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Know-How

fiber optics1
ISP Network

Fiber Optic Splitter Solution


Fiber Optic Splitter Solution

FS Official 2014-05-06

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, or sometimes called as beam splitter, is a passive optical component that can split an incident light beam into two or more light beams, and vice versa. The device 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.

Fiber Optic Splitter Overview

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 transmitted from a 1X4 equal ratio splitter, it will be divided into 4-fiber optic light by equal ratio that is 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. From a technology standpoint, there are two commonly used types of optical splitters: FBT (Fused Biconical Taper) and PLC (Planar Lightwave Circuit).

Figure 1: A single optical input is split into multiple output

Five Steps to Manufacture A Fiber Optic Splitter

In all, there are five steps to manufacture a fiber optic splitter. Each step requires strict control and management on 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 to the GR-1209 CORE specification.

How to Test the Quality of A Fiber Optic Splitter

The quality of a fiber optic splitter is mainly determined by six specifications, namely optical bandpass, insertion loss, return loss, uniformity, and directivity. The following part outlines how to test each specification.

 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.  The insertion loss is tested by using a light source and power meter. The reference power level is obtained and each of the output port of the optical splitter is measured.  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.  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.  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.

How Does Fiber Optic Splitter Work?

Fiber optic splitter is a key optical device in passive optical network (PON) systems, also know as passive optical splitter. As for the working principle of fiber optic splitter, it 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: The basic principle of fiber optic splitter

PLC Splitter vs FBT Splitter: What’s the Difference?

Splitter technology has forged ahead in the past few years by introducing PLC splitter. It turned out to be a more reliable type of device compared to the traditional FBT splitter. Similarly, both of them are alike in size and outer appearance, and both types of splitters provide data and video access for business and private customers. However, internally the technologies behind these splitters vary, thus giving service providers a possibility to choose a more appropriate solution.

Splitting Ratio Principle

The FBT splitter uses two (or more) fibers. The fibers' coating layer is removed. Both fibers, at the same time, are stretched under a heating zone thus forming a double cone. This special waveguide structure allows control of the splitting ratio via controlling length of the fiber torsion angle and stretch.

The PLC splitter is a micro-optical element using photolithographic techniques to form optical waveguide at medium or semiconductor substrate for realizing branch distribution function.

Upsides and Downsides

  PLC splitter FBT splitter
Upsides Equal splitter ratios for all branches Low cost
Losses are not sensitive to the wavelength Adjustable splitting ratio
Suitable for multiple operating wavelengths (1260nm-1650nm) Can work on three different operating bands (850nm, 1310nm, and 1550nm)
Higher spectral uniformity
Compact configuration; smaller size; small occupation space
Downsides Complex device fabrication process Losses are wavelength-dependent
Costlier than the FBT splitter in the smaller ratios Poor spectral uniformity
Temperature sensitive
Transmission distance can be affected because of the uncertain equal ratio
Susceptible to failure due to extreme temperatures or improper handling
The larger the split, the larger the encapsulation module

Optical Performance

Parameters PLC splitter FBT splitter
Manufacturing Consists of one optical chip and several optical arrays depending on the output ratio. The optical arrays are coupled on both ends of the chip. Two or more pieces of optical fibers are bound together and put on a fused-taper fiber device. The fibers are then drawn out according to the output branch and ratio with one fiber being singled out as the input.
Operating Wavelength 1260nm-1650nm 850nm, 1310nm, and 1550nm
Input/Output Cable Bare optical fiber, 0.9mm, 2.0mm, 3.0mm Bare optical fiber, 0.9mm, 2.0mm, 3.0mm
Input/Output One or two inputs with an output maximum of 64 fibers. One or two inputs with an output maximum of 32 fibers.
Temperature -40℃ to 85℃ -5℃ to 75℃
Reliable Splits Up to 1:64 Up to 1:8 (can be larger with higher failure rate)
Package Steel Tube (used mainly in equipment); ABS Black Module (Conventional) Steel Tube (used mainly in equipment); ABS Black Module (Conventional)
Cost Higher cost Lower cost

How to Choose the Right Fiber Optic Splitter?

In the previous text, we’ve discussed the difference between FBT and PLC splitters. If you are still confused about which one is the better option for your network, you may find the answer in this part.

Variable and unbalanced optical ratio is the most outstanding advantage of FBT splitter. Sometimes, considering the quantity of user and different transmitting distance, the fiber optical splitter should be adopted for the distribution of optical power in the line. Since the PLC splitter cannot afford the different optical ratio, it is the time to adopt the FBT splitter.

However, comparing with FBT splitter, PLC splitter has the advantages in some other important aspects. Insensitive at different wavelengths, so PLC splitter can work at different wavelength and won’t cause much loss. Single component can be split in many channels, reaching 64 or more. And PLC splitter has lower cost for multichannel. The more the channels are, the lower the cost is.

Considering the cost, split configurations below 1×4 are advised to use FBT splitter, while split configurations above 1×8 are recommended for PLC splitters. If only for a single wavelength transmission or dual, FBT splitter is better for save cost. If for PON broadband transmission, considering the future expansion and monitoring needs, PLC splitter is better.

Fiber Optic Splitter In Centralized and Cascaded PON Architectures

In the PON network, there are two common splitter architectures—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.

Fiber Optic Splitter In Centralized Architecture

The centrlized architecture generally uses a 1×32 splitters in the central office. The central office may be 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 architecture

Fiber Optic Splitter In Cascaded 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

Conclusion

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.

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OTN Solution Team
Senior Telecommunication Engineers

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