The plc splitter, as an important passive device in an ODN (Optical Distribution Network), influences important indicators such as the splitting ratio and optical channel loss of the entire optical link. The plc splitter is an essential piece of equipment in the planning, construction, operation, and maintenance of cable TV FTTH.
1. Basic knowledge of plc splitter
PLC splitter is a type of coupler. Different from the wavelength coupler used for multiplexing and demultiplexing, the plc splitter is a kind of power coupler. Its main function is to combine and split the optical signal according to the average or set ratio, to realize the distribution of optical power.
In the FTTH network, the plc splitter is used to transmit digital signals, and generally has one or two input ends and multiple output ends. In practical applications, 1-to-many plc splitters are widely used, such as Y-type (1×2) splitters and tree-shaped (1×N, N>2) splitters. If redundant protection of optical fiber links is required, X-type (2×2) splitter and star splitter (2×N, N>2) can be selected to form a ring network. The 2×N plc splitter is relatively cost-effective for construction and is generally used in the construction of high-reliability networks that require key guarantees. Under normal circumstances, FTTH networks will use more 1×N plc splitters.
According to different standards, plc splitters can be divided into the following types:
(1) According to the type of fiber, it can be divided into single-mode fiber splitter and multi-mode fiber splitter. Commonly used is a single-mode fiber splitter.
(2) According to the different production processes, it can be divided into two types: fusion taper type and planar waveguide type.
●The fused taper type is mainly to form a new structure by stretching two (or more) optical fibers with the protective layer stripped off to make them fully coupled. The optical power can be distributed according to a specific ratio through this combined structure, and theoretically, an all-fiber splitter with any splitting ratio can be produced.
●Planar optical waveguide splitter is a Y-shaped or multiple Y-shaped cascaded branched waveguide structure produced by planar dielectric optical waveguide technology and adopts integrated optical technology to complete various functional requirements.
(3) According to different packaging methods, it can be divided into box splitter, plug-in splitter, and mini splitter.
(4) According to the different splitting ratios, can be divided into two categories: equal splitting and unequal splitting.
(5) According to different working bandwidths, it can be divided into a single window, double window, triple window, and full-band plc splitter.
The performance indicators of the plc splitter mainly include loss, operation difficulty, repeatability, manufacturing cost, thermal stability, and mechanical stability. The most important indicators are insertion loss, uniformity, additional loss, and return loss. In the wired bidirectional network, the optical division recording used in the network for data uplink and downlink transmission should also consider its directivity to measure the anti-interference ability between different input ports.
In addition to satisfying the above-mentioned optical characteristics, the plc splitter should also have reliability, mainly to meet the mechanical test and environmental tests.
2. Application of plc splitter in FTTH network
The RF hybrid dual-fiber three-wave technology solution is a common application of plc splitters in FTTH networks. The RF hybrid solution refers to two channels for fiber-to-the-home technology. One channel uses RF technology to transmit broadcast signals, and the other channel uses PON technology to transmit data signals. At present, considering the construction cost, the dual-fiber three-wave technology is generally used in wired FTTH construction, that is, the unidirectional broadcast channel occupies a single fiber, the equipment room side is mainly an optical amplifier, and the user side equipment is the main optical receiver. The bidirectional data channel uses another fiber. The equipment on the equipment room side is mainly the OLT, and the equipment on the user side is mainly the ONU.
With this solution, the data transmission of the two channels can be physically isolated, and the interference between adjacent wavelengths can be effectively avoided. In the future, with the development of multiplexing and demultiplexing technology, the cost-effectiveness of single-fiber three-wave technology will become higher and higher, and the dual-fiber three-wave technology can smoothly transition to single-fiber three-wave technology.
3. Selection of plc splitter
The FTTH network has high requirements for link attenuation and performance indicators, such as return loss, insertion loss, etc. The following aspects should be paid attention to when selecting.
●The choice of split ratio.
The commonly used splitting ratios in FTTH networks are generally 2, 4, 8, 16, and 32. The selection of splitting ratios should be related to the performance of the equipment selected during design. Calculate the maximum optical loss value on the optical transmission channel according to the transceiver performance of the optical equipment, then subtract the loss of the optical cable itself, the loss of the optical cable splice point, the insertion loss of the pigtail, and the remaining value is the loss allowed by the plc splitter.
●Selection of the production process
The commonly used plc splitter technology in the industry is generally PLC and fused taper type, among which PLC type plc splitter with full wavelength is generally selected. In special cases, the splitting ratio of the plc splitter is not the nth power of 2, such as 3, 12, etc., the PLC plc splitter is more expensive, and the fusion taper type plc splitter can be selected.
●Choice of package form
Depending on the application of the plc splitter, different packaging methods are selected.
The plc splitter used at the first-level light splitting place is often used in the computer room. Choice of rack-mount or miniature packages.
The secondary optical splitting is set at the optical splitting node, generally, the plc splitter is placed in the optical splitting node box, and the box-type packaging method is often adopted.
The plc splitter used in the third-level light splitting often chooses the plug-in packaging method to facilitate future upgrades and expansions.
● Detection of plc splitter
After the plc splitter is purchased and delivered according to the application requirements, it must be checked and tested on arrival.
Common plc splitter testing instruments include optical power meter, optical echo tester, etc., which mainly test whether the performance of plc splitters, such as splitting ratio, attenuation, return loss, directivity, and uniformity, meets the requirements, appearance, repeatability, etc. Whether other mechanical skills such as performance after unplugging and plugging can meet the requirements, etc.
As an important passive device in the passive optical network, the plc splitter occupies a position that cannot be ignored in the FTTH network. The selection, detection, and application of the plc splitter should be considered differently according to different locations to ensure the performance quality of the entire FTTH network and enable the entire ODN network to have the ability to upgrade smoothly.
