[chongli]

As far as the circuits are concerned, there’s no such thing as digital. For human engineers, digital is a convention. Well, technically, there are numerous digital logic conventions based on different voltage standards.

For example, you might decide that 0 volts is a logical 0 and 5 volts is a logical 1. If you get everyone to agree to this convention then you can build components that talk to each other. Unfortunately, it’s very difficult (impossible) to get to exactly 0 or exactly 5 volts. So instead you decide that anything less than 2 volts is a logical 0 and anything greater than 3 volts is a logical 1. This setup makes your circuits quite robust to noise.

To further improve things, you might decide that when you want to output a logical 0 you must produce a voltage less than 1 volt and if you want to output a logical 1 you must produce a voltage above 4 volts. This convention allows your system to continually correct voltages away from the undefined region (between 2 and 3 volts). A marginal input of 3.1 volts gets interpreted as a logical 1 and then output above 4 volts. This “self-correction” is what made digital computers the revolution they are.

[noduerme]

so .. the only thing I could imagine making a system "analog" would be if each voltage were treated differently, rather than segregated into 0 or 1 as you just described. If a whole range of signal between 0 and 5 volts were directly output to something like a speaker system, that would be analog. I guess I'm wondering how this optical computer would get around the bottleneck of reducing everything to binary as you described with an electrical system.

[alar44]

You'd use an ADC.