A military outpost needs radar data from a hilltop 3 kilometers away. Radio jammers are active. Copper cable is impossible. Fiber is the only option—but the radar speaks RS232.
A factory floor has five VFDs running conveyors. Every time a motor starts, RS485 data from nearby temperature sensors turns to garbage. The control room is 200 meters away. Fiber is the only way to get clean data.
An MRI room at a hospital has a strong magnetic field. Nothing with metal can go inside. The MRI machine outputs status data over RS232 to a monitoring room outside. Fiber carries the signal—no metal, no interference.
In a park we need to control 20 cameras that can move around called PTZ cameras using RS485 signals from 1.5 kilometers away. The problem is that at such a distance and with so many devices the signal gets weak.. If we use fiber it works.
These four situations are all different but they have one thing, in common: they all need something called a serial to fiber converter. We need this because serial signals have two problems. They cannot go very far and they get interrupted easily. Fiber solves both of these problems.
The Market Reality
The global fiber media converter market was valued at $2.1–2.5 billion in 2024, growing at 8–10% annually . Industrial applications account for 35–40% of that demand, driven by the need to extend serial networks beyond copper limits and eliminate electromagnetic interference. According to field data, 20–30% of serial communication failures in industrial environments are traced to electrical noise from motors, VFDs, and high‑voltage lines .
A serial to fiber converter replaces the copper cable with glass. The electrical signal at one end becomes light, travels kilometers, and emerges as clean electrical signal at the other end. The devices at both ends don’t know anything changed.
Military: Field Communication, 3km to an Outpost
The scenario
Command post in a base. An outpost on a hill 3 kilometers away. Open terrain, no obstacles, but electronic jammers are active. Radar data from the outpost needs to reach command in real time.
The problem
- RS232 stops at 15 meters. Not possible.
- Wireless can be jammed or intercepted. Too risky.
- Burying fiber in the field? Not in a combat zone.
The solution
Two VT-FB820 units. One at the outpost, connected to the radar’s RS232 port and to fiber. One at command, fiber in, RS232 out to the computer.
Fiber is really good at ignoring interference. It is also very hard to tap into fiber. For example fiber can easily send signals over distances. Three kilometers is not a deal, for fiber.
Why FB820 instead of FB810?
Field environments are really easy to work with because they do not need any network configuration. You can just plug them in. They will work right away. This means there is one step for you to do and one less thing that can go wrong with the Field environments.
Industrial: VFD Interference, Garbled Data
The scenario
A factory floor with five VFDs controlling conveyors. Each VFD has an RS485 temperature sensor next to it. Sensor data needs to reach the control room 200 meters away.
The problem
When the VFDs start the electromagnetic interference messes up the RS485 communication. The data gets. Sometimes it is completely gone. This happens because the VFDs and the RS485 communication are not working together. The VFDs are causing problems, for the RS485 communication.
The solution
One converter per sensor. RS485 from sensor to converter, converter to fiber. Five fibers run to the control room, each connected to another converter, then RS485 to the monitoring computer.
Fiber completely isolates the signal from electrical noise. VFDs can run at full speed; data stays clean. According to the TIA/EIA‑485 standard , RS485 is rated for 1,200 meters, but that assumes a clean environment. In practice, interference is often the limiting factor.
Fiber completely isolates the signal from electrical noise. VFDs can run full speed, data stays clean.
Another option
If the data is going to be on the network at some point the VT-FB810 can handle that because it has TCP/IP built in. For a connection from one point, to another point the FB820 is a better choice. The VT-FB810 and the FB820 are both options. The FB820 is easier to use when you just need to connect two things.
Medical: MRI Room, No Metal Allowed
The scenario
Hospital MRI room. Strong magnetic field—anything with metal can’t go inside. Outside, a monitoring room needs real-time status data from the MRI machine. The machine outputs data over RS232.
The problem
Regular RS232 cable has metal. Can’t go in the MRI room. Wireless might also be affected by the field.
The solution
A fiber pass-through on the MRI room wall. Inside, one VT-FB820 is connected to the MRI’s RS232 port and to fiber. Outside, another VT-FB820, fiber in, RS232 out to the monitoring computer.
Fiber has no metal. Unaffected by magnetic fields. Data flows reliably while the MRI is running.
Security: Campus Cameras, 1.5km Coverage
The scenario
An industrial park with 20 PTZ cameras spread across 1.5 kilometers. Cameras are controlled over RS485 (pan, tilt, zoom). Control room needs to reach every camera reliably.
The problem
RS485 is rated for 1200 meters, but with that many devices at that distance, signal drops. Far-end cameras are hard to control.
The solution
Instead of one long RS485 bus, use fiber. Put one VT-FB810 in each camera zone. Connect cameras to it over short RS485 runs. Run fiber from each zone back to the control room.
So why do people like the FB810? The thing is, each zone on the FB810 operates on its own. This means that the zones do not interfere with each other. If you need to access the FB810 from else later on the FB810 has an IP stack that is ready, for that.
One Technology, Three Implementation Options
Not all serial to fiber converters are the same. The choice depends on how you need to access the data.
| Type | What It Does | Best For |
|---|---|---|
| Ethernet to Fiber | Converts 10/100M Ethernet to fiber | Cameras, switches, IP devices over distance |
| Serial to Fiber (Plug & Play) | Converts RS232/485/422 to fiber; auto‑detects serial settings | Point‑to‑point extension; no network integration needed |
| Serial to Fiber with TCP/IP | Converts serial to fiber and adds TCP/IP stack; configurable IP, virtual COM support | Remote access, SCADA integration, networked systems |
The plug-and-play type automatically figures out the baud rate, parity and data bits. You just connect it turn it on. It works. No configuration needed.
The TCP/IP type needs an IP address set. Then you can access the serial device from anywhere, over a network.
The Technical Detail: A and B Ends
Single‑fiber converters (which use one fiber instead of two) come in matched pairs. One end transmits at 1310 nm and receives at 1550 nm. The other end swaps them—transmits at 1550 nm, receives at 1310 nm.
This is why they’re labeled A and B. Two A ends won’t work. When you order, get them in pairs. Mark them so you know which is which at installation.
According to ITU‑T G.652 , standard single‑mode fiber supports wavelengths of 1310 nm and 1550 nm with minimal attenuation over distances up to 40 km. This makes it the default choice for industrial and long‑distance installations.
How to Choose: Three Questions
1. Is your device serial or Ethernet?
- Ethernet (cameras, switches) → VT-FB800
- Serial (PLC, meter, controller) → keep going
2. Do you need network access?
- Just need point-to-point, no IP required → VT-FB820
- Need remote access, SCADA integration → VT-FB810
3. How harsh is the environment?
All three are industrial grade: -40°C to 85°C, 9-24V DC, metal case. They’ll handle it.
One More Thing About A and B Ends
All three models come in A and B versions. They work in pairs—one A and one B. Two As won’t talk to each other.
The wavelengths are swapped:
- A end: transmits 1310nm, receives 1550nm
- B end: transmits 1550nm, receives 1310nm
When you order, get them in pairs. Mark them so you know which is which at installation.
One Last Thing
Serial to fiber isn’t new. But the reasons industries use it haven’t changed: distance and interference are still the two things that break serial networks.
- Military needs reliability and immunity to jamming.
- Industrial needs to solve interference from motors and drives.
- Medical needs isolation from magnetic fields.
- Security needs distance and manageable zoning.
If your situation matches one of these, the solution is the same: a pair of serial to fiber converters, a fiber cable, and a clean signal at the other end.
