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to travel from the sensor to a remote object and to return to the sensor. The range R of the
detected object is deduced from the measured full round-trip time T of the light pulse using the
simple relation R = c T / 2 n, where c is the speed of light in vacuum and n denotes the refractive
index of the medium in which the light pulse propagates.
Depending on the characteristics of the target’s surface, the light pulse is either absorbed,
totally reflected, or reflected diffusely. This causes different irradiances of the echo pulse at the
receiver, which are measured by the Leddar sensor. This measured irradiance depends on the
distance measured by the ToF principle and the angle of incidence that can be determined by
imaging-collecting optics that focus the reflected beam on the sensor’s photodetectors.
A 16-element photodetector is typically used in Leddar sensors (shown in Figure 1).
Figure 1. Signal travelling through the main components of a Leddar sensing module
Beam Pattern
The multiple-element photodetector has a rectangular sensing area. The purpose of the
emission optics of a Leddar sensor is to direct as much of the emitted light from one or more
LEDs into a pattern that best fits the photodetector geometry. The purpose of the reception
optics is to collect the backscatter of light from objects in that beam onto the photodetector.
The combined emission and reception optics solution can be designed to obtain different beam
widths. LeddarTech currently offers optics options with beam widths of approximately 3°, 9°,
18°, 24°, 34°, 45° and 95°. Figure 2 illustrates a simulated emission beam pattern of a Leddar
sensor with an overlay of the matching segments provided by the reception optics
corresponding to the photodetector elements.
Figure 2. Emission beam pattern and match to a 16-element photodetector