It’s late, pitch dark, and a self-driving car winds down a narrow country road. Suddenly, three hazards appear at the same time.
時間很晚了,天很黑, 有一台自動駕駛汽車 在鄉村道路上迂迴行駛。 突然,三樣危險物同時出現。
What happens next?
接下來會發生什麼事?
Before it can navigate this onslaught of obstacles, the car has to detect them— gleaning enough information about their size, shape, and position, so that its control algorithms can plot the safest course. With no human at the wheel, the car needs smart eyes, sensors that’ll resolve these details— no matter the environment, weather, or how dark it is— all in a split-second.
若這台車要突破這障礙物的阻擋, 它首先得要能偵測到它們—— 收集足夠的資訊,了解 它們的大小、形狀、位置, 這麼一來,它的控制演算法 就能夠繪出最安全的路線。 沒有人在操作方向盤, 這台車需要有聰明的眼睛, 即能夠分析這些細節的感測器—— 不論在什麼環境中、 什麼氣候下,不論天色有多黑—— 都要瞬間判斷。
That’s a tall order, but there’s a solution that partners two things: a special kind of laser-based probe called LIDAR, and a miniature version of the communications technology that keeps the internet humming, called integrated photonics.
這簡直是苛求,但有個 結合兩種東西的解決方案: 一種叫做雷射雷達的 特殊雷射探測器, 以及讓網際網路能一直忙碌的 一種迷你版本通訊技術, 叫做積體光學。
To understand LIDAR, it helps to start with a related technology— radar. In aviation, radar antennas launch pulses of radio or microwaves at planes to learn their locations by timing how long the beams take to bounce back. That’s a limited way of seeing, though, because the large beam-size can’t visualize fine details. In contrast, a self-driving car’s LIDAR system, which stands for Light Detection and Ranging, uses a narrow invisible infrared laser. It can image features as small as the button on a pedestrian’s shirt across the street. But how do we determine the shape, or depth, of these features?
若要了解雷射雷達,應該先了解 一項相關技術——雷達。 在航空上, 雷達天線會向飛機發射 無線電波或微波的脈衝, 計算波束反彈回來的時間, 推算出飛機的位置。 不過,這種看見的方式會受限, 因為大型波束無法 視覺化呈現精密的細節。 相對的,自動駕駛汽車的 雷射雷達系統, 也就是「光學定向和測距」系統, 使用狹窄的不可見紅外線雷射。 它的成像能夠精密到 連對街行人的鈕扣 這種小特徵都不放過。 但,我們要如何決定 這些特徵的形狀或深度?
LIDAR fires a train of super-short laser pulses to give depth resolution. Take the moose on the country road. As the car drives by, one LIDAR pulse scatters off the base of its antlers, while the next may travel to the tip of one antler before bouncing back. Measuring how much longer the second pulse takes to return provides data about the antler’s shape. With a lot of short pulses, a LIDAR system quickly renders a detailed profile.
雷射雷達會發射一連串 超短雷射脈衝來解析深度。 以鄉下道路上的麋鹿為例。 當汽車從旁邊開過時, 一個雷射雷達脈衝 會在它的鹿角基部散開, 而下一個脈衝則有可能會碰到 一支角的尖端,然後才反彈回來。 測量第二個脈衝花了 多少時間才彈回來, 這樣的資料就能用來 判斷角的形狀。 雷射雷達用大量的短脈衝 便能快速提供出細節的側寫資訊。
The most obvious way to create a pulse of light is to switch a laser on and off. But this makes a laser unstable and affects the precise timing of its pulses, which limits depth resolution. Better to leave it on, and use something else to periodically block the light reliably and rapidly.
