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LIDAR & Direct Time of Flight

LIDAR & Direct Time of Flight

LIDAR (Light Detection and Ranging) is a sensing technology for remote object detection and ranging, using a light source and receiver. Emitted light pulses hit objects, reflect, and return to the LIDAR system where the receiver detects the returning light pulse.

The time between sending and receiving a light pulse is dependent on the distance between the LiDAR system and the object. Knowing time allows you to calculate distance. The most straightforward implementation of this principle is Direct Time of Flight, or dTOF. The system emits short pulses of Near Infrared light. A portion of that energy is returned and converted in distance and optionally intensity and ultimately speed. By taking many samples, it is possible to filter out noise (detected light not being a reflection of the emitted pulse).

 

Flash vs. Scan

Flash vs. Scan

A LiDAR system can observe the complete field of view (FOV) at once, called Flash systems. Flash typically works well for short to mid-range (0-100m), and by capturing the complete scene at once also objects with high relative speeds can be detected properly. Another implementation is to focus on a subset of the FOV, consequentially look at the next subsets, until the complete FOV is covered, called Scanning. Scanning can focus the light on the subset instead of the full FOV, and therefore can do object detection at a longer range compared to Flash.

As a scanner only takes one subset of the FOV, it needs some steering principle to move the light beam from subset to subset. Current systems typically use a mechanical beam steering principle; either by rotating the complete sensor head (spinning LIDAR), or using mechanical components inside the sensor (Polygon mirrors, MEMS mirrors). More and more industry players acknowledge the risk these mechanical parts fail and therefore look for beam steering principles without any moving parts, or true solid state. 

Light Sources - VCSEL's

Light Sources - VCSEL's

ams supplies LIDAR systems with specific light sources, called VCSEL’s (Vertically Cavity Surface Emitting Laser). These VCSEL’s offer specific advantages over other types of light sources as for instance Edge Emitter Lasers:

  • A narrower wavelength bandwidth (especially over temperature) allows for more effective filtering at the receiver, resulting in improved signal to noise ratio.
  • Emitting a vertical cylindrical beam, the integration into the system is more straightforward.
  • As a VCSEL array typically comprises of 50-10k of individual emitters, the impact of a single emitter failure is much more limited compared to a typical EEL having just 1-3 emitters.

 

ams as leading VCSEL Supplier

ams as leading VCSEL Supplier

  • ams is the industry leader when it comes to VCSEL array power density, conversion efficiency and pitch
  • ams’ VCSEL manufacturing technology allows for great flexibility in layout design as number of pixels, their size and pitch, and common anode/ cathode vs. specific addressability patterns (row, column, section)
  • Leveraging 20 years of automotive experience (including ISO 26262), a significant footprint in 3D consumer electronics, and capabilities to co-develop emitter, current driver and optics.