Technology center

Optical fiber and cable

The composition and classification of optical fiber

1. Optical fibers can be divided into quartz optical fibers and plastic optical fibers according to their manufacturing materials. Quartz optical fibers are commonly used optical fibers. Quartz optical fibers are classified into single-mode optical fibers and multi-mode optical fibers according to their transmission modes. Plastic optical fibers are all composed of plastic, and are usually used for multi-mode short-distance applications.

2. Classification of silica fiber

Single mode fiber

G.652A (B1.1 referred to as B1); G.652B (B1.1 referred to as B1); G.652C (B1.3); G.652D (B1.3); G.655A optical fiber (B4) (long-distance trunk Use); G.655B fiber (B4) (for long-distance trunk lines)

Multimode fiber

50/125 (A1a is referred to as A1); 62.5/125(A1b)

Second, the structure of the optical cable

1. Outdoor optical cables mainly have three structures: central tube type optical cables, layered type optical cables and skeleton type optical cables. According to the use of optical fiber bundles and optical fiber ribbons, they can be divided into 6 types: ordinary optical cables and optical fiber ribbon optical cables. The structural characteristics of each optical cable:

(1) Central tube type optical cable (Executive standard: YD/T769-2003): The center of the optical cable is a loose tube, and the strengthening member is located around the loose tube. Such as the common GYXTW optical cable and GYXTW53 optical cable, the optical cable core The number is small, usually less than 12 cores.

(2) Stranded optical cable (Executive Standard: YD/T901-2001): The strengthening member is located in the center of the optical cable, and 5~12 loose tubes are twisted on the core strengthening member in a twisting manner. The twisting is usually SZ stranding. Such optical cables, such as GYTS, can be combined with loose tubes to obtain optical cables with larger core counts. The color separation of the stranded loose tube usually adopts the red and green led color spectrum to distinguish different loose tubes and different optical fibers. The number of stranded optical cable cores can be larger. At present, the number of stranded optical cable cores of our company can reach 216 cores or higher.

(3) Skeleton optical cable: the reinforcing member is located in the center of the optical cable, and the reinforcing member is a skeleton groove composed of plastic. The optical fiber or optical fiber ribbon is located in the skeleton groove. The optical fiber or optical fiber ribbon is not easy to be compressed, and the optical cable has good crush resistance. This kind of structural optical cable is rare in China, and it accounts for a small proportion.

(4) Figure 8 self-supporting structure. This type of optical cable can be incorporated into central tube and stranded optical cables. It is listed separately mainly because the structure of the optical cable is quite different from other optical cables. Usually there are central tube type and layer-stranded figure-8 self-supporting optical fiber cable.

(5) Flame-retardant optical cables for coal mines (Executive Standard: Q/M01-2004 Enterprise Standard): Compared with ordinary optical cables, the requirements for flame-retardant performance of optical cables are improved, and the optical cables are specially designed to be suitable for use in mine environments. Usually the outer sheath color is blue to facilitate the identification of the optical cable in the mine. According to the structure, it can be divided into two types of structures: central tube type optical cable and layered type optical cable.

1. Indoor optical cable

Indoor optical cables are classified according to the number of fiber cores, mainly single-core, dual-core and multi-core optical cables. Indoor optical cable is mainly composed of tight-buffered optical fiber, spun fiber and PVC outer sheath. According to the type of optical fiber, it can be divided into two categories: single-mode and multi-mode. Single-mode indoor cables usually have yellow outer sheath, and multi-mode indoor cables usually have orange outer sheath. Some indoor cables have outer sheath color. gray.

Third, the naming method of optical cable model

GY-outdoor optical cable for communication; GJ-indoor optical cable; MG-optical cable for coal mine

Strengthening member type

(No model)——Metal strengthening member; F——Non-metal strengthening member

Structure

D——Optical fiber ribbon structure; (unsigned)——Loose tube stranded structure; X——central tube structure; G——skeleton structure; T——filled type; Z——flame retardant structure; C8— —8-shaped self-supporting structure

Protective layer

Y——Polyethylene protective layer; W——Entrained steel wire steel-polyethylene adhesive protective layer; S——Steel-polyethylene adhesive protective layer; A——Aluminum-polyethylene adhesive protective layer; V——Polyethylene Vinyl chloride sheath

Outer sheath

53—Corrugated steel tape longitudinally wrapped armored polyethylene sheath; 23—Wrapped steel tape armored polyethylene sheath; 33—small steel wire wrapped armored polyethylene sheath; 43—thick steel wire wrapped armored polyethylene sheath Sheath; 333—Double thin steel wire wrapped armored polyethylene sheath

2. Optical fiber engineering

Optical fiber network system design

The design of optical fiber system generally follows the following steps:

1. First of all, find out what kind of network is to be designed, its current status, and why fiber is used.

2. According to the actual situation, choose the appropriate fiber optic network equipment, fiber optic cables, jumpers and other items for connection. The selection should be based on availability, and then based on performance, price, service, origin and quality.

3. Determine the route of the line according to the customers requirements and network type, and draw the wiring diagram.

4. When the route is long, the attenuation margin of the system needs to be calculated. The calculation can be carried out according to the following formula:

Attenuation margin = transmitted optical power-receiving sensitivity-line attenuation-connection attenuation

(dB) where line attenuation = optical cable length × unit attenuation; unit attenuation has a great relationship with fiber quality, generally 0.4~0.5dB/km for single mode; 2~4dB/km for multimode.

