How PLC Optical Splitters Work: Key Role in Modern GPON Networks

Optical splitter PLC is a passive device that divides the light signal from a single fiber optic cable among multiple output lines. Thanks to these splitters, internet providers can connect dozens of subscribers without running a separate cable from the central equipment to every home or apartment.

One of the most common types is the PLC splitter, which operates on planar optical waveguide technology. Let's explore how this technology works, how the light signal is divided, and why it is widely used in modern GPON networks.

What Is a PLC Optical Splitter?

A PLC splitter (Planar Lightwave Circuit) is an optical splitter where light is distributed across several channels using a system of miniature waveguides formed on a special substrate.

Unlike a standard electrical splitter, a PLC splitter does not convert light into electricity. The signal passes through the device in optical form, with its power being distributed among the outputs.

The core of the design is a small optical chip connected to the input and output fibers. Light enters the chip, passes through the waveguide system, and is directed to several outputs.

For instance, a 1×8 splitter has one input and eight outputs, allowing the signal from a single optical line to be distributed to eight subscriber lines.

A key feature of this technology is that it does not require electrical power. The passive optical splitter contains no electronic amplifiers or processors, so it operates without connecting to the power grid.

To better understand how light transmits information over long distances, it's helpful to learn about the structure of fiber optic cables. For a detailed overview, see the article How Fiber Optic Internet Works: Cable Structure, Speed, and Light-Based Data Transmission.

How Does an Optical Splitter Work?

The principle of a PLC splitter is based on distributing optical power among several channels. When a signal enters the input fiber, it moves into the waveguide system where it is sequentially divided into multiple streams.

Inside the PLC chip are special branching sections that direct light along different paths. For example, in a 1×8 splitter, the signal may first split into two channels, then four, and finally eight outputs.

The splitter does not create new independent signals. Each output receives the same input optical signal, but at reduced power. In GPON networks, subscriber equipment processes only the data addressed to it.

The main limitation of optical splitting is power loss. The more outputs a splitter has, the smaller the share of the original light stream each output receives.

For example, an ideal 1×2 splitter distributes roughly half the input power to each output. In a 1×8 model, each output gets about one-eighth; in a 1×32, just one thirty-second.

In practice, there are additional losses due to waveguide characteristics, connections, and other elements of the optical line. That's why network design must account not just for the number of subscribers, but also for the acceptable signal attenuation.

How Are PLC Splitters Used in GPON Networks?

One of the main uses for PLC splitters is in GPON (Gigabit Passive Optical Network) systems. This technology allows providers to serve many subscribers via a shared fiber optic infrastructure.

A typical GPON network uses three main components:

• OLT (Optical Line Terminal): The provider's device for sending and receiving data.
• PLC splitter: The passive splitter that distributes the optical signal to subscriber lines.
• ONT (Optical Network Terminal): The subscriber's device that converts the optical signal into data for the home network.

When data is sent from the provider, the signal leaves the OLT, travels along the trunk fiber, and reaches the splitter. The splitter distributes it among the connected ONTs.

Since the downstream signal physically arrives at all splitter outputs, each ONT processes only the traffic intended for it. To protect user data, GPON uses encryption for downstream transmissions.

The upstream principle is different. Subscriber devices transmit data in specially assigned time slots managed by the OLT. This prevents simultaneous transmission from multiple ONTs over the shared fiber.

For example, a single 1×32 PLC splitter can connect up to 32 subscribers. However, all share the GPON port's bandwidth, so each connection's speed depends on tariff limits and current network load.

To learn more about the architecture of such networks and connection features, see the article GPON: What Is It, How Modern Fiber Internet Works, and How FTTH Differs from Other Technologies.

Types of Optical Splitters and Signal Loss

Optical splitters differ by the number of outputs and the split ratio. The more subscribers need to be connected to a line, the more output channels the splitter should have.

The most common PLC splitter types include:

The values above are approximate and depend on the specific device's characteristics.

The attenuation of a PLC splitter shows how much the optical signal's power decreases as it passes through the splitter. For example, about 10 dB of loss means the power is reduced by roughly ten times.

It's not possible to increase the number of outputs indefinitely. Provider equipment and subscriber terminals have a limited optical budget-the maximum allowable loss for the entire connection. Besides the splitter, cable length, fusion splices, and optical connectors also affect this budget.

In addition to PLC, there are FBT splitters (Fused Biconical Taper), which divide light by fusing and stretching optical fibers when heated.

The main difference between PLC and FBT lies in their manufacturing technology. PLC offers stable power distribution among many outputs over a wide range of operating wavelengths. FBT is more often used in simpler setups with fewer channels, though specific characteristics depend on the splitter model.

Advantages and Limitations of PLC Splitters

The main advantage of PLC splitters is the ability to connect many subscribers without laying a separate optical fiber from the provider's equipment to every user. This reduces cabling costs and simplifies network expansion.

Other benefits include:

• No power requirement: The splitter works without electricity and doesn't need a backup power source.
• Compact size: Its small dimensions allow installation in distribution boxes and optical cabinets.
• Reliability: With no active electronic components, there are fewer possible failure points.
• Scalability: Providers can use splitters with different output counts depending on the number of subscribers.

However, the technology does have limitations. The main one is increasing optical loss as more users are connected. If the signal power drops below the receiver's sensitivity, the connection becomes unstable or fails completely.

Also, a PLC splitter does not increase network bandwidth. All subscribers connected to the same GPON port share the data transmission resource, and actual speeds depend on network load and equipment settings.

That's why it's important to consider the number of connections, optical line length, and allowable loss budget when choosing a splitter.

Conclusion

A PLC optical splitter enables light signals to be distributed among multiple subscribers without extra power or active network equipment. This allows providers to build compact and cost-effective GPON networks.

When choosing a splitter, it's crucial to consider the split ratio and signal attenuation. For a small number of connections, 1×4 or 1×8 models are suitable, while 1×16, 1×32, and 1×64 are used for larger distribution nodes. The final choice depends on the network's optical budget and equipment capabilities.