Time of Flight Cover glass

[John E KVAM]

What can you tell me about the cover glass used to protect the Time-of-Flight sensor and the electronics?A coverglass is used to protect the electronics, but because the ToF sensors have to see through it, there are several considerations.
There is an AppNote AN4907. the information focuses on the VL53L0X although all the information is applicable to all the ST ToF sensors.
AN5231  is also a good resource for the VL53l1X.
The basic problem is that not all the light penetrates the 'glass' and hits the target. Some of the light enters the coverglass, only to reflect back to the sensor. This is called 'crosstalk'. And it has to be managed, or one gets the wrong answer.
There are also some videos on the subject:
VL53L1X Dirty Cover Glass - is for the VL53L1X, although similar videos exist for the 6180 and VL53L0X.
Cover Glass selection for your ToF
The basics are these:

•Qualities that make a good coverglass are:

•Clear – transparent to 940nm light.

•Glass, Acrylic, PMMA and polycarbonate (PC) are good choices.

•Close – The closer the glass is to the sensor the better.

•Try for an air gap of less than 1mm.

•Parallel – try to keep the glass parallel to the sensor

•Thin – The thinner the better.

•1mm is a good thickness.

•Smooth – the texture of the glass should be flat as possible - haze

•Clean – Fingerprints and dirt will make things difficult.

•Consistent – Glass quality and air gaps should be consistent.

Each design is different, and requires a different solution. If a coverglass has to be thick for some reasons, then the other parameters have to be better to compensate. All the parameters above are additive, so being less than perfect on a couple is not bad, but one cannot ignore them all.