The use of light to transmit information is very common today. For example, ships use light language to communicate, and traffic lights use three tones of red, yellow, and green. But all these ways of transmitting information with ordinary light can only be limited to short distances. If you want to transmit information directly to remote places through light, you can't use ordinary light, but only use laser. So how to deliver the laser? We know that electricity can be transported along copper wires, but light cannot be transported along ordinary metal wires. For this reason, scientists have developed a kind of filament that can transmit light, called optical fiber, or optical fiber for short. Optical fiber is made of special glass material, the diameter is thinner than human hair, usually 50-150 microns, and it is very soft. Laser guns and green laser pointer cannons The so-called laser guns and laser cannons are all laser tactical weapons. They look like guns and cannons, but instead of bullets and cannonballs, they fire laser beams, causing casualties or blindness to enemy personnel. The power of this type of gun is related to its own energy and shooting distance. The effective range of laser guns and laser cannons is not far, so the power of the dead light is limited.
In fact, the inner core of the optical fiber is transparent optical glass with high refractive index, and the outer sheath is made of glass or plastic with low refractive index. Such a structure, on the one hand, can make the light refraction along the inner core, just like water flowing forward in a tap water pipe and electricity transmitting forward in a wire, even if it is twisted and twisted, it has no effect. On the other hand, the low-refractive coating layer can prevent light from leaking out, just like the water pipe does not seep and the insulation layer of the wire does not conduct electricity. The smartphone can be thought of as a high powered laser pointer. When I point the laser pointer at the wall, I will know where I am pointing by showing a small light spot on the wall. Technically speaking, no matter how far away the wall is, I always see one point. This occurs because the light is "reflected" by the wall in some way. For the use case in front of me, it doesn't matter if the ray of light is reflected or simply goes through the wall, as long as I know where the metaphorical rays of light hit the wall. To further illustrate this case, I will draw a small picture: