ODN (Optical Distribution Network) from the service convergence point to the user is generally divided into backbone, wiring, access, fiber to the home multiple segments.
The access section of traditional ODN cable construction involves a large number of fiber core splicing. In the user installation, the home section of the FTTH drop cable ends also need to be end-to-end splicing. Cable splicing has higher technical requirements for construction and maintenance personnel, and on-site construction operations are time-consuming, so the pre-terminated of ODN technology without the need for on-site fibers splicing came into being.
The Main Problems Faced By Traditional ODN In Building Maintenance
1. High failure rate of active connections
ODN in the conjunction box and splitter box are used in the activity of the connection.
As in the process of installation and maintenance often need to open and close the conjunction box and splitter box door, installation and maintenance personnel will find it very inconvenient, intentionally or unintentionally, the handover box and the splitter box door has become the state of always open, as shown in Figure.
Over time, by the impact of the environment, the box within the optical splitter, pigtail and other devices are easy to age, the connector end face is also susceptible to contamination, thus causing connection failure.
2. Inefficient construction and maintenance
In the construction of the access section of traditional ODN optical cable, the fusion splicing of optical fiber is involved at almost every optical fiber splitter box, as shown in Figure.
Cable placement, fiber fusion splicing, splitter box installation and other work can only be carried out step by step, can not be constructed in parallel, which also leads to the access of cable construction cycle is relatively long.
In the broadband subscriber installation, due to the access fiber optic cable deployment is completed at both ends need to be fused to a section of pigtail fiber into the end, as shown in the figure (the red arrow in the figure refers to the fusion point), which also increases the length of time required for the subscriber to put the installation.
3. High technical requirements for construction and installation and maintenance
The fusion splicing of optical fiber must be equipped with fusion splicing machines, and the operators also need certain skills, so the construction of traditional ODN, broadband users’ installation and maintenance of the technical requirements of the relevant personnel are relatively high.
Technologies Used In Pre-terminated ODNs
To solve the above problems faced by traditional ODNs in building and maintaining, pre-terminated ODNs use the following techniques.
1. Pre-terminated Technology
Pre-terminated refers to the two ends of the fiber optic cable in the factory pre-terminated movable connectors become pre-terminated optical cable, in the wiring equipment (conjunction box, splitter box) and fiber optic cable connection is also pre-terminated movable connectors become pre-terminated wiring equipment, so that in the ODN construction and installation and maintenance of the ODN fiber optic link connection does not need to be fusion splicing, only through the movable connection can be completed.
For example, the above figure for the access section of the pre-terminated cable, cable’s A side of the SC/APC waterproof connector, can be directly connected with the pre-terminated splitter box user port (equivalent to the ordinary splitter box in the optical splitter output port) for the activity of the connection, as shown in the figure below. Cable B side of the ordinary SC-type connector can be directly connected with the ONT.
In this way, when the user puts in the installation, the fiber optic cable in the access section only needs to be assembled on the spot to complete the connection of the fiber optic cable link, without the need for on-site fusion splicing.
2. Unequal Splitting
Traditional ODN adopts equal splitting optical, the introduction section of the cable model, fiber core distribution relationship is complex, the number of fiber core splicing, and is not suitable for the use of pre-termination.
ODN using unequal splitting optical, the introduction of optical cable can be used in a single-core optical cable, the cable model is less, the core connection relationship is simple, so the pre-terminated of the ODN is usually used unequal splitting optical.
The ODN networking model of unequal splitting optical mainly uses single chain and double chain, and the following figure shows the networking model of one of the branch chains when the networking model is double chain.
Only single-core pre-terminated cables are used in the fiber link from the pre-terminated optical intersection to the ONT.
3. Fully Sealed Protection Measures
The box of the pre-terminated optical conjunction and the box of the pre-terminated splitter box adopts a sealed structure, sealing the fused fiber unit and the optical splitter in the box/cassette, avoiding the influence of the surrounding environment and personnel’s accidental touch on the optical splitter and the connected fibers.
At the same time, the downlink interface of the pre-terminated optical intersection and the uplink/downlink interface of the pre-terminated splitter box are set outside the box/cassette body, and the interface adopts a type adapted to the pre-terminated cable so as to facilitate the connection with the pre-terminated cable.
