One of the simplest ways of keeping a computer system secure is by using an air gap — that is, never actually connecting the system to the network. This can often include other peripherals like USB drives and other removable storage as well, so getting information to and from secure (or compromised) systems behind air gaps can often present a challenge. But assuming you have local access to the computer and your parts bin handy, these optical solutions from [Nikolay] can allow data transfer to or from such off-line computers.
This is a companion discussion topic for the original entry at https://hackaday.com/2024/03/19/photoresistors-provide-air-gap-data-transfer-slowly/