This is a rich topic that includes many interesting side stories. This post is only introductory.
The optophone uses light and detection to translate printed type into sounds. To get the flavor, jump to 3:00 at the youtube link below:
While the early implementation was not a huge commercial success, the technology and thinking were important.
There are four documents linked above. Two are early (1914, 1920) and two are relatively modern. The Jameson article is fascinating.