Fiber optic connector technology has evolved during the last decades aided by many technological companies and individuals aimed to obtain the best solution to minimize power loss at lower cost as well as other problems, such as the form factor or rapid connection. This research has given to date the overwhelming figure of more than 100 different fiber optic connecting solutions introduced in the marketplace.
However, only a few of them still remain. The figure below presents some of the most significant connectors used by industry and research, which are reviewed some paragraphs below.
Generally, fiber optic connectors consist of male connectors with an extended ferrule that holds the fiber or fibers and helps for the correct fiber alignment with the counterpart fiber connector via a mating adapter that holds both fiber connectors in the right place and secures the mechanism. Variations in the ferrule position, size and termination as well as mating adapter fixation with the fiber connector have given the different fiber optic connecting solutions used to link LEDs, SLEDs, VCSELs, Lasers, spectrometers, OTDRs, OSAs and other devices.
Here, we will review only some of the most common fiber optic connectors but you can find more information about these in the TIA connector intermateability standards FOCIS-x (TIA-604-x).
SMA (SubMiniature version A): a screw-on type connector mainly used in industrial lasers, optical spectrometers, spectrometers and communications in multimode fiber. Ferrule diameter typically 3.14mm. It is not recommended for reflection applications due to the air gap between connectors that can give undesired reflections.
ST (Straight Tip): or Slotted Bayonet type Fiber Optic Connector was one of the most popular optical fiber connectors some decades ago but it is almost obsolete and replaced by small form factor connectors that enable multiple fiber connection. Ferrule diameter 2.5mm.
FC/PC (Ferrule Connector/Physical Contact) – FC/APC (Ferrule Connector/Angled Physical Contact): slotted screw on type connector. It is a connector with a threaded body designed for use in high-vibration environments. Commonly used with both single-mode and polarization maintaining optical fiber (SMF & PMF). Ferrule diameter typically 2.5mm. It has been replaced by SC connectors but it is still in use with single mode lasers, light sources and analyzers.
SC (Standard Connector): or Subscriber connector or square connector is a Push/pull type connector commonly used in communication applications replacing ST or FC connectors in patch panels either using single or multimode fibers. Ferrule diameter 2.5mm.
It is also important to pay attention to the colour code of the connector and the jacket itself in order to identify the fiber type. In this sense, orange, black and grey jackets identify multimode fibers while yellow jackets are associated to singlemode fibers. Concerning the connector bodies, beige and black are generally used for multimode fiber while blue and green (angled connectors) are associated to singlemode fibers. More information and details about this can be found in TIA 568 colour code for connector bodies.
Another important point to take into account is the fiber to fiber connection, which can cause serious headaches if you are not familiar with the connector mechanical configuration. In this sense, the connectors that lack of fixed orientation and enable fiber rotation, such as SMA, present an air gap between the fiber ends that prevents the fiber optic end from scratches at the expenses of an increase in power losses as well as undesired reflections in the air cavity. On the other hand, connectors with fixed position like ST and FC present direct fiber to fiber connection (physical contact) without an air gap reducing power losses and preventing undesired reflections, such as FC/PC connector or even optimizing the coupling with angled connectors, such as FC/APC as it is represented in Figure 2. Finally, it is important to remark that Pyroistech offers the possibility to configure your fiber coupled light source with any of the connectors mentioned above.
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