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It’s late, pitch dark, and a self-driving [br]car winds down a narrow country road.

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Suddenly, three hazards appear [br]at the same time.

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What happens next?

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Before it can navigate this [br]onslaught of obstacles,

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the car has to detect them—

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gleaning enough information about [br]their size, shape, and position,

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so that its control algorithms [br]can plot the safest course.

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With no human at the wheel,

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the car needs smart eyes, sensors [br]that’ll resolve these details—

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no matter the environment, [br]weather, or how dark it is—

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all in a split-second.

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That’s a tall order, but there’s a [br]solution that partners two things:

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a special kind of laser-based probe [br]called LIDAR,

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and a miniature version of [br]the communications technology

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that keeps the internet humming,[br]called integrated photonics.

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To understand LIDAR, it helps to start [br]with a related technology— radar.

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In aviation,

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radar antennas launch pulses [br]of radio or microwaves at planes

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to learn their locations by timing [br]how long the beams take to bounce back.

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That’s a limited way of seeing, though,

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because the large beam-size [br]can’t visualize fine details.

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In contrast, a self-driving car’s [br]LIDAR system,

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which stands for Light Detection [br]and Ranging,

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uses a narrow invisible infrared laser.

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It can image features as small as the [br]button on a pedestrian’s shirt

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across the street.

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But how do we determine the shape, [br]or depth, of these features?

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LIDAR fires a train of super-short laser [br]pulses to give depth resolution.

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Take the moose on the country road.

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As the car drives by, one LIDAR pulse [br]scatters off the base of its antlers,

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while the next may travel to the tip [br]of one antler before bouncing back.

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Measuring how much longer [br]the second pulse takes to return

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provides data about the antler’s shape.

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With a lot of short pulses, a LIDAR system[br]quickly renders a detailed profile.

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The most obvious way to create a pulse [br]of light is to switch a laser on and off.

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But this makes a laser unstable and [br]affects the precise timing of its pulses,

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which limits depth resolution.

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Better to leave it on,

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and use something else to periodically [br]block the light reliably and rapidly.

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That’s where integrated photonics come in.

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The digital data of the internet

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is carried by precision-timed [br]pulses of light,

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some as short as a hundred picoseconds.

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One way to create these pulses is [br]with a Mach-Zehnder modulator.

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This device takes advantage of a [br]particular wave property,

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called interference.

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Imagine dropping pebbles into a pond:

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as the ripples spread and overlap, [br]a pattern forms.

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In some places, wave peaks add [br]up to become very large;

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in other places, they completely [br]cancel out.

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The Mach-Zehnder modulator [br]does something similar.

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It splits waves of light along two [br]parallel arms and eventually rejoins them.

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If the light is slowed down and [br]delayed in one arm,

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the waves recombine out of sync and [br]cancel, blocking the light.

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By toggling this delay in one arm,

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the modulator acts like an on/off switch, [br]emitting pulses of light.

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A light pulse lasting a hundred [br]picoseconds

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leads to a depth resolution of a [br]few centimeters,

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but tomorrow’s cars will need [br]to see better than that.

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By pairing the modulator with a super-[br]sensitive, fast-acting light detector,

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the resolution can be refined [br]to a millimeter.

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That’s more than a hundred times better [br]

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than what we can make out with [br]20/20 vision, from across a street.

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The first generation of automobile LIDAR [br]has relied on complex spinning assemblies

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that scan from rooftops or hoods.

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With integrated photonics,

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modulators and detectors are being shrunk [br]to less than a tenth of a millimeter,

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and packed into tiny chips that’ll one [br]day fit inside a car’s lights.

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These chips will also include a clever [br]variation on the modulator

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to help do away with moving parts [br]and scan at rapid speeds.

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By slowing the light in a modulator [br]arm only a tiny bit,

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this additional device will act more [br]like a dimmer than an on/off switch.

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If an array of many such arms, each with [br]a tiny controlled delay,

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is stacked in parallel, something novel [br]can be designed:

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a steerable laser beam.

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From their new vantage,

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these smart eyes will probe and [br]see more thoroughly

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than anything nature could’ve imagined—

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and help navigate any number [br]of obstacles.

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All without anyone breaking a sweat—

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except for maybe one disoriented moose.