When splicing two optical fibers, two optical fibers due to the difference in position, shape, structure and the like, resulting in 100% of the energy can not enter from one fiber to another optical fiber, i.e., the connection loss occurs. In order to reduce connection loss as much as possible, precise alignment between the two optical fibers must. The main role of the optical fiber connector to connect two optical fibers is fast, the optical signal optical path may be formed continuously. The fiber optic connectors are how to achieve accurate optical fiber connection?
The fiber optic connector are many types, however, precise alignment between the optical fiber depends on two factors, one is a precision ceramic ferrule having an inner diameter, an outer diameter and concentricity, and the second band is slotted ceramic sleeve, this ceramic sleeve is a very clever design. From Figure 1 can be seen how the two optical fibers to achieve precise alignment by a ceramic sleeve, the inner diameter of the ceramic ferrule outer diameter of the sleeve is slightly smaller than, because slits, to insert the ferrule to the sleeve. The sleeve is expanded tightening the two ferrules to achieve precise alignment.
FIG 1 precise alignment between the two fibers
SMF single-mode fiber core diameter is only about 8 ~ 10μm, in order to ensure the connection between the low-loss, two optical fibers must be closely aligned. Can be seen from Figure 2 the two optical connection loss between the lateral displacement amount relationship, the relationship is exponential curve, a small lateral offset of 2.4μm to loss of 1dB will produce. Thus for single mode fiber connectors, lateral misalignment between the two optical fibers should be less than 0.5μm.
The relationship between the loss of the optical fiber connector of FIG. 2, the lateral slippage
Physical contact with the end face of the optical fiber
, however, only a precise alignment, the optical fiber connector is not enough. We know that the light at the interface of two different media reflection echo occurs. Quartz fiber refractive index of about 1.455 at 1.55μm, and therefore the fiber end reflection echo BR 3.4%. Affect the stability of the optical communication system according to the reflection, while each of the silica glass - air interface also introduce insertion loss of about 0.15dB. So that each optical fiber splice loss of 0.3dB increases.
It is generally permeable membrane by coating the end face to reduce the echo, but is not considered a problem in the coating of the optical fiber connector. First, AR coated film will increase the cost of the connector; secondly, the optical fiber connector is not fixed, repeated mating destroys antireflection coating. We can then coated antireflection film in the fiber end faces, and holding the fiber end does not contact it? Can be seen from Figure 3 the relationship between the longitudinal pitch of the optical fiber and two optical fibers butted loss, small losses introduced into the gap will be nearly 50μm of 1dB, this optical fiber communication system can not be tolerated.
So we get consensus must contact between end faces of two optical fibers and optical fiber can not be coated. Echo occurs between the two air boundary surface, the fiber end faces of different media to be discharged, such that the two fiber end faces to achieve physical contact (PC), as the media integration. Since the optical fiber is fixed to the intermediate ceramic ferrule, any rough ceramic surface, it will affect the physical contact between the optical fibers. To ensure that physical contact between the optical fiber, the ferrule is generally polished to have a spherical surface, the fiber end faces at the apex of the sphere, which is a second optical fiber connector in a smart design. As shown in FIG, 1 is a ferrule inserted into the sleeve, under pressure, deform the ferrule end surface, end surface modification can ensure physical contact between the optical fibers. Since physical contact depending on the end face deformation, and wear both ceramic has a certain elasticity, which is why it is not selected as the glass material of the ferrule.
FIG 3 is inserted and the relationship between the loss of fiber pitch
Further reduced echo
physical contact between the optical fiber may ensure a low-loss optical fiber splice point, but only the return loss RL reaches 55dB. Some applications require higher for the RL, the end face polished optical fiber connector is angled physical contact bevel called APC. FIG 4 a graph showing the relationship between the RL and increase the angle of the fiber end, the fiber end faces are usually milled to 8 ° bevel, an additional 36dB can RL, RL so overall the APC connector is typically greater than 65dB.
FIG 4 the return loss and the relationship between the fiber end face angles RL
The fiber optic connector is an optical fiber communication system, the most basic passive devices, optical fiber connector system of the basic technical requirements include low insertion loss IL, high return loss RL, i.e., as low as possible echo BR. However, as the most widely used optical passive devices, cost and ease of connection and technical indicators are equally important.
About HYC (HYC CO., LTD)
HYC (English abbreviation HYC) was founded in 2000, it is a global industry leader in passive optical components OEM / ODM and solutions provider specializing in optical communication passive infrastructure device development, manufacturing, sales and service. Main products are: four core optical fiber connector (High Density Data Center optical connector), the WDM wavelength division multiplexer, PLC optical splitter, the MEMS optical switch based passive optical device, the optical fiber is widely used to fIELD households, 4G / 5G mobile communication, Internet data centers, defense communications.