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Comprehensive analysis of the working principle of optical fiber connectors

Update:28-08-2020
Summary:

The epoxy resin thermosetting agent is used to glue the […]


The epoxy resin thermosetting agent is used to glue the optical fiber in the ceramic pin hole, and is positioned through the adapter sleeve to realize the butt connection of the optical fiber. Insertion loss is caused by the lateral deviation between two consecutive optical fibers, the longitudinal gap in the optical fiber connector, and the quality of the end face.

Users such as CATV systems should choose APC-type contact methods.

High-quality tight-buffered fiber optic cables, high-precision ceramic pins and assembly parts, and excellent assembly processing technology ensure the high quality of products.

Optical fiber connector is an indispensable device for connecting various devices in optical fiber communication system, and it is also the most used optical fiber device at present. Due to the gradual optical fiberization of local communication networks and the rising demand for metropolitan area networks and user access networks, the total demand for the global optical fiber connector market has continued to expand in recent years, and the annual growth rate in the next ten years is expected to be about 20%.

Although there are more than 70 kinds of optical connectors in the world, and new varieties are still appearing, the mainstream varieties in the market (especially the Chinese market) are still the precision ceramics with a diameter of φ2.5mm that have been inherited in the early years. Connectors composed of ferrules and ceramic tubes (such as FC, SC, ST, etc.). In addition, the demand for small connectors with φ1.25mm ceramic cores (such as LC, MU, etc.) and multi-core connectors (such as MTP, etc.) based on ribbon fiber connectors are gradually increasing.

Generally, the main optical characteristic indicators for measuring the quality of optical fiber connectors are Insert loss and Return loss. In addition, physical characteristics such as the geometric parameters of the ferrule end face that affect the quality and reliability of the product are increasingly being valued by system manufacturers or high-end customers. Starting from the working principle of the optical fiber connector, the following briefly introduces the insertion and return loss of the connector:

The optical fiber connector cannot be used alone. It must be interconnected with other connectors of the same type to form the optical path connection. At present, the more popular optical fiber connector assembly and docking method is: use epoxy resin thermosetting agent to connect the optical fiber Cement in the high-precision ceramic pin hole, and then make the two pins under the action of external force, through the positioning of the adapter sleeve, realize the butt connection between the optical fibers (see Figure 1).

Comprehensive analysis of the working principle of optical fiber connectors

As can be seen from Figure 1, ensuring that the cores of the two butted optical fibers are in a straight line when they are in contact is the key to ensuring the excellent connection quality of the connector. It mainly depends on the physical properties of the optical fiber itself, the manufacturing accuracy of the connector pins, and the connection Assembly and processing accuracy of the device. At the same time, the optical performance index of the optical fiber and the polishing quality of the pin end face also have a direct impact on the optical performance and reliability of the connector.

Insertion loss refers to the optical power attenuation caused by the connected connector to the system (that is, the relative decrease in the output power of the optical connector relative to the input power). Insertion loss is mainly caused by the lateral deviation between two consecutive optical fibers. As shown in Figure 1, if two optical fibers are arranged in a straight line and the lateral deviation is zero, the insertion loss caused by them is the smallest. But in the actual mating process of the connector, this is unlikely to be achieved because of the misalignment of the fiber core and the fiber cladding, the misalignment of the fiber cladding and the inner hole of the pin, and the concentricity of the inner hole and the outer diameter of the pin. Degree errors, etc., will cause lateral deviation between optical fibers. At the same time, the longitudinal gap and the quality of the end face in the optical fiber connector are also one of the factors that cause the insertion loss. The UPC plug contact method commonly used in recent years has better solved the longitudinal gap problem. In this way, the pin and the fiber end face are polished spherically, so that the two opposite pins are meshed together under the action of external force, so that the apex of the meshed fiber is deformed and flattened to form a sufficient butt of the fiber and reduce the number of fiber joints. The longitudinal gap. Return loss is a parameter used to measure the size of the back-reflected light on the connector end face. The essence of echo is light reflection. According to the principle of Fresnel reflection, Fresnel reflection occurs when light encounters two interfaces with different refractive indexes during transmission, causing signal superimposition or interference in the optical path. In a single-mode fiber system with a high transmission rate, especially a cable television system (CATV), the reflection phenomenon will cause a time lag in the transmission signal, which will delay the time the signal arrives at the user end, causing ghosting and degrading of the image.

The UPC contact method of the connector joint reduces the gap between the connection end faces, and in addition to reducing the insertion loss, it also reduces the reflection of the connection end face and improves the return loss. For users such as CATV systems, the APC type The contact method is a better choice: because the spherical normal of the end face of the ceramic ferrule of the APC type connector has an angle (usually 8°) with the axis of the fiber, the light reflected from the end face leaks out without returning to the core. Thereby greatly improving the return loss of the connector.

In summary, for an excellent connector jumper manufacturer, in order to ensure the high quality of the product, three factors are very important. They are high-quality tight-buffered fiber optic cables, high-precision ceramic pins and Assemble parts, and excellent assembly processing technology:

As far as optical fiber is concerned, the impact of optical fiber on the performance of the connector is mainly reflected in the attenuation coefficient of the optical fiber itself and the manufacturing tolerance of the optical fiber and cable (especially the core/cladding concentricity error): for longer connector jumpers, the optical fiber itself Excessive attenuation coefficient will cause the congenital deficiency of the connector jumper and increase the energy loss in the optical path; the large core/cladding concentricity error will easily cause the lateral deviation of the core. Therefore, high-quality optical fiber is essential for the low insertion loss of the product.

As far as the ceramic pin is concerned, the smaller concentricity error and the good match between the inner hole diameter and the outer diameter of the fiber cladding (ie small gap) can also reduce the lateral deviation of the core and reduce the insertion loss; at the same time, high precision Assembling the spare parts can ensure that the product is fully connected and in a good state of force during the connection, which directly affects the return loss.

And the excellent product manufacturing technology, including perfect process control, sophisticated grinding and testing equipment, and matching grinding and polishing process and quality monitoring, enables the product to meet the high-quality end face and optical characteristics indicators, and can be based on customers Adjust the geometric parameters of the end face of the ferrule within the scope of the corresponding standard requirements to improve the system connection and use reliability.

 

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