When you think of RS232, RS485 or RS422, you generally think of legacy serial communication protocols that continue to be used in a surprising number of applications. When you think of fiber optics, it's more long-distance telecommunication and networking applications that come to mind. So what do those older serial protocols, or USB, have to do with fiber optics, if anything? Turns out, quite a bit. And that's why there are fiber optic media converters, for communications projects that require both technologies.
Now just to recap, the serial RS232 communication protocol uses different voltage levels with respect to ground to go point-to-point at slow speeds and over short distances, like between a computer and a printer or a scientific instrument. RS422 uses twisted pairs for faster (and bi-directional) signals over longer distances, and it uses positive and negative and positive voltages. RS485 works like RS422, but uses an addressing scheme to talk with multiple devices. Converters and adapters are used to translate between computers and the various RS-232, RS-422, RS-485, TTL, USB and Ethernet devices. So far it's all strands and wires and making sure the leads are connected properly.
Now where do fiber optics come into play? That would be in situations where the serial communication protocols' speed and distance limitations interfere with a project. Serial communication was never meant for some of the complex applications the technology is being used today, and it has its inherent limitations: Large voltage swings, the need for positive and negative signals, and signal interference are all issues. In many applications, these issues can be addressed with fiber optics.
Fiber optics use light instead of electricity to pass along signals. This means higher speed, higher bandwidth, and inherent resistance to electromagnetic and radio frequency interference. Fiber optics is therefore a solution for systems where serial data protocols are used to communicate with remote locations. How do electrical wires communicate with optical fibers? Via fiber optics converters.
Beyond the obvious physical limitations of the various serial protocols, there are no hard rules as to when the use of fiber optics becomes advantageous or imperative. In many systems, copper-based connections exist side-by-side with fiber optic connections, with each type being used where it works best.
In terms of technology, adding fiber optics to a copper-based data communication system requires a transmitter, the fiber optic cable, and a receiver. Even though converting between electric signals and light might seem complex, fiber optic converters are generally simple to use and hassle-free in operation. Good converters are completely auto-sensing and self-adjusting, without the need for manual settings.
Also note that fiber optic converters can handle both single-mode and multi-mode. Single-mode systems use a single strand of fiber for distortion-free, high-speed long distance communication whereas multi-mode cables use less expensive multi-strand fibers that are a bit more prone to signal distortion. Each cable type requires the proper transceivers.
The point is that a lot of the limitations of RS232, RS422, RS485 and even USB and Ethernet communication systems can be addressed by including fiber optics. All the technology is freely available, and the required converters are inexpensive and mature.