Connection attenuation includes splice attenuation and joint attenuation. Splice attenuation is related to welding methods and the quality of personnel. Generally, heat fusion is 0.01~0.3dB/point; cold fusion is 0.1~0.3dB/point; joint attenuation has a great relationship with joint quality. Generally 1dB/point. The system attenuation margin is generally not less than 4dB.

5. When the calculation is unqualified, the design should be modified according to the situation before the calculation. This situation may sometimes be repeated several times.

1. Design example:

1. Transformation of campus network 1: According to its situation, use a LANart three-port repeater (twisted pair-optical fiber-thin cable) on one side of the existing thin cable network, and use a LANart backbone with optical fiber on the other side Twisted pair HUB. In the middle, a beam tube type 4-core outdoor multi-mode optical fiber cable with overhead or buried uniformity is fused into an indoor jumper with ST head (because the optical fiber interface of the equipment is ST type). Attenuation calculation: (Generally, multi-mode equipment does not need to be calculated within 2km, here is just an example)

Transmitting power: -16dBm

Receiving sensitivity: -29.5dBm

Line attenuation: 1.5km×3.5dB/km=5.25dB

Connection attenuation: The attenuation of 2 connectors is: 2 points×1dB/point=2dB

The two splicing points are: 2 points×0.07dB/point=0.14dB Attenuation margin = -16 dBm-(-29.5dBm)-5.25 dB-0.14dB-2 dB =6.11(dB) After the above calculation, you can see If the system capacity is greater than 4dB, the above options can meet the requirements.

2. The transformation of campus network 2: It is 14 buildings that need to be connected by optical fiber, and each building must have its own subnet (10Mbps Ethernet), and the distance between adjacent buildings is less than 2km. Consider using FDDI double-ring as the backbone, placing an FR2100 FDDI/Ethernet double-ring bridge in each building, and then connecting them with 6-core outdoor duct optical cables.

In each building, a fusion splicing method is used to switch the 6-core outdoor optical cable into three FDDI standard MIC head jumpers to connect to the FDDI bridge. In this way, 6 points are spliced in each building, and an optical fiber terminal box with one input and eight output is required. A total of 21 MIC jumpers, 14 terminal boxes, 84 splice points, and 14 6-core outdoor optical cables are required for 14 buildings. And 14 FDDI/Ethernet dual ring bridges. As the distance between buildings is small (less than 2km), it is generally not necessary to calculate the attenuation margin.

Three, optical fiber connector

MPO fiber optic connector

MPO fiber optic connector is a multi-core multi-channel plug-in connector. It is characterized by a rectangular ferrule with a nominal diameter of 6.4mm×2.5mm, and two guide holes with a diameter of 0.7mm on the left and right sides of the ferrule are used for positioning and centering with the guide pin. It is used for the connection of 2~12-core side-by-side optical fibers, and more often two rows of 24-core optical fibers are connected simultaneously. When docking, a spring installed at the end of the ferrule exerts an axial pressure on the ferrule until the outer frame of the connector is locked with the adapter. There is a male (convex) key on the upper side of the ferrule, which is used to limit the relative position between the connectors during connection to determine the correct connection sequence of the fiber. The connector interface is composed of a female plug with a guide pin hole and a male plug with a guide pin butt and locked in an adapter (as shown in the figure).

MPO type connector structure

MT ferrule is a key part to determine the connection characteristics of the connector. The ferrule has two guide holes (needles) and several fiber holes. The pitch of the guide hole (needle) and the fiber hole are 4.6mm and 0.25mm respectively. In order to obtain the low insertion loss of the single-mode fiber, the misalignment between the fiber hole and the design position must be less than or equal to 1 μm. According to the existing MT ferrule design standard, it is necessary to increase the number of cores of the connector to more than 12 cores. It is already difficult to arrange the optical fibers in one column on the end face of the ferrule. The above 2-D array ferrule. In the traditional MPO connector containing the MT ferrule, repeated insertion will cause cracks or damage to the end surface near the guide hole, which will eventually affect the stability of the insertion loss. By chamfering the proximal surface of the guide hole, the loss can be effectively reduced.

According to the grinding method of MT ferrule, MPO connectors can be divided into:

-MPO flat connector: MPO connector with flat ferrule end face

-MPO beveled connector: MPO connector whose ferrule end face is beveled (usually 8° angle)

Optical performance index of MPO type multimode optical fiber connector plug:

-The larger insertion loss of any plug through the standard adapter and standard plug is ≤0.7dB (including repeatability).

-The larger insertion loss of two plugs arbitrarily connected through the adapter is ≤1dB. 

Optical performance index of MPO type single-mode optical fiber connector plug:

-The larger insertion loss of any plug through the standard adapter and standard plug is ≤0.8dB (including repeatability); the return loss is more than 30dB (MPO/PC), and more than 50dB (MPO/APC).

-The larger insertion loss of two plugs arbitrarily connected through the adapter is ≤1dB; the return loss>20dB (MPO/PC),>40dB (MPO/APC).

Advantage

-Small size, smaller than SC type connector;

-High precision, precise MT guide pin and guide hole ensure the accuracy of fiber alignment;

-With high density and precise geometric design, it can support 12-72-core or even 96-core fiber connection.

application

-Application in high-density environment of data center;

-Fiber to the building (FTTB) application;

-Optical splitter, 40G/100G SFP, SFP+ and other optical transceiver equipment internal connection applications.