Autonomous Vehicle Engineering - March 2021 - 18

Sensors

TTP

Opto-electronics
expert Tom Jellicoe
says there are still
new lidar architectures coming out
and the industry
has not settled on
one type.

OEMs want 10x cheaper

Lidar development is in the process of transitioning from
what Jellicoe calls 'Generation 2' devices, of which many
are in use today, to higher performance and potentially
lower cost, solid-state Generation 3. The Gen-2s have
served as the gateway to OEM series production applications. They're defined by their ability to scan in two
dimensions. Instead of using a stack of up to 64 lasers and
detectors as was typical on the first-generation, mechanical-scanning lidars, the Gen-2 units are internally simpler.
They use up to five lasers and are generally more robust
than the " spinning bucket " types. Their optical beams
moving laterally and vertically to measure the entire scene.
" The two-dimension-scanning lidars are currently
the sweet spot of the technology for vehicles, " Jellicoe
explained. " They've worked through the automotive
development cycle and qualification. They don't have
the cost and complexity of the previous generation.
And they're pretty much what the OEMs need in
terms of performance, with several offering 200-meter
[656-ft] range and the field-of-view [FOV] and resolution the vehicle makers want. "
Cost for the Gen-2 devices, however, still averages
around $1,000 per sensor. " The OEMs want to knock
a zero off of that; they want it ten times cheaper, "
Jellicoe said. Some recent product debuts have pushed
specific-application sensors under a grand, notably
Velodyne's $500 Vellarray.
Following Bosch's entry into the lidar space, its
arch-rival Denso also joined the battle in a collaboration with Aeva, a Silicon Valley start-up. Founded in
2017, Aeva is one of four lidar companies to become
publicly traded via SPAC mergers this year. Founded
by two former Apple engineers, Aeva makes a lidar
sensor that gives a three-dimensional view of the
road. It also can measure the velocity of the objects

18 March 2021

it is sensing - its fourth dimension.
Aeva's sensor works on the frequency modulated
continuous wave (FMCW) principle that is now under
development by Mobileye and others. FMCW lidars
were conceived for use in fiberoptic communication.
" FMCW is very promising technology, " Jellicoe said.
" By providing that additional information, they can be
super-useful. The challenge is in the lasers you need. "
A conventional lidar works on time-of-flight; its
simple laser produces a single-wavelength pulse which
is then measured in time upon return. By comparison,
FMCW lidars feature tunable lasers that can change
wavelength, and can be modulated. They're designed
to the cost-point and size requirements of the opticcomms industry. They also cost in the " many thousands of dollars, " he said. The challenge for FMCW lidar
technology in autos is getting the laser to the size and
cost point for integration into an automotive sensor. " If
someone can crack that, it'll be really exciting. FMCW
would be Generation 4, " Jellicoe offered.

Apple lidar: gamechanger?

In the rapidly evolving lidar industry, the Gen-2 makers
currently have the momentum. They're driving cost
reduction by putting their devices in vehicles. In the
process, they're working out refinements in the time-honored product-development tradition of over-engineering
the initial unit, then optimizing it over time.
A tricky thing to get right is beam steering, using
a MEMS mirror or another component. " Getting it
right makes the rest of the design easier, putting all
those lasers on a mirror, " Jellicoe said. " If you focus
your R&D on improving the beam steering, you drive
down system costs. " The mirrors in a MEMs (MicroElectro Mechanical Systems) lidar measure up to 10
mm (0.393 in) across. Their high resonant frequency
helps protect them from certain vehicle vibrations,
also an attribute of solid-state lidars.
Solid-state Gen-3 lidars, without moving parts, use
three microchips. One contains the lasers that send the
light beams; another carries the detectors that receive
the beams. A third chip handles control, with optics on
the front end. " Elegant and simple, " Jellicoe said. " And
because they're based on semiconductor components,
they're easy to assemble, manufacture and qualify. The
price will drop massively with volume, " he said.

AUTONOMOUS VEHICLE ENGINEERING

Autonomous Vehicle Engineering - March 2021

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