.NETD)小于50mK的热红外成像系统。针对焦平面各像元的响应特性,研究了适用于热红外成像系统的非均匀性及盲元校正方法,提出了基于辐射定标的非均匀性校正和盲元检测。经实验验证,其校正效果优于两点定标法,且易于工程实现,基于辐射定标的结果可实现精确的温度反演。     

中波红外与长波红外推扫成像性能分析

基于长线阵中波红外和长波红外探测器的推扫成像技术,是实现高空间分辨率和高温度分辨率卫星对地观测的技术途径之一。随着长线阵红外探测器的发展,该技术受到高度关注,并已在一些领域得到应用。介绍了中波红外和长波红外谱段成像特点以及基于长线阵中波红外和长波红外探测器的卫星推扫成像技术发展现状。重点根据中波红外和长波红外谱段的波长、温度为300 K 目标的辐射强度以及光学系统和探测器参数,分析了它们的成像性能,包括调制传递函数(MTF)、地面像元分辨率(GSD)和噪声等效温差(NETD)。对于常温目标,在积分时间足够长的情况下,保持相同的MTF,中波红外比长波红外推扫成像可实现更高的空间分辨率和温度分辨率。结合分析结果,对充分发挥这两个谱段的成像性能提出了建议。     

Imaging one-dimensional and two-dimensional planar photodiode detectors fabricated by ion milling molecular beam epitaxy CdHgTe

Imaging one-dimensional (1-D) and two-dimensional (2-D) arrays of mid-wavelength infrared (MWIR) and long-wavelength infrared (LWIR) planar photodiodes were fabricated by ion milling of vacancy-doped molecular beam epitaxy Cd_xHg_1−xTe layers. Sixty-four-element 1-D arrays of 26×26 μm² or 26×56 μm² diodes were processed. Zero-bias resistance-area values (R₀A) at 77 K of 4×10⁶ Θcm² at cutoff wavelength λ_CO=4.5 μm were measured, as well as high quantum efficiencies. To avoid creating a leakage current during ball bonding to the 1-D array diodes, a ZnS layer was deposited on top of the CdTe passivation layer, as well as extra electroplated Au on the bonding pads. The best measured noise equivalent temperature difference (NETD) on a LWIR array was 8 mK, with a median of 14 mK for the 42 operable diodes. The best measured NETD on a MWIR array was 18 mK. Two-D arrays showed reasonably good uniformity of R₀A and zero-bias current (I₀) values. The first 64×64 element 2-D array of 16×16 μm² MWIR diodes has been hybridized to read-out electronics and gave median NETD of 60 mK.     

Demonstration and Performance Assessment of Large Format InP–InGaAsP Quantum-Well Infrared Photodetector Focal Plane Array

There have been various studies showing that InP-InGaAs quantum-well infrared photodetectors (QWIPs) are potential alternatives to AlGaAs-GaAs QWIPs in the long wavelength infrared (LWIR) band, especially for applications requiring high responsivity. Being on InP substrate, this material system also offers lattice matched mid-wavelength infrared (MWIR)/LWIR dual band QWIP stack when it is used with the AlInAs-InGaAs system. It is desirable to extend the cut-off wavelength of InP based LWIR QWIPs to , which can be accomplished by replacing the QW material with InGaAsP. In this paper, we report the first InP-InGaAsP QWIP focal plane array (FPA). The 640 512 FPA displayed remarkably low noise equivalent temperature difference (NETD) with very short integration times (46 mK at 66 K with and f/1.5 optics). The results show that these QWIPs can be operated with high responsivity (1 A/W) while offering bias adjustable gain in a wide range where the detectivity is almost constant at a reasonably high level.     

Large-Format Voltage-Tunable Dual-Band Quantum-Well Infrared Photodetector Focal Plane Array for Third-Generation Thermal Imagers

We report a large-format (640 times 512) voltage- tunable quantum-well (QW) infrared photodetector focal plane array (FPA) for dual-band imaging in the mid- and long-wavelength infrared (MWIR and LWIR) bands. Voltage-tunable spectral response has been achieved through a series connection of eight-well MWIR AlGaAs-InGaAs and 16-well LWIR AlGaAs-GaAs QW stacks grown by molecular beam epitaxy on GaAs substrate. The peak responsivity wavelength of the detectors is shifted from 4.8 to 8.4 mum as the bias is increased within the limit applicable by commercial read-out integrated circuits. The FPA with MWIR and LWIR cutoff wavelengths of 5.1 and 8.9 mum provides noise equivalent temperature differences of 20 and 32 mK (f/1.5) in these bands, respectively. The results are very encouraging for the development of low-cost large-format dual-band MWIR/LWIR FPA technology.     

