FC connector
Encyclopedia
The FC connector is a fiber-optic connector with a threaded body, which was designed for use in high-vibration environments. It is commonly used with both single-mode optical fiber
and polarization-maintaining optical fiber
. FC connectors are used in datacom
, telecommunications, measurement equipment, and single-mode laser
s. They are becoming less common, displaced by SC and LC connectors. The FC connector has been standardized in a FOCIS 4 (Fiber Optic Connector Intermateability Standards) in EIA/TIA-604-04.
made of zirconia ceramic or stainless steel
. The tip is then typically polished to produce a rounded surface, called "physical contact" polish. This surface profile means that when the fibers are mated they touch only at their core
s, allowing transmission with low loss. The fibers are spring-loaded to control the force as the plug is screwed into the receptacle. A key prevents the fiber from rotating while the connectors are being mated.
and lower back-reflection.
For applications requiring very low back-reflection, the fiber end-face is polished at an angle to prevent light that reflects from the interface from traveling back up the fiber. Because of the angle, the reflected light does not stay in the fiber core but instead leaks out into the cladding. Angle-polished connectors only mate properly to other angle-polished connectors. Mating to a non-angle polished connector causes very high insertion loss. Generally angle-polished connectors have higher insertion loss than good quality straight physical contact ones. "Ultra" quality connectors may achieve comparable back reflection to an angled connector when connected, but an angled connection maintains low back reflection even when the output end of the fiber is unmated.
Angle-polished connections are distinguished visibly by the use of a green strain relief boot. The connectors are typically designated "FC/APC" (for Angled Physical Contact), or merely "FCA".
There are two incompatible standards for key widths on FC/APC and polarization-maintaining (PM) FC/PC connectors: 2 mm ("Reduced" or "type R") and 2.14 mm ("NTT" or "type N"). Type R plugs will mate to any receptacle, but will fail to maintain precise rotation angle unless the receptacle is also type R. Type N plugs will not mate with type R receptacles and may not mate with standard FC/PC receptacles. Accurate rotation angle alignment is especially important for PM fiber, where rotational misalignment between mated fibers decreases the polarization extinction ratio of the connection. Some manufacturers mark reduced keys with a single scribe mark on the key, and mark NTT connectors with a double scribe mark.
Some connector designs have the key as a separate, indexable component. This can allow for some reduction in insertion losses (depending on the concentricity accuracy of the ferrule) by allowing the ferrule to be rotated to a more fortuitous alignment.
Single-mode optical fiber
In fiber-optic communication, a single-mode optical fiber is an optical fiber designed to carry only a single ray of light . Modes are the possible solutions of the Helmholtz equation for waves, which is obtained by combining Maxwell's equations and the boundary conditions...
and polarization-maintaining optical fiber
Polarization-maintaining optical fiber
In fiber optics, polarization-maintaining optical fiber is optical fiber in which the polarization of linearly polarized light waves launched into the fiber is maintained during propagation, with little or no cross-coupling of optical power between the polarization modes...
. FC connectors are used in datacom
Datacom
Datacom can refer to:* Data communications* DATACOM/DB, a relational database for IBM mainframes sold by Computer Associates...
, telecommunications, measurement equipment, and single-mode laser
Laser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...
s. They are becoming less common, displaced by SC and LC connectors. The FC connector has been standardized in a FOCIS 4 (Fiber Optic Connector Intermateability Standards) in EIA/TIA-604-04.
Design
The fiber end is embedded in a 2.5 mm ferruleFerrule
A ferrule is a name for types of metal objects, generally used for fastening, joining, or reinforcement...
made of zirconia ceramic or stainless steel
Stainless steel
In metallurgy, stainless steel, also known as inox steel or inox from French "inoxydable", is defined as a steel alloy with a minimum of 10.5 or 11% chromium content by mass....
. The tip is then typically polished to produce a rounded surface, called "physical contact" polish. This surface profile means that when the fibers are mated they touch only at their core
Core (optical fiber)
The core of a conventional optical fiber is a cylinder of glass or plastic that runs along the fiber's length. The core is surrounded by a medium with a lower index of refraction, typically a cladding of a different glass, or plastic...
s, allowing transmission with low loss. The fibers are spring-loaded to control the force as the plug is screwed into the receptacle. A key prevents the fiber from rotating while the connectors are being mated.
Polish options
Some manufacturers have several grades of polish, for example an FC connector may be designated "FC/PC" (for Physical Contact), while "FC/SPC" and "FC/UPC" may denote "super" and "ultra" polish qualities, respectively. Higher grades of polish give less insertion lossInsertion loss
In telecommunications, insertion loss is the loss of signal power resulting from the insertion of a device in a transmission line or optical fiber and is usually expressed in decibels ....
and lower back-reflection.
For applications requiring very low back-reflection, the fiber end-face is polished at an angle to prevent light that reflects from the interface from traveling back up the fiber. Because of the angle, the reflected light does not stay in the fiber core but instead leaks out into the cladding. Angle-polished connectors only mate properly to other angle-polished connectors. Mating to a non-angle polished connector causes very high insertion loss. Generally angle-polished connectors have higher insertion loss than good quality straight physical contact ones. "Ultra" quality connectors may achieve comparable back reflection to an angled connector when connected, but an angled connection maintains low back reflection even when the output end of the fiber is unmated.
Angle-polished connections are distinguished visibly by the use of a green strain relief boot. The connectors are typically designated "FC/APC" (for Angled Physical Contact), or merely "FCA".
Analysis
FC connectors' floating ferrule provides good mechanical isolation. FC connectors need to be mated more carefully than push-pull type connectors due to the need to align the key, and due to the risk of scratching the fiber endface while inserting the ferrule into the jack. FC connectors have been replaced in many applications by SC and LC connectors.There are two incompatible standards for key widths on FC/APC and polarization-maintaining (PM) FC/PC connectors: 2 mm ("Reduced" or "type R") and 2.14 mm ("NTT" or "type N"). Type R plugs will mate to any receptacle, but will fail to maintain precise rotation angle unless the receptacle is also type R. Type N plugs will not mate with type R receptacles and may not mate with standard FC/PC receptacles. Accurate rotation angle alignment is especially important for PM fiber, where rotational misalignment between mated fibers decreases the polarization extinction ratio of the connection. Some manufacturers mark reduced keys with a single scribe mark on the key, and mark NTT connectors with a double scribe mark.
Some connector designs have the key as a separate, indexable component. This can allow for some reduction in insertion losses (depending on the concentricity accuracy of the ferrule) by allowing the ferrule to be rotated to a more fortuitous alignment.
| Key type | Plug key width (mm) | Receptacle keyway width (mm) |
|---|---|---|
| Reduced | 1.97–2.02 | 2.03–2.08 |
| NTT | 2.09–2.14 | 2.15–2.20 |
See also
- Optical fiber cableOptical fiber cableAn optical fiber cable is a cable containing one or more optical fibers. The optical fiber elements are typically individually coated with plastic layers and contained in a protective tube suitable for the environment where the cable will be deployed....
Color coding of connector boot and fiber cable jackets