According to the speed formula: c=d/t, c is the speed of light, d is the distance, and t is the time. Then we measure the time the light takes between sending out and returning, and multiplying that by the speed of light is the distance.
But we know that the speed of light is 3x10^8m/s. For such a fast speed of light, the time measurement accuracy needs to reach the picosecond level, which requires the electronic timer to have a clock frequency of hundreds of GHz. Such a high frequency and precision make the measurement device expensive and difficult to manufacture, so we have sought a low-frequency measurement method.
Let's look at another speed formula: c=λ, c is still the speed of light, λ is the wavelength, and it is the frequency. Now, we modulate the light source into a sine pulse wave. When the light wave encounters the target object, it is reflected, and then the sensor is used to receive the reflected sine wave. At this time, the sine wave will produce a certain phase shift, and this phase shift is Can be used to calculate the distance the waveform travels.
The above figure is used to assist the explanation, which is the modulation frequency. The blue line represents the light wave function when it is emitted, and the red line represents the light wave function when it returns. There is a phase angle difference φ between them. Then use the phase angle with the formula: d=c φ /4π can calculate the distance between the object and the ToF deep-sensing lens.