In contrast to their electromechanical counterparts, with fiber-optic connectors no differentiation is made between plug and jack. Fiber-optic connectors contain a ferrule for the accommodation and exact positioning of the fiber end and are attached to one another via a coupler with a sleeve. A complete plug-in connection consists of the combination connector/coupler/connector. The two ferrules with the fiber ends must meet each other so precisely inside the connection that the least possible amount of light energy is lost or reflected (return loss). The determining factor is the geometric orientation and workmanship of the fiber in the connector.
Core diameters of 8.3m for single-mode or 50/62.5m for multi-mode fibers and ferrules with 2.5mm or 1.25mm diameter make a visual inspection of the connector condition without special equipment impossible. Naturally, one can determine on the spot if a connector is correctly snapped in and locked.
For all other characteristics – the “intrinsic values” – for example insertion loss, return loss, or mechanical stability, users must be able to rely on the manufacturer's data.
Connector Type Standard Info
ST 2.5mm MMF, SMF PC
IEC 61754-2 These connectors with bayonet-lock were the first PC connectors (1996). Thanks to this fact and the extremely robust design, they can still be found world-wide in LAN networks (primarily industrial). ST is the designation for
“straight type”. Square Connector or Subscriber Connector).
The compact design of the SC allows for a high packing density. It can be combined to duplex and multiplex connections. Although among the oldest connectors, it has excellent properties. To this day it is the most important WAN connector world-wide, thanks to excellent optical properties. SC is also wide-spread in a duplex version, particularly in upon a plastic ferrule that typically holds 12 or 24 fibers in one connector. In the meantime, connectors with up to 72 fibers are in development. The connector is distinctive due to its compact design and simple handling, but has disadvantages in optical performance and reliability.
Connector Type Standard Info licensed manufacturers in Switzerland, which also results in an unmatched standard of quality. The integrated protective shutter protects against dust and scratches, but also against laser beams.
The connector has a locking latch retention mechanism that is coded both mechanically and according to color. It is the first connector to achieve Grade A performance LC
1.25mm MMF, SMF PC, APC
IEC 61754-20 The connector belongs to a new generation of compact connectors. It was developed by the company Lucent (LC stands for Lucent Connector). Its construction is based upon a ferrule with 1.25 mm diameter. The duplex coupler matches the size of an SC coupler (SC footprint). This allows very high packing density, making its usage in data centers attractive. Is the defacto standard connector in the enterprise market due to the backing from the main equipment manufacturers.
The optical and mechanical performance is below the level of an SC-RJ or E-2000™.
SC-RJ 2.5mm MMF, SMF PC, APC
IEC 61754-24 As the name already reveals, the developers at R&M oriented themselves on the RJ45 format. Two SCs form a unit in the size of an RJ45. This is equivalent to the SFF (Small Form Factor). 2.5 mm ferrule sleeve technology is used. This is more robust and reliable when compared to the 1.25 mm ferrule. The SC-RJ impresses not only with its compact design, but also with optical and mechanical performance. It is an all-rounder – usable from Grade A to M, from single mode to POF, from WAN to LAN, from laboratory to outdoors. For the latter usage, the IP67 version of the SC-RJ is recommended. R&M has released a white paper covering the SC-RJ ("SC-RJ – Reliability for every Category").
Table 33: FO connector types
Approved in March 2007, the standard IEC 61753 describes application-oriented grades for connection elements in fiber-optic networks (see Table 34). The clear identification according to
The current requirements catalogue is based in part on IEC 61753. This standard defines loss values.
Additionally, the standards IEC 61755-3-1 and IEC 61755-3-2 play a role. They define geometric parameters for fiber-optic plug-in connectors. The interaction of these three standards creates the basis for the compatibility of fiber-optic plug-in connectors from different manufacturers and for the determination of manufacturer-neutral loss values.
Connection Attenuation Grade(dB)
Splice 0.3
Single Mode IL Mean IL >97%
Connector Grade A ≤0.07 ≤0.15 Connector Grade B ≤0.12 ≤0.25 Connector Grade C ≤0.25 ≤0.50 Connector Grade D ≤0.50 ≤1.00 Multi Mode IL Mean IL >95%
Connector Grade M ≤0.35 ≤0.50 Table 34: ISO11801 connector loss
Connection Return Loss Grade (dB)
Splice ≥60
Connector Grade 1 ≥60 (mated)
≥55dB (unmated) Connector Grade 2 ≥45
Connector Grade 3 ≥35 Connector Grade 4 ≥26 Table 35: FO connector RL
Overview of performance criteria of the new performances grades for data transmission in fiber-optic connections according to IEC 61753. The definition of Grade A has not yet been finalized. Criteria for multi-mode fibers are still under discussion.
Theoretically, the IL grades (A to D) can be mixed at will with RL grades. However, a Grade A/4 would not make sense, and for this reason the following common combinations have established themselves:
Grade 1 Grade 2 Grade 3 Grade 4
Connector Grade A
Connector Grade B
Connector Grade C
Connector Grade D () ()
Connector Grade M
Table 36: FO connector IL vs RL