For example, the appearance and interfaces of the pre-terminated optical conjunction are shown in Figure, wherein the fusion fiber unit can be opened for splicing the fiber core of the ordinary wiring optical cable.
Activity connections used in outdoor, underground and other environments that require waterproof and dustproof use of SC/APC waterproof connectors, the connector is fully sealed before and after the connection, to avoid the impact of ultraviolet rays, water vapor, dust and so on on the quality of the activity connection.
The factory value of insertion loss of common simplex optical connector is generally not more than 0.25dB/pcs.
In traditional communication engineering, considering the long-term influence of environment on the quality of movable connection, the attenuation standard of common simplex movable connection is 0.5dB/pcs.
The movable connection of the pre-terminated ODN generally has an insertion loss of no more than 0.3dB/each due to the use of full sealing protection measures.
Pre-terminated ODN products
Pre-terminated ODN products mainly include pre-terminated optical conjunction box, pre-terminated splitter box, pre-terminated fiber optic cable, pre-terminated distribution box and pre-terminated optical closure.
1. Pre-terminated Optical Conjunction Box
pre-terminated optical conjunction in the ODN network location equivalent to the wiring optical conjunction, length and width and a laptop size is about the same, the maximum support for the fusion tray 48-core splicing, a total of 4 wiring cable import and export and 8 single-core pre-terminated cable interface.
2. Pre-terminated Splitting Box
The pre-terminated splitter box is divided into cascade type and terminal type.
The cascade type has a built-in 1×5 or 1×9 optical splitter with one uplink port, one downlink port, and four or eight user ports, as shown in the figure below.
3. Pre-terminated Patch Cable
Pre-terminated patch cables are mainly divided into introduction type, hybird type and access type.
The introduction type is mainly used for the connection between pre-terminated optical conjunction to distribution box and distribution box to distribution box.
The main body of the cable adopts round introduction cable, which has good mechanical strength. Both ends of the cable are SC/APC waterproof connectors, as shown in Figure. The cable length specification is a multiple of 50m, and the maximum section length of the overhead cable is 500m, and the maximum section length of the pipe cable is 350m.
The hybird type only replaces the connector at one end of the introduction type with an ordinary SC connector, and the rest is the same as the introduction type, as shown in the figure below. The hybird type can be used for the connection of ordinary wiring optical conjunction (or ordinary distribution box) to the pre-terminated splitter box.
The main body of the access cable adopts the ordinary drop cable, the mechanical properties of the access pre-terminated cable is general, mainly used in indoor environments, such as the user to put the installation.
4. Pre-terminated branch box
In branch routing, the use of a chain-type networking structure for ODN causes routing detours for the introduction of fiber optic cables. When the route detour length is long (generally greater than 100 meters), the economy becomes unreasonable. At this time, the branch box can be added at the branch point of the route, as shown in the following figure.
The branch box has one input port and two output ports, all of which are SC/APC waterproof type interfaces, as shown in the figure.
The branch box contains a 1 × 2 unequal ratio optical splitter, the splitter of the two output ports optical power distribution ratio of 30/70, the insertion loss of about 6.0dB / 2.2dB.
4. Pre-terminated Optical Closure
Due to the limitation of the maximum segment length of the pre-terminated cable, when the link length between neighboring pre-terminated devices in the ODN link exceeds the maximum segment length of the pre-terminated cable, the pre-terminated cable needs to be connected through the pre-terminated connector box.
The simplex pre-terminated closure has only one single core adapter inside, as shown in the figure below.
Concluding Remarks
Pre-terminated technology is mainly applicable to the introduction section and household section of ODN, trunk section and distribution section are not suitable for pre-terminated due to the large number of fiber optic cable cores.
Pre-terminated technology improves the construction and maintenance efficiency and reduces the fault of active connection, but pre-terminated technology also has many shortcomings, such as: the attenuation of active connection is more than one times higher than fusion connection, pre-terminated of the length of the optical fiber cable segment specifications is difficult to adapt to the actual scene, etc., so pre-terminated technology needs to be further explored for the application of the scene.
