Suggestion: Promote Use of Retroreflectors for Enhanced VL53L Sensor Performance

[hgraminho]

Dear STMicroelectronics team,

I would like to suggest including references in your documentation—such as datasheets, application notes, or user manuals—for the VL53L family of time-of-flight range sensors regarding the use of retroreflective surfaces as a technique to enhance signal return levels in feasible applications.

In my experience across multiple VL53L-series devices, even small retroreflective tapes can greatly improve signal strength and extend the usable range, often surpassing performance obtained with standard Lambertian white targets. These retroreflectors significantly improve accuracy and reduce noise, especially at longer distances, where standard targets often yield weaker and noisier returns.

Unfortunately, many users and reviewers are unaware of this option, possibly due to the current documentation emphasizing only white diffuse targets as the ideal case. This can lead to underestimating the sensor’s true potential and, in some cases, favoring less suitable alternatives such as ultrasonic sensors.

Additionally, I’d like to suggest that your firmware or API could be expanded to allow for extended-range operation in situations where signal strength remains sufficient—even beyond the standard maximum distance—potentially limited today only by phase ambiguity rather than actual signal loss.

By acknowledging and supporting retroreflective materials as a design option, you can help product developers unlock the full potential of these sensors, especially in controlled environments where such enhancements are easy to implement.

Thank you for your excellent work and for considering this suggestion.

[John E KVAM]

Retroreflective tape is amazing stuff. 

For those who do not know, think those yellow stripes on safety vests - or stop signs. Light that hits this tape is sent back in exactly the same direction it came. 

And you are right in that it greatly extends the distance the sensor can 'see'. When used with the VL53L1CB or the VL53L4X, the sensor will detect a target up to 8 meters away. 

The only issue with this stuff is something called radar aliasing. (Google it for more info.) 

The Time of Flight sensors have a pulse repetition interval. And as we'd like to make as many pulses as possible, we allow enough time for the light to go out to 4meters and return. Then we send another pulse. 

But with a bright target (or a retroreflective one) we will have plenty of light with a target at say 6 meters.  

And that leads to an ambiguity. The light from pulse N goes out and does not come back until the pulse N+1 has been sent. As the photons are not marked, the returning photons get associated with the most recent pulse.

So our 6M target will come back as a 2M target because it's 2M past the 4M maximum. 

But we know this can happen and we use it to our advantage. 

We use a second, different pulse repetition interval. And this has a maximum of 4.8 meters as it's wrap point. 

Thus, our 6M target returns 2 meters with the first PRI and 6M - 4.8M= 1.2M for its second PRI.

We analyze this and knowing the ratio between the two, we can 'unwrap' the data and get the 6M distance. 

However, if you try hard enough - and use this material - you can get to the second wrap point. But it's way out there.  Not something to worry about, but do keep it in mind if distances beyond 8 meters are likely. 

(And the sensor does warn you if it detects a target beyond 8 meters.)