QWIP focal plane array theoretical model of 3-D imaging LADAR system

The aim of this research is to develop a model for the direct detection three-dimensional (3-D) imaging LADAR system using Quantum Well Infrared Photodetector (QWIP) Focal Plane Array (FPA). This model is employed to study how to add 3-D imaging capability to the existing conventional thermal imaging systems of the same basic form which is sensitive to 3–5 µm(mid-wavelength infrared, MWIR) or 8–12 µm (long-wavelength infrared, LWIR) spectral bands. The integrated signal photoelectrons in case of short integration time is required to transmit laser pulses with higher energy in order to obtain photoelectrons nearest those values obtained from the background photoelectrons in thermal imaging system with the longer interval of time. Since the operating conditions of the proposed system are of low levels for speckle diversity and high levels of signal photoelectrons, it was shown that the signal obeys the Gaussian probability density function. The evaluation of system performance of the proposed model shows that it needs a detector with low dark current and high transmitted energy to obtain satisfactory parameter values.     

星载高分辨率红外双谱段遥感器光学系统设计北大核心CSCD

针对高精度红外遥感成像的应用需求,提出了高空间分辨率、高噪声等效温差和大幅宽的中波/长波红外双谱段遥感成像技术方案,在太阳同步轨道获取地面目标的中波和长波红外辐射信息,谱段范围分别为3~5μm和8~12μm,中波红外谱段空间分辨率优于5 m,长波红外谱段空间分辨率优于10 m,幅宽大于20 km,噪声等效温差优于60 mK。根据噪声等效温差和光学传递函数等要求优化了光学系统指标参数,分析了二次成像同轴三反光学系统的冷光阑匹配原理,计算了光学系统初始结构参数,设计了光阑匹配型和出瞳匹配型中波/长波红外双谱段一体化光学系统,比较了两种方案光学系统的冷光阑匹配效果。     

长波红外偏振图像及其误偏振信息分析

给出了长波红外偏振图像融合的结果,对融合的偏振图像进行了定性分析和定量评价。研究表明,偏振图像的融合方法有多种,能产生多种图像融合结果。融合后的长波红外偏振图像凸显了目标的形状,细节更加清楚,边缘更突出,立体感更强。与原始红外图像比较,长波红外偏振图像灰度均值提高168%、灰度标准差提高194%,梯度提高468%。处理后的偏振图像和原始的红外图像比较说明了长波红外偏振成像能明显提高目标和背景之间的对比度,更加有利于目标的识别。和中波红外偏振图像相比,给出了长波红外偏振图像误偏振信息的来源,这些误偏振信息在后续的偏振信息处理中是要消除的,说明了中波红外偏振成像的效果好。     

基于NETD的红外探测系统作用距离分析

由于红外焦平面阵列(Infrared Focal Plane Array, IRFPA)已成为红外探测器发展的主流,用IRFPA的参数来评价红外探测系统的综合性能变得至关重要。推导了以噪声等效温差(Noise Equivalent Temperature Difference, NETD)参数表示的红外探测系统的作用距离方程,考虑了背景辐射和目标成像弥散效应对探测的影响,计算了不同能见度条件下系统对点源目标的作用距离。结果表明,大气能见度越好,红外探测系统的作用距离就越远。分析了红外探测系统的探测能力随NETD值的变化。随着NETD值的增大,红外探测系统对目标的作用距离显著减小。研究结果能为红外探测系统的设计和性能指标评价提供参考。     

Dual-colour thermal imaging with InAs/GaSb superlattices in mid-wavelength infrared spectral range

Based on type-II InAs/GaSb superlattice photodiodes, the first report of a dual-colour infrared camera with excellent NETD values<30 mK for the shortwave channel with a cutoff wavelength of 4.0 /spl mu/m and <17 mK for the longwave channel with 5.0 /spl mu/m cutoff is presented. The bispectral system, which offers a simultaneous and pixel-registered detection of both colours, allows remote imaging of carbon dioxide.