Angle-Dependent Crosstalk Between Two Adjacent VL53L1X Time-of-Flight Sensors

Abstract

Time-of-flight ranging sensors mounted side by side can disturb one another, but we found no published measurement of how this depends on the angle between them. We measured the extra ambient light one VL53L1X sensor sees when an identical neighbor 20 millimeters away also ranges, for one pair of sensors tested against a gray board at 0.3, 0.6 and 0.9 meters in two window sizes, with five repeats per setting, a divider test, and the whole sweep repeated after exchanging the two sensors. Three findings follow. First, the extra light fell to 10 percent of its peak at about 16 to 18 degrees of total angle between the sensors (half that per sensor) for a full sensor array and 8 to 11 degrees for a narrower window, and to 1 percent at about 20 to 22 and 11 to 13 degrees, growing with distance; a geometric model using the datasheet field of view overestimated these angles by three to seven degrees, and no single emitter beam angle fitted both windows. The extra light also arrived in bursts about every 1.9 seconds, consistent with unsynchronized sensor clocks, and after the sensors were exchanged the angles reproduced to within about 0.4 degrees, with the small difference in crossing angle between the two sensors following the unit, not its mounting position. Second, ranging itself was barely disturbed: a large rise in ambient rate at close range shifted the mean distance by half a millimeter or less. Third, near a sensor's acceptance threshold the neighbor widened the signal scatter and could change the share of accepted readings by up to about 20 percentage points, in either direction. A thin divider changed the effect by no more than about 4 percent in twelve of fourteen settings before the swap and fifteen of eighteen after it, consistent with, but not proof of, a shared-target path rather than direct coupling. Separating the sensors' pointing angles past this crossover is expected to remove the effect; a barrier was not shown to help, and ranging in turn, which avoids the interference by construction, was not tested.