Edmund Optics uses cookies to optimise and enhance the features and content on our website. By continuing to use this website, you consent to our use of cookies.

  • My Account
  •   
High Reflectivity Mirrors

Seeing Around Corners Using Lasers and Imaging

 

Captures images of objects around corners and behind obstacles

 

Light scattered back off of hidden target used to reconstruct a 3D model of the target

 

Involves scattering laser light off of surrounding objects onto a hidden target

 

Many potential benefits for autonomous vehicles, public health, and medical imaging

A direct line of sight between an object and a camera or detector is typically needed for every imaging application except for extreme cases such as light bending due to gravitational lensing in astronomy. But for the most part, imaging applications are limited to light propagating in a straight line. However, that is starting to change as some cutting edge research is opening up possibilities to image around corners and around obstacles. A combination of lasers, sensitive cameras, and computational reconstruction methods can be used to detect objects hidden by obstacles by scattering light off of surrounding objects.

The Future is Just Around the Corner

The process for non-line-of-sight imaging is similar to that of LiDAR (light detection and ranging), where a laser pulse is sent towards an object and the time-of-flight of the light scattering back off of the object is used to measure the distance between the object and a detector. However, non-line-of-sight imaging images objects obscured by obstacles by adding another scattering event to this process.1

3D printed mechanics used for prototyping
Figure 1: To image a hidden target obscured by some obstacle, ultrafast laser pulses are sent towards an object, such as a wall, near the target
3D printed mechanics used for prototyping
Figure 2: The laser pulse hits the wall, or other object near the target, and scatters off of it. This scattered light propagates towards the hidden target
3D printed mechanics used for prototyping
Figure 3: This light then scatters a second time off of the hidden target and propagates back towards the wall. The highly sensitive camera detects this secondary scatter as it hits the wall. A 3D model of the hidden target is formed by repeating this process for many different laser positions on the wall

Reconstructing a Model of the Hidden Target

Highly sensitive cameras such as single-photon avalanche photodiode array cameras are needed to measure the propagation of picosecond and femtosecond pulses of light in real time. The detector receives two different return signals: an initial signal of light scattered directly off of the wall and a secondary signal of light scattered off of the target, which is the signal used for non-line-of-sight imaging. This time-of-flight information is then used to reconstruct a series of ellipsoids that all overlap at a given point on the hidden target, allowing computational software to calculate the distance between the camera and the hidden target and recreate a 3D model of the target.

A 3D object can be broken down into a collection of many individual points that scatter light. The summation of all of these points can reconstruct a model of the original object. If the detector can distinguish return pulses with a temporal resolution of 100ps, this corresponds to a spatial resolution of points on the hidden target of approximately 1.5cm. 1

3D printed mechanics used for prototyping
Figure 4: Illustration of how non-line-of-sight imaging generates a 3D model of an obscured object by summing up a series of points determined through the process described in Figures 1-3

Real World Applications

Autonomous Vehicles

Autonomous Vehicles

Allow cars to sense approaching vehicles or pedestrians around corners before they are in the car’s direct line of sight2

Public Safety

Public Safety

Let law enforcement, firefighters, and emergency medical services detect presence of people in dangerous situations from a safe distance2

Medical Imaging / Microscopy

Medical Imaging / Microscopy

Investigate small 3D structures hidden from the system’s direct line of sight2

The Future of Non-Line-of-Sight Imaging

Taking this emerging technology and creating a practical solution for real-world use that is portable and not dangerous to observer’s eyes is extremely challenging. One of the main issues with non-line-of-sight imaging is the limited amount of light that makes its way back to the detector, which must be able to pick up this very small amount of light and differentiate it for any ambient light sources. The return signal to the detector is the result of two consecutive scattering events, leading to an extremely high loss. Return signals can be as low as one photon per laser pulse.1

However, the Stanford Computational Imaging Lab has developed a non-line-of-sight imaging system that works outdoors under indirect sunlight.2 They successfully imaged an object made out of retroreflective tape that was obscured by a wall, which bodes well for the future of this technology.

The lab of Aristide Dogariu of University of Central Florida is investigating non-line-of-sight imaging utilizing the spatial coherence of light hitting a wall instead of laser light scattered off of that wall and the target behind it.3 This could lead to modeling of the hidden target without requiring ultrafast laser illumination, making real-world applications of the technology more portable and easy to use.

More development is still needed before non-line-of-sight imaging technology becomes available in practical commercial systems, but it is a promising solution for the next generation of imaging applications.

References

1. Faccio, Daniele. “Non-Line-of-Sight Imaging.” Optics and Photonics News, vol. 30, no. 1, Jan. 2019, pp. 36–43.

2. M. O’Toole, D.B. Lindell, G. Wetzstein, “Confocal Non-Line-of-Sight Imaging Based on the Light-Cone Transform”, Nature, 2018.

3. Batarseh, M., et al. “Passive Sensing around the Corner Using Spatial Coherence.” Nature Communications, vol. 9, no. 1, 2018, doi:10.1038/s41467-018-05985-w.

Non-Line-of-Sight Imaging at Edmund Optics®

Edmund Optics® (EO) designs and manufactures imaging lenses and ultrafast laser optics, which are both used in non-line-of-sight imaging systems.

FAQ's

FAQ  Does EO sell full systems for non-line-of-sight imaging?
No, this technology is still largely limited to research settings and EO doesn’t sell non-line-of-sight imaging systems. However, EO does sell imaging lenses and ultrafast laser optics, which are components used in non-line-of-sight systems.
FAQ  Doesn’t the laser light initially scattering off of the wall overpower the secondary scatter of light off of the hidden target?

The light scattering directly off of the wall is much stronger than the secondary scatter of light off of the indirect object, but there is a time delay between them that allows highly sensitive detectors with a high enough temporal resolution to differentiate the two signals.2

FAQ  Once the time delay for the secondary scatter off of the hidden target is captured, how does the computational reconstruction software recreate a 3D model of the object?

The software first stores all measurements in a 3D spatial-temporal volume. It then resamples measurements along the time axis, convolves the result with an inverse filter in the frequency domain, and resampling result along depth axis to recover the hidden object.2

FAQ   How long does it take to reconstruct a 3D model of the hidden target after acquiring the data?

The Stanford Computational Imaging Lab’s non-line-of-sight imaging procedure only takes 0.5s to generate the 3D model.2

Resources

Application Notes

Technical information and application examples including theoretical explanations, equations, graphical illustrations, and much more.

Ultrafast Lasers – The Basic Principles of Ultrafast Coherence
Read  

LIDT for Ultrafast Lasers
Read  

 

Contact Us

What limitations do you face today in your optics applications? What are the next problems that you need to be solved? Contact us today to work with our team of engineers to discover solutions to your application questions.

 
Was this content useful to you?

Need a Quote?

Edmund Optics Facebook Edmund Optics Twitter Edmund Optics YouTube Edmund Optics LinkedIn Edmund Optics Instagram

×