How 10 leading companies are trying to make powerful, low-cost lidar

#News(IoTStack) [ via IoTForIndiaGroup ]

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The three big factors that distinguish lidar sensors
Beam-steering technology: Most leading lidar sensors use one of four methods to direct laser beams in different directions
• 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..
• 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.
• 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.
• 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.

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.
• 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.
• 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.

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