Everything about Fiber Optic Connectors

Standards for Fiber Optic Connectors

As an optical component, fiber optic connectors comply with several standards in telecommunications cabling or electrical engineering fields. Here is a table that provides part of the standards that fiber optic connectors accord with:

Fiber Optic Connector Definition

Fiber optic connector, or optical fiber connector, is a component to terminate the end of a fiber optic cable and enables quicker connection and disconnection than fiber splicing. It mechanically couples and aligns the fiber cores to make light pass successfully. Therefore, fiber optic connectors have an important impact on the fiber optic transmission reliability and the performance of the system. Normally speaking, high-quality optical connectors will lose very little light due to the reflection or misalignment of the fibers.

Structure of Fiber Optic Connectors

For an optical connector design, there are five key and important components: the fiber ferrule, the sub-assembly body, the connector housing, the fiber cable, and the stress relief boot. We'll take an SC connector for example to illustrate the structure of the fiber optic connector.

  • Fiber Ferrule The SC connector is built around a long cylindrical 2.5mm diameter ferrule, made of ceramic (zirconia) or metal (stainless alloy). A 124um-127um diameter high precision hole is drilled in the center of the ferrule, where stripped bare fiber is inserted through and usually bonded by epoxy or adhesive. The end of the fiber is at the end of the ferrule, where it is typically polished smooth.

  • Sub-assembly Body The ferrule will be assembled in the SC sub-assembly body that has mechanisms to hold the cable and fiber in place. The end of the ferrule is out of the sub-assembly body in order to mate with another SC connector inside a mating sleeve (i.e. adapter or coupler).

  • Connector Housing Then the connector housing will cover the connector sub-assembly body, which provides the mechanism for snapping into a mating sleeve (adapter) and holding the connector in place.

  • Fiber Cable Fiber cable and strength member (aramid yarn or Kevlar) are crimped onto the connector sub-assembly body with a crimp eyelet, increasing the strength of the mechanical handling of the connector while protecting the fiber inside at the same time.

  • Stress Relief Boot Stress relief boot covers the joint between the connector body and fiber cable to protect the fiber cable from mechanical damage. Stress relief boot designs are different for 900um tight-buffered fiber and 1.6mm-3mm fiber cable.

Key Features of Fiber Optic Connectors

The key characteristics of the fiber connectors include optical properties, interchangeability, repeatability, reliability, insertion times, etc.

  • Optical Properties: insertion loss and return loss are the two main parameters for the optical properties. The lower the insertion loss value, the better. Normally, a qualified connector should keep the insertion loss value below 0.5dB. Contrariwise, a higher return loss will indicate better performance of the connector. The typical value of the connector's return loss should not be less than 25dB, while practically not less than 45dB on account of the polishing process.

  • Interchangeability and Repeatability: Fiber optic connectors are universal passive devices, the fiber connector of the same type, can be used in any combination and can be used repeatedly.

  • High reliability: Outside plant applications may require fiber connectors to be located underground or outdoor walls. High-reliability connectors are needed in these harsh environments to make sure of smooth optical transmission.

  • Utilization Rate: Can be plugged more than 1,000 times generally. Therefore, a fiber connector that is easy to use will help users save lots of installation time and improve working efficiency.

Fiber Optic Connector Types

Based on different classification methods, fiber optic connectors can be divided into different types. According to the pin end surface of the connector, they can be divided into PC, UPC, and APC. According to the different transmission media, fiber connectors can be divided into single-mode and multimode fiber optic connectors. Multiple fiber optic connectors have been introduced to the market, but only a few represent the majority of the market, like LC, SC, FC, ST, and MTP/MPO connectors.

Fiber Connector Coupling Loss

Only the light that is coupled into the receiving fiber's core will propagate, while the rest of the light is not transmitted through the splice and is radiated out of the fiber. Ideally, the loss will be minimized if the two fiber cores are identical and perfectly aligned, the connectors or splices are properly finished and no dirt is present. Unfortunately, both the fiber and connector are subject to manufacturing tolerances that create less than perfect alignment.

Connector and splice loss is caused by many factors. For example, end gaps will influence the insertion loss and return loss. Therefore, optical connectors will adopt a number of polishing techniques to insure physical contact of the fiber ends to minimize back reflection. In addition, light from a fiber with a larger numerical aperture (NA) will be more sensitive to angularity and end gap, so transmission from a fiber of larger NA to one of smaller NA will be higher loss than the reverse. In other words, connecting larger fibers to smaller ones results in substantial losses, not only due to the smaller cores size, but also the smaller NA of most small core fibers.

Fiber Optic Connector Applications

Fundamentally speaking, the fiber optic cables with optical connectors are mainly used in telecom communication fields, from small or middle-sized offices to hyper-scale data centers. According to the chart, telecom accounted for the largest market share in terms of revenue in 2018, which is anticipated to continue its dominance in terms of size by 2025. Furthermore, increasing cloud-based applications, audio-video services, and Video-on-Demand (VoD) services will also stimulate demand. There is still a continued rise in global demand from the burgeoning IT industry regarding the availability of power-efficient, cost-effective, and high-level network infrastructure.

Besides, the oil & gas, military & aerospace, and medical application segments are poised to witness significant growth rates, owing to the increasing adoption of multimode and Plastic Optical Fiber (POF) across these application segments. For instance, military forces use the optical connector technology for a wide variety of ground, sea, air, and space solicitations, such as in avionics testing equipment modules and ground support systems in fighter planes.