1
00:00:08,145 --> 00:00:15,132
It’s late, pitch dark, and a self-driving 
car winds down a narrow country road.

2
00:00:15,132 --> 00:00:18,724
Suddenly, three hazards appear 
at the same time.

3
00:00:18,724 --> 00:00:20,846
What happens next?

4
00:00:20,846 --> 00:00:24,043
Before it can navigate this 
onslaught of obstacles,

5
00:00:24,043 --> 00:00:26,083
the car has to detect them—

6
00:00:26,083 --> 00:00:29,846
gleaning enough information about 
their size, shape, and position,

7
00:00:29,846 --> 00:00:34,208
so that its control algorithms 
can plot the safest course.

8
00:00:34,208 --> 00:00:35,762
With no human at the wheel,

9
00:00:35,762 --> 00:00:40,547
the car needs smart eyes, sensors 
that’ll resolve these details—

10
00:00:40,547 --> 00:00:43,898
no matter the environment, 
weather, or how dark it is—

11
00:00:43,898 --> 00:00:45,920
all in a split-second.

12
00:00:45,920 --> 00:00:50,159
That’s a tall order, but there’s a 
solution that partners two things:

13
00:00:50,159 --> 00:00:53,849
a special kind of laser-based probe 
called LIDAR,

14
00:00:53,849 --> 00:00:56,578
and a miniature version of 
the communications technology

15
00:00:56,578 --> 00:01:00,936
that keeps the internet humming,
called integrated photonics.

16
00:01:00,936 --> 00:01:06,006
To understand LIDAR, it helps to start 
with a related technology— radar.

17
00:01:06,006 --> 00:01:07,165
In aviation,

18
00:01:07,165 --> 00:01:11,866
radar antennas launch pulses 
of radio or microwaves at planes

19
00:01:11,866 --> 00:01:16,620
to learn their locations by timing 
how long the beams take to bounce back.

20
00:01:16,620 --> 00:01:18,593
That’s a limited way of seeing, though,

21
00:01:18,593 --> 00:01:22,679
because the large beam-size 
can’t visualize fine details.

22
00:01:22,679 --> 00:01:26,127
In contrast, a self-driving car’s 
LIDAR system,

23
00:01:26,127 --> 00:01:28,634
which stands for Light Detection 
and Ranging,

24
00:01:28,634 --> 00:01:32,190
uses a narrow invisible infrared laser.

25
00:01:32,190 --> 00:01:36,660
It can image features as small as the 
button on a pedestrian’s shirt

26
00:01:36,660 --> 00:01:38,123
across the street.

27
00:01:38,123 --> 00:01:42,483
But how do we determine the shape, 
or depth, of these features?

28
00:01:42,483 --> 00:01:48,267
LIDAR fires a train of super-short laser 
pulses to give depth resolution.

29
00:01:48,267 --> 00:01:50,746
Take the moose on the country road.

30
00:01:50,746 --> 00:01:55,853
As the car drives by, one LIDAR pulse 
scatters off the base of its antlers,

31
00:01:55,853 --> 00:02:00,721
while the next may travel to the tip 
of one antler before bouncing back.

32
00:02:00,721 --> 00:02:04,278
Measuring how much longer 
the second pulse takes to return

33
00:02:04,278 --> 00:02:06,882
provides data about the antler’s shape.

34
00:02:06,882 --> 00:02:13,192
With a lot of short pulses, a LIDAR system
quickly renders a detailed profile.

35
00:02:13,192 --> 00:02:18,557
The most obvious way to create a pulse 
of light is to switch a laser on and off.

36
00:02:18,557 --> 00:02:23,428
But this makes a laser unstable and 
affects the precise timing of its pulses,

37
00:02:23,428 --> 00:02:25,669
which limits depth resolution.

38
00:02:25,669 --> 00:02:27,044
Better to leave it on,

39
00:02:27,044 --> 00:02:33,031
and use something else to periodically 
block the light reliably and rapidly.

40
00:02:33,031 --> 00:02:35,987
That’s where integrated photonics come in.

