Many hardware personnel around these components will be familiar with the equipment used as switches and use at least three terminals to achieve this, one input, one output and one door. The typical devices that come to mind are bipolar transistors, triodes and old triode valves. Can a diode be used to switch signals even if there are only two terminals? Of course, and this is a proven and reliable technology, which is very common in test equipment and circuits that process RF signals. (video, embedded below.)
The trick is that the diode blocks the current in one direction, but allows the current to flow in the other direction, which is deliberately indicated by obvious symbols. Therefore, the DC signal cannot move upstream, but the AC signal is not. The signal can pass through the diode “in the wrong way”, causing small fluctuations in the current. In other words, if the diode is biased to on, the change of downstream voltage level will cause the current flowing through the diode to change, and the (smaller) AC signal will pass through. But if you remove the bias and turn off the DC bias voltage source, the diode will switch back to the non-conductive state and block the signal. This makes the diode a DC control switch for AC signals.
Although [imsai guy] proved this with a signal diode, as he explained, people usually use a pin diode, which has an additional inherent (undoped) region between P and N, allowing the device to be completely shut down, thereby significantly reducing leakage.
Of course, we have introduced diodes many times from different angles. There are always some things to learn. Check how high voltage diodes are constructed, diodes detect ionizing radiation, and finally this great series of our favorite two terminal devices.
Look, the simple diode is interesting after all!