Better Optical Sensing with New Time-of-Flight Technology
Kagan Pittman posted on July 13, 2015 |

Remote sensing is used to gather information on an object near a sensor without making physical contact with it. Optical time-of-flight measurement calculates the distance to a target from the round-trip time-of-flight between a sensor and that target.

 

Conventional optical time-of-flight sensors fall into three categories: direct time-of-flight, range-gated imaging, and phase detection. Although a new technology, it is already widely used in a long list of applications including:

 

  • Proximity detection, volume and distance measurement for conveyor belt systems,
  • Security and surveillance,
  • Level sensing detection and ranging,
  • Vehicle detection,
  • And collision avoidance sensors in heavy machinery.

 

For example, haul trucks and other large vehicles have plenty of blind spots and as a result accidents can occur, requiring advanced collision avoidance systems.

 

LeddarTech had such a challenge, tasked with providing optical time-of-flight sensors to a collision avoidance system provider. Leddar Sensors (45 degree beam) were positioned in strategic locations across mining haul trucks. Areas ahead of and behind large wheels were then able to be constantly monitored for obstacles – all of which can be seen on a drivers monitor screen.

 

Image courtesy LeddarTech
Image courtesy LeddarTech

 How it Works

 

Leddar optical time-of-flight sensing technology is based on direct time-of-flight measurement, but rather than working directly on the analog signal, Leddar light processing starts by sampling the receive echo for the detection range of the sensor. Leddar expands the sampling rate and resolution of this sampled signal. Finally, it analyzes the resulting discrete-time signal and recovers the distance for every object in its field

Image courtesy LeddarTech

Image courtesy LeddarTech

of view.

 

Where other methods implement detection and ranging mostly through hardware, Leddar light processing utilizes complex algorithms implemented in software.

 

Through signal processing, Leddar is capable of computing an accurate distance for an object with a very weak return echo.  Using various filters, it is also able to detect objects in the presence of nuisance signals caused by dust, snow or raindrops.

 

A Deeper Look into Leddar Technology


Image courtesy LeddarTech

Image courtesy LeddarTech

Implemented in standard submicron CMOS processes, the LeddarCore maximizes performance of optical time-of-flight sensors. When combined with a photodetector, a pulsed light source and optics, it forms a complete sensor system that can be integrated into a small footprint at a low cost.

 

A photodetector is responsible for converting light pulses into an electrical signal that can be read by the LeddarCore.  This technology allows Leddar sensors to use various types of detectors including PIN photodiodes and APDs.

 

Leddar technology used with low-cost silicon PIN photodiodes can achieve a long detection range and immunity to ambient light conditions.

 

PIN photodiodes exhibit a very high linearity, allowing tiny signals to be detected even in the presence of strong incident light. Multi-element arrays, either one- or two-dimensional, can be used to build 2D or 3D sensors with fast, parallel measurement without moving parts. These sensors can be used in applications requiring rapid and accurate presence, position or speed information.

 

What are the Benefits?


1.       High Range-to-Power Ratio

Compared with other optical time-of-flight technologies, Leddar can detect at a farther range with an equivalent amount of light.

2.       Capability to detect targets in low-visibility conditions.

Since each measurement is formed from hundreds to thousands of discrete light pulses, the likelihood that the technology is able to obtain reliable measurements under environmental conditions such as rain, snow, or dust is very high. 

3.       Ability to resolve multiple targets with a single detector element.

This benefit can be fully exploited with a diffuse light source, where a small object may not fully occupy the field of view and where the distance to background objects can be simultaneously measured. 

 

Leddar is a very flexible technology that is available in complete, finished sensor modules or packed in an IC format for optimal integration into custom solutions. Originally discovered by the National Optics Institute (INO) in Quebec City, Canada, Leddar optical time-of-flight sensing technology was developed and commercialized by LeddarTech.

 

Click here to download the whitepaper.

 

More information about Leddar technology, Leddar sensor IC and modules can be found at leddartech.com

 

LeddarTech has paid a fee for promotion of its optical time of flight sensors to ENGINEERING.com. It has had no editorial input to this post. All opinions are mine. – Kagan Pitman

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