Fiber optic technology helps move data across the world. It sends light through thin glass or plastic cables. This allows data to travel long distances at very high speeds. Older copper cables cannot handle the same speed and capacity. A light source is one of the most important parts of this system. It creates the light signals that travel through the fiber cable. Without it, the cable cannot carry any data.
This also relates to dark fiber. Dark fiber describes a fiber optic cable that someone has already installed but no one is using yet. No light passes through the cable, which is why people call it “dark.” Companies or organizations that use dark fiber must activate the network themselves. They begin the process by adding a light source to send signals through the cable.
What is a light source?
A light source is a device that changes electrical signals into light signals that travel through fiber optic cables. The signals move through the cable to a receiver on the other side. The receiver changes them back into usable data. The light is placed at the start of the connection, and the quality of its signals affects the whole system.
There are three types of light sources used across commercial fiber networks, and each one serves a different purpose.
LEDs are the most affordable option. They send out light in a wide, scattered pattern, which limits both the speed and reach of the signal. Because of that, LEDs tend to show up in older setups or lower-demand connections that stay under two kilometers.
Laser diodes produce a more focused and narrow beam of light. One type is the DFB laser, or Distributed Feedback laser. It keeps signal quality stable over distances up to 100 kilometers. Because of this, it is commonly used with single-mode fiber for long-distance network traffic between cities and regions.
VCSELs, or Vertical Cavity Surface Emitting Lasers, send light from the surface of the chip instead of the edge. They support high data speeds at a lower cost than traditional laser diodes. This makes them useful inside data centers, where distances are short but large amounts of data move constantly.
Why does this choice carry weight in dark fiber?
The light source choice carries weight in dark fiber because, unlike a managed network service, the operator gets the raw cable and is fully responsible for every active component sitting on top of it. That is what sets dark fiber apart, where someone else has already done the matching between equipment and infrastructure.
That responsibility comes with real consequences if the match is wrong. According to Mordor Intelligence, single-mode fiber held 71.83% of the dark fiber market revenue share in 2024. Single-mode cable has a very small core, so it needs a laser-based light source, specifically FP or DFB types, to keep the signal strong over long distances. Using the wrong source with that fiber type leads to weaker performance, shorter reach, and higher costs over time.
For long-haul and metro routes, DFB lasers remain the standard pick. For shorter, high-speed lit fiber connections inside a data center, VCSELs handle the load well. The choice always comes back to matching the light source to what the fiber and the route actually need.
The infrastructure underneath it all
The draw of dark fiber, especially for hyperscalers, OTT providers, and large telcos, comes down to control over their own network. According to Polaris Market Research, the global dark fiber market was valued at around USD 6.51 billion in 2024 and is expected to reach USD 16.87 billion by 2032. That growth shows how many organizations now want to own their connectivity setup rather than rely on a pre-built service made on someone else’s terms.
Choosing the right light source matters, but it only works as well as the fiber supporting it. A well-built route with solid redundancy gives operators a stable base for their active equipment to run on and deliver steady results.
ARNet is a dark fiber infrastructure provider that builds, owns, and operates its network across Southeast Asia, serving hyperscalers, OTT companies, and major telcos across Malaysia, Indonesia, Singapore, and Thailand. Its infrastructure supports any active equipment setup, whether that means DFB laser configurations on long-haul single-mode routes or VCSEL-based links inside data center environments. ARNet’s FiberGrid architecture includes multiple routing paths and built-in redundancy, backed by a 99.99% SLA and in-house teams running operations across 60 connected data centers in the region.
About the Author
Nabila Choirunnisa, Digital Marketing Executive at ARNet