Fiber optic cable in FTTH

The optical cables used in FTTH are mainly divided into backbone optical cables, distribution optical cables and user optical cables according to different usage positions. The number of cores of the backbone optical fiber cable will be relatively large, ranging from hundreds of cores to as many as thousands of cores. Usually, central tube type, layer stranding type and skeleton type optical fiber ribbon optical cable are used. The current ordinary outdoor optical cable can meet the requirements and can be conveniently installed. Utilize existing fiber optic cable resources. The distribution optical cable is the optical cable between the optical distribution point and the user access point. Depending on the location, there are three types of optical cables for distribution: outdoor optical cables, indoor and outdoor dual-purpose optical cables and indoor optical cables. The user optical cable is the optical cable from the user access point to the terminal equipment. When the user access point is placed outdoors, the outdoor section should be introduced with outdoor optical cables or indoor and outdoor dual-purpose optical cables; when the user access points are placed indoors or in buildings, the user optical cables should use indoor optical cables.

The following will mainly introduce several indoor optical cables that can be used as incoming optical cables and user optical cables and their applications.

Indoor fiber optic cable

The successive construction of optical fiber networks and high-speed broadband access networks of various layers, and the increasing popularity of computer networks continue to meet people's increasing demand for communication bandwidth. With the continuous extension of optical fiber to the user end, the application of indoor optical cable is increasing, and the market demand is increasing day by day. From the perspective of the inevitable development trend of vertical wiring system and optical fiber to the home and the demand for transmission room and all-optical network switching, the demand for indoor optical cables is the same as that of telephone distribution cables, which is no less than the demand for trunk optical cables, and it is very suitable for The transmission medium of FTTH. In addition, the FTTH solution of indoor optical cable can be used to realize the triple play of telephone, data and cable TV and video surveillance at the same time. The demand for indoor optical cables has great growth potential, and it is estimated that it will eventually account for about 50% of the total demand for optical fibers in the country.

Due to the special installation occasions of indoor optical cables, the requirements for indoor optical cables are also relatively strict. In addition to the necessary optical transmission and mechanical properties, the performance of the indoor optical cable must also meet the following characteristics: simple structure, small outer diameter, fire prevention, soft, easy to bend, easy to operate, etc., can also be done according to customer requirements Environmental protection, anti-rat, lightning protection, waterproof, etc., while indoor optical cables have much lower requirements than outdoor optical cables in terms of anti-ultraviolet radiation or waterproof performance. If it is really necessary to be waterproof, considering the ease of installation, a dry structure is generally adopted.

1. Bring in the optical cable

At present, the wiring method of both optical cables and other cables is the same, but there are some small changes in the route trend between different buildings. Let's use an example of a relatively common wiring method at present.

The main distribution frame (MDF) is installed in the public area of the building, and the optical cables lead to each floor through vertical rods, and then enter the room through horizontal pipes.

The optical cable used in Figure 1 is the drop optical cable. Users can choose user optical cables with different structures to realize FTTH according to needs and installation conditions. An 8-core suspension-type drop-in optical cable designed and developed by NTT Company is introduced.

This cable uses PVC tight-sleeved optical fiber, metal suspension wire, PVC or LSZH as flame-retardant sheath layer, suitable for indoor wiring, stable and reliable performance; produced by small bending radius optical fiber, has excellent bending resistance; flame retardant; construction Convenient and reliable. Special tools can be used to strip the cable, stripped from the "V" groove area of the optical cable to obtain tight-buffered optical fibers, and the operation is simple.

Figure 38 Stripping of suspended drop cable

2. User optical cable

User optical cables include single-core, double-core, bundle-tube multi-core, ribbon, "V"-shaped optical cables, metal armored flexible optical cables, etc. There are many specifications of the outer diameter of the optical cable, which can adapt to the requirements of different connector sizes and wiring space environments, and is suitable for indoor wiring.

Typical tight-buffered single/double-core optical cablel

The structure of single/dual-core indoor optical cable is relatively simple. The overall size is small, generally 3mm to 3.4mm, and the amount of materials other than optical fibers is reduced, which also improves the flexible bending performance of optical fibers, which is very beneficial for indoor wiring. Only one connector is needed, it is convenient to connect with the terminal equipment, easy to be accepted by users, and has a certain development prospect. In addition, if two loose tubes are twisted or twisted around the dielectric center piece, and then covered with aramid tow and outer sheath, a 4-core indoor optical cable can be made, but the size is still small, and the outer The diameter is 3.3mm~3.7mm, which can be used for LAN wiring.

Armored indoor flexible optical cable: l

With the advancement of FTTH, a cable that is as convenient as an electric wire will be needed at the user terminal (family, corridor). Fiber home Communications has designed an indoor and outdoor integrated optical cable - the armored indoor single-core optical cable and has applied for a patent. The specific structure. This product is equipped with a metal hose in the optical cable, which significantly improves the compression, tensile and bending resistance of the optical cable, and at the same time prevents damage from rat bites; the high-strength aramid fiber reinforcement ensures that the optical fiber has no tensile strain, and the outer diameter is the standard optical cable the outer diameter is suitable for the application of various connector components; the bending flexibility is good, and the minimum curvature radius can reach 10 times the cable diameter; it is flame retardant; small size and convenient construction.

This kind of optical cable is widely used in national defense communication, radio and television system, building intelligent control, power control system, transportation communication system, metropolitan area network and local area network. Specific applications include:

It is suitable for direct laying optical cables for indoor and outdoor connections along walls, roofs, mezzanines and conduits. The pigtails and active connecting cables for communication equipment produced with standard and strong structural design can be directly used for the connection between devices. Indoor horizontal wiring, vertical wiring in buildings, LAN network, suitable for connection of multiple information points, recommended for direct connection with end users. Between outdoor buildings, community backbone network cabling; outdoor cabling is directly brought indoors to reduce costs. Used as the tail cable of the backbone network, it is directly connected to the equipment in the building from the backbone network to isolate lightning and improve system reliability. The minimum bending radius is small, which can be used for large-capacity, multi-client indoor overall laying and unit wiring, and can be used independently as branches, and can be easily connected to each terminal. It is recommended for high-density wiring, small installation space and small installation curvature.