Frequently Asked Questions
What is a wide key and what is a narrow key on FC Connectors?
Narrow key connectors have a 2.0mm key and are used on and recommended
for most FC connectors including UPC, APC and PM connectors. They are
sometimes referred to as R Type. Wide key connectors have a 2.14mm key and
are required when mating an APC connector or a PM connector to a wide key
connector. They are sometimes referred to as N Type. TIA FOCIS-4, which
controls the widths of the keys, calls out 4 different standards but they can be
grouped into wide and narrow keys.
What is the difference between a PC and a UPC polish?
A UPC (Ultra Physical Contact) is a higher quality polish then a PC (Physical
Contact) polish. The UPC polish has less scratches and the higher quality as
measured by the improved return loss. UPC connectors typically have 45 to
50dB return loss while PC connectors produce 25 to 30 dB return loss. UPC
connectors mate to PC connectors without any problem.
What causes insertion loss in a connector?
Insertion loss in connectors typically comes from misalignment of the fibers or
bent fibers in the connectors. The misalignment comes from eccentricity of the
core in the fiber, eccentricity of the hole in the ferrule and most of all the
eccentricity of the fiber in the hole. Bending of the fiber typically comes from the
fiber being constrained at the back of the connector while the ferrule moves back
during mating.
Why do short wavelength single-mode cables have higher insertion loss
then longer wavelength cables?
The shorter the wavelength of light the smaller the mode field diameter (MFD) of
the fiber. Fiber for a 400nm purple laser has a 3.5um MFD while a 1550nm laser
requires a fiber with a 10.5um MFD. The 400nm fiber is 1/3 the diameter and 1/9
the area of the 15510nm fiber. If both fibers are misaligned by 1um the 1550nm
fiber will have approximately 0.16dB (3.5%) loss while the 400nm fiber will have
approximately 1.5dB (30%) loss.
Why do some short wavelength cables degrade over time?
Some short wavelength cables degrade over time as the fiber dopents darken
and the epoxy in the connector reacts with the short wavelength light. Both of
these problems can be avoided if the cable is designed and built properly.
What is the difference between Low OH and High OH multimode fibers?
Most multimode fibers are low OH but these fibers have high insertion loss below
600nm. Below 500nm High OH fibers are recommended. If multiple wavelengths
are used, please see the graph in the following link.
Why do connectors that have the fiber crimped to the center of the
connector have insertion loss?
In crimped connectors the cores are not offset but they are at an angle to each
other. This angle misalignment causes loss in the connector.
Narrow key connectors have a 2.0mm key and are used on and recommended
for most FC connectors including UPC, APC and PM connectors. They are
sometimes referred to as R Type. Wide key connectors have a 2.14mm key and
are required when mating an APC connector or a PM connector to a wide key
connector. They are sometimes referred to as N Type. TIA FOCIS-4, which
controls the widths of the keys, calls out 4 different standards but they can be
grouped into wide and narrow keys.
What is the difference between a PC and a UPC polish?
A UPC (Ultra Physical Contact) is a higher quality polish then a PC (Physical
Contact) polish. The UPC polish has less scratches and the higher quality as
measured by the improved return loss. UPC connectors typically have 45 to
50dB return loss while PC connectors produce 25 to 30 dB return loss. UPC
connectors mate to PC connectors without any problem.
What causes insertion loss in a connector?
Insertion loss in connectors typically comes from misalignment of the fibers or
bent fibers in the connectors. The misalignment comes from eccentricity of the
core in the fiber, eccentricity of the hole in the ferrule and most of all the
eccentricity of the fiber in the hole. Bending of the fiber typically comes from the
fiber being constrained at the back of the connector while the ferrule moves back
during mating.
Why do short wavelength single-mode cables have higher insertion loss
then longer wavelength cables?
The shorter the wavelength of light the smaller the mode field diameter (MFD) of
the fiber. Fiber for a 400nm purple laser has a 3.5um MFD while a 1550nm laser
requires a fiber with a 10.5um MFD. The 400nm fiber is 1/3 the diameter and 1/9
the area of the 15510nm fiber. If both fibers are misaligned by 1um the 1550nm
fiber will have approximately 0.16dB (3.5%) loss while the 400nm fiber will have
approximately 1.5dB (30%) loss.
Why do some short wavelength cables degrade over time?
Some short wavelength cables degrade over time as the fiber dopents darken
and the epoxy in the connector reacts with the short wavelength light. Both of
these problems can be avoided if the cable is designed and built properly.
What is the difference between Low OH and High OH multimode fibers?
Most multimode fibers are low OH but these fibers have high insertion loss below
600nm. Below 500nm High OH fibers are recommended. If multiple wavelengths
are used, please see the graph in the following link.
Why do connectors that have the fiber crimped to the center of the
connector have insertion loss?
In crimped connectors the cores are not offset but they are at an angle to each
other. This angle misalignment causes loss in the connector.
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