The story is similar to single-photo credits. As the name suggests, these are sensitive enough to detect a single photon. High sensitivity means that they suffer from a lot of noise. As a result, it takes sophisticated finishing to apply them to a suffering program. But a big advantage of SPADs is that they – like VCSEL – can be produced using conventional semiconductor techniques, and thousands of them can be packed on a single chip.
The combination of VCSEL and SPAD enables a dramatic simplification of conventional lidar designs. Velodyne’s original three – dimensional lidar mounted 64 individually packed lasers in a column on a spinning gimbal. Each laser had a matching detector. The complexity of this design and the need to accurately align each laser with the corresponding detector was one of the reasons why Velodyne̵
More recently, a number of companies have experimented with using small mirrors to “steer” a laser beam in a scanning pattern. This design requires only a single laser instead of 64. But it still involves at least one moving part.
On the other hand, Apple, Ouster and Ibeo build lidar sensors without moving parts at all. With hundreds or thousands of lasers on a chip, VCSEL-based lidars can have a dedicated laser for each point in the lidar’s field of view. And because all of these lasers come pre-packaged on a chip, mounting is much easier than for Velodyne’s classic spin design.
Newer iPhones already had another 3D sensor called the TrueDepth camera that enabled Apple’s FaceID feature. It also used a number of VCSELs allegedly supplied by Lumentum. TrueDepth works by projecting a grid of more than 30,000 dots on the face of a subject and then estimating the three-dimensional shape of the user’s face based on the way the grid pattern was deformed.
The iPad’s lidar sensor projects far fewer laser dots than the TrueDepth camera. An iFixIt video made with an infrared camera showed that the lidar projected a grid of only a few hundred pixels. But while the TrueDepth pattern attempts to guess depths based on the shape of the light falling on a subject’s face, the iPad’s lid sensor directly measures distances by measuring how long it takes for the light to bounce off an object and return to the camera. This process probably provides both better precision in depth measurements and also longer range.
More powerful sufferers also use VCSEL and SPAD
The performance of Apple’s lidar is far behind advanced sensors sold by specialized lidar companies. Velodyne, the company that invented three-dimensional lidar, shows a range of more than 200 meters for its most powerful lidar, while Apple’s sensor has a range of around five meters.
Other VCSEL-based lidars are significantly more powerful than Apple’s. The oyster’s most powerful VCSEL – based lidar, for example, has an area around 100 meters to detect objects with 10 percent reflectivity.
Oster’s current sensors are all Velodyne-style spinning units. They have 16 to 128 VCSELs in a row on a single chip – this chip is then mounted vertically on a spinning cardinal as Velodyne’s devices. The simplicity of this solid state design has enabled Ouster to subdue Velodyne on price and emerge as one of Velodyne’s biggest rivals. But these spinning lid sensors from Ouster still cost thousands of dollars – too expensive to use in ordinary cars, let alone smartphones.
Last week, Ouster announced plans to send a new solid state lidar without moving parts. Instead of arranging 16 to 128 lasers in a row as in Øuster’s current lidar, Øuster’s new unit will have more than 20,000 VCSELs arranged in a two – dimensional grid.
Ibeo follows a similar strategy and may be ahead of Ouster. Ibeo designed the very first lidar ever shipped in a mass-market car – the Audi A8. That lidar was primitive, with only four lines of vertical resolution. But Ibeo is now developing a new model called ibeoNext that will have a laser grid that is 128 x 80 pixels – slightly smaller than Ouster’s planned sensor, but significantly larger than Ibeo’s previous offering. Ibeo says that the sensor will have a range of 150 meters for objects with 10 percent reflectivity.
One last competitor worth mentioning here is Sense Photonics, which we covered back in January. Like the other companies we have discussed, Sense uses VCSEL and SPAD for its lidar. However, Sense uses a technique called micro-transfer printing to spread lasers out. This allows the lasers to use more power without encountering heat and eye safety issues. So far, Sense’s lidars have not had long range, but Sense boss Shauna McIntyre told Ars that the company is aiming for 200 meters range for an upcoming sensor that it will announce in early 2021.
Lidar is in the process of invading the car market
Ibeo, Sense and Ouster are all launching new, affordable designs because they expect an explosion of demand from the automotive industry. Lidar sensors can dramatically improve vehicles’ advanced driver assistance systems (ADAS).
For example, many consider Tesla to have one of the industry’s most advanced ADAS systems. But the company has a persistent problem with vehicles crashing into stationary objects – sometimes with fatal results. Lidar is better than cameras or radar for detecting stationary objects, so adding lidar to cars can prevent many of these crashes, while making ADAS systems more convenient for drivers.
Until now, lidar was considered too expensive for the car market, but that has begun to change, with more companies promising lidar sensors costing less than $ 1,000 in the next few years.
Ouster aims to have its ES2 sensor ready for mass production in 2024. The company says that it will initially cost $ 600 in volume, with the price falling to $ 100 in subsequent years.
Ibeo has not announced a price for IbeoNext, but the company says that it has already entered into an agreement with Great Wall Motors, a major car manufacturer in China, to start volume production in 2022.
Companies with non-VCSEL lidar designs are also rushing into this market. One of the most prominent is the Luminar, which announced a deal with Volvo in May. Volvo aims to have cars with Luminar lidar available in 2022.
These designs have different strengths and weaknesses. So far, Luminar’s lidar has boasted of longer range – as much as 250 meters. This is possible because Luminar uses lasers with a wavelength of 1550 nm – far beyond the visible light range. The liquid in the human eye is opaque to 1550 nm light, which means that Luminar’s lidar can use much more laser power without creating an eye safety hazard. Luminar’s lidar also offers a wider field of view than Ouster.