Non-preset fiber optic connection

With the large-scale application of FTTH, the application of field optical fiber connectors (optical fiber quick splicing connectors) is becoming more and more extensive, and people's discussion on the rapid optical fiber termination technology is gradually deepening. At present, there are mainly two viewpoints of pre-installed optical fiber connection theory and non-pre-installed optical fiber connection theory. The main representative manufacturers of pre-installed optical fiber connection products are 3M, Corning, Sumitomo, Fujikura and so on. In the past, it mainly encountered the bottleneck of optical fiber cutting technology, and was limited by the problem of on-site optical fiber cutting angle and surface defects, and the direct connection of on-site optical fibers could not be used. Therefore, most companies have been using pre-installed optical fiber technology to produce on-site connectors.

2. Continuation mechanism

The theory of non-preset fiber splicing means that the splicing point of the on-site splicing connector is set on the ferrule surface, and the on-site optical fiber cutting surface is connected with the pre-grinding optical fiber spherical surface of the ordinary connector, and there is only one connection point between the active connection of the two optical fibers. end technology. The theory of pre-installed optical fiber connection means that the connection point of the field connection connector is set in the V-shaped groove inside the connector, one end of the pre-installed optical fiber is glued in the ferrule, and the other end is aligned with the field fiber cutting surface in the V-shaped groove. Crimping, a light guide material with a refractive index similar to the core is placed in the splicing point - matching liquid, the end of the pre-installed optical fiber glued in the ferrule is ground in the factory to form a UPC or APC surface, which is pre-ground with the target connector Optical fiber spherical connection splicing, a termination technology with two connection points between the active connections of two optical fibers.

The field-cut optical fiber is aligned with the common connector fiber through the high-precision ceramic ferrule and fiber centering sleeve, and the field-cut fiber is fixed in the V-groove behind the quick connector ferrule. The spherical surface of the pre-polished optical fiber of the connector is closely attached by the micro-elastic deformation of the optical fiber on site. The surface of the optical fiber cutting on site needs to be treated, and there is no need to set the matching liquid between the connection points.

The guide fiber core is mainly made of light guide material with high refractive index, the material is dense and the purity is high. The cladding of the optical fiber is made of low-refractive-index light-guiding materials, including step type and graded type, and its cladding is even deliberately made of air holes or other structures to reduce the refractive index. When cutting the fiber, the cutting defects are mainly in the cladding area, the fiber core is the fracture surface, and the surface is very smooth, achieving a mirror effect, which is far from the grinding effect. The flat, fiber-cut surface can fully meet the requirements of fiber splicing.

Fiber splicing theory

3. Requirements for non-preset optical fiber splicing theory 3D

The success of the connection of the optical fiber line depends on the quality of the physical connection of the optical fiber, which is the geometric size of the end face of the non-preset optical fiber splice connector itself. If this geometry is not strictly controlled, there can be no long-term reliable connection to the network.

When the non-preset optical fiber splicing theory is applied to the field connector, the field optical fiber has special requirements on the state and position of the connector, and there is also a 3D standard. UNIKIT YT-2007 stipulates 6 technical parameters for the non-preset optical fiber splicing connector : Fiber height, fiber face depression, aperture gap, concentricity deviation, curvature radius and vertex offset. If the geometric size cannot meet the requirements, it will face the risk of deterioration of the optical connection index or even failure of the optical fiber link. Therefore, it is very important to correctly understand the geometric size of the end face.

(1) Fiber height

Fiber height is the distance from the fiber end face to the ferrule end face. This indicator is used to measure the contact between the optical fiber and the optical fiber. When the field connector is matched with the ordinary connector, the optical fiber concave will form the air gap between the optical fiber contacts, the Fresnel reflection phenomenon will occur, the insertion loss will increase, and the return loss will change. small (absolute value). Excessive protrusion of the fiber will increase the pressure between the fibers, increase the dynamic fatigue of the fiber, and damage the fiber, or transmit the pressure to the V-groove of the fixed fiber, destroy the fixation of the fiber, and affect the stability of performance.

