[39]Photography.

感谢收听,期待你对本期节目的评论留言哦～ 2017.7.8 Economist Science and Technology Photography Wide-eyed and lensless无透镜的 Cameras are about to get a lot smaller and flatter.THE pill-sized cameras in today’s mobile phones may seem miraculously[mɪ'rækjələslɪ] 奇迹般地tiny, given that a decade ago the smallest cameras available for retail sale were the size of a pack of cards. But Ali Hajimiri of the California Institute of Technology is unimpressed. In his opinion even these phone cameras are far too thick (witness the optical视觉的,眼睛的,bump隆起 on the back of most mobile phones), so he and his team plan to replace them with truly minuscule[ˈmɪnəskju:l]非常小的 devices that spurn蔑视 every aspect of current photographic[ˌfəʊtəˈgræfɪk] technology. Not only do Dr Hajimiri’s cameras have no moving parts, they also lack lenses镜头 and mirrors—in other words, they have no conventional optics镜片. That does away with the focal depth required by today’s cameras, enabling the New devices to be flat. The result, he hopes,will be the future of photography. Brave words. But, as an inventor, Dr Hajimiri has form to back them up. In 2002 he helped found a firm (now taken over by a bigger one) to build power amplifiers [ˈæmplɪfaɪə(r)]功率放大器 for mobile phones. More than 250m of these have been made. In 2004 he came up with the world’s first radar on a chip, which is now being used in prototype [ˈprəʊtətaɪp]雏形 self-driving cars. To round things off, in 2012 he created an all-silicon imaging system全硅成像系统 that uses the terahertz ['terəhɜ:tz]太（拉）赫（频率单位，等于百亿赫）part of the electromagnetic [ɪˌlektrəʊmægˈnetɪk] spectrum电磁波频谱 (which is slightly higher in frequency than radar) to see through objects opaque[əʊˈpeɪk]不透明的 to light. This system has found employment in everything from medical-diagnostics[ˌdaɪəg'nɒstɪks] 医疗诊断equipment to security scanners. The latest venture 冒险 moves his focus to higher frequencies still than terahertz waves—those of visible light. The new camera, known as an optical phased-array[无线电]相控(天线)阵的 receiver, or OPA, collects the light from which it forms its image using a grid格子of devices called grating couplers['kʌplə]光栅耦合器. The prototype (the blue structure pictured above, attached to a thick mounting block to make it easier to handle) has 64 of them. Grating couplers are optical antennae [ænˈteni:]天线. They collect light and send it to a device called a waveguide. This carries light around in a way analogous[əˈnæləgəs]相似的 to a wire carrying electricity. Flash, bang, wallop [ˈwɒləp]. What a picture. Each grating coupler is tiny—about five by two microns [ˈmaɪkrɒn] 微米 (millionths of a metre)—and so picks up only a minuscule amount of light. That signal has to be amplified. This is done by heterodyning['hetərədaɪnɪŋ]外差作用, a process which combines the light in the coupler with a minute laser beam激光束, strengthening the signal at the desired wavelength. To mimic the image-making role of the optics in conventional cameras, the OPA manipulates [məˈnɪpjuleɪt]处理; 巧妙地控制 incoming light using electrons电子. Dr Hajimiri compares the technique to peering through a straw麦秆;吸管while moving the far end swiftly迅速地 across what is in front of you and recording how much light is in each strawful. In the OPA this scanning effect is created by manipulating the light collected by the grating couplers electronically,using devices called photodiodes ['fəʊtəʊˌdɪˌəʊd]光敏二极管. These place varying densities of electrons into the amplified light’s path through the OPA, either slowing it down or speeding it up as it travels. That shifts the arrival times of the peaks and troughs[trɒf]低谷 of the lightwaves. This “phase shifting移相位，相移” results in constructive interference between waves arriving from the desired direction, which amplifies them. Light coming from other directions, by contrast, is cancelled through destructive interference. Change the pattern of electrons and you change the part of the image field the OPA is looking at. Scanning the entire field in this way takes about ten nanoseconds十亿分之一秒 (billionths of a second). The photodiodes, then, determine where the camera is pointing without any mechanical movement being needed. They also permit the camera to capture different kinds of images, such as close-ups特写镜头 and fish-eye views鱼眼视图. To zoom in 放大for a close-up, the device selects a specific part of the image and scans it more thoroughly. To zoom out缩小 for a fish-eye, it scans the entire optical field, including light from the edges of that field. To change from zoom to fish-eye takes nanoseconds. The processed 加工过的optical signal is then passed down the waveguide波导 to further photodiodes. These convert it into an electrical signal, which is used to create the final photo. Crucially, all this can be achieved in a stack of electronics five microns thick—about a fifteenth of the diameter [daɪˈæmɪtə(r)]直径 of a human hair. The exact size of any production version will depend on the job to be done. The prototype can manage fuzzy[ˈfʌzi]模糊的 images of barcodes[bɑ:'kəʊd] 条形码;, but not much else. To achieve the same resolution分辨率 as the camera in a modern Apple iPhone, Dr Hajimiri reckons an array of about 1m grating couplers will be needed. Allowing for the space between these, the result would, at the moment, have an area of 1cm2. This is similar to the area of an iPhone’s camera, but that camera is 1,000 times thicker. Dr Hajimiri thinks, moreover, that a production version of the new device would be smaller. He concedes [kənˈsi:d]承认 that there are challenges: improving the optical performance of the elements; suppressing [səˈpres]压制 spillover [ˈspɪləʊvə(r)] effects超溢效果 between different signals in the device; and honing the algorithms that calibrate 使合标准 the camera’s performance. But all these matters,he believes, can be dealt with and he envisages[ɪnˈvɪzɪdʒ]设想 his lensless cameras being commerciallyavailable within five years. Such tiny cameras would have uses far beyond eliminating the optical bumps from mobile phones. They might be deployed有效地利用, Fantastic Voyage-like, to take pictures inside blood vessels. Conversely [ˈkɒnvɜ:sli]反之, they could be combined into massive arrays to create lightweight but extremely large-aperture [ˈæpətʃə(r)] 光圈telescopes able to resolve images from the deepest parts of the universe. They might even be strewn 散落于to the winds, photographic dust particles scavenging [ˈskævɪndʒ]寻觅the energy they need from stray零散的 radio signals, and broadcasting what they see. Or they could be attached, almost invisibly, to walls, to act as spies. In the “Ringworld” series of science-fiction novels, the books’ author, Larry Niven,envisages spray-on devices called “webeyes” that can be applied to any surface, and used for such espionage [ˈespiənɑ:ʒ]侦察; 间谍活动. Cameras of the sort Dr Hajimiri is developing are scarily close to making that idea real.