Definition of indirect time-of-flight

Meadowlark Optics - Wave Plates 6/24 LB 2024

Photonics Dictionary

indirect time-of-flight: Indirect time-of-flight (iTOF) is a method used in 3D imaging and depth sensing to measure the distance to an object based on the time delay between the emission of a light pulse and the detection of its reflection, without directly measuring the time-of-flight of the light pulse itself. Instead, iTOF systems employ phase-shift measurement techniques to indirectly determine the phase difference between the emitted and received light signals, from which the distance to the object can be inferred.

Light source: iTOF systems typically use a modulated light source, such as a laser diode or LED, that emits continuous or modulated light signals with a known frequency or phase.

Modulation and demodulation: The light signal emitted by the source is modulated with a sinusoidal waveform, either by directly modulating the intensity of the light source or by using an external modulator. When the modulated light signal interacts with the object surface and reflects back to the detector, its phase is shifted relative to the emitted signal due to the object's distance and the phase delay incurred during reflection.

Phase measurement: The iTOF system measures the phase difference between the emitted and received light signals using phase detection techniques. This phase difference, often expressed in terms of radians or degrees, corresponds to the round-trip time delay of the light signal and can be used to calculate the distance to the object.

Distance calculation: The distance to the object is determined based on the measured phase difference, the wavelength of the light signal, and the modulation frequency or phase. By applying trigonometric relationships or phase-shift equations, the iTOF system calculates the object's distance from the phase difference between the emitted and received signals.

Applications: Indirect time-of-flight imaging is used in various applications requiring accurate depth sensing and 3D imaging, including robotics, augmented reality, gesture recognition, automotive lidar, industrial automation, and indoor navigation. It offers advantages such as high measurement accuracy, long-range capability, and robust performance in challenging lighting conditions.

Advantages: iTOF systems are less susceptible to ambient light interference and background noise compared to direct time-of-flight methods. They offer improved performance in outdoor environments and dynamic scenes where ambient light variations and object motion can affect depth measurements.

Overall, indirect time-of-flight imaging provides a reliable and efficient approach for capturing 3D spatial information, making it a valuable technology in numerous applications requiring precise depth sensing and object localization.