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

Suddenly, three hazards appear 
at the same time.

What happens next?

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.

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.

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?

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.

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.

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.

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.

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.

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.