若要創造脈衝光,最明顯的方式 就是把雷射開啟再關閉。 但這會讓雷射不穩定, 且會影響到脈衝的時間精準度, 這就會限制了深度的解析度。 最好是讓它一直開著, 用其他的東西定期、 快速地阻擋光線。
That’s where integrated photonics come in. The digital data of the internet is carried by precision-timed pulses of light, some as short as a hundred picoseconds. One way to create these pulses is with a Mach-Zehnder modulator. This device takes advantage of a particular wave property, called interference. Imagine dropping pebbles into a pond: as the ripples spread and overlap, a pattern forms. In some places, wave peaks add up to become very large; in other places, they completely cancel out. The Mach-Zehnder modulator does something similar. It splits waves of light along two parallel arms and eventually rejoins them. If the light is slowed down and delayed in one arm, the waves recombine out of sync and cancel, blocking the light. By toggling this delay in one arm, the modulator acts like an on/off switch, emitting pulses of light. A light pulse lasting a hundred picoseconds leads to a depth resolution of a few centimeters, but tomorrow’s cars will need to see better than that. By pairing the modulator with a super- sensitive, fast-acting light detector, the resolution can be refined to a millimeter. That’s more than a hundred times better than what we can make out with 20/20 vision, from across a street.
這就是積體光學上場的時候了。 網際網路的數位資料 由精確定時的脈衝光來傳輸, 有些短到一百億分之一秒。 (0.000 000 000 1 秒) 製造這類脈衝的方法之一, 就是用馬赫陳爾德干涉儀。 這個裝置會利用一種特殊的波特性, 叫做干涉。 想像把小卵石丟到池塘中: 漣漪散開和交疊時會形成圖案。 在某些地方,波峰會加疊 在一起,變得非常大; 在其他地方,它們則是完全抵銷。 馬赫陳爾德干涉儀的做法很類似。 它會沿著兩支平行的 臂桿把光波分開, 最終再將它們重新結合起來。 如果一支臂桿的光 被減緩下來並延遲, 重新結合的不同步光波 會彼此抵銷,使光線沒了。 透過在一支臂桿製造延遲, 干涉儀的功能就變成 像是開關,放出脈衝光。 維持一百億分之一秒的脈衝光 能夠產生出幾公分的深度解析度, 但未來的汽車需要 看得比那更清楚。 把干涉儀和超級敏感、 反應快速的光偵測器搭配使用, 解析度可以精密到一公釐。 這比雙眼視力 1.0 的人 看對街時能夠達到的解析度 還要清楚一百倍。
The first generation of automobile LIDAR has relied on complex spinning assemblies that scan from rooftops or hoods. With integrated photonics, modulators and detectors are being shrunk to less than a tenth of a millimeter, and packed into tiny chips that’ll one day fit inside a car’s lights. These chips will also include a clever variation on the modulator to help do away with moving parts and scan at rapid speeds.
第一代的汽車雷射雷達 要仰賴複雜的旋轉組件 從屋頂或是引擎蓋上做掃瞄。 有了積體光學, 干涉儀和偵測器被縮到 小於十分之一公釐, 裝載到小型晶片上, 將來可以放到車燈中。 這些晶片還將包括 巧妙變造的干涉儀, 得以擺脫可動的部件,以高速掃瞄。
By slowing the light in a modulator arm only a tiny bit, this additional device will act more like a dimmer than an on/off switch. If an array of many such arms, each with a tiny controlled delay, is stacked in parallel, something novel can be designed: a steerable laser beam.
這個額外的裝置 能將干涉儀的一支臂桿 只稍微減緩一點點, 它比較不像開關,更像調光器。 如果一長列這類 控制一點點延遲的臂桿 被平行堆疊起來, 就能設計出很新穎的東西: 可操控的雷射光束。
From their new vantage, these smart eyes will probe and see more thoroughly than anything nature could’ve imagined— and help navigate any number of obstacles. All without anyone breaking a sweat— except for maybe one disoriented moose.
有了這種新優勢, 這些聰明的眼睛將能夠 探索和看得更完整, 勝過任何大自然想像得出的東西, 導航通過障礙物,不管多少。 無需流汗,毫不費力—— 也許那隻迷惘的糜鹿除外。