Fiber Media Converter

Overview

A fiber media converter joins two Ethernet segments that speak different physical media: ordinary copper twisted pair on one side and optical fiber on the other. It exists because copper Ethernet is limited to about 100 m, while fiber carries the same gigabit traffic for kilometres and ignores electrical noise. This unit takes a 10/100/1000BASE-T link on its Copper RJ45 Port and bridges it to a 1000BASE-X fiber link through a pluggable optic in the SFP Fiber Port.

Everything sits on one Mainboard inside a small steel Enclosure that can sit on a desk, bolt to a wall, or clip to a DIN rail. An external adapter feeds the Power Input, a bank of Mode Switch Bank DIP switches selects how the unit behaves, and the LED Indicators report link and activity on both sides.

How it works

Frames arriving on the copper side pass through the RJ45 jack and its isolation magnetics into the copper PHY of the Switch / PHY IC. That two-port switch/PHY recovers the data, then hands it to the Media-Converter Controller, which forwards each frame to the fiber side. There a high-speed SerDes drives the SFP module electrically.

Inside the SFP Transceiver the electrical bitstream reaches the Laser Driver IC, which modulates the Laser Diode (TOSA) so it emits light pulses onto the transmit fiber. In the reverse direction, incoming light strikes the Photodiode (ROSA), whose tiny current is amplified back into clean logic levels and returned to the switch IC. The two optical fibers terminate at the module's LC connector.

The DIP switches change this behavior at the link level. They force a fixed speed instead of auto-negotiating, and they enable link-fault pass-through, which drops the copper link when the fiber link fails so the attached switch learns about the break immediately. Because the converter is a transparent layer-2 bridge, the devices at each end see one continuous Ethernet segment and need no configuration of their own.