Why can optocouplers effectively suppress sharp pulses and various noise interferences?

http://sop-4-optocouplerThe reason why optocouplers can effectively suppress sharp pulses and various noise interferences while transmitting signals, and greatly improve the signal-to-noise ratio on the channel, is mainly due to the following reasons:
(1) The input impedance of the optocoupler is very small, only a few hundred ohms, while the impedance of the interference source is relatively large, usually 105-106 Ω. According to the principle of voltage division, even if the amplitude of the interference voltage is large, the noise voltage fed to the input terminal of the optocoupler will be very small, and only a very weak current can be formed. Due to insufficient energy, the diode cannot emit light, which is suppressed.
(2) There is no electrical connection between the input and output circuits of the optocoupler, nor is there a common ground. The distributed capacitance between them is extremely small, and the insulation resistance is also very high. Therefore, various interference noises on one side of the circuit are difficult to be fed to the other side through the optocoupler, avoiding the generation of interference signals caused by common impedance coupling.
(3) Optocouplers can provide excellent safety protection, even when external devices malfunction or input signal lines are short circuited, they will not damage the instrument. Because the input and output circuits of optocoupler devices can withstand high voltages of several thousand volts.
(4) The response speed of optocouplers is extremely fast, with a response delay time of only about 10 μ s, making them suitable for situations where high response speed is required.