Lidar, short for light radar, is a crucial enabling technology for self-driving cars. The sensors provide a three-dimensional point cloud of a car's surroundings, and the concept helped teams win the DARPA Urban Challenge back in 2007. Lidar systems have been standard on self-driving cars ever since.

In recent years, dozens of lidar startups have been created to challenge industry leader Velodyne. They've all made big promises about better prices and performance. At the start of 2018, Ars covered the major trends in the lidar industry and why experts expected cheaper, better systems to arrive in the next few years. But that piece didn't go into much detail about individual lidar companies—largely because most companies were closely guarding information about how their technology worked.

But over the last year, I've gotten a steady stream of pitches from lidar companies, and I've talked to as many of them as I could. Ars has now been in contact with senior executives from at least eight lidar companies as well as others involved in the industry as customers or analysts. These conversations have provided a lot of insight not only into trends in the lidar industry in general but also about the technology and business strategy of individual companies.

Today, there are three big ways that lidar products differ from one another. And after laying these approaches out, it's easier to grasp the technology of ten leading lidar companies.

To keep this survey of the lidar landscape manageable, I'm sticking to independent companies that focus primarily on the lidar business. That means I won't cover Waymo's homebrew lidar technology, the lidar startups GM and Ford acquired in 2017, or the lidar efforts of bigger companies like Valeo (maker of the lidar in Audi's 2018 and 2019 versions of the A7 and A8), Pioneer, or Continental. It's hard to get these larger companies to give us details about their lidar technology—and there's plenty of ground to cover without them.

The three big factors that distinguish lidar sensors

The basic idea of lidar is simple: a sensor sends out laser beams in various directions and waits for them to bounce back. Because light travels at a known speed, the round-trip time gives a precise estimate of the distance.

While the basic idea is simple, the details get complicated fast. Every lidar maker has to make three basic decisions: how to point the laser in different directions, how to measure the round-trip time, and what frequency of light to use. We'll look at each of these in turn.

Beam-steering technology: Most leading lidar sensors use one of four methods to direct laser beams in different directions (two companies I cover here—Baraja and Cepton—use other techniques that they haven't fully explained):

Spinning lidar. Velodyne created the modern lidar industry around 2007 when it introduced a lidar unit that stacked 64 lasers in a vertical column and spun the whole thing around many times per second. Velodyne's high-end sensors still use this basic approach, and at least one competitor, Ouster, has followed suit. This approach has the advantage of 360-degree coverage, but critics question whether spinning lidar can be made cheap and reliable enough for mass-market use.

Velodyne created the modern lidar industry around 2007 when it introduced a lidar unit that stacked 64 lasers in a vertical column and spun the whole thing around many times per second. Velodyne's high-end sensors still use this basic approach, and at least one competitor, Ouster, has followed suit. This approach has the advantage of 360-degree coverage, but critics question whether spinning lidar can be made cheap and reliable enough for mass-market use. Mechanical scanning lidar uses a mirror to redirect a single laser in different directions. Some lidar companies in this category use a technology called a micro-electro-mechanical system (MEMS) to drive the mirror.

uses a mirror to redirect a single laser in different directions. Some lidar companies in this category use a technology called a micro-electro-mechanical system (MEMS) to drive the mirror. Optical phased array lidar uses a row of emitters that can change the direction of a laser beam by adjusting the relative phase of the signal from one transmitter to the next. We'll describe this technique in detail in the section on Quanergy.

uses a row of emitters that can change the direction of a laser beam by adjusting the relative phase of the signal from one transmitter to the next. We'll describe this technique in detail in the section on Quanergy. Flash lidar illuminates the entire field with a single flash. Current flash lidar technologies use a single wide-angle laser. This can make it difficult to reach long ranges since any given point gets only a small fraction of the source laser's light. At least one company (Ouster) is planning to eventually build multi-laser flash systems that have an array of thousands or millions of lasers—each pointed in a different direction.

Distance measurement

Lidar measures how long light takes to travel to an object and bounce back. There are three basic ways to do this:

Time-of-flight lidar send out a short pulse and measures how long it takes to detect the return flash.

lidar send out a short pulse and measures how long it takes to detect the return flash. Frequency-modulated continuous-wave (FMCW) lidar sends out a continuous beam whose frequency changes steadily over time. The beam is split into two, with one half of the beam getting sent out in the world, then being reunited with the other half after it bounces back. Because the source beam has a steadily changing frequency, the difference in travel distance between the beams translates to slightly different beam frequencies. This produces an interference pattern with a beat frequency that is a function of the round-trip time (and therefore of the round-trip distance). This might seem like a needlessly complicated way to measure how far a laser beam travels, but it has a couple of big advantages. FMCW lidar is resistant to interference from other lidar units or from the Sun. FMCW lidar can also use Doppler shifts to measure the velocity of objects as well as their distance.

lidar sends out a continuous beam whose frequency changes steadily over time. The beam is split into two, with one half of the beam getting sent out in the world, then being reunited with the other half after it bounces back. Because the source beam has a steadily changing frequency, the difference in travel distance between the beams translates to slightly different beam frequencies. This produces an interference pattern with a beat frequency that is a function of the round-trip time (and therefore of the round-trip distance). This might seem like a needlessly complicated way to measure how far a laser beam travels, but it has a couple of big advantages. FMCW lidar is resistant to interference from other lidar units or from the Sun. FMCW lidar can also use Doppler shifts to measure the velocity of objects as well as their distance. Amplitude-modulated continuous wave lidar can be seen as a compromise between the other two options. Like a basic time-of-flight system, AMCW lidars send out a signal and then measure how long it takes for that signal to bounce back. But whereas time-of-flight systems send out a single pulse, AMCW systems send out a more complex pattern (like a pseudo-random stream of digitally encoded one and zeros, for example). Supporters say this makes AMCW lidar more resistant to interference than simple time-of-flight systems.

Laser wavelength

The lidars featured in this article use one of three wavelengths: 850 nanometers, 905 nanometers, or 1550 nanometers.

This choice matters for two main reasons. One is eye safety. The fluid in the human eye is transparent to light at 850 and 905nm, allowing the light to reach the retina at the back of the eye. If the laser is too powerful, it can cause permanent eye damage.

On the other hand, the eye is opaque to 1550nm light, allowing 1550nm lidar to operate at much higher power levels without causing retina damage. Higher power levels can translate to longer a range.

So why doesn't everyone use 1550nm lasers for lidar? Detectors for 850 and 905nm light can be built using cheap, ubiquitous silicon technologies. Building a lidar based on 1550nm lasers, in contrast, requires the use of exotic, expensive materials like indium gallium arsenide.

And while 1550nm lasers can operate at higher power levels without a risk to human eyes, those higher-power levels can still cause other problems. At the CES show in Las Vegas this year, a man reported that a powerful 1550nm laser from an AEye lidar permanently damaged his camera. And, of course, higher-power lasers consume more energy, lowering a vehicle's range and energy efficiency.

With this background out of the way, let's look at 10 of the leading lidar companies.

Velodyne

Beam steering: Spinning

Distance measurement: Time-of-flight

Wavelength: 905nm

Velodyne invented modern three-dimensional lidar over a decade ago, and the company has dominated the lidar market ever since. Velodyne's distinctive spinning lidars continue to be ubiquitous on self-driving cars, and the company is likely to continue leading the market in 2019. But some industry observers question whether Velodyne can maintain its industry dominance in the coming years.

As recently as late 2017, Velodyne's flagship 64-laser lidar unit was selling for a reported $75,000 each. Velodyne introduced a new 128-laser model that's rumored to be even more expensive—as much as $100,000.

Asked about these figures, a Velodyne spokesman replied: "We don't reveal prices in the public domain, but the prices that are quoted in public domain are list prices for single units. The prices are significantly lower in automotive volumes and we are actively delivering to automotive OEMs at these lower prices."

Velodyne does sell less-expensive lidars, including a 16-laser "puck" model that was selling for $4,000 last year. Velodyne also has a solid-state model called the Velarray. Velodyne says that it's a 905nm system with a "proprietary frictionless beam-steering method." Velodyne expects it to eventually cost less than $1,000 in automotive volumes. However, these lidars do not deliver the high-end performance of Velodyne's spinning 64- and 128-laser models.

Some critics claim that Velodyne has struggled with manufacturing and product quality.

"The delicate moving lidar sensors that are its bread and butter have proven difficult to manufacture efficiently at high quality and can be frustratingly fragile in automotive applications," journalist Ed Niedermeyer wrote recently, citing sources in the autonomous vehicle sector.

A company spokesman disputed this characterization, saying that Velodyne "has over the years perfected the science of manufacturing these sensors at scale" and has "been proven to withstand harsh automotive grade environments."

Velodyne recently signed a licensing deal with Veoneer, an established company in the automotive supply chain. Veoneer has plenty of experience building components that meet car companies' exacting quality standards, and it may figure out ways to tweak Velodyne's classic design in ways that improve quality and bring down costs. But they'll have to move quickly, as a number of other companies are aiming to take Velodyne's lidar crown.