 Hi, welcome to the cover glass selection video for our direct time of flight sensors. I am Russell Wong, and in this video I will walk you through the critical step of picking the right cover glass for integrating our time of flight sensors into your application. Typically, our time of flight ranging module is used in conjunction with a window covering or cover glass. The cover glass serves the main purpose of providing physical protection to our time of flight sensor module. The cover window can be opaque with either one or two unpainted apertures to permit IR light to be emitted and received. The cover glass can be darkened to visible light, but should be still transparent to 940 nanometer invisible light. The cover glass must fulfill some optical and mechanical requirements in order to guarantee the optimal ranging performance. Let's focus on the optical requirements first. The two quality metrics are haze and transmission. Embedded particles, holes, and other rough surfaces are major contributors to light scattering in cover glass. In order to minimize the haze, an ideal cover glass window should have no structural defects in the plastic or glass material. No surface particles, defects, smudges, or fingerprints that could scatter light. Anti-reflectance coatings are not recommended. The fingerprint coatings have negative effects, but they might be better than the fingerprints themselves. Also cover glass transmission should be more than 90% in near IR in order to ensure the optimal ranging with the IR emitter and the receiver. There are also mechanical guidelines to be followed. 1. Small air gap. Less than 0.5mm will be perfect. 2. Consistent cover glass. One millimeter is a good thickness. 3. Consistent cover glass material with a tight tolerance on haze and thickness. And lastly, for optimal performance, the cover glass should be parallel to VL53 time of flight sensor. If it is not possible with industrial design to have a small air gap of less than half a millimeter and a cover glass thickness of one millimeter, then it is essential to place a gasket, a small piece of foam or rubber, between the top of our device and bottom of the cover glass, filling the space between the two surfaces. You need to put two holes or openings in your gasket, one for the emitter and one for the transmitter, to guide photons from the transmitter to the receiver. This gasket reduces undesired signal reflection off of the cover glass, which is called crosstalk. Crosstalk is an issue that can occur when placing a cover glass on top of our time of flight devices. So what is crosstalk? The crosstalk is defined as a signal from the emitter that takes a wrong path and gets into the receiver. The red line shows the undesirable crosstalk path. The green line in the figure shows the intended optical path. In this case, light is emitted from the VIXL, hits the target, and is received in the SPAT array, resulting in the correct distance reading. When a cover glass is introduced, the photons can reflect off of the cover glass, buzzing between the device and the cover glass multiple times before traveling to the receiver, which will read at a very short distance instead of the total range. Our time flight sensors can tolerate and in some cases compensate for a certain amount of crosstalk, but the crosstalk needs to be minimized in order to ensure the optimal performance of the device. Our aim in this presentation was to show you the best cover glass properties that will give you the least amount of crosstalk, but on top of that, you need to do calibration in order to get rid of the remaining crosstalk. The gasket helps to prevent the photons from following the red path. In this figure, we show the effect of the cover glass on ranging. The green dotted line is the ideal. The red line is what happens when you add a poorly selected cover glass, and the blue line is what happens when you have a very poor cover glass. The worse the quality of the cover glass, the higher the air at longer distances. Once the crosstalk is quantified, crosstalk compensation can be applied through the calibration procedure. Crosstalk compensation is a feature embedded in the APIs for all ST time flight sensors. With our newer histogram based time flight sensors, the crosstalk issue disappears at longer distances, but you will need to account for it. For more on crosstalk characterization and the calibration process, please refer to the API user manual for the sensor you are using, as well as the additional videos on cover glass, crosstalk, and calibration. In conclusion, there are both optical and mechanical considerations in order to pick a correct cover glass for your time flight sensor. When it comes to the optical characterization, the clear cover glass with optical transmission of 90% or higher is recommended. The cover window must pass through the IR light at 940 nanometers. Any loss of signal will directly affect the VL53L5CX performance. Choose a smooth cover glass with low haze. Haze is a measurement of roughness and particle inclusion in the glass. Factors for both transmission and haze should be provided by the cover glass vendor. Choose a cover glass material made of glass or plastic with no anti-reflectance coating. Dirt, smudges, fingerprints, grease, dust, water, or anything that can be on top of the cover glass will increase your crosstalk, avoided as much as possible. Here are some mechanical considerations. Tight air gap. The closer the glass is to the sensor, the better. Try for an air gap of less than one millimeter. Parallel. Try to keep the glass parallel to the sensor. Thin cover glass. The thinner, the better. One millimeter is a good thickness for cover glass. For more information and application support for VL53L5CX or any of our time flight sensors, please refer to st.com slash time of flight. And remember, our technology always starts with you.