In today’s optical network topologies, the advent of fiber optic splitter is significant in helping users maximize the performance of optical network circuits. Fiber optic splitter contains multiple input and output ends. Whenever the light transmission in a network needs to be divided, fiber optic splitter can be implemented for the convenience of network interconnections.
A fiber optic splitter is a device that splits the fiber optic lights into several parts by a certain ratio. For example, when a beam of fiber optic light is transmitted from a 1x4 equal ratio splitter, it will be divided into 4-fiber optic light by equal ratio. Each beam is 1/4 or 25% of the original source one. A fiber optic splitter is different from WDM. WDM can divide the different wavelength fiber optic light into different channels. Fiber optic splitter divides the light power and sends it to different channels.
Figure 1: A single optical input is split into multiple output
The working principle of the fiber optic splitter can be generally described in the following way. When the light signal transmits in a single-mode fiber, the light energy can not entirely concentrated in the fiber core. A small amount of energy will be spread through the cladding of 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. And this is how fiber optic splitter comes into being.
Figure 2: Fiber Optic Splitter Working Principle
From a technology standpoint, there are two commonly used types of optical splitters: FBT (Fused Biconical Taper) and PLC (Planar Lightwave Circuit). The main differences are shown in the table below.
|Types||PLC Splitter||FBT Splitter|
|Wavelength Range||1260-1650 nm||850nm, 1310nm, 1490nm, and 1550nm|
|Splitting Ratio||Equal splitter ratios for all branches||Splitter ratios can be customized|
|Dimensions||Small||Large size for multi-channel|
|Temperature||-40℃ to 85℃||-5℃ to 75℃|
|Advantages||Losses are not sensitive to the wavelength; Higher spectral uniformity||Low cost; Adjustable splitting ratio|
|Disadvantages||Complex device fabrication process; Costlier than the FBT splitter in the smaller ratios||Losses are wavelength-dependent; Temperature-sensitive; The larger the split, the larger the encapsulation module|
To learn more about FBT vs. PLC Splitters: FBT Splitter vs. PLC Splitter: What's the Difference?
As PLC splitter has the advantages of flexible working wavelength, good stability, low-temperature loss, and a smaller failure rate, people prefer to use PLC splitters rather than FBT splitters. Nowadays, there are five typical packaging types of PLC splitters on the market to suit various applications: Bare Fiber Optical Splitter, Blockless Fiber Splitter, ABS Splitter, LGX Splitter, and Rack-Mount Splitter. You can choose the optimal one according to your requirements. For more details of these five types of PLC splitters, click How Many Fiber Optic Splitter Types Are There?
Apart from the type of fiber optic splitter, the splitting ratio is also a significant element in choosing the right fiber optic splitter. Different ratios may perform differently in PON networks. When using 1:32 OLT splitter, the network can receive a qualified fiber optic signal in 20km. If your distance between OLT and ONU is short, like in 5km, you can also consider about 1:64 splitting ratio. There are also 1x4 and 1x8 OLT splitters that can be applied in PON networks. More information about the splitting ratio: How to Design Your FTTH Network Splitting Level and Ratio?
Fiber optic splitter is a key optical device in passive optical network (PON) systems - centralized and cascaded architecture. The centralized splitter uses single-stage splitter located in a central office in a star topology. The cascading splitter approach uses multi-layer splitters in a point to multi-point topology.
The centralized architecture generally uses 1×32 splitters in the central office located anywhere in the network. The splitter input port is directly connected via a single fiber to a GPON/GEPON optical line terminal (OLT) in the central office. On the other side of the splitter, 32 fibers are routed through distribution panels, splice ports and/or access point connectors to 32 customers’ homes, where it is connected to an optical network terminal (ONT). Thus, the PON network connects one OLT port to 32 ONTs.
Figure 3: Fiber optic splitter in centralized PON architecture
A cascaded architecture may use a 1×4/1×8 splitter residing in an outside plant enclosure/terminal box. This is directly connected to an OLT port in the central office. Each of the four fibers leaving this stage 1 splitter is routed to an access terminal that houses a 1×8/1×4, stage 2 splitter. In this scenario, there would be a total of 32 fibers (4×8) reaching 32 homes. It is possible to have more than two splitting stages in a cascaded system, and the overall split ratio may vary (1×16 = 4 x 4, 1×32 = 4 x 8, 1×64 = 4 x 16, 1×64 = 8 x 8).
Figure 4: Fiber optic splitter in cascaded PON architecture
In all, there are five steps to manufacture a fiber optic splitter. Each step requires strict control and management of various parameters like environment, temperature, and detailed precision on assembly and equipment.
Step One: Components Preparation
Generally three components are needed. The PLC circuit chip is embedded on a piece of glass wafer, and each end of the glass wafer is polished to ensure highly precise flat surface and high purity. The v-grooves are then grinded onto a glass substrate. A single fiber or multiple ribbon fiber is assembled onto the glass substrate. This assembly is then polished.
Step Two: Alignment
After the preparation of the three components, they are set onto an aligner stage. The input and output fiber array is set on a goniometer stage to align with the PLC chip. Physical alignment between the fiber arrays and the chip is monitored through a continuous power level output from the fiber array.
Step Three: Cure
The assembly is then placed in a UV (ultraviolet) chamber where it will be fully cured at a controlled temperature.
Step Four: Packaging
The bare splitter is aligned and assembled into a metal housing where fiber boots are set on both ends of the assembly. And then a temperature cycling test is needed to ensure the final product condition.
Step Five: Optical Testing
In terms of testing, three important parameters such as insertion loss, uniformity and polarization dependent loss (PDL) are performed on the splitter to ensure compliance to the optical parameters of the manufactured splitter in accordance with the GR-1209 CORE specification.
The quality of a fiber optic splitter is mainly determined by five specifications, namely optical bandpass, insertion loss, return loss, uniformity, and directivity. The following part outlines how to test each specification.
1. The optical bandpass can be tested by connecting the optical splitter to an optical spectrum analyzer with a high-powered light source having a central wavelength of the required bandpass. The attenuation across the required bandpass shall meet the splitter requirements.
2. The insertion loss is tested by using a light source and power meter. The reference power level is obtained and each output port of the optical splitter is measured.
3. The return loss is tested by using a return loss meter. The input port of the splitter is connected to the return loss meter and all the output ports are connected to a non-reflective index matching gel.
4. The uniformity of the optical splitter can be determined by referring to the results from the insertion loss test to ensure that the difference between the highest loss and the lowest loss is within the acceptable uniformity value.
5. Directivity can be measured in a manner similar to the insertion loss test. However, the light source and power meter are connected to each of the input ports and two output ports.
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.