41
00:02:35,987 --> 00:02:37,829
The digital data of the internet

42
00:02:37,829 --> 00:02:41,051
is carried by precision-timed 
pulses of light,

43
00:02:41,051 --> 00:02:44,473
some as short as a hundred picoseconds.

44
00:02:44,473 --> 00:02:49,104
One way to create these pulses is 
with a Mach-Zehnder modulator.

45
00:02:49,104 --> 00:02:52,865
This device takes advantage of a 
particular wave property,

46
00:02:52,865 --> 00:02:54,658
called interference.

47
00:02:54,658 --> 00:02:57,613
Imagine dropping pebbles into a pond:

48
00:02:57,613 --> 00:03:01,550
as the ripples spread and overlap, 
a pattern forms.

49
00:03:01,550 --> 00:03:05,464
In some places, wave peaks add 
up to become very large;

50
00:03:05,464 --> 00:03:08,450
in other places, they completely 
cancel out.

51
00:03:08,450 --> 00:03:11,517
The Mach-Zehnder modulator 
does something similar.

52
00:03:11,517 --> 00:03:17,292
It splits waves of light along two 
parallel arms and eventually rejoins them.

53
00:03:17,292 --> 00:03:20,784
If the light is slowed down and 
delayed in one arm,

54
00:03:20,784 --> 00:03:25,703
the waves recombine out of sync and 
cancel, blocking the light.

55
00:03:25,703 --> 00:03:28,335
By toggling this delay in one arm,

56
00:03:28,335 --> 00:03:33,606
the modulator acts like an on/off switch, 
emitting pulses of light.

57
00:03:33,606 --> 00:03:36,380
A light pulse lasting a hundred 
picoseconds

58
00:03:36,380 --> 00:03:39,790
leads to a depth resolution of a 
few centimeters,

59
00:03:39,790 --> 00:03:43,303
but tomorrow’s cars will need 
to see better than that.

60
00:03:43,303 --> 00:03:47,595
By pairing the modulator with a super-
sensitive, fast-acting light detector,

61
00:03:47,595 --> 00:03:50,878
the resolution can be refined 
to a millimeter.

62
00:03:50,878 --> 00:03:52,781
That’s more than a hundred times better 


63
00:03:52,781 --> 00:03:57,337
than what we can make out with 
20/20 vision, from across a street.

64
00:03:57,337 --> 00:04:02,925
The first generation of automobile LIDAR 
has relied on complex spinning assemblies

65
00:04:02,925 --> 00:04:05,777
that scan from rooftops or hoods.

66
00:04:05,777 --> 00:04:07,494
With integrated photonics,

67
00:04:07,494 --> 00:04:12,508
modulators and detectors are being shrunk 
to less than a tenth of a millimeter,

68
00:04:12,508 --> 00:04:17,837
and packed into tiny chips that’ll one 
day fit inside a car’s lights.

69
00:04:17,837 --> 00:04:21,806
These chips will also include a clever 
variation on the modulator

70
00:04:21,806 --> 00:04:27,275
to help do away with moving parts 
and scan at rapid speeds.

71
00:04:27,275 --> 00:04:31,097
By slowing the light in a modulator 
arm only a tiny bit,

72
00:04:31,097 --> 00:04:36,208
this additional device will act more 
like a dimmer than an on/off switch.

73
00:04:36,208 --> 00:04:40,708
If an array of many such arms, each with 
a tiny controlled delay,

74
00:04:40,708 --> 00:04:44,786
is stacked in parallel, something novel 
can be designed:

75
00:04:44,786 --> 00:04:47,492
a steerable laser beam.

76
00:04:47,492 --> 00:04:48,848
From their new vantage,

77
00:04:48,848 --> 00:04:52,248
these smart eyes will probe and 
see more thoroughly

78
00:04:52,248 --> 00:04:54,681
than anything nature could’ve imagined—

79
00:04:54,681 --> 00:04:57,544
and help navigate any number 
of obstacles.

80
00:04:57,544 --> 00:05:00,098
All without anyone breaking a sweat—

81
00:05:00,098 --> 00:05:03,988
except for maybe one disoriented moose.