(2) Depressed fiber surface

The fiber face depression is the distance from the concave peak to the valley of the fiber end face that is cleaved in situ. This indicator is also used to measure the contact between the optical fiber and the optical fiber. When the field connector is mated with the ordinary connector, the concave fiber surface will form the air gap between the optical fiber contacts, changing the insertion and return loss.

(3) Aperture clearance

Aperture clearance refers to the difference between the aperture of the quick connect connector ceramic ferrule and the field fiber. This indicator is used to measure the repeatability of the contact between the optical fiber and the optical fiber. When the field connector is matched with the ordinary connector, the excessive aperture gap will cause instability of the optical fiber fitting state and change the insertion and return loss.

(4) Concentric deviation

Concentricity deviation refers to the concentricity between the outer diameter of the ceramic ferrule of the quick-connect connector and the through hole of the optical fiber. This indicator is used to measure the contact alignment of the optical fiber to the optical fiber. When the field connector is mated with the ordinary connector, the poor concentricity will change the insertion and return loss.

(5) Radius of curvature

The radius of curvature refers to the radius of the curve of the end face of the ferrule. The field connector uses the pressure of the spring to achieve the close contact between the ceramic ferrule and the end face of the optical fiber of the ordinary connector. The radius of curvature is used to control the compressive force to maintain the fiber center matching force. The unqualified curvature radius will gradually increase the pressure on the fiber, and even damage the fiber end face.

(6) Vertex offset

The vertex offset is the distance from the highest point of the ferrule end face curve to the axis of the fiber core. Excessive apex offset will reduce the effective coupling area of ​​the fiber, thereby increasing insertion loss and return loss.

Among these indicators, fiber height and fiber face concavity have the greatest impact on field connectors, followed by aperture gap and concentric deviation, while curvature radius and vertex offset are basically guaranteed. This is due to the micro-elasticity of the field fiber. Deformation sticking principle, minimizing the influence of curvature radius and vertex offset.

4. The connection advantage of non-preset optical fiber connection

The insertion loss of the field connector using the non-preset fiber splicing theory is less than 0.3 dB, and the return loss is greater than -40 dB.

The core of the non-preset fiber splicing theory is to reduce one splicing point to achieve ultra-low loss of optical fiber splicing, and the splicing performance is the same as that of standard connectors. Reduced the field connection standard from 0.5 dB to 0.3 dB. The requirements for the matching optical fiber connector are reduced, and the curvature radius, vertex offset and optical fiber height of the matching connector have little effect on the connection, and the application range is wide, which improves the optical fiber connection performance. The splicing point of the optical fiber is on the end face, and the cleanliness of the environment and operation is not required during splicing. After the splicing, directly cleaning the splicing end face of the optical fiber can achieve the best splicing effect. After the connection is completed, the operation effect of the optical fiber connection can be visually inspected, and the connection quality can be judged at the first time, so as to avoid post-correction and reduce the construction cost. Since there is no internal connection point, when the end face of the ferrule encounters dust, moisture and water mist, the surface can be cleaned to make the fault easy to handle.

5. Application of non-preset optical fiber connection theory

The factory-made optical fiber connector used for fiber jumper, its production process is ferrule suction glue - optical fiber stripping - fiber penetration - drying - grinding - fixed into an end; using non-preset optical fiber splicing theory, its production process is optical fiber Stripping - cutting - threading - grinding - fixing into ends. The connector produced by the non-preset fiber splicing theory has few production processes, saves time, and can be opened and used repeatedly, which greatly improves the production efficiency of the factory fiber jumper and reduces the cost.

The application of non-preset optical fiber technology has completely changed the traditional optical fiber jumper manufacturing method and the direction of on-site quick connection products, which can provide more reliable and durable optical fiber link products, and provide technical support for the early realization of a high-speed information society.