The story is analogous to a single photon avalanche diode. As the title implies, these are delicate enough to detect a single photon. Extreme sensitivity means that they pass through different types of noise. As a result, it takes subtle post-processing to use them for software like lidar. However a major advantage of SPADs is that – like VCSELs – they are often fabricated using standard semiconductor methods, and 1000 of them can be packaged on a single chip.
The combination of VCSEL and SPAD allows for a dramatic simplification of standard lidar designs. Velodyne’s unique three-dimensional lidar mounted 64 individually packaged lasers in a column on a spinning gimbal. Each laser had a corresponding detector. The complexity of this design and the need to align each laser exactly with its associated detector was one of the reasons Velodyne’s early lidar items were so expensive.
Recently, several companies have experimented with using small mirrors to “drive” the laser beam into the scanning sample. This design requires only one laser instead of 64. However it still involves at least one shifting half.
Against this, Apple, Ouster, and Ibeo are building lidar sensors without any shifting components. With 1000 lasers on a single chip, VCSEL-based lidar can have a dedicated laser for each level within the view of the lidar. And since all those lasers are pre-packaged on a single chip, the drawing is far less complicated than in Velodyne’s original spinning design.
Current iPhones already had another 3-D sensor called the TrueDepth digital camera that enabled Apple’s FaceID feature. It additionally used an array of VCSELs supplied by Lumentum. TrueDepth works by projecting a grid of more than 30,000 points onto a subject’s face, then estimating the three-dimensional form of the person’s face, based on the best way to distort the grid’s sample. .
The iPad’s lidar sensor initiates far fewer laser dots than a TrueDepth digital camera. An iFixIt video made with an infrared digital camera confirmed the lidar projecting a grid of only a few hundred pixels. However, while the TrueDepth sampler tries to estimate depth based on the form of sunlight falling on a subject’s face, the iPad’s lidar sensor quickly measures distance by measuring how long it takes to bounce off an object and return to digital. Time consuming camera. Of course in this course each achieves higher precision in depth measurement and moreover longer variation.
Highly effective lidar additionally uses VCSEL and SPAD
The efficiency of Apple’s lidar lags behind high-end sensors purchased by specialized lidar corporations. Velodyne, the company that invented three-dimensional lidar, for its strongest lidar covers distances of more than 200 meters, while Apple’s sensors have a range of about 5 meters.
Other VCSEL-based lidars are also significantly more effective than Apple’s. For example, Auster’s strongest VCSEL-based lidar boasts a diversity of around 100 meters for detecting objects with 10-percent reflectance.
Oster’s current sensors are all Velodyne-style spinning items. They have 16 to 128 VCSELs in a row on a single chip—this chip is then mounted vertically on a gimbal spinning like the Velodyne’s objects. The simplicity of this solid-state design has allowed the Oster to undercut the Velodyne in price and certainly emerge as one of the Velodyne’s biggest rivals. However, these spinning lidar sensors from Ouster still cost $1000—too expensive to use in mainstream vehicles, to say nothing of smartphones.
Last week, Oster announced plans to ship a new solid-state lidar without any transfer components. As an alternative to arranging 16 to 128 lasers in a row like Oster’s current lidar, Oster’s new unit can accommodate up to 20,000 VCSELs arranged in a two-dimensional grid.
Ibeo is following a similar technology and may even be ahead of Ouster. Ibeo designed the first lidar shipped in a mass-market automotive—the Audi A8. That lidar was primitive, with only four strains of vertical decision. Although Ibeo is now making a new model called the ibeoNext that may feature a laser grid that measures 128 x 80 pixels—slightly smaller than Ouster’s intentional sensor but significantly larger than Ibeo’s previous options. Ibeo says its sensor can have 150-meters of variation for objects with 10-percent reflectance.
One final contender to mention here is Sense Photonics, which we covered again in January. Like the other companies we mentioned, Sense is using VCSEL and SPAD for its lidar. Nonetheless, Sense is using a method called micro-transfer printing to get its lasers out. This allows the laser to use more energy without the problems of heat and eye protection.