The Optical Splitters for FTTX Applications

A fiber splitter is a very important passive component that used in the optical network system to achieve the optical signals' coupling, branching, and distributing, just the same with the coacial cable transmission system does. An optical splitter is fiber optical tandem device with multiple import or output terminals. Generally we often use M x N to indicate a splitter with M import and N output numbers. The optical splitters that used in the CATV system, are generally 1 x 2, 1 x 3 or the 1 x N fiber splitters that composed by them.

Fiber optic splitter is the passive components for FTTH PON (passive optical network). Gigabit Ethernet Passive Optical Network (GPON) splitters play an important role in Fiber to the Home (FTTH) networks by allowing a single PON network interface to be shared among many subscribers. Networks implementing BPON, GPON, EPON, 10G EPON, and 10G GPON technologies all use these simple optical splitters.

Every passive optical network, no matter GPON, EPON systems are comprised by the Optical Line Termination (OLT), the Optical Network Unit (ONU) and Optical Distribution Network (ODN). The ODN is the most important component is the FTTx systems which is the physical channel of the optical transmission between the OLT and ONU. It is composed by fiber optic cables, optical connectors, and most importantly, the fiber splitters as well as ancillary equipment connecting these devices.

There are two basic splitter technologies for the passive optical network: Fused Biconical Taper (FBT) and Planar Lightwave Circuit (PLC), which correspond with to types of fiber splitters, FBT splitter, also know as FBT coupler, and PLC splitter. Fused Biconical Taper is the older technology and generally introduces more loss than the newer PLC splitters.
The PLC Splitter contains no electronics and use no power. Both PLC and FBT splitters are used in PON networks. A PON network may be designed with a single optical splitter, or it can have two or more splitters cascaded together. Since each optical connection will add the optical attenuation, a single splitter is superior to multiple cascaded splitters. One net additional coupling (and source of attenuation) is introduced in connecting two splitters together.

With the accessing network construction boom and the increasing subscribers trend in the market. PLC splitter will no double to become the main force in the market, the PLC optical splitters has the features of digitization, networking, broadband, miniaturization and easy maintenance, etc.

Spectroscopic Principle of An Optical Splitter

Fiber splitter or fiber optic splitter is one of the most important passive devices in the fiber network, an optical fiber having a plurality of inputs and a plurality of output terminals tandem device, commonly used in M × N to indicate a splitter M inputs and N outputs. The optical splitter used in the CATV system, are generally 1 × 2, 1 × 3, and composed of them 1 x N optical splitter. Just the same with the coaxial cable transmission system, in a optical network system, an optic signal of a optical network system also needs to coupled to the branch distribution, which require a important fiber optic passive component - the optical splitter.
Optical splitter can be divided into two types according to the spectroscopic principle: Fused Biconical Taper (FBT) and Planar Lightwave Circuit (PLC). FBT splitter is to side fuse two or more fiber together. While the PLC splitter is a micro-optical components product, which adapt of the lithography, forming an optical waveguide in the medium or on a semiconductor substrate. Basically the two type of fiber splitter share the similar spectroscopic principle. Both of them are coupled to each other by changing the optical fiber between the evanescent field (the degree of coupling, the coupling length) as well as to change the radius of the optical slender to achieve different size branching amount. On the contrary, things that combining multiple optical signals or vice versa into one single can be called Fiber synthesizer.
FTB Coupler
The working principle of FTB method is to fuse two or more optical fiber that without coating layer together by melting them under a high temperature environment, stretching the both sides to form a double cone zonespecial waveguide structured. Different spectral radios can be obtained by controlling the length of the fiber torsion angle and stretched. Finally, pull the cone on the quartz substrate with a curable adhesive curing and insert into a stainless brass. That’s how an FTB coupler formed.
There are some disadvantages of this method. Due to the coefficient of thermal expansion of the curing adhesive with a quartz substrate, the stainless steel tube inconsistencies, the degree of thermal expansion and contraction will be inconsistent when the ambient temperature changes. This is likely to cause damages to the optical splitter, which would become worse if in the wild. This is also the main reason that this fiber optic splitter is easy to get damaged. However, due to the making method of the FBT Coupler is simple, inexpensive, easy to connect to external fiber as a whole, and resistance in for-mechanical vibration and temperature changes, and other advantages, it has become the mainstream manufacturing technology in current the market.
PLC Splitter
The PLC splitter adopted semiconductor production process like photolithography, etching, developing technology and more. Waveguide array is located on the upper surface of the chips, the shunt function is integrated on the chip, which is implemented 1:1 branching on a chip. Then then coupled the multi-channel optical fiber array in the input terminal and output terminal of the chip, respectively, and last encapsulating.
Comparing with FTB coupler, PLC splitter shares some obvious advantages: meeting transmission needs of different wavelengths, compact structure, small size, uniform spectroscopic etc. At the same time, the main drawback of the PLC splitter is the complicated production process while the chip monopoly by several companies, as well as the cost disadvantages versus the FBT splitters.