LightCode Photonics’ active solid-state 3D cameras are based on the direct Time-of-Flight (dToF) measurement principle and incorporate an additional 2D RGB camera for high-confidence computationally efficient object detection applications either as a standalone solution or as a part of a 2D/3D fusion perception system.
LightCode Photonics’ cameras are based on direct ToF technology, which uses a sub-nanosecond electronic stopwatch and a pulsed light source to measure the flight time of an emitted and subsequently detected pulse (Figure 1), eliminating the need for computationally heavy processing. Due to the speed of light, the device measuring the arrival time of a photon must have a timing resolution of <1 nanosecond as it affects the accuracy of the distance measurement. Advances in photodetector technology have given rise to highly sensitive silicon-based photodetectors – SPADs. SPAD temporal response (timing) properties are suitable for dToF-based 3D imaging systems, and the detector’s single-photon sensitivity allows for increased detection ranges and a higher probability of detection.
Having the transmitted laser pulses as short as possible is beneficial as it increases the range detection accuracy and different objects within the field-of-view of one pixel are better resolved along the depth axis. In addition, having shorter pulses with high peak power increases the signal-to-noise ratio over ambient background noise as the laser pulse reflections appear as more prominent peaks in the detected signal. In contrast, the time-averaged power of the laser is kept low ensuring compliance with laser safety standards. LightCode has patent-pending technology for creating sub-nanosecond laser pulses from VCSEL diodes, which are several times shorter than the competitor systems. Direct ToF technology is typically employed in the form of scanning 2D and 3D LiDARs and is rare among 3D cameras.
Figure 1. Direct ToF detection utilizes a high-speed electronic timer which is initiated simultaneously with a narrow pulse width high-peak light pulse emission. Emitted light pulse scatters on different objects on the scene and reflects back to the receiver side of the sensor, where the light pulses are registered and linked to the flight time. As the speed of light in various conditions is known, the distance between the camera and the target object can be calculated as D = (T * c) / 2, where D is the object distance, T is the measured flight time and c is the speed of flight.
Time Correlated Single Photon Counting
Figure 2. Photon timing histogram acquired with TCSPC for Figure 1. A dToF receiver can differentiate return pulses from many different objects in its Field-of-View (FoV) as long as the temporal resolution of the system is sufficient and an adequate amount of light is reflected from objects. In this case, up to three peaks are distinguishable from the background signal.
RGB + Depth data
Figure 3. Illustrative image with RGBD data, where each color block represents the object distance with respect to the LightCode's camera, with blue being the closest and red the farthest object.
Medium-range 3D dToF camera designed for indoor service robotics including features like simultaneous dual-resolution output and multiple returns.
Upcoming generations of TrueSight 3D cameras include outdoor operation, increased range, and field-of-view, and significantly reduced form factor.