What Is a Fiber Optic Splitter?

Posted on December 7, 2012
September 29, 2020

In today's optical network topologies, the advent of fiber optic splitter contributes to helping users maximize the performance of optical network circuits. Fiber optic splitter, also referred to as optical splitter, or beam splitter, is an integrated waveguide optical power distribution device that can split an incident light beam into two or more light beams, and vice versa, containing multiple input and output ends. Optical splitter has played an important role in passive optical networks (like EPON, GPON, BPON, FTTX, FTTH, etc.) by allowing a single PON interface to be shared among many subscribers.

How Does Fiber Optic Splitter Work?

Generally speaking, when the light signal transmits in a single mode fiber, the light energy cannot be entirely concentrated in the fiber core. A small amount of energy will be spread through the cladding of the fiber. That is to say, if two fibers are close enough to each other, the transmitting light in an optical fiber can enter into another optical fiber. Therefore, the reallocation technique of optical signal can be achieved in multiple fibers, which is how fiber optic splitter comes into being.

Fiber Optic Splitter Working Principle

Specifically speaking, the passive optical splitter can split, or separate, an incident light beam into several light beams at a certain ratio. The 1x4 split configuration presented below is the basic structure: separating an incident light beam from a single input fiber cable into four light beams and transmitting them through four individual output fiber cables. For instance, if the input fiber optic cable carries 1000 Mbps bandwidth, each user at the end of output fiber cables can use the network with 250 Mbps bandwidth.

1x4 Split Configuration

The optical splitter with 2x64 split configurations is a little bit more complicated than the 1x4 split configurations. There are two input terminals and sixty-four output terminals in the optical splitter in 2x64 split configurations. Its function is to split two incident light beams from two individual input fiber cables into sixty-four light beams and transmit them through sixty-four light individual output fiber cables. With the rapid growth of FTTx worldwide, the requirement for larger split configurations in networks has increased to serve mass subscribers.

Fiber Optic Splitter Types

Classified by Package Style

The optical splitter can be terminated with different forms of connectors, and the primary package could be box type or stainless tube type. Fiber optic splitter box is usually used with 2mm or 3mm outer diameter cable, while the other is normally used in combination with 0.9mm outer diameter cables. Besides, it has variously different split configurations, such as 1x2, 1x8, 2x32, 2x64, etc.

Classified by Transmission Medium

According to the different transmission mediums, there are single mode optical splitter and multimode optical splitter. The multimode optical splitter implies that the fiber is optimized for 850nm and 1310nm operation, whereas the single mode one means that the fiber is optimized for 1310nm and 1550nm operation. Besides, based on working wavelength differences, there are single window and dual window optical splitters—the former is to use one working wavelength, while the latter fiber optic splitter is with two working wavelengths.

Classified by Manufacturing Technique

FBT splitter is based on traditional technology to weld several fibers together from the side of the fiber, featuring lower costs. PLC splitter is based on planar lightwave circuit technology, which is available in a variety of split ratios, including 1:4, 1:8, 1:16, 1:32, 1:64, etc, and can be divided into several types such as bare PLC splitter, blockless PLC splitter, ABS splitter, LGX box splitter, fanout PLC splitter, mini plug-in type PLC splitter, etc.

Normally speaking, the FBT splitters provide cost-effective solutions while the PLC splitters suit for high-density applications. The following chart has summarized several factors comparing between PLC splitter and FBT splitter.

Type PLC Splitter FBT Coupler Splitters
Operating Wavelength 1260nm-1650nm (full wavelength) 850nm, 1310nm, 1490nm and 1550nm
Splitter Ratios Equal splitter ratios for all branches Splitter ratios can be customized
Performance Good for all splits, high level of reliability and stability Up to 1:8 (can be larger with higher failure rate)
Input/Output One or two inputs with an output maximum of 64 fibers One or two inputs with an output maximum of 32 fibers
Housing Bare, Blockless, ABS module, LGX Box, Mini Plug-in Type, 1U Rack Mount Bare, Blockless, ABS module
Figure PLC Splitter FBT Coupler Splitters

Fiber Optic Splitter Application in PON Networks

Optical splitters, enabling the signal on the optical fiber to be distributed between two or more optical fibers with different separation configurations (1×N or M×N), have been widely used in PON networks. FTTH is one of the common application scenarios. A typical FTTH architecture is: Optical Line Terminal (OLT) located in the central office; Optical Network Unit (ONU) situated at the user end; Optical Distribution Network (ODN) settled between the previous two. An optical splitter is often used in the ODN to help multiple end-users share a PON interface.

Fiber Optic Splitter Application in PON

Point-to-multipoint FTTH network deployment can be further divided into the centralized (single-stage) or cascaded (multi-stage) splitter configurations in the distribution portion of the FTTH network. A centralized splitter configuration generally uses a combined split ratio of 1:64, with a 1:2 splitter in the central office, and a 1:32 in an outside plant (OSP) enclosure such as a cabinet. A cascaded or distributed splitter configuration normally has no splitters in the central office. The OLT port is connected/spliced directly to an outside plant fiber. The first level of splitting (1:4 or 1:8) is installed in a closure, not far from the central office; the second level of splitters (1:8 or 1:16) is situated at terminal boxes, close to the customer premises. Centralized Splitting vs Distributed Splitting in PON Based FTTH Networks will further illustrate these two splitting methods that adopt fiber optic splitters.

How to Choose the Right Fiber Optic Splitter?

In general, a superior fiber optic splitter needs to pass a series of rigorous tests. The performance indicators that will affect the fiber optic splitter are as follows:

  • Insertion loss: Refers to the dB of each output relative to the input optical loss. Normally, the smaller the insertion loss value, the better the performance of the splitter.

  • Return loss: Also known as reflection loss, refers to the power loss of an optical signal that is returned or reflected due to discontinuities in the fiber or transmission line. Normally, the larger the return loss, the better.

  • Splitting ratio: Defined as the output power of the splitter output port in the system application, which is related to the wavelength of the transmitted light.

  • Isolation: Indicates a light path optical splitter to other optical paths of the optical signal isolation.

Besides, uniformity, directivity, and PDL polarization loss are also crucial parameters that affect the performance of the beam splitter.

For the specific selections, FBT and PLC are the two main choices for the majority of users. The differences between FBT splitter vs PLC splitter normally lie in operating wavelength, splitting ratio, asymmetric attenuation per branch, failure rate, etc. Roughly speaking, the FBT splitter is regarded as a cost-effective solution. PLC splitter featuring good flexibility, high stability, low failure rate, and with wider temperature ranges can be used in more kinds of applications.

For the expenses, the costs of PLC splitters are generally higher than the FBT splitter owing to the complicated manufacturing technology. In specific configuration scenarios, split configurations below 1×4 are advised to use FBT splitter, while split configurations above 1×8 are recommended for PLC splitters. For a single or dual wavelength transmission, FBT splitter can definitely save money. For PON broadband transmission, PLC splitter is a better choice considering future expansion and monitoring needs.

Concluding Remarks

Fiber optic splitters enable a signal on an optical fiber to be distributed among two or more fibers. Since splitters contain no electronics nor require power, they are an integral component and widely used in most fiber-optic networks. Thus, choosing fiber optic splitters to help increase the efficient use of optical infrastructure is key to developing a network architecture that will last well into the future.