Avalanche photodiode array detector for eye-safe 3D imaging

用于人眼安全 3D 成像的雪崩光电二极管阵列探测器

• 批准号: ST/F503331/1
• 负责人: Jonathan Storey
• 金额: $ 5.67万
• 依托单位: Hovemere Ltd
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2008
• 资助国家: 英国
• 起止时间: 2008 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=ST%2FF503331%2F1
• 关键词: Avalanche; photodiode; array; detector; eye

Many civilian and military applications require the ability to imaging a scene in very low visible light level conditions. It basically provides 2-dimensional (2D) information for the objects of interest. It is used in situations such as security and surveillance during the nights, fire fighting in smoke-filled buildings during a fire, as well as rescue operations in foggy mountainous areas. In operation, a 2D imaging system uses a laser to send out light pulses towards objects that the user wants to image. Some of the light is reflected by these objects. The imaging system has an array of photodiodes made of semiconductor materials to detect the reflected light, by converting light into electrical currents. The term photodiode derives from the facts that they are diodes and that they detect photons, which make up light. The photodiode arrays (each pixel is a photodiode) are similar to those used in digital cameras. A specially designed readout circuit then reads the electrical current in each pixel to generate an image with intensity scales relating to the light intensity falling on each pixel. A 2D imaging system becomes a 3D imaging system when the range (distance between the imaging system and the objects of interest) is also measured. The readout circuit is modified to measure the time elapsed from sending out the light pulse to detecting the reflected light. Since the speed of light travelling in air is known, we can obtain the range. Such system is far more useful than one with only 2D capability. Clutters outside the area of interest can be eliminated easily, presenting a simpler and easier to interpret image to the users. This leads to better detection of concealed or camouflaged objects. With the range information, the system can also be modified to measure concentration of greenhouse gases at different altitudes in the atmosphere. The photodiode array performance often determines the overall performance of an imaging system. Using more advance photodiodes, namely the avalanche photodiodes (APDs), which provides amplification of the electrical currents through avalanche multiplication in the semiconductor materials, improves the imaging system. Hence APD arrays are found in high performance 3D imaging systems. However presently available APD arrays must operate with light with wavelengths of 760 and 1400 nm. These wavelengths present particular hazards because they are invisible to human (visible wavelength range is approximately from 400nm to 700 nm), but are still focused on the retina so can cause severe damage to eyes. The wavelength of 1.5micron is much more suitable for eye-safe operation because its threshold for causing eye damage is several orders of magnitude higher than those of shorter wavelengths. In addition the 1.5micron wavelength light penetrates fog and smoke well therefore operations of imaging systems using 1.5micron wavelength light is less affected by varying weather conditions. There is however no APD arrays that can detect 1.5mm wavelength light available, preventing realisation of eye-safe 3D imaging systems. The University of Sheffield and Lidar Technologies Limited (LT) are therefore working together to develop 1.5mm wavelength APD arrays which will be compatible with eye-safe high performance 3D imaging systems. LT, with strong interest and experience in 3D imaging systems, and Sheffield will first determine the key requirements on APD performance to ensure technology compatibility. Sheffield will use their APD knowledge on design and semiconductor parameters to produce optimised APD designs within the specifications. APD wafer growths and performance validation of the APD wafers will be carried out in Sheffield. LT and Sheffield will work together to determine the required array specifications and have the arrays produced commercially in the UK using the APD wafers validated by Sheffield. LT will test the APD arrays with assistance from Sheffield.

许多民用和军事应用需要在非常低的可见光水平条件下对场景进行成像的能力。它基本上为感兴趣的对象提供二维（2D）信息。它被用于夜间的安全和监视，火灾期间烟雾弥漫的建筑物的消防，以及雾山区的救援行动。在操作中，2D成像系统使用激光器向用户想要成像的对象发送光脉冲。一些光线被这些物体反射。成像系统具有由半导体材料制成的光电二极管阵列，以通过将光转换为电流来检测反射光。术语光电二极管源于它们是二极管并且它们检测构成光的光子的事实。光电二极管阵列（每个像素是一个光电二极管）类似于数码相机中使用的光电二极管阵列。然后，一个专门设计的读出电路读取每个像素中的电流，以生成一个图像，该图像具有与落在每个像素上的光强度相关的强度标度。当距离（成像系统和感兴趣的对象之间的距离）也被测量时，2D成像系统变成3D成像系统。读出电路被修改为测量从发出光脉冲到检测反射光所经过的时间。既然光在空气中的速度是已知的，我们就能求出它的射程。这样的系统比仅具有2D能力的系统有用得多。感兴趣区域之外的杂波可以很容易地消除，从而向用户呈现更简单且更容易解释的图像。这导致更好地检测隐藏或隐藏的物体。利用距离信息，该系统还可以被修改以测量大气中不同高度处的温室气体浓度。光电二极管阵列的性能通常决定了成像系统的整体性能。使用更先进的光电二极管，即雪崩光电二极管（APD），其通过半导体材料中的雪崩倍增提供电流的放大，改进了成像系统。因此，APD阵列在高性能3D成像系统中被发现。然而，目前可用的APD阵列必须用波长为760和1400 nm的光操作。这些波长存在特定的危害，因为它们对人类是不可见的（可见光波长范围约为400 nm至700 nm），但仍然集中在视网膜上，因此可能对眼睛造成严重损害。1.5微米的波长更适合于眼睛安全操作，因为它对眼睛造成伤害的阈值比较短波长高几个数量级。此外，1.5微米波长的光可以很好地穿透雾和烟，因此使用1.5微米波长的光的成像系统的操作受变化的天气条件的影响较小。然而，没有APD阵列可以检测1.5mm波长的光，这阻碍了人眼安全的3D成像系统的实现。因此，谢菲尔德大学和Lidar Technologies Limited（LT）正在合作开发1.5 mm波长APD阵列，该阵列将与人眼安全的高性能3D成像系统兼容。LT对3D成像系统有着浓厚的兴趣和经验，谢菲尔德将首先确定APD性能的关键要求，以确保技术兼容性。谢菲尔德将利用他们在设计和半导体参数方面的APD知识，在规格范围内生产优化的APD设计。APD晶片生长和APD晶片的性能验证将在谢菲尔德进行。LT和谢菲尔德将共同确定所需的阵列规格，并使用经过谢菲尔德验证的APD晶片在英国进行阵列的商业生产。LT将在谢菲尔德的协助下测试APD阵列。